35. Virology 💢 Flashcards
2 theories of how viruses fit into the tree of life?
- RNA world theory: life arose with the viruses 2. Reductionist theory: viruses came after cellular life, they are reduced versions of cellular organisms * mimiviruses and megaviruses may be the missing link
What are Ribozymes?
- RNAs that can catalyze specific reactions (similar to enzymes) - ribozymes (produced in lab) can catalyze their own synthesis - natural fans: cleave RNA, viral replication, tRNA biosynthesis
Examples of DNA viruses?
- herpes, smallpox, mimivirus DNA -> RNA -> protein
Examples of RNA viruses?
- Rhino, influenza, SARS RNA-> protein
Examples of Retroviruses?
- HIV RNA -> DNA (through reverse transcriptase) -> RNA -> protein
Pros and cons of a DNA virus
pros: lower mutation rate, more stable (can carry more genes), no dsRNA phase cons: lower mutation rate, slower replication
Pros and cons of RNA virus
pros: fast replication rate, high mutation rate cons: high mutation rate, limited sequence space (less stable), dsRNA phase, degrades faster, humans don’t have dsRNA (easy to identify)
What happens frequently in reverse transcriptase?
- 1 mutation per virus, much more common in retrovirus
What are some challenges in developing HIV vaccines?
- high mutation rate - integration into host genome - infects immune privileged region of host - targets immune system - multiple serotypes - costs and time involved in development - vaccine safety concerns
What is the diversity in HIV strains
- 25-30% in circulating HIV strains - mutation rate is - 1 base change per genome
What effects can a mutation have on a virus?
- not all mutations are advantageous: some hinder the virus, some prevent virus replication, and some are silent ( have no effect) - Some allow a competitive advantage, and some allow escape from antiviral drugs
antiretroviral drug classes
- reverse transcriptase inhibitors (NRTIs) - Fusion/entry inhibitors - Integrase inhibitors - Protease inhibitors
Difference b/t nucleosides and nucleotides?
- nucleosides: sugar+ base 3 phosphorylation events required for activity -nucleotide: sugar+base+phosphate, 2 phosphorylation events required for activity
Nucleoside analogs??
prevent adding of next nucleoside on to the chain looks like nucleoside but doesn’t have site to bind to next nucleoside so it is a chain terminator
3TC (Epivir/Iamivudine)
-FDA approved 1995 - reverse transcriptase inhibitor - nucleoside analog: mimics cytidine -> acts as a chain terminator
DLV (Rescriptor/delavirdine)
- FDA approved 1997 - Reverse transcriptase inhibitor (non-nucleoside) - binds RT catalytic site, blocking polymerase fxn
Reverse transcriptase mutations?
- only takes 1 or 2 mutations of virus to make reverse transcriptase drugs ineffective
DRV (darunavir/Prezista)
- FDA approved 2006 protease inhibitor: binds the active site preventing the processing of viral protein precursors - compete with the natural substrate
EVG (Elvitegravir)
- FDA approved 2014 - Allosteric integrase inhibitor (prevents functional multimers from forming (dimers of dimers= tetramer)
MVC (Selzentry/maraviroc)
- FDA approved 2007 - entry inhibitor (receptor antagonist) drug binds receptor (CCR5), preventing HIV from binding - mutant bind receptor in a different conformation
T20 (Fuzeon/entuvirtide)
- FDA approved 2003 - HIV fusion inhibitor - mimics viral protein to displace it in the fusion complex (binds p41 and prevents formation of the entry pore)
Vacc-4x
therapeutic vaccine in clinical trials 9phase 2) peptide vaccine -> dropped viral load but didn’t slow CD4 T cell decline
SB-728T gene therapy
in phase 1/2 trials modifies a CD4 T cell CCR5 receptor, making it non-functional, prevents HIV entry - harvest patient T cells, make mutation and replicate, and put back into pt - this mutation occurs naturally and confers HIV resistance - expensive and time consuming
Interleukin
IL-7: trial abandoned b/c IL-7 increased the number of CD4+ T cells but that increased viral load too IL-2: increased number of CD4+ T cells but didn’t significantly decrease clinical events or death, even when combined with antiretrovirals
Chloroquine
- antimalarial - drops pH in vacuoles - disrupts Env protein gp120, inhibits maturation - drops viral load, doesn’t affect T cells so doesn’t stop T cells from decreasing
What can be done to prevent escape mutants?
- combo drugs Atripla (3) Complera (4) Stribild (4) Triumeq (3) Combivir (4)
Difference b/t viral and human evolution
- humans: complicated, multiple polymerases, error prone, and non-error prone sites, at most 1 mistake/ 100 million, proofreading and correcting machinery, and we only have a couple kids in a lifetime - viruses: often 1 mistake per genome, no proofreading, often whole populations knocked out, billions of genomes made per day
Potential effects of viruses on human evolution
- immune system diversity - ABO blood system (decreased A allele frequency after smallpox epidemic) - endogenous retroviruses (1% of genome) - cell surface mutations (ex: CCR5)
What does it mean that viruses are a part of us?
- they are a part of our regulation of host gene expression - they take part in placental formation - reason why there is immunosuppression during pregnancy - promoters, enhancers and proteins can be coopted by the host for its own purposes (placenta formation) - can be fixed or mobile, and no human endogenous retroviruses (ERVs) are capable of replication
What are endogenous retroviruses (ERVs) associated with in humans?
- MS - schizophrenia - cancer - autoimmune diseases - amayotrophic lateral sclerosis (ALS)
Mutation in humans that allow them to be resistant to HIV infection?
-mutation prevents an HIV corrector from being made by the cell, and therefore HIV can’t infect people with this mutation (CCR5 delta 32 mutation) -> positive selection for this mutation
Hypothesis for why mutation has been selected in specific regions (Europe, Asia, North Africa)?
- either plague (bacteria) or smallpox (virus)
How can humans drive viral evolution?
- each infection is a population - zoonosis: virus mutating to be able to pass from one species to another - humans as an enviro: immune system and viral recombination - antiviral drugs: promote resistance and mutations
difference b/t epidemic and pandemic?
- epidemic: greater than expected incidence “outbreak” ex: SARS, Dengue - pandemic: spread over a large geographical area (b/t continents) ex: HIV, smallpox, H1N1 (seasonal flu not a pandemic)
Why do viruses start epidemics and then pandemics?
- increased virulence (severity of disease or ability to spread) - intro into novel setting - changes in host susceptibility to the infectious agent - changes in host exposure to the infectious agent
Transmission modes of viruses?
- iatrogenic (blood transfusion) - vertical - vector borne - droplet - fecal-oral - sexually
Zoonosis?
- disease that can pass from another species to humans or humans to another species - often diseases are adapted to their host and more deadly when they jump hosts (ex: Ebola) - Many viruses can pass from animal reservoir to humans, but have difficulties transmitting human to human - issues: domestication, deforestation, bush meat
BSL-4 viruses
- aerosol viruses - severe/fatal viruses w/ no vaccines or other txs: - bolivian and argentine hemorrhagic fevers - marburg virus - ebola virus - lassa virus - crimean-congo hemorrhagic fever - small pox
What are some challenges in developing HIV vaccines?
- high mutation rate - integration into host genome - infects immune privileged region of host - targets immune system - multiple serotypes - costs and time involved in development - vaccine safety concerns
What is the diversity in HIV strains
- 25-30% in circulating HIV strains - mutation rate is - 1 base change per genome
What effects can a mutation have on a virus?
- not all mutations are advantageous: some hinder the virus, some prevent virus replication, and some are silent ( have no effect) - Some allow a competitive advantage, and some allow escape from antiviral drugs
antiretroviral drug classes
- reverse transcriptase inhibitors (NRTIs) - Fusion/entry inhibitors - Integrase inhibitors - Protease inhibitors
Difference b/t nucleosides and nucleotides?
- nucleosides: sugar+ base 3 phosphorylation events required for activity -nucleotide: sugar+base+phosphate, 2 phosphorylation events required for activity
Nucleoside analogs??
prevent adding of next nucleoside on to the chain looks like nucleoside but doesn’t have site to bind to next nucleoside so it is a chain terminator
3TC (Epivir/Iamivudine)
-FDA approved 1995 - reverse transcriptase inhibitor - nucleoside analog: mimics cytidine -> acts as a chain terminator
DLV (Rescriptor/delavirdine)
- FDA approved 1997 - Reverse transcriptase inhibitor (non-nucleoside) - binds RT catalytic site, blocking polymerase fxn
Reverse transcriptase mutations?
