Virology Flashcards
Viral Recombination
Exchange of gene between 2 viral genetic sequences of one virus by crossing over within regions of significant base sequence homology
Viral Reassortment
Exchange of segments between two viruses with different segmented genomes (ex influenza virus), usually happens when the two viruses infect the same cell. High frequency recombination
Complementation
When 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein. The non mutated virus “complements” the mutated one by making a functional protein that serves both viruses
Phenotypic mixing
Occurs when simultaneous infection of a cell with 2 viruses
Genome of virus A can be partially or completely coated w/ the surface proteins of virus B
Type B protein coat determines the tropism or infectivity of the hybrid virus.
Progeny from this hybrid infection have type A coat that is encoded by its type A genetic material
Live attenuated vaccines
Induce humoral AND cell-mediated immunity
Can revert to virulence on rare occasions
No boosters needed for live attenuated vaccines
Dangerous to give live vaccines to immunocompromised patients or their close contacts (except for MMR)
Ex: smallpox, yellow fever, chicken pox (VZV), polio virus (Sabin), MMR, influenza (nasal)
Killed vaccines
Induce ONLY humoral immunity but are stable and will not revert to virulence
Ex: rabies, influenze (injected), polio (Salk) –> RIP
Recombinant
Uses recombinant virus
Ex: HBV (antigen = recombinant HBsAg), HPV (recombinant of type 6, 11, 16, 18)
DNA viral genomes
All DNA viruses except the Parovirus (part of a virus, ssDNA) are dsDNA
All are linear except papilloma, polyma, and hepadnaviruses (all 3 are circular)
RNA viral genome
All RNA viruses are ssRNA except Reovirus (repeato-virus, dsRNA)
Positive stranded RNA viruses: I went to a retro (retrovirus) toga (togavirus) party, where i drank flavored (flavivirus) Corona (coronavirus) and ate hippy (hepevirus) Californian (calicivirus) pickles (picornavirus)
Naked viral genome infectivity
Purified nucleic acids of most dsDNA (except poxvirus and HBV) and positive strand ssRNA (like mRNA) viruses are infectious
Naked nucleic acids of negative strand ssRNA and dsRNA viruses are not infectious and require polymerases contained in the complete virion to function and replicate
Viral replication
DNA viruses: all replicate in the nucleus (except poxvirus)
RNA viruses: all replicate in the cytoplasm (except influenza virus and retrovirus)
Viral envelopes
Naked (nonenveloped) viruses include: papillomavirus, adenovirus, parovirus, polymomavirus, calicivirus, picornavirus, reovirus, and hepevirus
–> give PAPP smear and CPR to naked Heppy
Enveloped viruses generally acquire their envelopes from plasma membranes, but herpesvirus acquire from nuclear membrane
Hepadnavirus
DNA virus, enveloped, partially ds and circular
HBV: acute or chronic hepatitis, vaccine available, not a retrovirus but has reverse transcriptase
Adenovirus
DNA virus, naked, ds and linear
Causes febrile pharyngitis, pnemonia, conjunctivitis (pink eye)
Parovirus
DNA virus, naked, ss and linear (negative strand), smallest DNA virus
B19 virus: aplastic crisis in sickle cell disease, “slapped cheeks” rash in children (erythema infectiosum, 5th disease), rheumatoid arthritis-like symptoms in adults
Papillomavirus
DNA virus, naked, ds, circular
HPV: warts (1,2,6,11), CIN, cervical cancer (16,18)
Polyomavirus
DNA virus, naked, ds, circular
JC virus: progressive mutlifocal leukoencephalopathy (PML) in HIV
BK virus: transplant patients, commonly target kidneys
Poxvirus
DNA virus, enveloped, ds, linear, largest DNA virus
Smallpox, cowpox, molluscum contagiosum (flesh-colored dome lesions with central umbilicated dimple)
HSV1
DNA virus, enveloped, ds, linear
Gingivostomatitis, keratoconjunctivitis, temporal lobe encephalitis, herpes labialis (lips), latent in trigeminal ganglia
Transmitted by respiratory secretions, saliva
HSV2
Herpes genitalis, neonatal herpes, latent in sacral ganglia
Transmitted by sexual contact or perinatally
