Virology Flashcards
Mutations can produce antigenic, drug-resistant or attenuated variants
Genomic reassortment causes epidemics
Complementation: one virus produces a protein that can be used by another virus
Phenotypic mixing: two different viruses infect the same cell
Viral genetics
Naked viruses with double-stranded circular DNA and an icosahedral nucleocapsid
Least 100 types
Direct contact or sexually
Infect squamous cells and induce formation of cytoplasmic vacuole (koilocytes)
Genes E6 and E7
HPV
Only causes disease in immunocompromised hosts
Causes progressive multifocal leukoencephalopathy (PML) in patients with AIDS
JC Polyoma Virus
Only causes disease in immunocompromised hosts
Causes hemorrhagic cystitis and neuropathy and in patients with solid organ (kidney) and bone marrow transplants
BK Polyoma Virus
Enveloped virus with icosahedral nucleocapsid and linear double-stranded DNA
Herpes Simplex Viruses
Member of flavivirus family Most common cause of epidemic encephalitis Most prevalent in SEA transmitted by Culex mosquitoes Thalamus infarcts on CT scan
Japanese B Encephalitis
Flavivirus
Bird-mosquitoes-man cycle
Initial self-limited febrile illness with progression to neuroinvasive disease
West Nile Fever
“Thread-like” viruses
Longest viruses
Outbreak of hemorrhagic fever in Zaire (1976)
100% mortality rate
Ebola Hemorrhagic Fever
Retrovirus causing adult T-cell leukemia and a HTLV-associated myelopathy
HP: malignant T cells with flower-shaped nucleus
Human T-cell lymphotropic virus (HTLV)
Envelope virus with two copies (diploid) of a single-stranded, positive-polarity RNA genome
Most complex of the known retroviruses
Many serotypes
Human Immunodeficiency Virus
Enveloped virus with an icosahedral nucleocapsid and one ss-positive-RNA
Transmission: respiratory droplet, transplacental
Infection confers lifelong immunity
Prevented by giving live-attenuated vaccine
Should not be given to immunocompromised patients or to pregnant women
Rubella virus
Incubation of 14-21 days
Prodrome followed by 3-day maculopapular rash and posterior auricular LAD
Face-trunk-arms-legs
Immune complex polyarthritis in adults
German measles
p24, p7 proteins
p17 protein
Gag gene
Function:
- nucleocapsid (p24, p7)
- matrix (p17)
Reverse transcriptase protein
Protease protein
Integrase protein
Pol gene
Function:
- transcribes RNA genome into DNA (reverse transcriptase)
- cleaves precursor polypeptides (protease)
- integrates viral DNA into host cell DNA (integrase)
gp120 protein
gp41 protein
env gene
Function:
- attachment to CD4 protein ANTIGENICITY CHANGES RAPIDLY (gp120)
- fusion with host cell (gp41)
Group-specific antigen
Located in the core
Not known to vary
Antibodies against p24 do not neutralize HIV infectivity but serve as important serologic markers of infection
p24
Interacts with the CD4 receptor
Gene mutates rapidly –> many antigenic variants
Antibody neutralizes HIV infectivity, but the rapid appearance of variants –> difficult to prepare vaccine
High mutation rate may be due to lack of an editing function in the reverse transcriptase
gp120
Most immunogenic region of gp120
V3 loop
Mediates the fusion of the viral envelope with the cell membrane at the time of infection
gp41
Proteins: tat
Function: activation of transcription of viral genes
Tat gene
Proteins: rev
Function: transport of late mRNAs to cytoplasm
rev gene
Proteins: Nef
Function: decreases CD4 and class I MHC proteins
nef gene
Proteins: Vif
Function: enhances hypermutation
vif gene
Proteins: vpr
Function: transport in nondividing cells
vpr gene
Proteins: vpu
Function: enhances virion release
vpu gene
Transmission: Original source - chimpanzee Transfer of body fluids Transplacental and perinatal Needlestick
Human Immunodeficiency Virus
Stages of infection (HIV)
- phase 0 (infection)
- phase 1 (window period)
- phase 2 (seroconversion)