- only takes 1 or 2 mutations of virus to make reverse transcriptase drugs ineffective
DRV (darunavir/Prezista)
- FDA approved 2006 protease inhibitor: binds the active site preventing the processing of viral protein precursors - compete with the natural substrate
EVG (Elvitegravir)
- FDA approved 2014 - Allosteric integrase inhibitor (prevents functional multimers from forming (dimers of dimers= tetramer)
MVC (Selzentry/maraviroc)
- FDA approved 2007 - entry inhibitor (receptor antagonist) drug binds receptor (CCR5), preventing HIV from binding - mutant bind receptor in a different conformation
T20 (Fuzeon/entuvirtide)
- FDA approved 2003 - HIV fusion inhibitor - mimics viral protein to displace it in the fusion complex (binds p41 and prevents formation of the entry pore)
Vacc-4x
therapeutic vaccine in clinical trials 9phase 2) peptide vaccine -> dropped viral load but didn’t slow CD4 T cell decline
SB-728T gene therapy
in phase 1/2 trials modifies a CD4 T cell CCR5 receptor, making it non-functional, prevents HIV entry - harvest patient T cells, make mutation and replicate, and put back into pt - this mutation occurs naturally and confers HIV resistance - expensive and time consuming
Interleukin
IL-7: trial abandoned b/c IL-7 increased the number of CD4+ T cells but that increased viral load too IL-2: increased number of CD4+ T cells but didn’t significantly decrease clinical events or death, even when combined with antiretrovirals
Chloroquine
- antimalarial - drops pH in vacuoles - disrupts Env protein gp120, inhibits maturation - drops viral load, doesn’t affect T cells so doesn’t stop T cells from decreasing
What can be done to prevent escape mutants?
- combo drugs Atripla (3) Complera (4) Stribild (4) Triumeq (3) Combivir (4)
Difference b/t viral and human evolution
- humans: complicated, multiple polymerases, error prone, and non-error prone sites, at most 1 mistake/ 100 million, proofreading and correcting machinery, and we only have a couple kids in a lifetime - viruses: often 1 mistake per genome, no proofreading, often whole populations knocked out, billions of genomes made per day
Potential effects of viruses on human evolution
- immune system diversity - ABO blood system (decreased A allele frequency after smallpox epidemic) - endogenous retroviruses (1% of genome) - cell surface mutations (ex: CCR5)
What does it mean that viruses are a part of us?
- they are a part of our regulation of host gene expression - they take part in placental formation - reason why there is immunosuppression during pregnancy - promoters, enhancers and proteins can be coopted by the host for its own purposes (placenta formation) - can be fixed or mobile, and no human endogenous retroviruses (ERVs) are capable of replication
What are endogenous retroviruses (ERVs) associated with in humans?
- MS - schizophrenia - cancer - autoimmune diseases - amayotrophic lateral sclerosis (ALS)
Mutation in humans that allow them to be resistant to HIV infection?
-mutation prevents an HIV corrector from being made by the cell, and therefore HIV can’t infect people with this mutation (CCR5 delta 32 mutation) -> positive selection for this mutation
Hypothesis for why mutation has been selected in specific regions (Europe, Asia, North Africa)?
- either plague (bacteria) or smallpox (virus)
How can humans drive viral evolution?
- each infection is a population - zoonosis: virus mutating to be able to pass from one species to another - humans as an enviro: immune system and viral recombination - antiviral drugs: promote resistance and mutations
difference b/t epidemic and pandemic?
- epidemic: greater than expected incidence “outbreak” ex: SARS, Dengue - pandemic: spread over a large geographical area (b/t continents) ex: HIV, smallpox, H1N1 (seasonal flu not a pandemic)
Why do viruses start epidemics and then pandemics?
- increased virulence (severity of disease or ability to spread) - intro into novel setting - changes in host susceptibility to the infectious agent - changes in host exposure to the infectious agent
Transmission modes of viruses?
- iatrogenic (blood transfusion) - vertical - vector borne - droplet - fecal-oral - sexually
Zoonosis?
- disease that can pass from another species to humans or humans to another species - often diseases are adapted to their host and more deadly when they jump hosts (ex: Ebola) - Many viruses can pass from animal reservoir to humans, but have difficulties transmitting human to human - issues: domestication, deforestation, bush meat
BSL-4 viruses
- aerosol viruses - severe/fatal viruses w/ no vaccines or other txs: - bolivian and argentine hemorrhagic fevers - marburg virus - ebola virus - lassa virus - crimean-congo hemorrhagic fever - small pox
What is a maculopapular rash?
Some areas are raised and some areas are flat
What is a dermatomal distribution of a rash indicative of?
Shingles
What components of the virus can be used in virus detection?
Virus isolation and electron microscopy to visualise the virus itself Protein components (antigens) Genetic components (RNA or DNA) The host response (antibody or cell responses)
What is the main method of virus detection?
PCR
What technique is used for antibody detection?
Enzyme immunoassay – detects antibodies and antigens
Define sensitivity.
Low rate of false negatives
Define specificity.
Low rate of false positives
What does quantification of the genomes allow assessment of?
Viral load
What is the difference between IgM and IgG in terms of when theirlevels rise following infection?
IgM is a marker of RECENT infection IgG rises later on
What does positive IgG and absent IgM indicate?
Past infection or immunisation
What is targeted in the detection of HIV?
Antibody and p24 antigen
What other investigations are performed on people who are identified as HIV positive?
Typing (HIV 1 or HIV2) Repeat blood sample and EDTA blood for HIV viral load (for genotyping and baseline resistance testing)
What test is used to confirm a positive IgM result?
Antibody avidity testing
Describe how antibody avidity changes in infection.
Early on in the infection, avidity is LOW Then you get maturation of the antibody response so the avidity will increase over a period of 3-6 months If you have HIGH antibody avidity, then it is unlikely that the infection occurred in the last 3 months
What is immunofluorescence useful for?
Direct detection of viral antigens
What is the term given to the method of PCR that allows testing for more than one virus using a single test tube?
Multiplex PCR
What is sampled when testing for meningitis/encephalitis?
CSF Stools and throat swab (for enterovirus detection) Blood
What is sampled when testing for causes of diarrhoea/vomiting?
Stool (and vomit)
What must happen first before PCR is performed to identify the genome of an RNA virus?
The RNA must be reverse transcribed by reverse transcriptase to dsDNA dsDNA is the start point of PCR
Describe the process of PCR.
The dsDNA is denatured by heating it The primers then bind to the single stranded DNA and Taq polymerase joins complementary nucleotides to the template strand
What are the applications of sequencing viral genomes?
Antiviral resistance testing Phylogenetic analysis
What is a virus made of?
No cell wall, made up of nucleic acid components: -protein coat (capsid) -nucleic acid core, or genome -some have lipoprotein envelope -viruses containing envelope are antigenic in nature -Viruses are obligate intracellular parasites - Use host enzymes, don’t have metabolic machinery of their own.
Where do viruses replicate in the host?
certain ones multiply in cytoplasm and others do so in the nucleus -most have to replicate so many times before they illicit symptoms in the host and before the dx is made.
Process of viral infection and replication?
- Absorption: binds to host cell 2. Penetration: virus injects genome into host cell 3.Viral genome replication: viral genome replicates using the host’s cellular machinery 4. Assembly: viral components and enzymes are produced and begin to assemble. 5. Maturation: viral components assemble and viruses fully develop. 6. Release: newly produced viruses are expelled from the host cell.
What must antiviral drugs do to be effective?
must either: - block viral entry into or exit from the cell - be active inside the host cell
What is the MOA of most anti-viral drugs?
many are purine or pyrimidine analogs. -Many are prodrugs: so they must be phosphorylated by viral or cellular enzymes in order to become active. - anti-viral agents inhibit active replication so the viral growth resumes after drug removal.
What is an important part of fighting viral infections?
current anti-viral agents don’t eliminate non-replicating or latent virus ***Effective host immune response remains essential for recovery from viral infection. -clinical efficacy depends on achieving inhibitory concentration at site of the infection within the infected cells
What are the anti-HSV/VZV agents? Herpes/Varicella/Zoster
acyclovir (zovirax) famciclovir (famvir) valacyclovir (valtrex)
MOA of anti-HSV/VZV agents?
