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

Orthomyxo- & Paramyxoviruses

Enveloped negative-sense respiratory viruses — influenza changes yearly through its segmented genome; measles, mumps, RSV and parainfluenza use a fusion protein and make syncytia.

FOCUS ON
Influenza: hemagglutinin (binds sialic acid, entry) and neuraminidase (release); drift vs shift; secondary S aureus or pneumococcal pneumonia; oseltamivir within 48 h; yearly vaccine. Measles: cough, coryza, conjunctivitis → Koplik spots → rash head to toe; complications: pneumonia (most deaths), encephalitis, SSPE years later; vitamin A. Mumps: parotitis, orchitis, aseptic meningitis, pancreatitis. RSV: bronchiolitis in infants (wheezing); nirsevimab, palivizumab. Parainfluenza: croup (barking cough, steeple sign).
VIRUS · DISEASE
MECHANISM
CLINICAL PICTURE
CLUE · TREATMENT
Influenza
Orthomyxovirus, 8 segments; HA binds sialic acid, NA cleaves it for release
Abrupt fever, myalgia, headache, cough; elderly, infants, pregnancy at risk
Oseltamivir/zanamivir (NA inhibitors), baloxavir (cap-dependent endonuclease)
Antigenic drift
Point mutations in HA/NA
Seasonal epidemics
Annual vaccine (inactivated; live intranasal option for healthy 2–49)
Antigenic shift
Reassortment of segments between human and animal strains (influenza A only)
Pandemics
Pigs and birds as mixing hosts
Post-influenza pneumonia
Damaged ciliated epithelium
Recovery, then new fever and productive cough; necrotizing pneumonia
S aureus (incl. MRSA), S pneumoniae, H influenzae
Measles (rubeola)
Paramyxovirus; extremely contagious (airborne); infects respiratory epithelium and lymphocytes (transient immunosuppression)
Prodrome: cough, coryza, conjunctivitis, high fever → Koplik spots (white spots on buccal mucosa) → maculopapular rash from head down
Warthin-Finkeldey giant cells · vitamin A reduces mortality
Measles complications
Viral or bacterial superinfection; immune-mediated
Pneumonia (giant-cell in immunocompromised), otitis, acute encephalitis; SSPE 5–15 years later
SSPE: ↑ measles antibody in CSF, myoclonus, dementia
Mumps
Paramyxovirus; saliva/droplets
Bilateral parotitis; orchitis (post-pubertal, rarely sterility), aseptic meningitis, pancreatitis
↑ serum amylase · MMR
RSV bronchiolitis
Pneumovirus; F protein → syncytia
Infant < 2 years in winter: rhinorrhea → cough, wheezing, crackles, tachypnea, apnea in preterm
Supportive (O₂, fluids) · nirsevimab or palivizumab (anti-F mAbs) for prevention · maternal vaccine
Croup (laryngotracheobronchitis)
Parainfluenza; subglottic edema
Child 6 mo–3 yr: barking cough, inspiratory stridor, hoarseness, worse at night
Steeple sign on AP neck film · dexamethasone, nebulized epinephrine
Human metapneumovirus
Pneumovirus
Bronchiolitis and pneumonia similar to RSV
Older children, elderly
MMR vaccine
Live attenuated
Two doses (12–15 months, 4–6 years)
Contraindicated in pregnancy, severe immunodeficiency

Mechanism — influenza drugs by step

HA binds sialic acidEntry
→
UncoatingM2 channel (amantadine — resistance)
→
mRNA cap-snatchingBaloxavir blocks
→
NA releases virionsOseltamivir blocks

Paramyxovirus syndromes

VIRUS
SYNDROME
SIGN
Measles
Fever, 3 Cs, rash
Koplik spots
Mumps
Parotitis, orchitis
↑ amylase
RSV
Bronchiolitis
Wheezing infant
Parainfluenza
Croup
Steeple sign

How it's tested

COMMON CONFUSIONCroup (parainfluenza; barking cough, steeple sign, well-appearing) vs epiglottitis (Hib; toxic, drooling, thumbprint sign).
THE TRAPOnly influenza A undergoes antigenic shift; influenza B has no animal reservoir and only drifts.
YOUR APPROACHRespiratory virus → age and season → hallmark sign (Koplik, parotitis, wheeze, bark) → complication → targeted prevention.

If you see… think…

New fever and cavitating pneumonia a week after flu → S aureus superinfection
Pandemic strain after swine/avian gene mixing → antigenic shift
Drug blocking neuraminidase → oseltamivir
Cough, coryza, conjunctivitis, then white spots on buccal mucosa → measles (Koplik)
Teen with dementia and myoclonus years after measles → SSPE
Supplement that lowers measles mortality → vitamin A
Swollen parotids and painful testis → mumps
Wheezing 4-month-old in January → RSV bronchiolitis
Barking cough and steeple sign → croup (parainfluenza)
Monoclonal antibody to prevent RSV in infants → nirsevimab / palivizumab