Exam Review 1 Flashcards
What is a virus?
An infectious, obligate intracellular parasite comprising genetic material (DNA or RNA) surrounded by a protein coat and/or an envelope derived from a host cell membrane
How do viruses replicate?
replicate by assembly of pre‐formed components into many particles
How are viruses cultivated/cultured?
- primary human foreskin fibroblast (made from fresh tissues); 2. mouse fibroblast cell like (3T3); 3. HeLa cells (human epithelial cell line); NOTE: 3T3 and HeLa are continuous cell lines
What are synctia?
fusion of several cells to create 1 giant cell
What is a plaque assay?
Allows determination of viral count; series of dilutions; want the count to be between 10 and 100; add agar overlay, can later be removed for staining and counting
How can a virus be measured?
hemagglutination, electron microscopy, viral enzymes, serology, nucleic acid
How many kinds of viral genomes are there?
7
What is the key rule of viral genomes?
They must make mRNA that can be read by host ribosomes b/c they’re parasites (can’t carry out protein synthesis on their own)
What are the rules of + and - strand DNA and RNA?
mRNA is always + strand; DNA of equivalent polarity is also the + strand; RNA and DNA complements of + strands are - strands; Not all + RNA is mRNA
What is encoded in the viral genome?
Gene products and regulatory signals for: replication of the viral genome, assembly and packaging of the genome, regulation and timing of the replication cycle, modulation of host defenses, spread to other cells and hosts
What is NOT encoded in the viral genome?
No genes encoding the complete protein synthesis machinery, no genes encoding proteins involved in energy production or membrane biosynthesis, no classical centromeres or telomeres
What are examples of dsDNA viruses? (double stranded)
adenovirus, herpesvirus, papillomavirus, polyomavirus, poxvirus
How are dsDNA genomes copied?
Either by DNA pol that they bring with them or by the DNA pol from the host
How are gapped dsDNA genomes copied?
This genome can’t be copied - it has to be repaired! Reverse transcriptase helps to complete the double stranded DNA
How is ssDNA copied?
Has to be converted to dsDNA
What is unique about RNA genomic viruses?
Host cells have no RNA-dependent RNA polymerase (RdRp), so RNA viruses encode RdRp, which produces RNA genomes and mRNA from RNA templates
How does dsRNA replicate?
Viruses carry RdRp; copy the + RNA strand
Which family of viruses are ssRNA + sense with DNA intermediate?
Retroviruses! (HIV, HTLV)
How do retroviruses work?
+ stranded RNA genome - looks like an mRNA… but it’s not translated! RNA is copied to a single strand of -DNA and then to double stranded DNA through reverse transcriptase (brought in w/ the particle - RNA is not translated)
What is a provirus of a retrovirus?
Integrated retroviral DNA in the host genome
What are some examples of ssRNA - sense?
paramyxovirus (measles, mumps), rhabdovirus (rabies), filovirus (ebola, marburg), orthomyxovirus (flu), arenavirus (lassa)
What is reassortment?
Typically occurs when there is a segmented genome; when 2 strains coinfect a cell, then new virus particles can also mix, enabling a lot of genetic diversity
What is the example of viral therapy in ABCD1 transporter?
Treatment for x-linked adrenoleukodystrophy; patient’s marrow derived hematopoietic stem cells infected with lentiviral vector with normal ABCD1 transporter gene; re-infused into patient; neurological status improved or stabilized
What does it mean that viruses are metastable?
Must protect the genome (stable) AND come apart on infection (unstable)
How does symmetry affect viruses?
Identical protein subunits are distributed with helical symmetry for rod-shaped viruses and platonic polyhedra symmetry for round viruses
What is helical symmetry?
Coat protein molecules engage in identical, equivalent interactions with one another and with the viral genome to allow construction of a large, stable structure from a single protein subunit (interact with each other and with the RNA - all non-covalent interactions so that they come apart)
How can you make a round capsid from proteins with irregular shapes?
all round capsids have precise numbers of proteins (multiples of 60 are common); spherical viruses come in many sizes, but capsid proteins are 20-60 kDa
What is icosahedral symmetry?
Looks like icosahedron (solid w/ 20 faces, each an equilateral triangle), allows formation of a closed shell with smallest number (60) of identical subunits; interactions of all molecules with their neighbors are identical (head to head, tail to tail, etc) - NOT covalently bound
What is an envelope?
Lipid bilayer derived from host cell (viral genome does not encode lipid synthetic machinery); acquired by budding from membrane (can be any cell membrane, but is virus-specific); nucleocapsids inside the envelope may have helical or icosahedral symmetry
How do viruses leave cells?
Released by budding or lysing, some can move from cell to cell, can be released at apical or basolateral domains
How does neurominidase affect viruses leaving cells?
don’t want to rebind to cell ; neurominidase (glycoprotein enzyme) cleaves SA from surface of the cell - as it’s inserted into the cell, it clears the surface of the cell to prevent reinfection
How does oseltamivir work? Zanamivir?
