Virology

Question 1

Viral Recombination

Answer 1

Exchange of gene between 2 viral genetic sequences of one virus by crossing over within regions of significant base sequence homology

Question 2

Viral Reassortment

Answer 2

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

Question 3

Complementation

Answer 3

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

Question 4

Phenotypic mixing

Answer 4

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

Question 5

Live attenuated vaccines

Answer 5

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)

Question 6

Killed vaccines

Answer 6

Induce ONLY humoral immunity but are stable and will not revert to virulence

Ex: rabies, influenze (injected), polio (Salk) –> RIP

Question 7

Recombinant

Answer 7

Uses recombinant virus

Ex: HBV (antigen = recombinant HBsAg), HPV (recombinant of type 6, 11, 16, 18)

Question 8

DNA viral genomes

Answer 8

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)

Question 9

RNA viral genome

Answer 9

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)

Question 10

Naked viral genome infectivity

Answer 10

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

Question 11

Viral replication

Answer 11

DNA viruses: all replicate in the nucleus (except poxvirus)

RNA viruses: all replicate in the cytoplasm (except influenza virus and retrovirus)

Question 12

Viral envelopes

Answer 12

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

Question 13

Hepadnavirus

Answer 13

DNA virus, enveloped, partially ds and circular

HBV: acute or chronic hepatitis, vaccine available, not a retrovirus but has reverse transcriptase

Question 14

Adenovirus

Answer 14

DNA virus, naked, ds and linear

Causes febrile pharyngitis, pnemonia, conjunctivitis (pink eye)

Question 15

Parovirus

Answer 15

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

Question 16

Papillomavirus

Answer 16

DNA virus, naked, ds, circular

HPV: warts (1,2,6,11), CIN, cervical cancer (16,18)

Question 17

Polyomavirus

Answer 17

DNA virus, naked, ds, circular

JC virus: progressive mutlifocal leukoencephalopathy (PML) in HIV

BK virus: transplant patients, commonly target kidneys

Question 18

Poxvirus

Answer 18

DNA virus, enveloped, ds, linear, largest DNA virus

Smallpox, cowpox, molluscum contagiosum (flesh-colored dome lesions with central umbilicated dimple)

Question 19

HSV1

Answer 19

DNA virus, enveloped, ds, linear

Gingivostomatitis, keratoconjunctivitis, temporal lobe encephalitis, herpes labialis (lips), latent in trigeminal ganglia

Transmitted by respiratory secretions, saliva

Question 20

HSV2

Answer 20

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

Question 21

HHV3, VZV

Answer 21

Chicken pox, shingles, encephalitis, pneumonia, latent in trigeminal ganglia

Transmitted by respiratory secretions

Question 22

HHV4, EBV

Answer 22

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)

Question 23

HHV5, CMV

Answer 23

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

Question 24

HHV6

Answer 24

Causes Roseola

High fevers for several days that can cause seizures, followed by diffuse macular rash

Transmitted by saliva

Question 25

HHV7

Answer 25

Less common cause of Roseola

Question 26

HHV-8

Answer 26

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

Question 27

Reoviruses

Answer 27

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

Question 28

Picornaviruses

Answer 28

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

Question 29

Hepevirus

Answer 29

RNA virus, naked, SS positive, linear, icosahedral HEV: hepatitis E

Question 30

Calicivirus

Answer 30

RNA virus, naked, SS positive, linear, icosahedral Norovirus: viral gastroenteritis

Question 31

Flavivirus

Answer 31

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

Question 32

Togavirus

Answer 32

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)

Question 33

Retrovirus

Answer 33

RNA virus, enveloped, SS positive, linear, icosahedral Have reverse transcriptase HTLV (human T lymphotrophic virus): T cell leukemia HIV

Question 34

Coronavirus

Answer 34

RNA virus, enveloped, SS positive, linear, helical "Common cold" and SARS

Question 35

Orthomyxovirus (influenza virus)

Answer 35

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

Question 36

Genetic shift vs genetic drift

Answer 36

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

Question 37

Rhabdovirus

Answer 37

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

Question 38

Paramyxovirus

Answer 38

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)

Question 39

Filovirus

Answer 39

RNA virus, enveloped, SS negative, linear segmented, helical Ebola virus

Question 40

Arenavirus

Answer 40

RNA virus, enveloped, SS negative, circular segmented, helical Lymphocytic choriomeningitis virus

Question 41

Bunyavirus

Answer 41

RNA virus, enveloped, SS negative, circular segmented, helical California encephalitis Congo hemorrhagic fever

Question 42

Delta virus

Answer 42

RNA virus, enveloped, SS negative, circular, uncertain capsid shape HDV: "defective" virus that requires HBV co-infection to function

Question 43

Hepatitis viruses

Answer 43

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

Question 44

Anti-HAV IgM

Answer 44

IgM antibody to HAV Best test to detect active hep A

Question 45

Anti HAV IgG

Answer 45

IgG antibody Indicate prior HAV infection and/or prior vaccination Protects against reinfection

Question 46

HBsAg

Answer 46

Antigen found on surface of HBV Indicates current HBV infection

Question 47

Anti0HBs

Answer 47

Antibody to HBsAg Indicates immunity to hep B

Question 48

HBcAg

Answer 48

Antigen associated w/ core of HBV

Question 49

Anti-HBc

Answer 49

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)

Question 50

HBeAg

Answer 50

A second, different antigenic determinant in the HBV core | HBeAg indicates active viral replication and therefore high transmissibility

Question 51

Anti-HBe

Answer 51

Antibody to HBeAg, indicates low transmissibility

Question 52

HIV virus

Answer 52

Retrovirus Diploid genome (2 molecules of RNA) Three important structural genes and proteins 1. 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 2. Gag (p24): capsid protein 3. 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

Question 53

HIV diagnosis

Answer 53

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)

Question 54

Common diseases of HIV patients

Answer 54

Systemic: cough, hepatosplenomegaly, tongue ucler (histoplasma) Dermatologic: hairy leukoplakia (EBV), thrush (candida) Gastrointestinal: chronic diarrhea (cryptosporidium) Neurologic: abscess (toxo, CD4 <50)

Question 55

Prions

Answer 55

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)