dna and rna viruses

DNA viruses we discusses

• adenovirus

• polyomavirus

• papillomavirus

• herpesvirus

• hepatitis B

RNA viruses we discussed

• rotavirus

• picornavirus

• hantavirus

• rabies

• measles

• respiratory syncytial virus (RSV)

• influenza

• HIV

what is adenovirus known for?

• DNA

• range of illnesses it can cause (conjunctivitis, gastroenteritis, respiratory infections)

• major cause of epidemic conjunctivitis

• long residence times on surfaces — up to 30 days

is polyomavirus tested on

no <3

papillomavirus (HPV) strains

• DNA

• most strains sexually transmitted

• stains 16 and 18 are the 2 major strains implicated in 70% of all cervical cancer

• strains 6 and 11 are the 3 strains implicated in severe genital warts

HPV vaccine

Gardasil 9 — protects against 9 different strains

reduces risk of HPV related cancers by 90%

HPV cancers

high oncogenic potential, but only a few strains implicated

• females

  • cervix 55%

  • anus and vulva 15% each

• males

  • oropharynx 78%

  • anus 14%

  • penis 8%

herpesvirus general

• DNA

• latent infection, permanent

• sexually transmitted

herpesvirus strains

alpha strain

• site of entry = epithelial (symptomatic and infectious location

• site of latency = neural tissues

• types = oral, genital, chicken pox/ shingles

gamma strain

• site of entry = mucosal

• site of latency = lymphoid tissue

• epstein-barr virus 4-mononucleosis

  • near universal presence in humans — 90% of population

  • infects through saliva

poxvirus

• only DNA virus that doesn’t try for latency, only acute

• smallpox

not on review sheet?

hepatitis B mechanisms

• caused by hepadnaviridae (DNA)

• usually acute, but can become chronic

  • constant release of new virions

• unique replication strategy — reverse transcriptase

  • integration into genome

  • host cell makes viral mRNA

  • mRNA goes to ribosomes to make viral components or packaged into capsid

  • reverse transcriptase converts RNA to DNA

hepatitis B in adults versus children

adults

• chronic 5-6% of time

• 15% mortality due to liver damage

infants – much more dangerous

• chronic 90% of time

• 25% mortality due to liver trauma

hepatitis B and cancer

implicated in 80% of liver cancers

RNA viruses acute or chronic

usually acute — lytic cycle

other than hepatitis c and retrovirus

positive versus negative sense RNA

• positive = strand can function directly as mRNA

• negative = strand doesn’t code for anything, must synthesize complement

rotavirus

• dsRNA

• leading cause of gastroenteritis in children — high mortality rate

• highly infectious

  • secreted in trillions/ mL of stool, infectious dose only in the tens

  • binds to sialic acid receptors — ubiquitous

• oral vaccine = successful, has rare side effect that is severe but easily treatable

picornavirus

• RNA

• examples

  • rhinovirus = common cold

  • polio

    • rarely symptomatic, but 25% is still a lot of people

    • paralytic polio more severe in adults than children (not usually the case)

hantavirus

• RNA

• spread through rodent droppings, be careful how you clean your attic

• high mortality rate and very rapid onset — respiratory disease, cardiogenic shock

rabies

• ssRNA

• infects nervous system

• slow onset but fatal without treatment

  • can treat with post-exposure prophylaxis (immunoglobulin and vaccine) before symptomatic – very effective

• milwaukee protocol can be used if symptomatic, but almost never works (medically induced coma, aggressive antiviral treatment)

measles

• RNA

• highly infectious bc attaches to sialic acid receptors

• symptoms = high fever, kolpik spots in mouth, widespread rash

• MMR vaccine

respiratory syncytial virus (RSV)

• caused by paramyxovirus (RNA)

• majority of severe acute respiratory infections in children

• highly infectious — sialic acid

influenza

• caused by orthomyxovirus (RNA)

• segmented genome — can recombine!!

• 3 types

  • A - can shift and drift, only form with pandemic potential

  • B - can drift

  • C - can’t do either

genetic drift

infleunzas A and B

random mutations accumulate in genes for antigenic determinants, leading to differentiation into a different strain

genetic shift

influenza A only

when a host is infected with multiple strains, the genome segments can recombine in an intermediary host and result in a severe antigenic change — completely new virus

influenza viral antigens

hemagglutinin = initial attachment

neuraminidase = cell to cell spread

human immunodeficiency virus (HIV)

• from retrovirus = only classes of RNA viruses to integrate into gene

• life cycle

  • enters cell

  • viral RNA converted to DNA by reverse transcriptase

  • viral DNA integrates into genome

  • new viral RNA and proteins made, move to surface

  • virus matures by protease cleaving primary receptor spike

HIV receptors

• primary receptor = CD4

• secondary receptors = CXCR4 or CCR5

stages of HIV infection

1. acute

   • flu-like symptoms

   • most infectious here, high levels in blood

2. clinical latency

   • 6-10 yrs

   • symptomatic but infectious

   • CD4 cells slowly depleting, virus slowly increasing

3. AIDS

   • starts at constitutional symptoms (lethargy, malnutrition, wasting, etc)

   • dwindling supply for CD4 cells — severe immunocompromisation