Microbiology - Virology Flashcards
Naked virus with icosahedral capsid components
Capsid + Nucleic acid
Enveloped virus with icosahedral capsid
Surface protein
Lipid bilayer
Capsid
Nucleic acid
Enveloped virus with helical capsid
Surface protein
Lipid bilayer
Helical capsid with nucleic acid inside
Recombination
exchange of genes between two chromosomes by crossing over within regions of significant base sequence homology
Reassortment
when viruses with SEGMENTED genomes (e.g. influenza virus) exchange segments. High-frequency recombination.
- Cause of influenza pandemics
Complementation
when 1 of 2 viruses that infect cell has a mutation that results in nonfunctional protein
Nonmutated virus “complements” the mutated one by making a functional protein that serves both viruses
Phenotype mixing
- occurs co-infection of a cell by two viruses
Genome of virus A can be partially or completed coated (forming pseudovirion) with surface proteins of virus B
Type B protein coat determines infectivity (tropism) of hybrid virus - Progeny from infection have a type A coat that is encoded in type A genetic material
Live attenuated viruses
induce humoral and cell-mediated immunity but have reverted back to virulence on rare occasions
Examples of live attenuated viruses
- Smallpox
- Yellow fever
- Chickenpox (VZV)
- Sabin’s polio virus
- MMR
- Influenza (intranasal)
Killed virus vaccine
induce only humoral immunity but are stable
Examples of killed viruses
Rabies
Influenza (injected
Salk Polio
HAV vaccines
Recombinant
HBV antigen (antigen = HBsAg), HPV (6, 11, 16, 18)
DNA viral genomes
All DNA viruses except PARVOVIRIDAE are dsDNA
- all are linear except (PAPILLOMA-, POLYOMA-, and HEPADNAVIRUSES [circular])
Parvovirus
ssDNA
RNA viral genomes
All RNA viruses except Reoviridae are ssRNA
Reoviridae
dsRNA
Positive stranded RNA viruses
“I went to a “RETRO” “TOGA” partry where I drank “FLAV”ored “CORONA” and ate “HIPPY” “CALI”fornia “PIC”kles
- Retrovirus
- Togavirus
- Flavovirus
- Coronavirus
- Hepevirus
- Calcivirus
- Picornavirus
Infectious naked viral genomes
purified nucleic acids of most dsDNA (except poxviruses and HBV) and (+) ssRNA viruses are infectious.
Non-infectious naked viral genomes
- Naked nucleid acids of (-) ssRNA and dsRNA viruses are not infectious. They need polymerases contained in complete virion
Virus ploidy
all viruses are haploid (with 1 copy of DNA or RNA) except retroviruses, which have 2 identical ssRNA molecules (= diploid)
DNA virus replication
all replicate within nucleus (except poxvirus)
RNA virus replication
all replicate in the cytoplasm (except influenza virus and retroviruses)
Viral envelopes
Give "PAPP" smears and "CPR" to a "NAKED HEPP"y Naked include - Papillomavirus - Adenovirus - Picornavirus - Polyomavirus - Calcivirus - Hepevirus
DNA viruses
"HHAPPPPy" H= Hepadna H= Herpes A = Adenoviruses P = Pox P = Parvo P = Papilloma P = Polyoma
DNA virus characteristics
- double stran ded (except parvovirus)
- linear (except papolloma, polyoma, and hepadna)
- are icosahedral except poxvirus
- replicate in the nucleus party (except pox)
Herpesviruses
- enveloped
- ds and linear
HSV-1
- oral (and some genital lesions), spontaneous temporal lobe encephalitis (most common cause of spontaneous encephaltitis in US)
keratoconjunctivitis - Latent in trigeminal ganglia
- transmitted through respiratory and saliva secretions
HSV-2
- Herpes genitalis
- Neonatal herpes
- Latent in sacral ganglia
- transmitted via sexual contact, perinatal
VZV
Varicella-zoster (chicken pox, shingles)