All 3 are guanine nucleoside analogs. - all are phosphorylated by a viral thymidine-kinase, then metabolized by host cell kinases to nucleotide analogs. ** The analog inhibits viral DNA-polymerase and only actively replicating viruses are inhibited
Acyclovir (zovirax)
guanosine analog -topical, oral, and IV
Spectrum of Acyclovir?
HSV 1 and 2, VZV, and possible EBV *DOC for HSV genital infections, herpes labialis/orolabial, HSV encephalitis, HSV infections in immunocompromised and pregnant pt
Pharmokinetics of acyclovir?
oral bioavailability: 20-30% distribution to all tissues including CNS -renal excretion: >80% -half life: 2-5 hours -topical, oral and IV
Acyclovir safety
Pregnancy: B lactation: safe renal dosing: adjust if CrCl
Acyclovir MOA
inhibition of viral synthesis of DNA -uptake by infected cell -competes with deoxyguanosine triphosphate for viral DNA polymerases: *chain termination -> inactivated viral DNA polymerase
What cells is acyclovir selectively activated in?
in cells infected with herpes virus -uninfected cells don’t phosphorylate acyclovir.
When would you take acyclovir for genital/mucocutaneous HSV?
Take it for first episode: frequent dosing (trying to prevent it from reocurring) Recurrence and suppression if pt has frequent recurrence.
Adverse effects of Acyclovir
-reversible renal toxicity -Neuro symptoms: encephalopathic changes - somnolence, hallucinations, confusion and coma. -TTP/HUS in immunocompromised -GI sxs -HA -rash -photosensitivity -anemia
Resistance to acyclovir and MOA of resistance
MIC>2-3 mcg/mL -mostly occurs in immunocompromised - 3 basic resistance mechanisms exist: 1. reduced or absent thymidine kinase 2. altered TK substrate specifity 3. alterations in DNA poly. - there is cross resistance to famciclovir and valacyclovir
Why tx with acyclovir?
genital herpes: shortens duration of sxs, viral shedding time, and time to resolution of lesions recurrent genital herpes: shortens course of time by 1-2 days long term tx: decreases frequency of both symptomatic recurrences and asymptomatic viral shedding -> decreases sexual transmissions. Varicella Zoster: decreases total number of lesions and duration of varicella (if begun w/in 24 hours after onset of rash).
Famciclovir (Famvir)
cyclic guanine analong: -converted to penciclovir in the liver and intestines -penciclovir is used only topically whereas famciclovir can be administered orally. - PO only
Spectrum of famciclovir
HSV 1 & 2, VZV, maybe in EBV - in vitro to HBV
Pharmacokinetics of famciclovir
oral bioavailability: 77% 1st pass metabolism in intestine and liver: results in conversion to penciclovir Renal excretion: > 80% half life: 2-3 hours - Just PO
Famciclovir safety
Pregnancy: B lactation: unknown, caution advised Renal dosing: adjust dose for CrCl
MOA of famciclovir
Similar to acyclovir -> inhibition of viral synthesis of DNA, uptake by infected cell and competes with deoxyguanosine triphosphate for viral DNA polymerases -> inactivates viral DNA polymerase -it is converted to penciclovir triphosphate and compared to acyclovir triphosphate, penciclovir 3xP has lower affinity for viral DNA polymerase but does have longer intracellular half life
Famciclovir uses
zoster (shingles), and genital and orolabial HSV (for 1st occurence, recurrence and suppression)
Famciclovir adverse effects
-neutropenia -thrombocytopenia -neurological sxs: encephalopathic changes -> somnolence, hallucinations and delirium - GI sxs -HA, fatigue -abnormal LFT’s
Resistance to Famciclovir
- mutations in viral TK or DNA polymerase -cross resistance with acyclovir in TK negative strains -May still have activity in TK altered strains -resistance to HBV due to pt mutation (viral DNA polymerase)
Valacyclovir (Valtrex)
Prodrug of acyclovir: rapidly and almost completely converted to a acyclovir, same MOA, same spectrum, same mechanism of resistance
Pros and cons of Valacyclovir
Advantage: more convenient dosing, better oral bioavailability (55%) cons: more pricey than acyclovir
Pharmokinetics of Valacyclovir
oral bioavailability: 55% -undergoes rapid and extensive 1st pass effect to yield acyclovir -food doesn’t affect absorption -renal excretion: >50% Half life: 2-3 hours Administration: oral
Valacyclovir safety
Pregnancy: B lactation: safe renal dosing: adjust for CrCl
dosing of Valacyclovir
varies with infection type/severity -1st episode of HSV: hit em’ hard -> 1000 mg PO bid x 7-10 days shingles: PO tid x 7 days
Adverse effects of Valacyclovir
-reversible renal toxicity -neuro sxs: encephalopathic changes -> somnolence, hallucinations, confusion, coma -TTP/HUS: immunocompromised -GI, HA, rash, photosensitivity, elevated LFTs
What is the cheapest of the 3 HSV drugs and most preferred?
Acyclovir cheapest, but you have to admin more often. Can tx encephalitis with this too by IV - used b/c it has broader spectrum -> recommended for varicella or zoster in immunocompromised
What is used to treat HSV keratoconjunctivitis?
trifluridine (viroptic -> ophthalmic application) - this is active against acyclovir resistant strains
Anti-CMV agents
Ganciclovir
Spectrum of Ganciclovir
oral, IV, intraocular CMV, EBV, HSV/VZV, human herpesvirus 6 (for CMV and EBV: 10x more potent than acyclovir)
Ganciclovir is DOC for?
CMV retinitis in immunocompromised pt, and prevention of CMV disease in transplant patients
pharmacokinetic of Ganciclovir
oral bioavailability: 50% is excreted unmodified in urine renal excretion: >90% half life: 2-4 hours admin: oral, IV, intraocular
Ganciclovir safety
pregnancy: C (adverse fetal effects in animal studies) lactation: unsafe renal dosing: adjust dose for CrCl
MOA of Ganciclovir
competes with deoxyguanosine triphosphate similar to acyclovir - but in CMV -> viral encoded phosphotransferase coverts to ganciclovir triphosphate -unlike acyclovir, ganciclovir contains 3’ OH group allowing for DNA to continue
Adverse effects of Ganciclovir
reversible pancytopenia, fever, rash, phlebitis (IV), confusion, renal dysfunction, psychiatric disturbances, seizures
Influenza agents
- oseltamivir - zanamivir - amantadine (used in parkinsons now) - Rimantadine
MOA of influenza and neuraminidase inhibitors -> oseltamivir/zanamavir
influenza: contains an enzyme neuraminidase which is essential for the replication of the virus -so neurominidase inhibitors prevent the release of new visions and their spread from cell to cell.
Neuraminidase inhibitors effectiveness
effective against both types of influenza A and B -don’t interfere with immune response to influenza A vaccine -can be used for both prophylaxis and acute tx
Oseltamivir (Tamiflu) MOA
oral neuraminidase inhibitor: cleaves terminal sialic acid residues on glycoconjugates and destroys receptors -newly formed visions adhere to cell surface and limit spread.
Spectrum of Oseltamivir (Tamiflu)
Influenza A and B in kids and adults, avian flu, H5N1 disease
Adverse effects of Tamiflu
N/V, HA
When do you want to administer Oseltamivir (Tamiflu)
for tx of Influenza A and B: w/in 48 hours of sx onset, if high risk -> 72 hours - prophylaxis: w/in 48 hours of exposure
Zanamivir (Relenza)
Neuraminidase inhibitor, given via inhalation spectrum: uncomplicated influenza A and B and some strains of Avian influenza
Adverse effects of Zanamivir (Relenza)
nasal and throat discomfort -bronchospasm
Amantadine (Symmetrel) and Rimantadine (Flumadine)
MOA: prevents release of viral nucleic acid into host cell spectrum: influenza A, however resistance is frequent (Symmetrel not as effective anymore -> doesn’t work on B) Adverse effects: seizures, anticholinergic, CNS, edema, blurry vision
Is Amantadine or Rimantadine recommended in US?