Flu inhibitors - inhibit neurominidase
When does secondary viremia occur?
As a consequence of viral replication in organs distal to the site of entry
At what layer of skin can virus replicate?
dermis
How does the skin prevent viral replication?
Skin inactivates virus by desiccation, acids, or other inhibitors on skin or by commensal organisms
What is the primary entry point for viruses?
mucosal surfaces
Why does the respiratory tract prevent infection?
- produce a lot of mucus!; 2. mucociliary escalator moves liquid from lungs to esophagus; 3. swept by cilia to esophagus where it is swallowed; 4. filtering of particles in sinuses; 5. immune cells and antibodies in lower regions
What syndromes affect the upper respiratory tract? The lower?
Upper: rhinitis, pharyngitis, laryngitis; lower: tracheitis, bronchitis, bronchiolitis, bronchopneumonia
What part of the eye can a virus infect?
sclera, conjunctiva
What is one of the big barriers in the mucosal layer that prevents systemic infection?
virus has to compromise the basement membrane, and many viruses can’t traverse this membrane
What is a sendai virus?
normally released @ apical side, but you can make a viral mutant that will release at both apical and basolateral parts of the cell - spreads sendai virus throughout the body (lethal infection) - importance of polarized spread
What are the types of viremia?
Passive (inoculation), primary (virus replicating in the first cells that it finds), secondary (replicating in distal cells, disseminated)
How are viruses spread by respiratory secretions?
aerosols produced by speaking, sneezing, coughing; can contaminate hands, tissues
What is the clinical course of Dengue fever?
Primary infection is typically asymptomatic or acute febrile illness with headache, back and limb pain, and rash. Normally self limited (1-2 weeks). In 1/14,000 cases, hemorrhagic fever occurs, can lead to death. Antibodies to dengue made.
What happens when a patient gets Dengue more than once?
Much worse the second time - incidence of hemorrhagic fever and shock syndrome skyrockets; this is because antibodies to the first dengue bind to other serotypes and make them easier to get into macrophages
What are general properties of latent viruses?
Viral gene products are replicated in low numbers or not at all; cells harboring the latent genome are poorly identified by the immune system; viral genome stays intact
What is the difference between disseminated and systemic?
Disseminated: an infection that spreads beyond the primary site of infection; systemic: many
organs become infected
What is Respiratory Syncytial Virus?
RSV - ubiquitous infectious disease; most common cause of viral respiratory infection in childhood; essentially all children infected by age 2; marked seasonality
Who is at particular risk for RSV?
very young infants, premature babies, immunocompromised children, congenital heart or lung disease
What is the virus responsible for RSV?
member of paramyxoviridae (like measles, mumps, etc), ssRNA, negative strand, enveloped virus, F (fusion) protein and G (hemagglutinin) protein responsible for attachment and are main targets of immune response
What do RSV vaccines primarily target?
F protein
What does RSV form?
synctia - multi-nucleated giant cells
How is RSV spread?
respiratory secretions; survives on fomites (tabletops, toys, stethoscopes), very common HAI
Where does RSV replicate?
ciliated epithelial cells in nasopharynx, small bronchioles, and type 1 neumocytes in alveoli
What complications can RSV cause?
bronchiolitis, pneumonia, airway sensitivity, wheezing, hypoxia
What is the clinical course of RSV?
Incubation period = 3-6 days; Duration of uncomplicated RSV = 1-3 weeks; Progression of clinical syndromes: 1. upper respiratory tract disease (rhinorrhea and congestion with or without fever); 2. croup (laryngotracheobronchitis) - cough, stridor; 3. bronchiolitis (about 50% of cases) - cough, wheeze; air trapping crackles, wheezes on examination; 4. pneumonia - more severe respiratory distress, hypoxia; can also cause otitis media, apnea (in infants)
Does RSV spread to other systems?
No viremic phase, risk of invasive disease is low; viral replication is low during symptomatic phase of disease (much of the pathology is due to immune response)
How is RSV diagnosed?
clinical diagnosis, viral culture, rapid antigen detection, RT-PCR (gold standard)
What is the immune response to RSV?
Incomplete immunity; single serotype but 2 subgroups; antibody-mediated immunity is directed at F and G proteins; immune response causes most symptoms
How is RSV treated?
Largely supportive (O2 if needed, secretion management, intubation if required); bronchodilators are controversial, steroids have NO BENEFIT, ribavirin is used in severe immunocompromised cases - no clear benefit
How should RSV be prevented?
hand hygiene, cleaning of fomites, contact isolation for patients in hospital; monoclonal antibody prophylaxis
Does RSV have a vaccine?