- Encephalitis
- Pneumonia
- Latent in dorsal root or trigeminal ganglia
- transmitted via respiratory secretions
EBV
HHV-4
- mononucleosis
- Burkitt’s lymphoma
- Hodgkin’s lymphoma
- Nasopharyngeal carcinoma
- Latent in B cells
CMV
Congenital infection
Mononucleosis (negative monospot) - immunocompetent patietnts
Pneumonia
Retinitis
Infected cells have “owl’s eye” inclusions
- Latent in mononuclear cells
HHV-6
Roseola
High fevers for several days that can cause seizures, followed by a diffuse macular rash
HHV-8
Kaposi’s sarcoma (HIV patients)
Hepadnavirus
- enveloped
- double stranded and partial circular
- acute or chronic hepatitis
- vaccine available - contains HBV surface antigen
- not retrovirus but has reverse transcriptase
Adenovirus
- non-enveloped
- double stranded and linear
- febrile pharyngitis - sore throat; acute hemorrhagic cystitis
- pneumonia
- conjunctivitis
Parvovirus
- non- enveloped
- single stranded and linear negative DNA
- B19 - aplastic crises in sicke cell disease, “slapped cheeks” rash in children - erythema infectiosym (fifth disease)
- RBC destruction in fetus leads to hydrops fetalis and death
- Pure RBC aplasia and rheumatoid arthritis-like symptoms in adults
Papillomavirus
- non-enveloped
- double stranded and circular
- HPV - warts (1,2,6,11)
- Cervical cancer (16, 18)
- Vaccine is available
Polyoma virus
- non-enveloped
- double stranded and circular
JC virus - associated with PML in HIV
BK virus - transplant patients, commonly kidney
Poxvirus
- enveloped
- double stranded and linear (largest DNA virus)
- smallpox
- vaccinia (cowpox)
- molluscum contagiosum - flesh colored dome lesions with central dimple
HSV identification
PCR is test of choice
Tzanck test - a smear of an opened skin vesicle to detect multinucleated giant cells seen HSV-1, HSV-2, and VZV
** Infected cells have intranuclear Cowdry A inclusions
EBV
A herpesvisus
- can cause mononucleosis, hepatosplenomegaly, pharyngitis, and lymphadenopathy
- peak incidence (15 - 20 y.o)
- Atypical lymphocytes seen in peripheral smear are not infected B cells but rather cytotoxic T cells
- Positive Monospot test
- associated with Hodgkin’s, Burkitt lymphomas as naseopharyngeal carcinoma
Positive Monospot
- heterophile antibodies detected by agglutination of sheep/horse RBCS
Reoviruses
- nonenveloped
- linear dsRNA with 10-12 segments
- icosahedral (double)
- Coltivirus - Colorado tick fever
- Rotavirus - #1 cause of fatal diarrhea in children
Picornaviruses
- non-enveloped \+ SS linear RNA - icosahedral "PERCH" Poliovirus Echovirus Rhinovirus Coxsackievirus Hep A virus
Hepevirus
-non-enveloped
+ SS linear RNA
- icosahedral
HEV
Calciviruses
- nonenveloped
- SS + linear RNA virus
- icosahedral capsid
- Norovirus - viral gatsroenteritis
Flaviviruses
- enveloped SS + linear RNA
- icosahedral
- HCV
- Yellow fever
- Dengue
- St. Louis encephalitis
- West Nile virus
Togaviruses
- enveloped
- SS + linear RNA and icosahedral
- Rubella
- Eastern & Western equine encephalitis
Retroviruses
- enveloped
- SS + linear RNA
- icosahedral
- have reverse transcriptase
- HTLV - T-cell leukemia
- HIV - AIDS
Coronaviruses
enveloped SS + linear RNA
Helical
Common cold and SARS
Orthomyxoviruses
Enveloped
SS - linear RNA
8 segments
Influenza virus
Paramyxoviruses
Enveloped SS - linear RNA Nonsegmented Parainfluenza - croup RSV - bronchiolitis in babies - treated w/ ribavirin Measles Mumps
Rhabdoviruses
Enveloped
SS - linear RNA
Helical
Rabies
Filoviruses
Enveloped
SS - linear RNA
Helical
Ebola/Marbug hemorrhagic fever - often fatal!
