01112013 - Picornavirus, Coronavirus, Calicivirus, Reovirus

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Picornavirus, Coronavirus, Calicivirus, Reovirus Characteristics

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RNA Viruses!
- Not usually life-threatening
- Treatment is supportive/for symptoms
- Serum IgG is best defense (past exposure)
- Big concern = spreading around pop. to high-risk patients

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Picornavirus group members

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- Enteroviruses = naked, survive GI tract
- PACER mnemonic = Polio, HepA, Coxsackie, Echo, Rhino (cold)

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Picornavirus transmission/proliferation

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Transmission via fecal/oral route (contaminated water, produce, seafood, etc.)
- Replication in oropharynx (tonsils), Peyer's patches, gets into blood
- Encounters target tissues via blood stream

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Picornavirus target tissues

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Liver - HepA
- Meninges - Echo, polio, coxsackie - cause meningitis
- Brain - polio, coxsackie - cause encephalitis, paralysis
- Muscle - Echo, coxsackie A & B - affect heart (myocarditis, pericarditis) and thorax (pleurodynia)
- Skin - Echo, coxsackie A - cause hand-foot-and-mouth disease, rash, herpangina
*** Major symptoms only occur in small % of patients...

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Echovirus

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Actually means "coxsackie-like", but is new variant that we're not sure of
- Called echo to at least place in picorna family

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Pico RNA virus overview

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Small, icosohedral, very resistant to acid/adverse conditions (GI tract)
- Large family
- VPG protein involved in packaging into capsid (not necessary though, naked genome sufficient for infection)
- Have poly-A tail - look just like mRNA - get translated, infect easily
- Most are cytolytic (release 100,000 new viruses) - HepA is exception!
- Mostly pediatric cases - kids don't wash hands, adults have prior exposure and IgG's

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Picornavirus proliferation

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mRNA-like genome translated into long polyprotein initially
- Proteolytic cleavage of polyprotein = new viral genome components
- Cleavage via viral protease - potential drug target (but severity is low anyways....)

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Picornavirus lab diagnosis

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PCR or reverse transcriptase to verify infection
- Most not a big deal though - low return for expense of test

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Polio symptoms

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- Many patients asymtomatic
-Pharyngeal paralysis in pharyngeal muscles - difficulty breathing - iron lungs
- Muscle paralysis in small % of patients
- Vaccine now - no one worries

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Polio vaccine types

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IPV (Salk) vaccine - heat killed viral shells - favored today
- OPV (Sabin) vaccine later introduced - live, modified version
- OPV pros = Can spread by itself, giving population immunity
- OPV cons = Could actually revert to polio, can hurt immunocompromised people
- Combination has almost eradicated polio worldwide

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HepA contraction, characteristics, treatment

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Usually contracted in poor sanitation conditions - sewage in drinking water, etc.
- Could also get from contaminated seabeds - oyster bed gets raw sewage, rainfall brings contaminants
- HepA = fever, vomiting, jaundice - many cases asymptomatic too
- Vaccine for HepA
- For immunocompromised or those worried about livers = can give pooled immunoglobulins (IgG's)

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Coxsackie, Echo contraction/prevention

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No vaccines for these - probably due to rarity, variety of emerging species - no "one-size-fits-all"
- Contraction = Fecal/oral route
- Initial targets = tonsils, Peyer's patches on intestines
- Prevention = soap, water, sanitation

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Coxsackie A symptoms

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Herpangina = fever, sore throat, small red vesicles at back of throat
- Hand, foot, & mouth syndrome = fever, oral vesicles, tender lesions @ extremities

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Coxsackie B symptoms

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Pleurodynia = fever, headache, pleuritic pain/problems breathing
- Myocarditis/pericarditis = inflammation, chest pain, potential heart failure

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Coxsackie/Echovirus meningitis presentation

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Stiff neck, fever, potential rash/sore throat
- CSF looks normal (glucose not getting eaten, no excess proteins, etc.)
- Rash/sore throat preceding meningitis suggest aseptic (non-bacterial) meningitis

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Coronavirus (SARS) overview

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Cause SARS, colds
- Enveloped, +RNA virus
- Envelope E2 protein binds to receptor of host respiratory cells - membrane fusion
- Active process of getting into cells with receptor
- Infectious droplets - because eveloped, needs to stay wet

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Coronavirus (SARS) symptoms

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Flu-like symptoms - fever, aches, chest pain, shortness of breath

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Coronavirus (SARS) diagnosis

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Chest radiograph - alveolar consolidation (opacity)
- RT-PCR, immunochemistry

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SARS vs. Common cold

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SARS tends to cause high fever, respiratory distress, difficulty catching breath, etc.
- Common cold due to rhinovirus, coronavirus only has low-grade fever, cough, etc.

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Reovirus (Rotavirus), Calicivirus (Norovirus) overview

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- Naked RNA viruses, transmitted fecal/oral route
- High fever, vomiting, diarrhea (12-60 hours)
- Treatment is supportive (Drink lots of water, Pepto bismol, etc.)
- Diagnosis via PCR, immunochemistry
Adults - probably a calicivirus (Norovirus, etc.)
Children (>2) - probably rotavirus (a reovirus)
- Prevention - sanitation; Rotavirus has new vaccine!

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Reovirus (rota) unique feature

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dsRNA
- Also, cause a very watery diarrhea!

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Rotavirus infection mechanism

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GI proteases cleave proteins, enhance infectivity
- Asymptomatic in adults, significant in young children
- NSP4 protein = toxin, causes diarrhea, water loss