No - existed in 1960s, caused incomplete immunity and then exacerbated disease in infants
What is the monoclonal antibody prophylaxis for RSV?
targets F glycoprotein; monthly doses during RSV season (only given to very high risk patients); very costly; typically given to the following: Premature infants less than 29 weeks gestation or less than 32 weeks + chronic lung disease (O2 required more than 28 days of life), Hemodynamically significant heart disease, Neuromuscular disorder/ congenital anomaly impaired ability to clear secretions, Immunocompromised chemotherapy, heart transplant, etc, Cystic fibrosis with chronic lung disease or nutritional compromise
What is the structure of influenza?
Orthomyxoviridae; ssRNA, negative-sense, enveloped virus; viral genome in 8 segments; HA (hemagglutinin), NA (neuraminidase (influenza A, B)) = immunodominant antigens and determinants of viral serotype (e.g., H1N1 vs. H3N2)
How is influenza named?
Type/ host species (human default)/ location/ year (HA/NA type) Influenza A/ California/ 2009 (H1N1)
What is the pathogenesis of influenza?
infects columnar epithelial cells of respiratory tract; Replication early (1-3 days), shedding for ~7 days (1-2 weeks in children); Children can shed 48 hours before symptoms, Adults can shed 24 hours before symptoms; Destruction of epithelial cells, increased mucus production, ciliary stasis; Local cytokine production; Antibody responses to HA, NA important for future immunity
How is influenza transmitted?
Inhalation of fewer than 3 virus particles can cause infection; Nasopharyngeal secretions of infected individuals contains up to 10 million infectious viruses/mL; Influenza virus particles can remain infectious for 24 to 48 hours on smooth surfaces and for up to 5 minutes on the hands
What are the symptoms of influenza?
Fever (may be very high), chills, headache, myalgias, arthralgias, dry cough, nasal discharge (NOTE: these are all considered “flu-like illness”); young children may have atypical course (“sepsis-like” syndrome, GI symptoms, croup/bronchiolitis, otitis media)
What are potential complications of influenza?
pneumonia, bacterial superinfection common (with pneumococcus, S. aureus, and group A streptococci), myocarditis, encephalitis, myositis, Reye syndrome rare
What is the incubation period and duration of illness for influenza?
Duration of illness = 4-8 days of acute illness, 1-2 weeks convalescence
What is the main reservoir of the flu?
Birds are the main animal reservoirs; Other susceptible species include humans, pigs, dogs, cats, ferrets, mink, camels, seals, whales
Why is influenza affected by antigenic shift and drift?
Influenza lacks RNA proofreading enzymes; RNA-dependent RNA polymerase (copies viral genome) makes error ~ 1:10 thousand nucleotides (~length of influenza vRNA)
What is antigenic drift?
slow change in viral surface antigens over time; due to direct mutation
What is antigenic shift?
Reassortments of vRNA occurs when more than one type of influenza virus infects a single cell; Results in rapid change in viral genetics and sudden large change from one antigen to another
What is a pandemic?
Widespread human infection - not a surrogate marker for disease severity; Novel viruses must replicate in human cells, be transmissible between humans, and be associated with little pre-existing immunity in populations in order to have pandemic potential.
How is influenza diagnosed?
clinical, Viral culture, Rapid antigen testing (solid-phase) - Sensitivity may only be 50-70% (lower for H1N1); PCR testing (done at NYP, gold standard)
How is influenza treated?
Adamantanes, Neuraminidase inhibitors; Early treatment (within 48 hours of illness) greatest benefit and reduces complications
What are adamantanes?
amantidine, rimantidine: effective for influenza A only, target M2 ion channel, interfere with uncoating, resistance common, may develop on therapy, prophylaxis (both) and treatment (amantidine only)
What are neuraminidase inhibitors?
zanamivir, oseltamivir, peramivir: effective for influenza A and B, resistance emerging, including among novel H1N1 strains, prophylaxis and treatment, early initiation of therapy (less than 72 hours for efficacy)
When should influenza be treated?
Ideally before 48 hours of illness have elapsed
Who should be treated for influenza?
anyone hospitalized or at high risk for severe influenza or complications; bimodal age (younger than 2 or over 65); Chronic pulmonary, cardiac, renal, hepatic, hematologic (including sickle cell), diabetes, neurologic or neurodevelopmental conditions; Immunosuppression; Pregnant or postpartum; children on long-term aspirin therapy; American Indians/Alaska Natives; morbidly obese; nursing home residents
What are the types of flu vaccine?
Inactivated vaccine - given IM; live, attenuated vaccine - given intranasally
What are the recommendations for IM flu vaccine?
Whole influenza virus grown in eggs; formalin-fixed whole virus or “split-virus” formulations; 1 dose/year except for children under age 9 getting first vaccination (2 doses); immunity in about 1-2 weeks, lasts about 6 months; Everyone older than 6 months of age can get it (including you!)