Tzanck test (genital herpes): smear of opened skin vesicle to detect multinucleate giant cells
HHV3, VZV
Chicken pox, shingles, encephalitis, pneumonia, latent in trigeminal ganglia
Transmitted by respiratory secretions
HHV4, EBV
Mononucleosis, characterized by fever, hepatosplenomegaly, pharyngitis, and lymphadenopahty (posterior cervical nodes)
Transmitted by respiratory secretions and saliva (kissing disease)
Infects B cells, atypical reactive cytotoxic T cells seen on blood smear
Detect by positive monospot test (heterophile antibody)
HHV5, CMV
Congenital infection, mononucleosis (negative monospot), pnemonia, retinitis
Infected cells have characteristic “owl eye” inclusions
Latent in mononuclear cells
Transmitted congenitally and by transfusion, sexual contact, saliva, urine, transplant
HHV6
Causes Roseola
High fevers for several days that can cause seizures, followed by diffuse macular rash
Transmitted by saliva
HHV7
Less common cause of Roseola
HHV-8
Causes Kaposi sarcoma, a neoplasm of endothelial cells
Seen in HIV/AIDS and transplant patients
Dark/violaceous flat and nodular skin lesions representing endothelial growths. Can also affect GI tract and lungs
Transmitted by sexual contact
Reoviruses
RNA virus, naked, DS segmented, linear, icosahedral
Rotavirus:
The most important global cause of infantile gastroenteritis
Causes villous destruction with atrophy leads to decreased absorption of Na+ and loss of K+
CDC recommends vaccination of all infants
Picornaviruses
RNA virus, naked, SS positive, linear, icosahedral
RNA is translated into 1 large polypeptide that is cleared by proteases into functional viral proteins.
All are fecal-oral spread except for rhinovirus
PERCH
Poliovirus
Echovirus: aseptic meningitis
Rhinovirus: “common cold”, destroyed by stomach acid
Coxsackievirus: aseptic meningitis, myocarditis, hand/foot/mouth disease, pericarditis
HAV: acute viral hepatitis
Hepevirus
RNA virus, naked, SS positive, linear, icosahedral
HEV: hepatitis E
Calicivirus
RNA virus, naked, SS positive, linear, icosahedral
Norovirus: viral gastroenteritis
Flavivirus
RNA virus, enveloped, SS positive, linear, icosahedral
Yellow fever: transmitted by Aedes mosquitoes, symptoms include high fever, black vomits, and jaundice
HCV: chronic hepatitis
West Nile virus
Togavirus
RNA virus, enveloped, SS positive, linear, icosahedral
Rubella:
Once known as German measles
Fever, postauricular lymphadenopathy, fine rash
Causes mild disease in children but serious congenital disease (blueberry muffin appearance signifying extra medullary hematopoiesis)
Retrovirus
RNA virus, enveloped, SS positive, linear, icosahedral
Have reverse transcriptase
HTLV (human T lymphotrophic virus): T cell leukemia
HIV
Coronavirus
RNA virus, enveloped, SS positive, linear, helical
“Common cold” and SARS
Orthomyxovirus (influenza virus)
RNA virus, enveloped, SS negative, linear 8-segmented, helical
Contain hemagglutinin (promotes viral entry) and neuraminidase (promotes proven virion release) antigens
Patients at risk for fatal bacterial superinfection
Rapid genetic changes
Genetic shift vs genetic drift
Sudden Shift is more deadly than graDual Drift
Genetic shift: causes pandemics. Reassortment of viral genome, segments undergo high-frequency recombination, such as when human flu virus recombines w/ swine flu virus
Genetic drift: causes epidemics. Minor changes based on random mutation
Rhabdovirus
RNA virus, enveloped, SS negative, linear, helical
Rabies virus:
Bullet-shaped virus
Negri bodies commonly found in Purkinje cells of cerebellum and in hippocampal neurons
Travels to the CNS by migrating in a retrograde fashion up nerve axons
Long incubation period (weeks to months)
Progression of disease: fever, malaise –> agitation, photophobia, hydrophobia –> paralysis, coma –> death
Post-exposure treatment is wound cleansing and vaccination +/- rabies immunoglobulin treatment
More commonly found in bats, raccoons, and skunks bites
Paramyxovirus
RNA virus, enveloped, SS negative, linear, helical
Parainfluenza: croup