NO not currently recommended for influenza because too much resistance - it is being used for extrapyramidal sx and parkinsonism though
Pharmacokinetics of Amantadine
oral bioavailability: 50-90% - crosses BBB extensively, and Rimantadine doesn’t. -PO
Ribavarin
purine nucleoside analog MOA: not fully understood, inhibition of RNA polymerase Spectrum: DNA and RNA viruses are susceptible, including influenza, HCV, parainfluenza, RSV, Lassa virus
Therapeutic uses of Ribavarin
DOC for: RSV bronchitis and pneumonia in hospitalized children (aerosol), lassa fever alternate drug: influenza, parainfluenza, measles virus in immunocompromised pts - used in combo with interferons for HCV
Safety of Ribavarin
Available: PO and inhalation IV available through CDC Preg: X (teratongenic) lactation: probably unsafe
Adverse effects of Ribavirin
BBW-hemolytic anemia resp. deterioration depression suicidal ideation bacterial infections psych. effects anxiety, fatigue, dizziness
Hepatitis?
swelling or inflammation of the liver in response to: drugs, toxins, excessive alcohol, infections from bacteria or viruses
Hepatitis A
typically spreads when infected individuals improperly handle food or water
Hepatitis B
often transmitted by sexual intercourse, sharing of needles or contact with contaminated blood (vaccine available)
Hepatitis C
more likely to cause permanent liver damage, genes mutate very fast, new genotypes make developing an effective vaccine impossible so far
Hepatitis A tx
clears on its own with rest and adequate hydration
Hepatitis B tx
May clear on its own. Chronic cases may be tx with: - interferon - Nucleoside Reverse Transcriptase inhibitors (NRTI) such as -> emtricitabine tenofavir entacavir lamivudine (some patients may need liver transplant)
Hepatitis C epidemiology
chronic infection that afflicts about 170 million people worldwide -annual mortality: 350,000 15,000 in the US
Hepatitis C standard treatment
synthetic, injectable version of interferon plus the antiviral drug ribavarin - this combo shows benefit or cure in 25-75% of patients -SE: significant or intolerable -> severe flu-like sxs, fatigue, depression, anemia -Virus often becomes resistant to medication, allowing disease to worsen
Anti-viral drugs for hepatic viral infections
- interferons - lamivudine - cytosine analog - HBV -Entecavir - guanosine analog- HBV (lamivudine resistance strains) -Ribavarin - Hep C (w/ interferons)
New drugs for Hep C
To be effective - drug has to incorporate itself in the virus’s genetic code so as to halt replication - to avoid potentially debilitating side effects the med needs to enter the liver quickly and directly avoiding as many other organs as possible
New formulation for Hepatitis
called sofosbuvir (Sovaldi) study showed 295/327 patients treated with sofosbuvir as well as ribavarin and interferon showed no signs of virus in blood after 12 weeks -> approved by FDA in 2013 in combo with rivabarin
Sofosbuvir paired with ledispasvir
cured at least 94% of patients with genotype 1 disease, mixed in single daily pill (Harvoni) -> cure rates >90% with 12 weeks and no significant SE’s.
What is downfall of new drugs for Hep C
>$100,000 for 12 week course of treatment. Many people with Hep C poor and/or incarcerated
Cost of sofasbuvir?
$594 dose, treatment would run nearly $12 billion dollars - much cheaper in Canada and Germany -What the heck U.S.?
What is a virus?
- submicroscopic, obligate intracellular parasite (Can’t survive outside of cell, use host machinery -> can’t replicate or express genes w/o help of living cell) - Formed within cells from the assembly of preformed components, whereas other agents reproduce - Virons are the complete infective particle and don’t grow. It lacks needed components that cells have to reproduce. - No viruses known to have the genetic info needed to produce metabolic energy for replication - When a virus infects a cell, it marshals the cell’s ribosomes, enzymes and much of cellular machinery to replicate - Viral replication produces many progeny, that when complete, leave the host cell to infect other cells in the organism
What kind of cells do viruses infect?
- all types of living cells - animals, plants and bacteria - viroids: small circular RNA molecules with a rod like secondary structure that possess no capsid or envelope
What is a virus made of?
A virus particle, also known as a vision is essentially a nucleic acid (DNA or RNA) enclosed in a protein shell or coat. - Viruses are extremely small, approx: 15-25 nm in diameter
Variations in viruses?
- may be dsDNA, dsRNA, ssDNA, or ssRNA - The type of genetic material found in a particular virus depends on the nature and function of the specific virus - so dsDNA viruses must enter the host cell’s nucleus before it can replicate - ssRNA viruses replicate in host cell’s cytoplasm. - the genetic material isn’t typically exposed but covered by a protein coat. The viral genome can consist of a very small number of genes or up to hundreds of genes depending on the type of virus
The viral capsid?
- the protein coat that envelopes viral genetic material - composed of protein subunits called capsomeres - have several shapes: polyhedral, rod, or complex - fxn is to protect the viral genetic material from damage - in addition to protein coat: some viruses have specialized structures -> the flu virus has a membrane-like envelope around it’s capsid, and the envelope has both host cell and viral components and assists the virus in infecting its host
The process of the viral infection?
- adsorption: virus binds to host cell - penetration: virus injects its genome into host cell - viral genome replication: viral genome replicates using host’s cellular machinery - assembly: viral components and enzymes are produced and begin to assemble - Maturation: viral components assemble and viruses fully develop - release: newly produced viruses are expelled from the host cell
Key components of current classification system?
- type of symmetry of the virus capsid - presence or absence of a lipid envelope - type and structure of the viral nucleic acid and the strategy used in its replication
What does hemagglutinin allow viruses to do?
- binds to host cells, this is how viruses can switch b/t strains so they can infect other species -> virulent, lethal to humans -> can become pandemics
What are the Class 1 viruses?
HAPP viruses: dsDNA - Herpesvirus (cold sores, genital herpes, chicken pox, mono) - Adenovirus (resp diseases) - Papovavirus (warts, cervical cancer) - Poxvirus (small pox, cowpox)
Class II viruses?
ssDNA - parvovirus
Class III viruses?
- dsRNA coronavirus picornavirus (polio, common cold) Togavirus (rubella, yellow fever) Hep C virus
Class IV viruses?
positive ssRNA itself acting as mRNA - Rhabdovirus (rabies) - Paramyxovirus (measles, mumps) - Orthomyxovirus (influenza viruses) - Bunyavirus (Korean hemorrhagic fever) - Arenaviruses
Class V viruses
- negative ssRNA used as template for mRNA synthesis Reovirus (diarrhea)
Class VI viruses
positive ssRNA with DNA intermediate in replication - retrovirus (leukemia, AIDS)
Class VII viruses
dsDNA with an RNA intermediate in replication - Hep B virus
Viral exanthematous diseases?
- chickenpox/Herpes zoster - infectious mono - Roseola infantum (6th disease or Erythema subitum) - 5th disesae (Erythema infectiosum) - Measles - Rubella - Enteroviral exanthems: coxsackievirus, echovirus
What does exanthematous disease mean?
- characterized by or of the nature of an eruption or rash - the most frequent cause of exanthematous diseases are viral infections, which provoke skin alterations either directly or via the reaction of the immune system - in many distinct parainfectious clinical pictures, several viruses from quite different groups are able to produce a specific exanthem
Ddx of exanthematous eruptions?
- Rickettsial infections (tick borne illnesses) - Mycoplasma pneumoniae - syphilis (hands and soles) - typhoid fever - bacterial toxins (staph aureus: TSS -> pinpoint rash on abdomen - drug eruptions - live-virus vaccinations
All of the Human Herpes Viruses?
HHV-1: Herpes Simplex Virus 1 (HSV1) HHV-2: HSV2 HHV-3: VZV HHV-4: EBV (mono: elev lympho) HHV-5: CMV HHV-6: exanthema or Roseola HHV-7: T-lymphotropic virus HHV-8: virus assoc with Kaposi’s sarcoma (AIDS defining illness)
HSV 1 and 2 generally associated with what?
orolabial herpes: typically HSV-1 genital herpes: HSV-2 can affect almost all body tissue - these are mutlinucleated giant cells, intranuclear inclusion bodies (where viral assembly is taking place)
Epidemiology of HSV
>90% have abs to HSV-1 by age 30 - HSV 2 abs are rare b/f puberty 10-40% of general U.S. adult pop. have HSV-2 abs
Pathophysiology of HSV?
virus infects through mucosal membranes or abraded skin - latent infections are harbored in neuronal cells: in trigeminal ganglia and in pre-sacral ganglia
Clinical presentation of HSV oral-facial lesions?
- dew-drop on a rose petal - oral-facial lesions: primary infections: Gingivostomatitis (painful -> swollen lips) and pharyngitis most frequent, this is commonly seen in children and young adults - fever, malaise, myalgias, inability to eat, irritability and cervical adenopathy lasts 3-14 days - recurrence: Herpes labialis (cold sores)
Clinical presentaion of HSV urogenital lesions
- dew drop on rose petal - caused by either HSV-1 or 2 - systemic: HA, fever, malaise, and myalgia local: vesicular lesions of external genitalia with pain, itching, dysuria, vagina and urethral d/c, tender inguinal lymph adenopathy - usually present with early, tingly sensation and tenderness in affected area, with low grade fever - tx during this time= best results
What is often more severe primary infection or recurrent infections?
