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Mumps

Chapter 213 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Viral (incl. HIV) · Chapter 213

Key Clinical Points

  1. Mumps is an acute, self-limited, systemic viral illness caused by a paramyxovirus from the Rubulavirus genus.
  2. MMR vaccination has reduced cases by >99% in the US, but outbreaks occur due to waning immunity or viral evolution.
  3. Parotitis is the hallmark feature; complications include orchitis, pancreatitis, meningitis, and hearing loss.
  4. Diagnosis confirmed by RT-PCR (preferred) or serology (IgM); negative tests in vaccinated patients do not rule out infection.
  5. No specific antiviral therapy exists; management is supportive.
  6. Orchitis is the most common complication in postpubertal males, potentially causing temporary sterility.
  7. Mumps is the only cause of epidemic parotitis; other causes include influenza, parainfluenza, and other viruses.
  8. Hearing loss occurs in up to 4% of unvaccinated patients and is usually transient.
  9. Mortality is exceedingly rare, but encephalitis carries a mortality rate of ~1.5%.
  10. The 'Panda sign' on gallium scan is also characteristic.

1. DEFINITION & OVERVIEW

• Definition: Acute, self-limited, systemic viral illness typically characterized by parotitis or other salivary gland swelling. • Epidemiology Status: As of 2023, mumps is endemic in the United States. • Clinical Significance: Mumps is the only cause of epidemic parotitis; other causes include influenza, parainfluenza, and other viruses.

1.1 Historical Context & Vaccination Policy

• Pre-Vaccine Era: Prior to 1967, >100,000 cases occurred annually in the US. • Policy Shifts: One-dose policy implemented in 1977; two-dose policy in 1989. • Post-Vaccination Trends: ◦ Cases declined to ~300 annually by early 2000s. ◦ Post-2006 resurgence with outbreaks in vaccinated populations (e.g., 150 outbreaks and 9,200 cases reported during the 2016–2017 peak). • Setting of Outbreaks: Most occur in settings with close contact (universities, correctional facilities).

1.2 Current Status

• Global Reach: Mumps vaccine introduced in 123 WHO member states. • Vaccine Impact: ◦ Two-dose MMR programs reduced incidence by 97–99%. ◦ One-dose programs reduced incidence by 87–88%. • Recent Trends: ~150–700 cases reported annually in the US as of 2023; post-2020 reduction likely due to social distancing.

2. EPIDEMIOLOGY

• Global Incidence: ◦ Without vaccination: 100–1,000 cases per 100,000 population. ◦ Epidemic peaks occur every 2–5 years. • Historical Data: ◦ 1999–2018: >500,000 annual cases reported to WHO. ◦ 2019–2021: 160,000–270,000 cases (impacted by data collection challenges). • US Context: Pre-vaccine era (>100,000/year) vs. post-1989 two-dose policy (~300/year).

2.1 Risk Factors for Vaccinated Persons

• Failure of Immunity: ◦ Failure to develop immune response. ◦ Low-level immunity insufficient for protection. ◦ Waning immunity over time. ◦ Lower vaccine-induced antibody levels against circulating strains. ◦ Reduced subclinical immunologic boosting due to low disease incidence.

2.2 Global Vaccination Status

• Two-dose MMR programs: Reduced incidence by 97–99%. • One-dose programs: Reduced incidence by 87–88%. • Current Reach: Vaccine introduced in 123 WHO member states as of 2021.

3. ETIOLOGY & PATHOPHYSIOLOGY

• Pathogen: Paramyxovirus (Rubulavirus genus). ◦ Type: Single-stranded, negative-sense RNA (~15.3 kb) with seven major proteins. ◦ Serotype: Only one serotype exists; genotype G was predominant in US cases (2015–2017). ◦ Vaccine strains: Derived from genotypes A, B, or N. • Transmission: Respiratory droplets or saliva. • Timeline: ◦ Incubation period: 16–18 days (range 12–25). ◦ Infectious period: 2 days before to 5 days after parotitis onset. • Pathology: ◦ Salivary glands: Perivascular mononuclear-cell infiltrates, hemorrhage, edema, and acinar/duct cell necrosis. ◦ Testes: Germinal epithelium necrosis in orchitis.

3.1 CNS Pathophysiology

• Subclinical Involvement: Up to 55% show CSF pleocytosis. • Aseptic Meningitis: ◦ Prevalence: ≤1% in vaccinated, up to 10% in unvaccinated. ◦ Clinical course: Self-limited, no long-term sequelae. • Encephalitis: ◦ Prevalence: ≤1% of patients. ◦ Severity: High fever, altered consciousness, seizures; mortality ~1.5%. • Mechanism: Pathogenesis involves para/postinfectious processes rather than direct viral CNS invasion.

4. CLINICAL FEATURES

• General Presentation: ◦ Asymptomatic or non-specific respiratory symptoms. ◦ Parotitis: Typically lasts 5 days (range 3–7); bilateral in ~2/3 cases; may cause presternal pain from lymphatic obstruction. • Radiology: ◦ 'Panda sign' on gallium scan is characteristic.

