Mumps

Overview

• Goldman-Cecil Medicine, p. 3568
• Cummings Otolaryngology, p. (block 17)

Virology

• Virus: Paramyxovirus (RNA, enveloped, negative-strand)
• 12 genotypes (A-N); genotype G predominates in the United States
• Spreads via respiratory droplets from salivary, nasal, and urinary secretions
• No known animal reservoir, insect vector, or human carrier state
• Virus enters via the upper respiratory tract, replicates in epithelium and parotid gland, then disseminates to glandular and CNS tissues

Epidemiology

• Incubation period: 12-25 days
• Contagious period: 2 days before to 5 days after symptom onset (asymptomatic individuals can also transmit)
• Peak incidence in spring (temperate climates); little seasonal variation in tropics
• 85% of cases (unvaccinated populations) occur in children under 15
• Pre-vaccine era: >150,000 US cases/year (1968); the MMR vaccine (introduced 1977, 2-dose schedule added 1989) reduced cases to <300/year by early 2000s
• Outbreaks persist in vaccinated populations - college campuses, close-knit communities (a 2006 multi-state outbreak involved >6,500 cases; 2009-2010 New York outbreak >3,500)

Clinical Features

Prodrome (precedes parotitis by 1-2 days)

• Low-grade fever, headache, myalgia, anorexia, arthralgia, malaise

Classic Parotitis

• Bilateral in 75% of cases (one side typically swells first, the other within 1-5 days)
• Localized pain and edema of the parotid gland
• Otalgia, trismus, dysarthria, dysphagia
• Pain worsens with eating/chewing
• Physical exam: non-pitting, tense, firm edema; overlying skin stretched with a glazed appearance - no erythema or warmth
• Submandibular gland occasionally affected
• Displacement of the pinna (ear) from bilateral parotid swelling
• Cummings Otolaryngology, p. (block 17)

Complications

• Bradley and Daroff's Neurology in Clinical Practice, p. 1679
• Goldman-Cecil Medicine, p. 3568

Diagnosis

Lab Findings

• Leukopenia (occasional)
• Elevated serum salivary-type amylase
• Elevated serum lipase (if pancreatitis)

Serology (IgM)

• In unvaccinated individuals: 80-90% sensitive if collected >3-5 days after symptom onset
• In vaccinated individuals: only 9-47% sensitive - serology alone is unreliable

Nucleic Acid Testing (NAAT/PCR)

• Detection of mumps RNA via NAAT from buccal swab (saliva)

• 90% sensitive if collected within ≤2 days of symptom onset

• Recommended approach: collect BOTH buccal swab (NAAT) AND blood (serology) in all compatible cases

Antibody Kinetics (complement-fixing antibodies)

• S antibodies (against nucleoprotein core): appear earliest, peak at 10-14 days, disappear in 8-9 months - indicate active infection
• V antibodies (against surface hemagglutinin): appear later, persist for years at low levels
• Fourfold rise in antibody titer is diagnostic for acute infection
• The mumps skin test has no diagnostic value in acute infection (hypersensitivity develops 3-4 weeks post-exposure)
• Tietz Laboratory Medicine, p. (block 39)
• Cummings Otolaryngology, p. (block 17)

Differential Diagnosis of Parotitis

• Coxsackievirus A and B
• ECHO virus (enteric cytopathic human orphan virus)
• Cytomegalovirus
• Lymphocytic choriomeningitis virus

Treatment

• Bed rest
• Adequate hydration
• Oral hygiene
• Dietary modifications to minimize salivary gland secretory activity (avoid sour/acidic foods)
• Analgesics for pain and fever
• Fever typically resolves before glandular swelling, which can persist for several weeks

Prevention & Vaccination

• Live attenuated MMR vaccine (Jerry Lynn strain for mumps component)
• Route: subcutaneous injection
• Schedule: first dose at 12-15 months, second dose at 4-6 years
• Antibodies persist at least 5 years (likely much longer in most individuals)
• Important caveat: prior 2-dose vaccination does NOT rule out mumps - in one college campus outbreak, 76% of cases had received two MMR doses
• Contraindications: immunocompromised patients, neomycin allergy, pregnancy
• A third MMR dose has been recommended during outbreaks to boost protection in vaccinated populations

Mumps in Pregnancy

• Transplacental transmission is rarely reported
• Mumps in first trimester has been associated with increased spontaneous abortion risk
• Not associated with congenital malformations (unlike rubella)
• MMR vaccine is contraindicated during pregnancy

CNS Mumps - Special Notes

• Mumps meningitis may precede parotitis and can occur without any salivary gland enlargement in 40-50% of cases
• A distinct syndrome - "mumps virus-associated acute encephalopathy" - presents with early coma, raised ICP, and prolonged seizures, with acellular CSF (normal glucose/protein) but elevated CSF inflammatory cytokines; distinguished from classic meningoencephalitis
• Outcomes range from full recovery to death
• Bradley and Daroff's Neurology, p. 1679