- primary infection usually more severe than recurrences but may be asymptomatic - vesicles form moist ulcers after several days, and crust over in 1-2 weeks if left unaddressed recurrences often: involve fewer lesions - tend to be labial - heal faster - are induced by stress, fever, infection, sunlight, chemo, pregnancy
What complications can HSV cause?
- ocular disease (#1 cause of blindness (hepatic keratitis) - Neonatal and congenital infections - Bells palsy (facial droop) - Encephalitis and recurrent meningitis - Herpes is most common cause of viral encephalitis in US - will see disseminated herpes in immunocompromised (AIDS)
What should be tested during pregnancies?
TORCHS: To: toxoplasmosis R: rubella C: CMV H: herpes and HIV S: syphilis
Dx of HSV?
- usually clinically made - clinical dx should be confirmed with lab testing, the dx can be made by viral culture( can’t be crusted over), PCR, Tzanck prep, direct fluorescence AB, and type-specific serologic tests. The choice of test varies with the clinical presentation - Viral culture - 50% sensitive - real-time HSV PCR: more sensitive to confirm HSV in clinical specimens obtained from genital ulcers, mucocutaneous sites, and CSF (amplifies the virus), its particularly useful for the detection of asymptomatic HSV shedding - ****There is enhanced sensitivity of HSV PCR compared to viral culture
What is the preferred dx test of HSV?
- PCR assay
Describe the HSV direct fluorescent ab test?
- many dx labs provide a rapid type-specific direct fluorescent ab (DFA) test to detect HSV in clinical specimens. This test is specific and reproducible (have to have an immune response though)
- What is the HSV serology test?
- type specific abs to HSV develop during the first several weeks after infection and persist indefinitely. The availability of type-specific abs has also facilitated greater accuracy in epidemiological surveys
Tzanck smear for HSV?
- Tzanck smear: may demonstrate the cytopathic effect of the virus (multinucleate giant cells), and can be performed on lesion scrapings from pts with active genital lesions. However it has limited utility since it has low sensitivity and specificity and is only helpful if + - furthermore, only a viral culture can determine whether the infection is due to HSV-1 or HSV-2
Management of HSV?
- acute infections: antiviral agents only shorten duration of sxs by 1-2 days (acyclovir, famciclovir, valcyclovir) -suppressive therapy: taken daily to prevent reactivation (spendy)
Where will Herpes present?
- can present on fingers (herpetic whitlow) -in the mouth -> primary: gingivostomatitis (sores all over mouth) - On the cornea (hepatic keratitis) - genitals (don’t miss the cervix)
What are the 2 clinical presentations of VZV?
- primary infection: chicken pox - recurrent infections: Herpes zoster
Epidemiology of VZV?
- humans only known reservoir of VZV - primary infection: transmission likely by resp. route - recurrent infection: VZV probably infects dorsal root ganglia during primary infection. Mechanism or stimulus for reactivation of latent infection in unknown.
Pathophys of VZV?
incubation pain: 10-21 days (usually 14-17) - infected persons are infectious 48 h before onset of vesicular rash, throughout vesicle formation (4-5 days), and until all vesicles are crusted.
Clinical presentation of primary infection: chickenpox
- rash, fever (100-103F), lasting 3-5 days, malaise - skin lesions are hallmark of disease: maculopapules, vesicles, and scabs in varying stages of development (“crops” of lesions - compared to small pox which lesions occur at same time ) on an erythematous base of 5-10 mm - distribution is centripetal (see on trunk) - Not as umbilicated as smallpox
Clinical presentation of recurrent VZV recurrent infection: Herpes zoster or “shingles”
- unilateral vesicular eruptions which develop within a single dermatome (T3 to L3 most common). Often assoc. with severe pain
Dxs in VZV?
- usually clinically made - tests can include: specialized complement fixation and virus neutralization in cell culture Fluorescent ab test of smear of lesions
progress of VZV infection?
- thin walled vesicle with clear fluid forms on a red base 2. The vesicle becomes cloudy and depressed in center (umbiliicated) with and irregular (scalloped) border 3. A crust forms in the center and eventually replaces the remaining portion of the vesicle at the periphery
When would you tx Herpes Zoster with IV acyclovir?
- when it is on the face and the eye is involved (can lead to blindness)
Management of VZV infections?
- primary infection prevention: vaccination (reduce outbreak by 50%) - primary disease: prevent secondary infections - Recurrent infection: zoster take antivirals (high dose): - acyclovir, famciclovir and analgesics - can give immunoglobulin w/in days of outbreak will decrease severity of outbreak
Infectious mononucleosis (EBV) epidemiology
- EBV (HHV-4) -> 2 variants: EBV-1, EBV-2 - B-cell lymphotropic virus primarily transmitted in saliva (4-8 wk incubation period) - 50% have had primary infection before adolescence (80% of daycare kids exposed to mono -> get over it easily) -Peak incidence occurrence: (big problem in adolescents and adults) ages 14-16 for girls ages 16-18 for boys - EBV shed from oropharynx for up to 18 months post-infection
Clinical presentation of mono (EBV) - clinical triad?
- subclinical or mild when infected during childhood - infectious mono defined by transient appearance of heterophil Ab and clinical triad: - fever/chills: 7-14 days duration (may be prodromal) - lymphadenopathy: rarely exceed 3 weeks duration (posterior chain -B cells multiplying) - Severe pharyngitis with exudates: maximal for 5-7 days and resolved over following 7-10 days (only exception when virus causes exudates)
Other common signs/sxs of primary infection of mono?
-HA, malaise, anorexia - soft palatal petechiae - maculopapular rash (especially with admin. of amoxicillin/PCN) - splenomegaly and mild hepatic tenderness in up to 50%
What neoplasms is EBV associated with?
- nasopharyngeal carcinoma - B-cell lymphomas (Burkitt’s lymphoma)
Lab findings in infectious mono (EBV)
- throat culture to check for B-hemolytic strep - monospot - Heterophil abs (90-95% of adolescents will be Ab +) become positive w/in 4 weeks after onset of sxs, are specific but not sensitive in early illness - atypical lymphocytosis in about 75% - EBV-specific immune response: EBV ab titers directed at several Ags -> EB virus capsid antigen (VCA), ABs to EBV nuclear antigen - EBNA
Complications of infectious mono?
- bacterial strep pharyngitis (develop a rash) - hematologic: thrombocytopenia, neutropenia - splenic rupture - neurologic: CN palsies (Bell’s palsy); Guillain-Barre syndrome; encephalitis
Management of infectious mono? (EBV)
- 95% of pts have self-limited disease in most cases requiring only supportive therapy - Acetaminophen or NSAIDS - warm salt water gargles - adequate rest (return to work/school based upon sx) - avoid contact sports for 6-8 weeks from onset - fever disappears in 10 days - lymphadenopathy and splenomegaly in 4 weeks
Epidemiology of CMV
- approx 1% of newborns infected - virus spread by: prolonged close contacts, blood/body fluids: transfusion (containing viable leukocytes), maternal-fetal transmission, STD - lifelong “infection” once infected - Congenital CMV occurs almost exclusively when preg. woman acquires primary infection (vs. reactivation) - perinatal CMV occurs when infant is infected at time of delivery through an infected birth canal or postnatal contact with maternal milk or or other secretions (40-60% transmission rate through nursing if mother infected)
When are the three times that you are most likely going to see CMV (worry about infection)?
- in pregnancy (babies) - transplant patients - in HIV (AIDS defining illness, shows up when CD4
Clinical presentation of congenital CMV?
- cytomegalic inclusion disease - ranges from inapparent infection (most) to severe/disseminated (-5%) - Petechiae, hepatosplenomegaly, jaundice common (60-80%) - microcephaly, growth retardation, prematurity (30-50%)
Clinical presentation of perinatal CMV?
- poor wt gain, adenopathy, rash, hepatitis, anemia, and atypical lymphocytosis
Clinical presentation of CMV mono?