Arenaviruses
Enveloped
SS - CIRCULAR RNA
2 segments
Helical
LCMV - lymphocytic choriomeningitic virus
Lassa fever encephalitis - spread by mice
Bunyaviruses
Enveloped SS - CIRCULAR RNA 3 segments Helical California encephalitis Sandfly/Rift valley fevers Crimean-Congo hemorrhagic fever Hantavirus - hemorrhagic fever, pneumonia
Delta virus
Enveloped
SS - CIRCULAR RNA
Uncertain capsid
HDV - defective virus that requires HBV co-infection
Negative stranded viruses
must transcribe negative strand to positive
Virion brings its own RNA-dependent RNA polymerase
Mneumonic for negative stranded viruses
"Always Bring Polymerase Or Fail Replication" A = Arenaviruses B = Bunyaviruses P = Paramyxoviruses O = Orthomyxoviruses F = Filoviruses R = Rhabdoviruses
Segmented viruses
All are RNA viruses "BOAR" B = Bunyavirus O = Orthomyxoviruses (influenza viruses) A = Arenavirueses R = Reoviruses
Picornaviruses
Poliovirus Echovirus Rhinovirus Coxsackievirus Hepatitis A
Picornaviruses
RNA is translated into 1 large polypeptide that is cleaved by proteases into functional viral proteins
- Can cause viral meningitis (EXCEPT Rhinovirus and HAV)
- All are enteroviruses (fecal-oral spread) except rhinovirus
Rhinovirus
A picornavirus Non-enveloped RNA virus Causes common cold > 100 serologic types Acid labile - destroyed by stomach acid Doesn't infect GI tract (unlike other picornaviruses)
Yellow fever virus
Flavivurs (also an arbovirus)
- transmitted by Aedes mosquitos
- Has monkey or human resevoir
Sx: high fever, black vomitis, and jaundice
Rotavirus
Common WORLDWIDE cause of infantile gastroenteritis
- segmented dsRNA virus
- major cause of acute diarrhea during winter esp. in day care centers, kindergartens
- villous destruction with atrophuy leads to decreased absorption of NA and loss K
Influenza viruses
Orthomyxoviruses
Enveloped, negative ss RNA viruses with 8 segments
Hemagglutinin - promotes viral entry
Neuraminidase - promotes progeny virion release
- patient at risk for fatal bacterial superinfection
Rapid genetic changes
Mode of protection from influenza viruses
Killed viral vaccine is MAJOR mode of protection
Another vaccine contains live, temp sensitive mutant that replicates in the nose but not in lung
Genetic shift/antigenic shift
- causes pandemics
- reassortment of viral genome
- segments undergo high-frequency recombination such as human flu A virus with swine flu A virus
Genetic drift
- causes epidemics
- minor (antigenic drift) - changes based on random mutation
Rubella virus
togavirus
causes rubella, known as German measles
- Fever, posterior auricular lymphadenopathy,
- Truncal rash that starts at head and descends
- causes mild disease in children but serious congenital disease
Paramyxovirus
- disease in children
- parainfluenza (croup: seal-like barking cough)
- Mumps, Measles
- Contain surface F protein, which causes respiratory epithelial cells to fuse and form multinucleated cells
RSV
Paramyxovirus - causes brionchiolitis, pneumonia in infants
Palivizumab (monoclonal antibody against F portein) prevents pneumonia caused by RSV infection in premature infants
Measles
paramyxovirus
- Kolik spots (red spots with blue-white cente on buccal mucosa)
- descending maculopapular rash
- subacute sclerosing panencephalitis and giant cell pneumonia (in immunosuppresed)
- rash presents last and spreads from head to toe, includes hands and feet (vs. trunk in Rubella)
3 C’s of Measles
Cough
Coryza (rhinitis, inflammation of nasal mucosa)
Conjunctivitis
Mumps
Paramyxovirus Parotitis Orchitis (inflammation of testes) Asceptic meningitis - Can cause sterility in puberty
Paramyxovirus Parotitis Orchitis (inflammation of testes) Asceptic meningitis - Can cause sterility in puberty
Bullet-shaped virus
- Negri bodies - cytoplasmic inclusions in neurons infected by rabies virus
- Found in Purkinke cells of cerebellium
- Post exposure treatment is wound cleansing and vaccine with/without rabies immunoglobulin
Rabies
- Has long incubation period (weeks to months) before symptom onset
- Travels to CNS by migrating in a retrograde fashion up nerve axons
- Progression of disease: fever, malaise –> agitation, photophobia, hydrophobia –> paralysis, coma –> death
- Associated with bat, raccoon, skunk bites than dog bites in US
Hep A virus
RNA picornavirus
- transmitted fecal-orally
- no carries
- short incubation (weeks)
- no HCC risk
- assymptomatic, acute, alone
HBV
DNA hepadnavirus
- transmitted parentally, sexually, maternal-fetal
- carrier state possible
- long incubation (months)
- HCC risk as it integrates with host genome and acts as oncogene
HCV
RNA flavivirus
- transmitted primarily in blood, IV drug users, post-transfusion
- carrier state
- long incubation
- HCC risk from chronic inflammation
- associated with cryoglobulin
HDV
RNA deltavirus transmission: Parental, Sexual, Maternal-Fetal Carrier state -Superinfection (after chronic HBV) - Co-infection (with acute HBV) - defective virus, dependent on HBV
HEV
RNA hepevirus
- transmitted fecal orally, especially with waterborne epidemics
- no carrier ste
- short incubation
- no HCC risk
- high mortality in pregnent women
Anti-HAV (IgM)
IgM antibody to HAV, best test to detect active Hep A
Anti-HAV (IgG)
IgG antibody indicates prior HAV infection and/or prior vaccination; protects against new infection
HBsAg
antigen found on surface of HBV
indicates HBV infection
Anti-HBsAg
antibody to HBsAg
- indicates immunity to Hep B
HBcAg
Antigen associated with core of HBV
Anti-HBV
antibody to HBcAg
IgM = acute/recent infection
IgG = prior exposure or chronic infection
HBeAg
indicates active viral HBV replication and thus high transmissibility
Anti-HBe
antibody to e antigen; indicates low transmissibility
Window period
- can occur 5-6 months after exposure
- no HBsAg but Anti-HBe Anti-HBcIgM
HIV
diploid genome (2 molecules of RNA)
reverse transcriptase synthesizes dsDNA from RNA
dsDNA integrates into host genome
- virus binds to CCR5 (early) or CXCR4 (lates) co-receptor and CD4 on T cells
- binds to CCR5 and CD4 on macrophages
Homozygous CCR5 mutation
= immmunity from HIV
Heterozygous CCr5 mutation
= slower course of HIV
Structural proteins associated with HIV
- env (gp 120 and gp41) - formed from cleavage of gp160 to form envelope proteins
- gp120 - attachment to CD4+ T cells
- gp41 - fusion and entry
-gag (p24) - capsid protein
pol - reverse transcriptase, aspartate protease integrase
HIV diagnosis
- intially with ELISA (high sensitivity, low specificity)
- confirmed with Western blot (high specificity)
HIV/PCR viral load
tests determine the amount of viral RNA in plasma.
