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

Rotavirus, Coronaviruses, Rabies & Rubella

Four RNA viruses with their own signatures — infant diarrhea, pandemic respiratory disease, a uniformly fatal encephalitis and a mild rash with devastating congenital effects.

FOCUS ON
Rotavirus: dsRNA, segmented, naked; villous damage → watery diarrhea in unvaccinated infants (winter–spring, daycare); live oral vaccine (small intussusception risk). SARS-CoV-2: spike binds ACE2; fever, cough, anosmia → pneumonia, ARDS, thrombosis. Rabies: bullet-shaped rhabdovirus; bat, raccoon, skunk, fox, dog bites; travels retrograde along axons → encephalitis (agitation, hydrophobia) → coma, death; Negri bodies; post-exposure: wound care + rabies immunoglobulin + vaccine. Rubella: mild rash with postauricular nodes; congenital → cataracts, deafness, PDA, "blueberry muffin" rash.
VIRUS · DISEASE
MECHANISM
CLINICAL PICTURE
CLUE · PREVENTION
Rotavirus gastroenteritis
Reovirus (dsRNA, double capsid); NSP4 enterotoxin; villus blunting → ↓ absorption
Infant 6 mo–2 yr: vomiting, fever, profuse watery diarrhea, dehydration
Most common severe childhood diarrhea worldwide · oral rehydration
Rotavirus vaccine
Live oral, given at 2 (and 4, 6) months
Rare intussusception
Avoid with history of intussusception, SCID
Common-cold coronaviruses
+ssRNA, enveloped
Mild upper respiratory infection
Second to rhinovirus
COVID-19
SARS-CoV-2 spike binds ACE2 (TMPRSS2 primes); airway, lung, endothelium
Fever, cough, loss of smell/taste → viral pneumonia, ARDS, thrombosis, myocarditis; MIS-C in children
PCR or antigen · nirmatrelvir-ritonavir, remdesivir; dexamethasone if hypoxemic · mRNA/protein vaccines
SARS · MERS
Bat origin; civet (SARS), camel (MERS)
Severe pneumonia
MERS: Arabian Peninsula
Rabies — transmission
Rhabdovirus; saliva of bats (most US cases), raccoons, skunks, foxes; dogs (worldwide)
Bat bite may go unnoticed (sleeping room)
Long incubation (weeks–months; shorter if bite near head)
Rabies — pathogenesis
Binds nicotinic ACh receptor at NMJ → retrograde axonal transport (dynein) → CNS → spreads out to salivary glands
Prodrome: fever, tingling at bite site → furious (agitation, hydrophobia, hypersalivation) or paralytic form → coma, death
Negri bodies (cytoplasmic inclusions) in Purkinje cells, hippocampus
Rabies post-exposure prophylaxis
Passive + active immunization
Wash wound; rabies immunoglobulin into wound; inactivated vaccine days 0, 3, 7, 14
Observe healthy dog/cat 10 days instead · always for bat contact
Rubella (German measles)
Rubivirus (+ssRNA); respiratory spread
Mild fever, fine rash starting on face that spreads fast and fades in 3 days, postauricular/occipital nodes; arthralgia in women
MMR
Congenital rubella
First-trimester infection
Cataracts, sensorineural deafness, PDA (or pulmonary artery stenosis), microcephaly, "blueberry muffin" rash
Check immunity before pregnancy; don't vaccinate during

Mechanism — rabies travels up the nerve

Bite inoculates virusMuscle replication
→
Binds NMJ ACh receptor
→
Retrograde transportDynein, to CNS
→
EncephalitisNegri bodies
→
Centrifugal spreadSaliva

The long incubation is the window for post-exposure prophylaxis — once symptoms start, it's almost always fatal.

Rubella vs measles

FEATURE
RUBELLA
MEASLES
Illness
Mild
Severe, high fever
Prodrome
Little
Cough, coryza, conjunctivitis
Clue
Postauricular nodes
Koplik spots
Rash
Fades in 3 days
Confluent, lasts ~1 week
Congenital
Cataracts, deafness, PDA
Not a classic TORCH cause

How it's tested

COMMON CONFUSIONCongenital rubella (cataracts, PDA, deafness) vs congenital CMV (periventricular calcifications, deafness) vs toxoplasmosis (diffuse calcifications, hydrocephalus, chorioretinitis).
THE TRAPA bat found in a room with a sleeping person counts as an exposure — give full post-exposure prophylaxis even without a visible bite.
YOUR APPROACHIdentify the hallmark (infant watery diarrhea, ACE2 pneumonia, hydrophobia, postauricular nodes) → prevention step (vaccine, PEP, pre-pregnancy immunity).

If you see… think…

Unvaccinated 1-year-old with vomiting and watery diarrhea in winter → rotavirus
Only double-stranded RNA virus on the exam → rotavirus (reovirus)
Rare adverse effect of rotavirus vaccine → intussusception
Receptor used by SARS-CoV-2 → ACE2
Fever, agitation, painful throat spasms when drinking → rabies
Eosinophilic cytoplasmic inclusions in Purkinje cells → Negri bodies (rabies)
Bat found in a child's bedroom → rabies immunoglobulin + vaccine
Mild rash with postauricular lymphadenopathy → rubella
Newborn with cataracts, deafness and continuous murmur → congenital rubella
Bullet-shaped enveloped virus → rhabdovirus (rabies)