- heterophil Ab negative mono syndrome (looks like mono but negative for mono spot, usually don’t have strep throat) - prolonged high fevers, profound fatigue and malaise - myalgias, HA, and splenomegaly are frequent - exudative pharyngitis and cervical adenopathy are rare - occasional rubelliform rash
Dx of CMV mono
- viral culture: MOST impt dx study in the eval of suspected CMV disease is the viral culture - CMV may be cultured from virtually any body fluid or organ system. Blood, urine, saliva, cervicovaginal secretions, CSF, bronchoalveolar lavage fluid, and tissues from bx specimens are all approp. specimens for culture - PCR - Ag assays - Tissue confirmation w/ AIDS related CMV : CMV GI or neuron disease, CMV pneumonitis = death
What is characteristic to CMV congenital infection in babies?
blueberry muffin lesions
Tx of CMV
Ganciclovir
What is fifth disease (Erythema infectiosum)?
caused by Human parvovirus B19 - respiratory tract is probably route of transmission
Clinical presentation of fifth disease?
- mild febrile exanthematous disease with little or no prodrome - low-grade fever, varying degrees of conjunctivitis, upper respiratory complaints, cough, myalgia, itching, nausea, and diarrhea are initial signs and sxs - Classic “slapped face” lesion: indurated, confluent erythema of the cheeks, fiery red - circumoral pallor - bilateral symmetric eruptions (maculopapular slightly raised blotchy areas with reticular or lacy pattern) appear on the arms, legs and trunk about one day later - Rash (when it occurs) usually lasts 1 week and may disappear then reappear in the same area a few hours later
Dx of Fifth disease?
- usually made clinically in kids - labs: elevated titer of IgM anti-parvovirus abs - PCR in serum
Tx of Fifth disease?
- symptomatic tx: NSAIDS
Roseola (infantum) epidemiology and pathophysiology?
- epidemiology: benign disease of infants 6 m to 4 yo (most commonly seen in children
Clinical presentation of Roseola (infantum)?
- first manifestations occur after 5-15 days incubation period with abrupt onset irritability and fever (up to 105 F) lasting 3-5 days - rash appears several hours after sudden drop in temp: faint small (2-3 mm) macules or maculopapules over neck and trunk extending to thighs and buttocks will last a few hours or up to 1-2 days management: symptomatic only
If child has seizure what test should be done?
- Lumbar puncture because you are worried about meningitis and encephalitis
Measles (Rubeola) epidemiology
- occurs only in human and remains worldwide health problem despite a vaccine - transmitted through nasopharyngeal secretions (directly or airborne droplets) to respiratory mucous membranes or conjunctivae of susceptible persons - Highly contagious: infectious from 5 days after exposure to 5 days after skin lesions appear
Clinical presentation of measles (rubeola)
- Koplik’s spots (small, red, irregular lesions with blue white centers) appear on oral mucosa 1-2 days before rash (look like salt on mucosa) - Brick red, irregular maculopapular rash: first appears on forehead, spreads downward over face, neck, and trunk and appears on feet by 3rd day “outward and downward” - can affect palms and soles last - lesions usually coalescence and disappear in same order as appearance after about 3 days - prodromal sxs subside 1-2 days after rash appears
Dx Measles (rubeola)
- usually clinical - labs: neutropenia, detection for IgM abs with ELIZA
Tx of measles (rubeola)
- isolation of pt - bedrest - antpyuretics - fluids - can have some bacterial disease complications, if so, tx with approp. abxs. - This is a vaccine preventable disease!!! complications: heart, and encephalitis
Rubella (german measles, 3-day measles) epidemiology
- nasopharyngeal secretions transmit virus - caused by Togavirus - transplacental transmission results in congenital rubella syndrome - age is an important determinant of the severity of Rubella (milder than measles)
Clinical presentation of Rubella?
- viral exanthemous primary disease is generally milder than rubeola - no prodromal in children - adults: prodromal illness precedes rash by 1-8 days and consists of malaise, HA, and fever (devastating in pregnancy: congenital rubella syndrome) - lymphadenopathy: large, tender, post-auricular and sub occipital nodes are most often involved, splenomegaly or generalized lymphadenopathy may be present - Rash appears 14-21 days after exposure and follows same pattern as rubeola (starts cephalically) lesions have lighter hue than measles, lesions usually remain discrete versus coalescent form and last 1-5 days (most commonly 3 days). Small red lesions (Forchheimer’s spots) may appear on soft palate (not pathognomonic)
Clinical presentation of congenital rubella syndrome?
-heart malformations (patent ductus arteriosus, interventricular septal defect, pulmonic stenosis) - eye lesions (corneal clouding, cataracts, chorioretinitis, microphthalmia) -microcephaly - mental retardation - deafness - thrombocytopenic purpura - hepatosplenomegaly - intrauterine growth retardation
Management of congenital rubella syndrome?
- Prevention - vaccinate all women of childbearing age (if already pregnant, wait until 2nd trimester when not as immunocompromised because it is a live virus
Dx and Tx of rubella
- leukonpenia - virus isolation and serologic tests of immunity: fluorescent ab tests, IgM abs to Togavirus Tx: acetaminophen provides symptomatic relief
Complications of Rubella
- exposure during pregnancy: congenital rubella: heart defects, cataracts, glaucoma, psychomotor retardation - post infectious encephalopathy - This is vaccine preventable disease!!!!
Epidemiology of mumps?
- etiologic agent: paramyxovirus - disease occurs most frequently in the spring - spread by respiratory route but less contagious than measles or chickenpox
Clinical presentation of the mumps
12-25 days incubation period - at least 25% of infections are subclinical - parotitis: parotid swelling (salivary adenitis) is first indication of illness and usually occurs suddenly: may be preceded by prodrome of malaise, anorexia, fever (up to 103F) and pharyngitis - glandular enlargement progresses over 1-3 days and subsides about a week after max enlargement - pain and tenderness may be marked or absent - epididymoorchitis: complicates 20-35% of post pubertal males, testicular involvement usually appears 7-10 days after onset of parotitis but may precede it or be simultaneous: - usually unilateral - acutely tender painful swollen testicle persist 3-7 days and subsides gradually - epididymis often palpable as swollen tender cord - heralded by recurrence of malaise, fever (103-106F), chills, HA, N/V -tx: no specific tx
Worst possible complication of mumps:
meningitis
What are the common cold viruses?
rhinovirus coronavirus adenovirus
influenza like illnesses?
influenza A virus influenza B virus
Influenza etiology?
- caused by members of Orthomyxoviridae family of viruses - Types A, B, and C are based on antigenic characteristics of the nucleoprotein (NP) and matrix (M) protein Ags. - Type A viruses undergo further surface antigenic classification: Hemagglutinin (H) ags (H1-3) Neuraminidase (N) ags (N1-2) - major antigenic shifts occur regularly: type A viruses about every 3 years (changes frequently, can swap with swine or avian, makes it very deadly) type B viruses about every 5 years - influenza outbreaks occur every year
Clinical presentation of influenza?
- abrupt onset of systemic sxs: HA, fever (38-41C), chills, myalgia, malaise: - accompanied by respiratory signs/sxs: cough, pharyngitis - dyspnea, hyperpnea, cyanosis, diffuse rales or signs of consolidation are evidence of pulmonary complications - acute illness generally resolves within a week
Complications of influenza?
- pneumonia (staph aureus) - Reye’s syndrome (especially children 2-16 yo) - Myositis, rhabdomyolysis, myoglobinuria (elderly: dehydrated and confused) - myocarditis and pericarditis
Dx influenza?
- rapid flu swab (Nasal, throat) - Leukopenia
Symptomatic tx for influenza?
- acetaminophen - rest - fluids - abx if pneumonia suspected
Anti-influenza virus drugs
- Neuraminidase inhibitors (used the most) Oseltamivir (Tamiflu) Zanamivir (Relenza) - Adamantane derivatives/M2 inhibitors (proton channel through viral envelope -> blocks acidification): amantadine rimantadine
Management and prevention of influenza?
- vaccination: trivalent inactivated influenza virus vaccine provides partial immunity for few months to 1 year - given in Oct or Nov of each year - CI when allergic eggs - Vaccination of high risk groups: - chronic cardiac or pulmonary disease (including asthma) - pregnant women - residents of chronic care/nursing facilities - over age 65 - chronic medical disorders: DM, renal disease, hemoglobinopathies, immunosuppressed - individuals who care for high risk populations
Epidemiology of Bronchiolitis?