High viral load associated with poor prognosis
Also use viral load to monitor drug therapy
AIDS diagnosis
< 200 CD4
- HIV with AIDS defining condition (e.g PCP pneumonia)
- CD4/CD8 < 1.5
ELISA/Western blot
looks for antibodies to viral proteins
are often falsely negative in the first 1-2 months of HIV infection
- Falsely positive initially in babies born to infected mothers (anti-gp120 crosses placenta)
Four stages of infection
- Flu-like (acute)
- Feeling fine (latent) - virus is replicating in lymph nodes
- Falling count
- Final crisis
HIV + with low grade fevers, cough, hepatosplenomegaly, tongue ulcer
Histoplasmosis capsulatum
- causes pulm symptoms in “healthy” patients
- oval yeast cells within macrophages, CD4 < 100
HIV + w/ fluffy white cottage cheese lesions
C. albicans
- pseudohyphase
- oral if CD4 < 400
- esophageal if CD4 < 100
HIV + w/ superficial vascular proliferation
Bartonella henselae (causes bacillary angiomatosis) - biopsy shows neutrophilic inflammation
HIV+ w/ chronic watery diarrhea
Cryptosporidium
- acid fast cysts seen in stool when CD4 < 200
HIV + w/ encephalopathy
- JC virus reactivation (cause of PML)
- results in demyelination of oligodendrocytes CD4 < 200
HIV + w/ brain abscesses
Toxoplasmosis gondii
- many ring-enhancing lesions on imaging
- CD4 < 100
HIV+ w/ meningitis
- C. neoforms
- India ink stain reveals yeast with narrow-based budding and large capsule
- CD4 < 50
HIV + w/ retinitis
CMV
- cotton wool sports on fundoscopic exam and may occur with esophagitis
CD4 < 50 cells
HIV + dementia
Directly associated with HIV
- may have differentiate from other causes
HIV + with superficial neoplastic proliferation of vasculature
HHV-8 (Kaposi’s sarcoma)
- biopsy reveals lymphocytic inflammation
- don’t confuse with bacilliary angiomatosis
HIV + with hairy leukoplakia
EBV
- often on lateral tongue
HIV+ w/ non-Hodgkin’s lymphoma
EBV
- often on oropharynx (Waldeyer’s ring)
HIV+ w/ squamous cell carcinoma (of anything!!)
HPV
- in gay men, may have anal HPV
HIV + with primary CNS lymphoma
EBV
- multiple or focal, differentiate from toxoplasmosis
HIV + with interstitial pneumonia
CMV
- biopsy reveals cells with intranuclear (owl’s eye) inclusion bodies
HIV + with invasive aspergillosis
Aspergilosis fumigatus
- pleuritic pain, hemoptysis, infiltrates on imaging (acute angled hyphae)
HIV+ with pneumonia
Pneumocystis jirovecci
- especially in CD4 < 200 cells
HIV + with TB-like disease
Mycobacterium avium-intracelluaire
- esp in CD4 < 50 cells
Envelope proteins for HIV
- acquired from budding from host cell plasma membrane
- gp120: docking protein for attachment to CD4
- gp41: transmembrane protein for fusion and entry
Gap(p24) protein
HIV capsid protein
p17 associated with HIV
Matrix protein
pol gene
HIV
- reverse transcriptase
- aspartate protease
- integrase
