STEPTRACKERMICROBIOLOGY + NEUROLOGY + GASTROENTEROLOGY | RNA VIRUSES | HIGH-YIELD REVIEW

Picornaviruses & Caliciviruses

Small, naked, positive-sense RNA viruses spread fecal-orally or by respiratory route — from paralysis and myocarditis to colds, hepatitis A and cruise-ship vomiting.

FOCUS ON
Picornaviruses: polio (anterior horn cells → asymmetric flaccid paralysis), echovirus (aseptic meningitis), rhinovirus (common cold; acid-labile, grows at 33 °C, ~100 serotypes), coxsackie A (herpangina, hand-foot-mouth) and B (myocarditis, pericarditis, pleurodynia), hepatitis A. Single polyprotein cleaved by viral protease. Enteroviruses (polio, echo, coxsackie) peak in summer–fall and are the leading cause of aseptic meningitis. Norovirus (calicivirus): very low infectious dose, outbreaks on cruise ships, nursing homes → vomiting-predominant gastroenteritis.
VIRUS · DISEASE
MECHANISM
CLINICAL PICTURE
CLUE · PREVENTION
Poliovirus — paralytic polio
Replicates in oropharynx and gut → viremia → destroys anterior horn motor neurons
Fever, then asymmetric flaccid paralysis, ↓ reflexes, no sensory loss; bulbar respiratory failure
Most infections asymptomatic · CSF lymphocytes
Polio vaccines
IPV (Salk, inactivated, IM) · OPV (Sabin, live)
OPV gives gut IgA and herd immunity but can revert (vaccine-derived polio)
IPV used in the US
Echovirus · enteroviral meningitis
Fecal-oral, summer–fall
Fever, headache, neck stiffness, rash; infants: sepsis-like illness
CSF: lymphocytes, normal glucose · CSF enterovirus PCR
Coxsackie A — herpangina
Oropharyngeal infection
Fever, painful vesicles on soft palate and tonsillar pillars
Children in summer
Coxsackie A16 — hand-foot-mouth
Enterovirus A71 also
Oral ulcers + vesicles on palms and soles (and buttocks)
Daycare outbreaks
Coxsackie B — myocarditis
Direct myocyte injury + lymphocytic inflammation
Young adult with chest pain, HF or arrhythmia after viral illness; may → dilated cardiomyopathy
Most common viral myocarditis cause
Coxsackie B — pleurodynia
Intercostal muscle infection
Sudden sharp pleuritic chest pain, fever ("devil's grip")
Also pericarditis, neonatal sepsis
Rhinovirus — common cold
Binds ICAM-1; acid-labile (no GI infection); best at 33 °C (nose)
Rhinorrhea, congestion, sore throat; triggers asthma exacerbations
Many serotypes → no vaccine
Hepatitis A
Fecal-oral; naked, acid-stable; liver cell injury immune-mediated
Acute hepatitis with jaundice; no chronic carrier state
See 7.05 · vaccine
Norovirus
Calicivirus; resists drying and alcohol; ~10–100 particles infect
Abrupt vomiting, watery diarrhea, cramps for 1–3 days
Most common cause of adult viral gastroenteritis · bleach cleaning
Enterovirus D68
Respiratory enterovirus
Severe asthma-like illness; acute flaccid myelitis in children
Polio-like paralysis

Mechanism — why polio paralyzes without numbness

Gut replicationPeyer patches
→
Viremia
→
Anterior horn cells destroyedLower motor neuron
→
Flaccid, areflexic, atrophySensation intact

IPV vs OPV

FEATURE
IPV (SALK)
OPV (SABIN)
Type
Killed
Live attenuated
Route
Injection
Oral
Gut IgA
Little
Strong
Reversion risk
None
Yes
Immunocompromised
Safe
Avoid

How it's tested

COMMON CONFUSIONHand-foot-mouth (coxsackie A; oral ulcers + palm/sole vesicles) vs herpangina (coxsackie A; posterior palate only) vs HSV gingivostomatitis (anterior mouth, gums).
THE TRAPRhinovirus can't infect the gut because it's acid-labile, even though it's a picornavirus.
YOUR APPROACHSeason (summer–fall) + child + aseptic meningitis, rash or myocarditis → enterovirus → which member by organ.

If you see… think…

Asymmetric flaccid paralysis, normal sensation, unvaccinated → poliovirus
Aseptic meningitis in August → enterovirus (echo, coxsackie)
Vesicles on soft palate in a febrile child → herpangina (coxsackie A)
Oral ulcers and palm/sole vesicles at daycare → hand-foot-mouth (coxsackie A16)
Young adult with heart failure after a "flu" → coxsackie B myocarditis
Sudden stabbing chest-wall pain with fever → pleurodynia (coxsackie B)
Receptor for rhinovirus → ICAM-1
Cruise-ship outbreak of vomiting → norovirus
Viral protease cleaving one large polyprotein → picornavirus
Polio vaccine that can revert → OPV (Sabin)