RSV (member of paramyxovirus genus) major respiratory pathogen of young children - transmitted primarily by close contact with contaminated fingers or fomites - annual epidemics occur in late fall, winter or spring - incidence rates are highest in infants 1-6 months of age and accounts for 20-25% of hospitalizations in infants/young children (babies can’t cough up the thick bronchial secretions) - disease is milder in older children/adults
Clinical presentation of Bronchiolitis (RSV)?
infants: commonly presents as rhinorrhea, low-grade fever, cough, wheezing, mild systemic sxs severe illness: tachypnea, dyspnea, hypoxia, cyanosis even apnea may ensue - diffuse wheezing, rhonchi and rales (may not see wheezing) - clinical presentation of adults/older children: common cold presentation - younger children/infants: bronchiolitis, tracheobronchitis and pneumonia
Dx of bronchiolitis?
Get O2 sats!!! - rapid RSV with nasal washings using viral Ag ID using ELIZA or immunofluorescent assay - culture of nasopharyngeal secretions
Tx of bronchiolitis?
- antiviral therapy: ribavirin - sx relief: contact isolation, respiratory therapy, oxygen, secretion removal, hydration, antibronchospastic agents
Epidemiology of Croup
- caused by parainfluenza viruses: 4 major serotypes type 1: most frequent cause of croup (laryngotracheobronchitis) in children type 2: similar but less severe type 3: causes bronchiolitis and pneumonia in infants - account for up to 22% of respiratory illness in children, very mild disease in adults
Clinical presentation of Croup?
- acute febrile illness in children (50-80%) - coryza, sore throat, hoarseness, and variably croupy cough - breathing difficulty accompanied by a barking cough - much worse at night (day 3 the worst!)
Management of croup
sx relief: cool or moist air can bring relief - try bringing child into steamy bathroom or outside into the cool night air - a cool air vaporizer, set it up in the child’s bedroom and use it for the next few nights - Acetaminophen - ER tx: aerosolized racemic epinephrene predisone in ER and to go (oral) - after 3 hours of good presentation -> send them home - avoid cough medicines because they suppress coughs and you want to get rid of inflammation, but don’t want to suppress cough and make child lethargic and sleepy
Rabies epidemiology
-caused by rhabdovirus - 2 epidemiologic forms: urban: unimmunized domestic cats/dogs sylvatic: skunks, foxes, raccoons, wolves and bats
Clinical presentation of rabies (4 stages)
1) Prodrome: usually persists 1-4 days. Fever, HA, malaise, myalgias, increased fatigability, anorexia, N/V, pharyngitis, nonproductive cough -paresthesias and/or fascicultations around site of inoculation suggestive of rabies 2) Acute encephalitis: development of excessive motor activity, excitation, and agitation - confusion, hallucinations, combativeness, muscle spasms, meningismus, seizures and focal paralysis quickly follows - hyperesthesia with excessive sensitivity to bright light, noise or touch is common - Fever (up to 105F), dilated irregular pupils, increased lacrimation, salivation, perspiration, and postural hypotension occur -3) Profound brainstem dysfunction: occur shortly after onset of encephalitic phase, difficulty swallowing (with increased salivation) produces characteristic foaming at the mouth. Violent involuntary contractions of diaphragm and accessory, respiratory, pharyngeal and laryngeal muscles - coma and respiratory failure follow - recovery (rarely)
lab findings of Rabies
- isolation of virus (saliva, CSF or brain tissue) - indirect serologic evidence of immune response - direct antigent detection (skin or brain bxs)
Management of rabies?
- prevention: pre-exposure vaccinations: domestic animals, high risk individuals: animal handlers, veterinarians, cave explorers, lab workers - post-exposure prophylaxis: immunoglobulin
Ddx Variola versus varicella?
Variola (smallpox): rash starts on the face, lesions same stage, deep lesions, often palms, soles, centrifugal rash, Back>abdomen, multiloculated vesicles Varicella: rash starts trunk, lesions in crops, superficial lesions, never palms/soles, centripedal rash, back=abdomen, uniloculated vesicles
disease course of smallpox?
- Day 0 -> exposure - Day 12-14 -> fever, malaise, non-productive cough, HA, backache, joint pain -Day 14-16 -> papular rash on face -> extremities - Day 16-18 -> papular -> vesicular -> pustular - Day 22-26 -> crusted lesions - Day 28-30 -> resolving 10% will develop malignant disease and die 5-7 days after incubation
Vaccine for small pox?
- d/c’d in early 1970’s, but has been reinstituted b/c of concerns about bioterrorism, - routine vaccine, in the absence of a case of small pox is not recommended for those under 18 live vaccine: site becomes red, itchy in 3-4 days vesicle umbilicates and evolved into well formed pustule by day 6-11 - pustule scabs over b/t week 2 and 3 - scab falls off by end of 3rd week, leaving a scar
What is a key difference between internal virus proteins and surface antigens?
Internal viral proteins vary less
Describe the process of presentation of viral peptides on MHC Class I.
Viral peptides are chopped up by the proteasome These peptides are then fed through the TAP protein into the endoplasmic reticulum In the endoplasmic reticulum, it will be loaded onto an MHC class I molecule and it will then move to the cell surface where T cells can recognise the antigen
State three viruses (and the proteins involved) that evade antigen loading onto TAP.
EBV – EBNA1 – this cannot be chopped up by the proteasome HSV – ICP47 – blocks access of the peptides to the TAP protein CMV – US6 – blocks ATP binding to TAP
State two viruses (and the proteins involved) that modulate tapasin function and prevent MHC transport.
NOTE: tapasin is involved in loading MHC molecules Adenovirus E3-19K – prevents recruitment of TAP to tapasin and retains MHC in the ER CMV – US3 – binds to tapasin and prevents loading of peptides onto MHC
State one virus (and the protein involved) that interferes with MHC presentation at the cell surface.
KSHV (Kaposi Sarcoma Herpes Virus) – kK3 – induces polyubiquitination and internalisation of MHC
What do NK cells recognise on the cell surface that triggers killing of cells?
Missing self – lack of MHC on the cell membrane is not healthy
How do viruses evade this mechanism of NK-mediated killing infected cells?
Viruses encode MHC analogues (e.g. CMV gp UL40) – virally encoded MHC is useless but it fools the NK cells Upregulate MHC
Which cells does HIV target?
CD4+ T cells
Which cells does Ebola kill?
Dendritic cells Macrophages T cells (by the bystander response)
In what subset of the population does HMCV (human cytomegalovirus) cause disease?
Immunocompromised
What is the problem with HCMV with regards to bone marrow transplantation?
HCMV infects 60-90% of the population If HCMV is present in donated bone marrow, it could cause problems in the immunocompromised recipient
Explain how our knowledge about HCMV has allowed improved medical outcomes in bone marrow transplantation.
HCMV encodes UL138, which leads to loss of MRP-1 from the infected cell surface MRP-1 is a transporter of toxic drugs out of the cell Loss of MRP-1 leads to accumulation of certain molecules in the infected cell Vincristine is a toxic drug that accumulates in the infected cells and kills them So treating donated cells with vincristine before the transplant can eliminate CMV
What is antigenic drift?
Continued rapid evolution driven by antigenic pressure from the host
What is antigenic shift?
Introduction of new subtypes of the virus from an animal source NOTE: when they come from an animal source, the antigens don’t look like anything that humans have seen before
How else can viruses cause regular infections without changingtheir antigen profile?
They can have several genetically stable serotypes that co-circulate E.g. rhinovirus has more than 120 antigenically distinct serotypes
How many serotypes of influenza are there?
4
How many serotypes of poliovirus are there and what type of vaccine was produced for polio?
3 – trivalent vaccine NOTE: one of the serotypes has been eradicated now
What are the features of dengue haemorrhagic fever (DHF)?
Leakage of plasma from capillaries leads to: Increased haematocrit Increased red cell count Decrease in protein Tendency to severe bruising and bleeding
What is the treatment for DHF?
IV fluids
How many serotypes of dengue are there?
4
Explain the significance of the presence of multiple serotypes ofdengue with regards to the pathogenesis of DHF.
Infection with one serotype will cause antibody production Antibody generated against this serotype will bind to but NOT neutralise infection with another dengue serotype This can lead to ANTIGEN DEPENDENT ENHANCEMENT (ADE) causing Dengue Haemorrhagic Feve
What can viruses do to glycoprotein antigens that hinder antibody access to the antigens?
Heavily glycosylate the antigens
What does Ebola viruse have a high content of that makes them appear like apoptotic bodies?
Phosphatidyl serine lipids
What is the benefit to Ebola virus of appearing like apoptotic bodies?
