Virology Flashcards
(13 cards)
Enveloped v. Non-enveloped viruses
Enveloped: Outer covering of virus – lipid bilayer/glycoproteins from host membrane
Helps viruses avoid immune system, allows virus to bind host cell receptors
Fuses with host cell membrane for virus to penetrate host cell
Sensitive to desiccation in environment
Transmission typically respiratory, parenteral, sexual
Non-envelope: very resistant to environment
Often transmitted by the fecal-oral route
Viral Replications: ss(+)RNA, ss(-)RNA, dsDNA, retroviruses
ss(+)RNA: uses host machinery to make polyprotein & cleave it (cytoplasm)
ss(-)RNA: encodes viral RNA-dependent RNA polymerase (cytoplasm)
Creates its own ss(+)RNA/mRNA to replicate/make more copies
dsDNA: replicates in nucleus, can encode its own polymerases
early mRNA: regulatory proteins for DNA replication, host cell machinery
late mRNA: structural proteins to protect/build virus
Retrovirus: encodes reverse transcriptase – viral-RNA dependent DNA polymerase
Creates dsDNA and uses Integrase to insert itself into host genome
Transcription regulated by host cell
CMV
Herpesvirus – large dsDNA, icosahedral capsid, enveloped
Transmission: Close contact with infectious fluids (urine)
Primary Infection: asymptomatic/subclinical
Latency: survives in circulating mononuclear cells, PMNs, vascular endothelial cells
CM: Immunocompetent – infectious mononucleosis (heterophile-negative mono)
HIV/AIDS – retinitis, polyradiculopathy, esophagitic, colitis
Transplant Host – CMV syndrome (fever, leukopenia, atypical lymphocytosis,
Hepatosplenomegaly, myalgia, arthralgia)
Interstitial pneumonitis, hepatitis, colitis
Diagnosis: PCR, histology, Treatment: ganciclovir, foscarnet
Influenza A/B
Orthomyxovirus – 8 segmented ss(-) RNA, helical, enveloped
Influenza A: infects humans, birds, mammals, gene reassortment allows for re-infection
Subtypes: depend on H (hemagglutinin) and N (neuraminidase) surface antigens
Antigenic drift: minor changes due to single mutations, epidemics
Antigenic shift: major changes due to gene reassortment, pandemics
Influenza B: infect only humans, no reservoir in non-humans
No subtypes/antigenic variation, only causes epidemics, not pandemics
Transmission: respiratory droplets, fomites, direct person-to-person
Clinical Manifestations: fever, chills, cough, nasal congestion, myalgias, headaches
Rotavirus
Reovirus – 11 segmented dsRNA, icosahedral capsid, non-enveloped
Major cause of acute GE requiring hospitalization of infants/children worldwide
No reinfections possible; typically only limited to infants young children
Novel Replication: TLP becomes DLP in cell cytosol
Transcription occurs inside DLP to produce ss(+)RNA (hide dsRNA from damage)
Highly communicable: TM: stool, contaminated hands/objects
Resistant to low pH
Pathogenicity: NSP4 Enterotoxin – stimulates anion movement across membrane
Promotes diarrhea
Clinical presentation: vomiting/fever 2-3 days, then profuse watery diarrhea 4-5 days
Diagnosis: Rapid antigen test, Treatment: supportive, Vaccine: good efficacy!
Norovirus
Calicivirus – ss(+)RNA, icosahedral capsid, non-enveloped
Cupcake-like appearance on EM
Highly contagious, Highly stable, not inactivated by alcohol/mild detergents
Transmission: Aerosolized by vomiting or toilet flush, 24-48hr incubation
Clinical Manifestation: most common cause of acute GE in US (90% non-bacterial GE)
Most common cause of foodborne disease outbreaks in US
Reinfections possible due to unusually high mutation rate
Diagnosis: PCR, Treatment: supportive
Rhinovirus
Picornavirus – ss(+)RNA, icosahedral capsid, non-enveloped
Clinical Manifestations: Symptomatic respiratory illness, colds
Transmission: Respiratory droplets, fomites, direct person-to-person
Rapid onset of infection: binds to ICAM on respiratory epithelial cells
Optimal temp for replication is 32C – why only infects nose/upper airways
Many serotypes allow for reinfection
Coronavirus
Coronavirus – ss(+)RNA, helical capsid, enveloped
Cause a significant infection of common colds, bronchitis, pneumonia
Source: bats (SARS – Chinese horseshoe bats)
SARS-CoV: zoonotic transmission via civets; cause leukopenia, thrombocytopenia
MERS-CoV: zoonotic transmission via camels
Spread via respiratory droplet; need to isolate patients to stop epidemic
HHV-8
Herpesvirus – dsDNA, icosahedral capsid, enveloped
Oncogenic: Causes Kaposi’s sarcoma, Castlemann’s disease, Primary Effusion Lymphoma
Transmission: Deep French kissing (saliva)
Vast majority of cells latently infected so anti-virals not effective
HRSV
Paramyxovirus – ss(-)RNA, helical capsid, enveloped
Clinical Manifestations: major cause of lower respiratory tract illness in young kids
Repeated infections common
Most severe illnesses in immunocompromised
Diagnose: PCR, antigen-detection; fusion protein vaccine in development
Prevention: MAB against RSV surface fusion protein for high-risk infants
HMPV
Pneumoviridae – ss(-)RNA
Second most common cause of lower respiratory tract infection in young children
Less severe than HRSV
Diagnosis: RT-PCR, no treatment, no vaccine
Parvovirus B19
Parvovirus – small ssDNA, icosahedral capsid, nonenveloped
Transmission: respiratory droplets, maternal-fetal intrauterine
Clinical Manifestations: Fifth disease (erythema infectiosum – slapped cheeks) in kids
Acute Symmetric Polyarthropathy in women, aplastic crisis in anemics
Chronic anemia in AIDS, hydrops fetalis in newborns
Pathogenicity: capsid proteins target blood group P antigen
-causes arrest of erythroid precursor development
HPV
Most common STI in US, leads to cervical cancers in women through cervical dysplasia
HPV Vaccine decreases cervical cancer as well as head/neck/anal cancers (anti-cancer!)