4.1 CNS Complications

• Aseptic meningitis: Self-limited, no long-term sequelae. • Encephalitis: High fever, altered consciousness, seizures; ~1.5% mortality. • Other CNS issues: Cerebellar ataxia, facial palsy, hydrocephalus, Guillain-Barré syndrome.

4.2 Complications in Vaccinated vs Unvaccinated

• Hearing loss: 4% unvaccinated vs. <1% vaccinated. • Orchitis: 30% unvaccinated postpubertal males vs. 6% vaccinated. • Oophoritis: 7% unvaccinated vs. ≤1% vaccinated. • Pancreatitis: 4% unvaccinated vs. <1% vaccinated. • Meningitis: Up to 10% unvaccinated vs. ≤1% vaccinated.

5. DIFFERENTIAL DIAGNOSIS

• Infectious Parotitis: ◦ Influenza A (H3N2), parainfluenza 1–3, EBV, HHV-6/7, HSV, coxsackievirus A, adenovirus, parvovirus B19, echovirus, LCMV, HIV. • Non-infectious Parotitis: ◦ Sarcoidosis, Sjögren’s syndrome, Mikulicz’s syndrome, uremia, diabetes, drug use. • Unilateral Parotitis: Suggests ductal obstruction, cysts, or tumors.

5.1 Differential Diagnosis of Orchitis/Oophoritis

• Orchitis: Testicular torsion, bacterial infections (prostate/UTI), STIs (chlamydia/gonorrhea), coxsackievirus, varicella, echovirus, CMV. • Oophoritis: ST1s (chlamydia/gonorrhea).

6. INVESTIGATIONS & DIAGNOSIS

  1. Virologic Testing:
  2. Method: RT-PCR (preferred) or viral culture.
  3. Specimens: Buccal swab (best), blood, urine, CSF.
  4. Procedure: Parotid gland massage before buccal swab; urine yield increases up to 10 days post-onset.
  5. Serologic Testing:
  6. Method: mumps-specific IgM or fourfold rise in IgG.
  7. Timing: IgM detectable within 5 days in unvaccinated; peaks at 7 days.
  8. Limitations: Vaccinated patients often lack detectable IgM; false positives possible.
  9. Clinical Interpretation:
  10. Note: Negative virologic/serologic tests in vaccinated patients do not rule out infection.

6.1 Diagnostic Summary

• Preferred Method: RT-PCR. • Serology Limitation: IgG testing is not recommended for immunity assessment due to pre-existing titers.

7. MANAGEMENT & TREATMENT

  1. Supportive Care:
  2. Parotitis: Analgesics, warm/cold compresses.
  3. Orchitis: Cold compresses, scrotal support, anesthetic blocks.
  4. Other (Oophoritis, Pancreatitis, Hearing loss): Supportive care.
  5. Post-Exposure Management:
  6. MMR vaccine: Not recommended for post-exposure prophylaxis.
  7. Monitoring: Close contacts should self-monitor for 25 days after last exposure.
  8. Immunity Assessment: IgG titers not reliable for assessment in close contacts.

7.1 Clinical Management Steps

• Parotitis: Analgesics, warm/cold compresses. • Orchitis: Cold compresses, scrotal support, anesthetic blocks. • Hearing Loss: Supportive care.

8. PROGNOSIS & COMPLICATIONS

• Orchitis: ◦ Testicular atrophy in 30–50% of affected testes. ◦ Potential for temporary sterility (not confirmed as permanent). • Hearing Loss: ◦ Usually transient; may be associated with vestibular symptoms. • Encephalitis: ◦ Permanent sequelae in survivors; higher mortality in adults (~1.5%). • Other: Myocarditis, nephritis, thyroiditis.

8.1 Long-term Sequelae

• Orchitis: Testicular atrophy (30–50%); potential for temporary sterility. • Hearing Loss: Usually transient; may be associated with vestibular symptoms.

9. SPECIAL CONSIDERATIONS

• Vaccine Effectiveness: ◦ Two-dose MMR: ~97–99% protection. ◦ One-dose program: 87–88% reduction in incidence. • Safety Profile: ◦ No significant adverse effects beyond common vaccine reactions (fever, rash).

9.1 Vaccine Summary

• Two-dose MMR: 97–99% protection. • One-dose program: 87–88% reduction.

10. KEY PEARLS & CLINICAL TRAPS

• Clinical Rule: Negative virologic/serologic tests in vaccinated patients do not rule out mumps. • Sterility: Orchitis may cause temporary sterility but no evidence of permanent infertility. • Epidemic Marker: Mumps is the only cause of epidemic parotitis. • Hearing Loss: Usually transient; often unilateral in unvaccinated patients. • Diagnostic Preference: RT-PCR is the preferred method for confirmation.

10.1 High-Yield Points

• Panda Sign: Characteristic finding on gallium scan. • Immune Status: IgG titers are not reliable for assessing immunity in close contacts.