They are rapidly taken up by macropinocytosis and, hence, taken away from antibody surveillance
How does the structure of Ebola affect antibody access to antigens?
Ebola has a long filamentous shape with lots of folds The folds may make the glycoproteins inaccessible to antibody
Name two factors produced by Ebola that allow it to evade detection by the innate immune system.
VP35 VP24
What important factor does Ebola encode that also helps deal with the antibody response?
Soluble glycoprotein – this acts as an antibody decoy and it is immunosuppressive (inhibits neutrophils) NOTE: GP2 and retrovirus glycoproteins also have an immunosuppressive peptide
Which virus is only suppressive in macaques?
Reston virus
How does Measles infect cells?
Via SLAM proteins (CD150)
Why did the measles vaccine have a much larger effect on childhood mortality than expected?
Measles can infect memory lymphocytes (these are SLAM positive) and erase immunological memory So a measles virus infection can result in a 2-3 year decrease in immunological memory that leads to morbidity and mortality from otherdiseases
What is the most common cause of sporadic encephalitis worldwide?
Herpes simplex encephalitis
Which subset of the population is herpes encephalitis most common in?
Most common in childhood – affecting previously healthy individuals on primary infection with HSV-1
What is interferon?
Transferrable factor produced when the cells are exposed to virus
What is the effect of interferon binding to interferon receptors on cells?
It binds to specific receptors and signals the de novo transcription of hundreds of interferon stimulated genes (ISG)
What are the three functions of type I interferons?
Induce antimicrobial state in infected and neighbouring cells Modulate innate immune response to promote antigen presentation and NK cells but inhibit proinflammation Activate the adaptive immune response
What are the type I interferons?
IFN alpha and IFN beta
What is the first interferon to be produced in a viral infection?
IFN beta
Which cells produce IFN beta?
All cells produce IFN beta and all tissues have IFNAR receptors
What is IFN beta induction triggered by?
IRF-3
Name a cell type that is specialised for producing IFN alpha.
Plasmacytoid dendritic cells
What do these cells express high levels of?
IRF-7
How many genes are there for IFN alpha and IFN beta?
Alpha – 13/14 isotypes Beta – ONE
Which IFN comes under type II interferon?
IFN-gamma - specialist immune signalling molecule
Which cell types produce this IFN?
Produced by activated T cells and NK cells
Which receptor do these IFNs signal through?
IFNGR
Which IFN falls under type III IFN?
IFN-lambda
Which receptors do type III IFNs signal through?
L-28 receptors IL-10 beta receptors
Where are these receptors mainly present?
Epithelial surfaces E.g. respiratory epithelium and gut
Which organ is IFN lambda very important in?
Liver
How does the innate immune system recognise non-self?
PRRs (pattern recognition receptors) on innate immune cells recognise PAMPs (pathogen-associated molecular patterns) NOTE: they often sense nucleic acids
Name two receptors that are involved in detecting the presence of viruses and state where they are found.
RIG-I like receptor (RLRs) – cytoplasmic Toll-like receptors (TLRs) – plasma membrane + endosomal membrane
Describe RIG-I signalling.
RIG-I like receptors will recognise single stranded RNA in the cytoplasm of the cell and it will signal through MAVS (mitochondrial) This will signal further downstream, leading to generation of IFN-beta transcripts
Describe TLR signalling.
TLR detects nucleic acids in the endosome (this isn’t normal) It will signal to molecules outside the endosome (MyD88) and send various transcription factors to the nucleus It will result in the switching on of expression of IFN alpha
Describe DNA sensing.
Mainly done by cGAS This is an enzyme that binds to dsDNA in the cytoplasm and synthesises cGAMP (second messenger) cGAMP diffuses to STING (found on endoplasmic reticulum) This triggers phosphorylation of the same sets of transcription factors and signalling molecules the RNA viruses were triggering
Describe the structure of IFN receptors for IFN alpha and IFN beta
They are heterodimers of IFNAR 1 and IFNAR 2
Describe the signalling from IFNAR receptors
IFN binds and the IFN receptor activates Jak and Tyk, which goes on to phosphorylate the STAT molecules STAT molecules dimerise and combine with IRF-9 It then goes to the nucleus, binds to a promoter and regulates transcription
What is IFITM3?
Interferon-induced transmembrane protein 3 These sit on the membrane of endosomes, in cells that have been previously stimulated by IFN It prevents fusion of the virus membrane with the endosomal membrane so the virus gets trapped in the endosome NOTE: mice and people lacking IFITM3 get more severe influenza
What are Mx1 and Mx2?
GTPases with a homology to dynamin Mx can form multimers that wrap around nucleocapsids of incoming viruses – this nullifies the viral genomes Mx1 – inhibits influenza Mx2 – inhibits HIV
Describe the actions of Protein Kinase R.
It phosphorylates the alpha subunit of eIF2 (initiation factor) that is important in translation This prevents ribosomes from binding to mRNA so NO NEW GENES WILL BE TRANSLATED It also phosphorylates NFkB, which is an important transcription factor that is part of the interferon and inflammatory response
When is PKR activated by cells?
It is an extreme measure and a last resort – only activated when the cell has no other option
Name a family of genes that suppress the cytokine signalling and turn off the response.
SOCS
State some mechanisms of viral evasion of the IFN response.
Avoid detection by hiding the PAMP Interfere globally with host cell gene expression and/or protein synthesis Block IFN induction cascades Inhibit IFN signalling Activate SOCS Replication strategy that is insensitive to IFN
Explain how hepatitis C controls the interferon response.
NS3/4 This is a protease that cleaves MAVS MAVS is important in detecting Hep C through the RIG-I pathway So Hep C is not detected
Explain how influenza controls the interferon response.
NS1 Acts an antagonist to interferon induction by binding to the RIG-I/TRIM25/RNA complex and preventing activation of the signalling pathway It also prevents nuclear processing of newly induced genes NS1 also migrates to the nucleus where it prevents the export of newly synthesised genes
What type of virus are Pox and Herpes viruses?
Large DNA viruses
What do Pox viruses encode that helps deal with the interferonresponse?
They encode soluble cytokine receptors that mop up IFN and prevent it from reaching its receptors
Describe a potential therapeutic use of this feature
This could be useful in autoimmune or inflammatory conditions where IFN and other cytokines are produced in abundance
Name two proteins produced by HIV that helps deal with restriction factors and state what they target.
Vif – APOBEC Vpu – Tetherin
Describe the normal action of APOBEC.
APOBEC is involved in the innate immune resistance to retroviruses and hepadnaviruses APOBEC modifies some of the nucleotides in reverse transcription and makes them into the wrong version APOBEC deaminates dC to dU in the minus strand of viral cDNA during reverse transcription This leads to G to A hypermutation resulting in ERROR CATASTROPHE This results in so many mutations that the viral genome becomes nonsense and the virus can’t replicate
What is the effect of Vif on APOBEC?
Vif counteracts the activity of APOBEC and targets it for degradation This removes the interference of APOBEC with reverse transcription
Describe the normal action of tetherin.
Tetherin sits on the cell surface of infected cells and binds to viruses that try to escape the cell to go and infect other cells This limits the spread of viral infection
What is the effect of Vpu on tetherin?
Vpu pulls tetherin back from the cell surface and targets it for degradation
What are two proteins produced by Ebola virus that are particularly important in dealing with the immune response?
VP35 VP24
What do these proteins do?
VP35 – inhibits the RIG-I pathway VP24 – stops the signal getting through from the IFN beta receptor to the nucleus (stops the STAT1 molecule from getting to the nucleus)
What two techniques can be used to observe the skewing of the immune response by viruses?
Transcriptomimics – shows changes in mRNA production Proteomimics – shows changes in protein expression
Describe how viral infections can cause cytokine storm.
Lots of virus propagation –> lots of interferon being produced –> massive release of TNF alpha and other cytokines
What is a serious consequence of cytokine storm?
Pulmonary fibrosis – due to accumulation of immune cells in the lungs
Explain why viruses that cannot control the interferon can beused as the next generation of live attenuated vaccines.
They will be able to infect the cells and it will replicate sufficiently to be able to mount an immune response but it wont replicate to the extent where it causes disease
The downside of this feature of the viruses is that these virus particles can’t be propagated in normal healthy cells. What is the solution to this issue?
Propagate the viruses in cells that are deficient in the IFN response
Explain why interferons are not frequently used as an antiviral therapy.
They stimulate the production of several cytokines and this causes several unpleasant side effects