What are the recommendations for intransal flu vaccine?
Preferential for children 2-8 years old, can be given to healthy people 9-49 years old
What is the structure of herpesvirus?
enveloped, dsDNA
What is the advantage of enveloped viruses?
They’re more labile in the environment
What is the epidemiology of HSV?
Agent is ubiquitous, no seasonality, 58% HSV1 seropositivity and 17% HSV2 seropositivity by adulthood, vast majority are asymptomatic or unrecognized
What is the epidemiology of CMV?
Agent is ubiquitous, no seasonality, 59% seropositivity by adulthood, vast majority are asymptomatic or unrecognized
How is CMV transmitted?
person-to-person or via infected fomites (i.e., contaminated surfaces); can be shed in urine, saliva, cervicovaginal secretions, breast milk, possibly semen, intrauterine, blood transfusion, organ transplantation
What is the pathogenesis of CMV?
- Infection of Endothelial Cells (GU, upper GI, Respiratory Tract); 2. Infection of Trafficking Leukocytes; 3. Hematogenous Dissemination via Leukocytes to Multiple Tissues; 4. Symptomatic Disease or Asymptomatic Infection; can have latent infection in myelomonocytic stem cells and circulating monocytes and later reactivation
What can CMV cause?
mono, congenital infection, hepatitis, retinitis, pneumonitis, graft vs host disease, encephalopathy; linked to atherosclerosis
What happens in congenital CMV?
Infection can cause brain damage that may result in mental retardation, spasticity, seizures, deafness and/or blindness; characterized by hepatosplenomegaly, Lymphadenopathy, Respiratory distress, Rash (“blueberry muffin baby”), Microcephaly; see Elevated LFTs, Thrombocytopenia, Pneumonitis
How is CMV diagnosed?
Serology – IgG and IgM detection; Virus isolation; Antigen (pp65) detection; CMV DNA PCR
How is CMV treated?
Ganciclovir and Valganciclovir; Foscarnet; Cidofovir; Viral DNA polymerase inhibitors used for pre-emptive and prophylactic therapy in immunocompromised patients with CMV infection (does not eradicate the persistent infection)
How is HSV transmitted?
person-to-person (rarely by fomites) - perinatal, skin-to-skin, sexually
How is HSV shed?
saliva, oro-facial lesions, genital lesions and secretions, tears (?); HSV-1 more commonly shed from oral cavity, HSV-2 more commonly from genital tract
What is the pathogenesis of HSV?
- Virus transmission to mucosal surface or abraded epithelium; 2. Uptake by sensory nerves; 3. Retrograde transport to sensory ganglia; 4. Establishment of latent infection; 5. Productive viral replication in sensory neurons; 6. Anterograde transport to mucosal and cutaneous sites; 7. Lesion formation, viral replication
What are manifestations of HSV?
Clinical manifestations are determined by portal of entry, immune status of the host, and whether the infection is primary or recurrent; HSV is a neurotropic virus that infects sensory ganglia hence pain is a common manifestation of mucocutaneous HSV infections
What are putative associations of HSV?
Exposure to neurotropic herpesviruses have been associated with diminished cognitive performance and increased risk or Alzheimer’s disease. If causal links exist there is likely to be gene by environment effects.
How is HSV diagnosed?
Serology – IgG and IgM detection - NOTE: Anamnestic IgM responses can occur; IgM tests unreliable; most tests cannot accurately distinguish HSV-1 and HSV-2; Virus isolation; HSV DNA PCR
How is HSV treated?
Acyclovir and Valacyclovir, Penciclovir and Famciclovir, Foscarnet; All are viral DNA polymerase inhibitors; For life threatening HSV infections use I.V. acyclovir; Valacyclovir use can reduce risk of transmission of genital herpes from infected to susceptible partner; NOTE: Therapy does not eradicate latent infection
How can HSV be prevented?
In neonatal cases: Cesarean delivery, Antivirals in final 4 weeks of gestation (unproven); Genital: Abstinence, Valacyclovir use by infected partner, Condom use (limited benefit)
Are there vaccines for CMV? HSV?
No - both in development
How can you remember dsDNA viruses?
“Please Help Hillary Perfectly Prepare for the Presidency of America” o Poxvirus (molluscum) o Hepadnavirus (HBV) o Herpesvirus (HSV) o Parvovirus (B19) o Papillomavirus (HPV)! o Polyomavirus (JC, BK)! o Adenovirus
How can you remember - strand ssRNA viruses?
“Always Bring Polymerase Or Fail Replication” o Arenavirus, Bunyavirus (hantavirus) o PaRaMyxovirus (Parainfluenza, RSV, Measles/Mumps) o Orthomyxovirus (influenza) o Filovirus (Ebola) o Rhabdovirus (Rabies)