- phase 3 (latent period)
- phase 4 (early symptomatic)
- phase 5 (aids)
HIV acquired through sexual intercourse, blood, or perinatally
Phase 0 - INFECTION
Rapid viral replication but HIV test is negative
Phase 1 - WINDOW PERIOD
Peak of viral load, positive HIV test, mild flu-like illness, lasting 1-2 weeks
Phase 2 - SEROCONVERSION
Asymptomatic, CD4 goes down, lasts 1-15 years
Phase 3 - LATENT PERIOD
CD4 500 to 200, lasts 5 years, mild mucocutaneous, dermatologic and hematologic illnesses
Phase 4 - EARLY SYMPTOMATIC
CD4 <200, lasts 2 years, AIDS-defining illnesses develop
Phase 5 - AIDS
Distinguished from all other RNA viruses by the presence of an unusual enzyme, reverse transcriptase
Reverse transcriptase - which converts a single-stranded RNA viral genome into double-stranded viral DNA
Retroviridae
Infected during the 1st trimester
Associated abnormalities: Patent ductus arteriosus Congenital cataracts Sensorineural deafness Mental retardation
Congenital Rubella Syndrome
Enveloped virus with one piece of single-stranded, positive-polarity RNA
Hypervariable region in envelope glycoprotein
6 serotypes
Diagnosis by anti-HCV or HCV RNA
Transmission:
- most prevalent blood-borne pathogen
- major mode: blood-borne (IV drug abusers)
- minor modes: needle-stick, vertical transmission, sexual
Pathogenesis:
- replication in liver by liver-specific micro-RNA
- hepatocellular injury due to immune attack
- alcoholism greatly enhances rate of hepatocellular CA
- chronic carriage of HCV is much higher than HBV
Spectrum of disease:
- incubation period of 8 weeks
- clinical presentation resembles hepatitis B
- autoimmune reactions
- main cause of essential mixed cryoglobulinemia
Hepatitis C Virus
Treatment:
Acute hepatitis C - interferon
Chronic hepatitis - peginterferon
Liver transplantation for severe cirrhosis
Enveloped virus with helical nucleocapsid and one piece of single-stranded, positive-polarity RNA
Prominent club-shaped spikes form a “corona”
2 serotypes
Transmission:
- horseshoe bat (reservoir)
- Civet cat (intermediate host)
- respiratory droplet transmission
Spectrum of disease:
- COMMON COLDS (2nd most common colds)
- severe acute respiratory syndrome (SARS)
Coronavirus
DNA VIRUSES
DNA Viruses are HHAPPPy viruses
Hepadna
Herpes
Adeno
Pox
Parvo
Polyoma
Papilloma
All DNA viruses have DOUBLE-stranded DNA except
PARVOVIRUS
All DNA viruses have linear DNA except
Papilloma
Polyoma
Hepadna
All DNA viruses are icosahedral except
All DNA viruses replicated in the nucleus except
POXVIRUS
Naked virus with icosahedral symmetry
Single-stranded DNA genome
One serotypes
MOT: respiratory droplets & transplacental
Not oncogenic
No vaccine
Parvovirus B19 (FIFTH DISEASE)
NAKED DNA viruses double-stranded linear DNA and an icosahedral nucleocapsid
Only virus with fiber (PENTON)
41 antigenic types
MOT: aerosol droplet, respiratory fecal-oral, direct contact
Spectrum of disease: URT: pharyngitis, conjunctivitis, coryza LRT: bronchitis, atypical pneumonia GIT: acute gastroenteritis GUT: hemorrhagic cystitis Histopath: COWDRY TYPE B intranuclear inclusions
Not oncogenic
Has vaccine
Adenovirus
NAKED DNA viruses with double-stranded circular DNA and an icosahedral nucleocapsid
Least 100 types
MOT: direct contact or sexually
Pathogenesis:
Infect squamous cells and induce formation of cytoplasmic vacuole (koilocytes)
Genes E6&E7
Is oncogenic
Has vaccine
Human Papillomavirus
Bright red cheek rash (slapped cheeks) with fever, coryza and sore throat
Erythema Infectiosum (FIFTH DISEASE)
Transient by put severe aplastic anemia in children
Sickle cell anemia, thalassemia or spherocytosis
Aplastic crisis
Fetal infections on PARVOVIRUS
1st trimester: fetal death
2nd trimester: hydrops fetalis
Immune-complex arthritis of small joints
Arthritis
Pancytopenia in immunodeficiency patients in PARVOVIRUS
CHRONIC B19 infection