RSV: bronchioloits in babies, treat w/ ribavirin, prevent w/ palivizumab
Measles virus: Koplik spots (bright red spots w/ blue-white center on buccal mucosa) followed by descending maculopapular rash, 3 Cs (cough, coryza, conjunctivitis)
Mumps virus: parotitis, orchitis, aspetic Meningitis (POM)
Filovirus
RNA virus, enveloped, SS negative, linear segmented, helical
Ebola virus
Arenavirus
RNA virus, enveloped, SS negative, circular segmented, helical
Lymphocytic choriomeningitis virus
Bunyavirus
RNA virus, enveloped, SS negative, circular segmented, helical
California encephalitis
Congo hemorrhagic fever
Delta virus
RNA virus, enveloped, SS negative, circular, uncertain capsid shape
HDV: “defective” virus that requires HBV co-infection to function
Hepatitis viruses
HAV (RNA, picornavirus): fecal oral, short incubation, no HCC risk, asymptomatic, acute
HBV (DNA, hepadnavirus): parenteral, sexual, maternal-fetal, long incubation, can act as oncogene for HCC
HCV (RNA, flavivirus): blood (IVDU), long incubation, HCC from chronic inflammation, cirrhosis, chronic
HDV (RNA, delta virus): parenteral, sexual, maternal-fetal, need HBV to function, superinfection leads to poor prognosis
HEV (RNA hepevirus): fecal-oral (waterborne), short incubation, no risk for HCC, high mortality in pregnant women
Anti-HAV IgM
IgM antibody to HAV
Best test to detect active hep A
Anti HAV IgG
IgG antibody
Indicate prior HAV infection and/or prior vaccination
Protects against reinfection
HBsAg
Antigen found on surface of HBV
Indicates current HBV infection
Anti0HBs
Antibody to HBsAg
Indicates immunity to hep B
HBcAg
Antigen associated w/ core of HBV
Anti-HBc
Antibody to HBcAg
IgM= acute/recent infection
IgG= prior exposure or chronic infection
Positive during window period (period between infection and reliable testing, can present w/ negative test but still be infective)
HBeAg
A second, different antigenic determinant in the HBV core
HBeAg indicates active viral replication and therefore high transmissibility
Anti-HBe
Antibody to HBeAg, indicates low transmissibility
HIV virus
Retrovirus
Diploid genome (2 molecules of RNA)
Three important structural genes and proteins
- Env (gp120 and gp41): formed from cleavage of gp160 to form envelope glycoproteins, gp120 attaches to host CD4+ T cells while gp41 is responsible for fusion and entry
- Gag (p24): capsid protein
- Pol: reverse transcriptase, aspartate protease, integrase
Reverse transcriptase synthesizes dsDNA from RNA, dsDNA integrates into host genome via integrase
Virus binds CCR5 (early) or CXCR4 (late)
Homozygous CCR5 mutation: HIV immunity
Heterozygous CCR5 mutation: slower course
“F”our stages of untreated HIV infection: flu-like (acute), felling fine (latent), falling count, final crisis
HIV diagnosis
Presumptive diagnosis made with ELISA (sensitive, high false positive, SNNOUT)
Positive ELISA results confirmed w/ Western blot (specific, high false negative, SPPIN)
Both tests look for viral proteins via antibodies and are often falsely negative in the first 1-2 months and falsely positive initially in babies born to infected mother due to placental transfer of proteins
HIV PCR determines viral load in plasma with high viral load associated w poor prognosis. Also used to monitor effect of drug therapy
AIDS diagnosis w/ less than 200 CD4+ (normal 500=1500)
Common diseases of HIV patients
Systemic: cough, hepatosplenomegaly, tongue ucler (histoplasma)
Dermatologic: hairy leukoplakia (EBV), thrush (candida)
Gastrointestinal: chronic diarrhea (cryptosporidium)
Neurologic: abscess (toxo, CD4 <50)
Prions
Caused by conversion of a NORMAL protein termed prion protein (PrPc) to a beta pleated form (PrPsc), which is transmissible.
PrPsc resist protease degradation and facilitates conversion of PrPc to PrPsc
Accumulation of PrPsc results in spongiform encephalopathy and dementia, ataxia, and eventually death
Can be sporadic (Creutzfeldt-Jakob disease, rapidly progressive dementia)
Can be inherited (Gerstmann-Straussler-Scheinker syndrome)
Can be acquired (Kuru)
