Mumps

Chapter 213 | Part 5: Infectious Diseases

KEY CLINICAL POINTS

• Mumps is a self-limiting viral illness caused by a paramyxovirus, with parotitis as the hallmark feature.
• Global mumps incidence has declined by 97–99% in countries with routine two-dose MMR vaccination, but outbreaks persist in vaccinated populations.
• Vaccination with MMR (or MMRV) is the cornerstone of prevention, with two doses recommended for children and high-risk adults.
• Complications include orchitis, oophoritis, hearing loss, meningitis, and encephalitis, with higher risk in males and adults.
• Diagnosis relies on RT-PCR for viral detection or serologic testing for IgM/IgG antibodies, with no specific antiviral treatment.

1. DEFINITION & OVERVIEW

Mumps is an acute, self-limited, systemic viral illness characterized by parotitis or other salivary gland swelling. It is caused by the mumps virus, a paramyxovirus from the Rubulavirus genus. The disease is endemic globally but has been significantly reduced through vaccination programs. However, outbreaks continue in vaccinated populations, particularly in settings with close contact.

Mumps Virus Genotypes

Genotype	Prevalence in U.S.	Vaccine Strains
A	Common	Jeryl Lynn
B	Rare	Jeryl Lynn
N	Rare	Jeryl Lynn
G	98% of genotyped specimens (2015–2017)	Jeryl Lynn

1.1 Epidemiology

Mumps occurs worldwide and is endemic in many countries. Annual incidence ranges from 100–1000 cases per 100,000 population without routine vaccination. Global incidence is challenging to estimate due to limited data collection. The U.S. reported ~300 cases annually by the early 2000s, but cases increased after 2006, with peaks in 2016–2017. Outbreaks are common in vaccinated populations, especially in universities, correctional facilities, and close-knit communities.

1.2 Pathogenesis

Humans are the sole natural reservoir. Transmission occurs via respiratory droplets or saliva. The incubation period is 16–18 days (12–25 days range). Virus replicates in nasal mucosa, spreads via lymphatics to regional lymph nodes, and causes viremia. It infects salivary glands, testes, kidneys, CNS, and other organs. Viral entry into CNS occurs via choroid plexus or mononuclear cells during viremia.

2. EPIDEMIOLOGY

Mumps is endemic in many countries, with annual incidence of 100–1000 cases per 100,000 population without vaccination. Global incidence is difficult to estimate due to limited data collection. The U.S. reported >500,000 cases annually (1999–2018) but saw a decline to ~300 cases/year by the early 2000s. Since 2006, cases have increased, with peaks in 2016–2017 (150 outbreaks, 9200 cases). Outbreaks occur in vaccinated populations, especially in settings with close contact. The pandemic disrupted vaccination services, increasing risk of outbreaks.

2.1 Risk Factors

Risk factors include waning immunity after vaccination, low antibody levels to wild-type strains, lack of exposure to wild-type virus, and subclinical boosting. Outbreaks are common in vaccinated populations, particularly in universities, correctional facilities, and close-knit communities.

2.2 Demographics

Mumps is more common in males than females (due to orchitis risk). Adults are more likely to develop complications than children. Pregnancy is generally benign, but maternal infection may increase risk of fetal loss.

3. ETIOLOGY & PATHOPHYSIOLOGY

Mumps is caused by the mumps virus, a single-stranded, negative-sense RNA virus from the Paramyxoviridae family. It has 12 genotypes (A–N, excluding E and M), with genotype G predominant in the U.S. The SH protein exhibits hypervariability, used for molecular epidemiology. The virus is rapidly inactivated by formalin, ether, chloroform, heat, and UV light. It infects salivary glands, testes, kidneys, CNS, and other organs, causing inflammation and tissue damage.

4. CLINICAL FEATURES

Typically presents with parotitis (bilateral, 3–7 days duration) or other salivary gland swelling. Asymptomatic cases occur in ~20% of unvaccinated and unknown proportion of vaccinated. Complications include orchitis (30% unvaccinated, 6% vaccinated), oophoritis, mastitis, pancreatitis, hearing loss (4% unvaccinated), meningitis, encephalitis, and CNS involvement (up to 55% subclinical). Hearing loss is sudden, unilateral, and transient in 4% of unvaccinated. Orchitis may lead to infertility, testicular atrophy, or anti-sperm antibodies.

5. DIFFERENTIAL DIAGNOSIS

Mumps is the only cause of epidemic parotitis, but other causes include influenza (H3N2), parainfluenza, Epstein-Barr, HHV-6/6B, HSV-1/2, coxsackievirus, adenovirus, parvovirus B19, echovirus, lymphocytic choriomeningitis virus, HIV, sarcoidosis, Sjögren’s syndrome, Mikulicz’s syndrome, uremia, diabetes, drug-induced parotitis, and non-infectious causes like ductal obstruction, cysts, or tumors.

6. INVESTIGATIONS & DIAGNOSIS

Diagnosis confirmed by RT-PCR (preferred) or viral culture. Serologic testing for IgM or fourfold IgG rise may be used, but negative results in vaccinated patients do not rule out mumps. Buccal swabs (with parotid massage) are optimal for viral detection. Urine specimens may be used but are less sensitive. CSF and blood samples may show pleocytosis or elevated amylase/lipase in meningitis/pancreatitis. Aseptic meningitis occurs in ≤ 1% of vaccinated patients.

6.1 Diagnostic Algorithm

1. Suspect mumps in patients with parotitis or complications. 2. Confirm with RT-PCR (blood, saliva, urine, CSF) or serology (IgM/IgG). 3. Rule out other causes of parotitis (e.g., influenza, other viruses, non-infectious causes). 4. Use CSF analysis for CNS involvement.

7. MANAGEMENT & TREATMENT

Supportive care is the mainstay. Analgesics, warm/cold compresses, and local anesthetic blocks may alleviate symptoms. No specific antiviral therapy. Orchitis management includes cold compresses and scrotal support. Mumps immune globulin is not recommended. Post-exposure prophylaxis is not advised for close contacts. MMR vaccine is the primary prevention strategy.

8. PROGNOSIS & COMPLICATIONS

Mumps is generally benign but can lead to complications: orchitis (30% unvaccinated), oophoritis (7% unvaccinated), hearing loss (4% unvaccinated), meningitis ( ≤ 1% vaccinated), encephalitis ( ≤ 1%), pancreatitis (4% unvaccinated), and CNS involvement (up to 55% subclinical). Mortality from encephalitis is ~1.5%. Permanent infertility may occur in 30–50% of orchitis cases. Hearing loss is rare but may be permanent.

9. SPECIAL CONSIDERATIONS

Pregnancy: Generally benign, but maternal infection may increase risk of fetal loss. Pediatrics: Orchitis rare in children. Elderly: Higher risk of complications. Vaccination: Two doses recommended for children (12–15 months, 4–6 years) and high-risk adults. Reinfection is more common than previously thought. MMR vaccine effectiveness: 72% after one dose, 86% after two doses. Third dose recommended during outbreaks for high-risk groups.

10. KEY POINTS & CLINICAL PEARLS

• Mumps is a self-limiting viral illness with parotitis as the hallmark.
• Vaccination with MMR (or MMRV) is the best prevention.
• Two doses recommended for children and high-risk adults.
• Complications include orchitis, oophoritis, hearing loss, and CNS involvement.
• Diagnosis confirmed by RT-PCR or serology.
• No specific antiviral treatment; supportive care is the mainstay.
• Post-exposure prophylaxis with immune globulin is not recommended.
• Mumps reinfection is more common than previously thought.