Mumps Virus/Mumps

Classification

General Characteristics

Structure

• Subfamily Rubulavirinae
• Family Paramyxoviridae
• Single-stranded, linear, negative-sense RNA virus
• Enveloped virus
• Large helical capsid carries RNA-dependent RNA polymerase in the virion.

Clinically relevant species

• The family Paramyxoviridae consists of 3 genera:
  • Paramyxovirus: includes the parainfluenza viruses and mumps virus 
  • Pneumovirus: includes respiratory syncytial virus
  • Morbillivirus: includes the measles virus
• The Paramyxoviridae family causes 30%–40% of all acute respiratory infections in infants and children.
• The mumps virus exists as a single genotype.

Disease

• Only infects humans
• Begins with prodromal symptoms
• Can be asymptomatic in 20% of patients
• Initial infection occurs in the upper respiratory tract → spreads to parotid glands (parotitis)
• Subsequent systemic disease/viremia can spread the infection to the following organs:
  • Testes (orchitis)
  • Ovaries
  • Thyroid (thyroiditis)
  • Pancreas (pancreatitis)
  • Brain (encephalitis/meningitis)

Epidemiology

Epidemiology

• Incidence in the United States: 100–1000 cases annually
• Peak incidence: late winter to early spring
• Since the implementation of the 2-dose measles, mumps, rubella (MMR) vaccine, cases have reduced by > 99%:
  • Prior to widespread vaccination, about 50% of children contracted mumps.
  • Mumps is still mainly a childhood disorder, but vaccination has raised the average age of presentation.
• Gender-based prevalence:
  • Men and women develop parotitis at approximately the same rate.
  • Men are much more likely to develop meningitis than women (3:1).

Transmission

• Humans are the only reservoir.
• Mumps is a highly contagious infection transmitted through:
  • Respiratory droplets
  • Person-to-person contact
  • Contaminated fomites
• The contagious period begins before the onset of clinical symptoms, and asymptomatic shedding may occur.

Pathogenesis and Clinical Presentation

Pathophysiology

• The primary site of viral replication is the upper respiratory epithelium.
• Primary viremia: 
  • The virus spreads to the local lymphoid tissue.
  • Can be found in saliva for up to 7 days
  • Moment of highest transmissibility occurs just before the development of parotitis.
• Secondary viremia: 
  • Usually involves the parotid gland (parotitis)
  • May also spread to the CNS, testis/epididymis, thyroid gland, pancreas, and ovaries, leading to the inflammation of these structures
  • Can now be detected in the blood, urine, and CSF
  • The virus is excreted in the urine in its infectious form during the 2 weeks following the onset of clinical illness.

Clinical presentation

The incubation period is 2–3 weeks.

After the incubation period, prodromal symptoms occur for 3–5 days, including:

• Generalized malaise
• Low fever
• Headache
• Poor appetite
• Myalgias

After the prodromal period, the patient may present asymptomatically (20% of cases) or develop symptoms depending on the affected organ:

• Parotitis: 
  • Affects 40% of cases
  • Bilateral swelling of the parotid glands and ostium of the Stensen duct
  • Also called “chipmunk cheeks”
  • Presents with pain while chewing and swallowing
• Orchitis:
  • Affects 20%–30% of postpuberal men 
  • Inflammation of the testes, usually unilateral
  • Presents with pain, tenderness, edema, redness, and warmth of the scrotum, as well as fever and nausea
  • May lead to testicular atrophy, but hormonal functions and fertility is usually preserved
• Oophoritis:
  • Affects 5%–10% of postpuberal women
  • Inflammation of the ovaries
  • Usually presents as pelvic pain, and rarely affects fertility 
• Pancreatitis
• Aseptic meningitis/encephalitis

Complications

• The clinical course is more severe and complications are more likely if the infection occurs in adulthood.
• In pregnancy, mumps is associated with a higher rate of spontaneous abortion.
• Orchitis and oophoritis may lead to infertility (rare).
• Encephalitis (mortality rate of 1.5%)
• Acute unilateral deafness (rare)

Diagnosis

Mumps is usually diagnosed on clinical grounds and no confirmatory laboratory testing is needed.

• A physical exam confirms the presence of swollen glands, classically the parotid.
• As with any inflammation of the salivary glands, serum amylase levels will be elevated.
• If uncertainty exists about the diagnosis, nasopharyngeal swabs, urine, blood, fluid from the buccal cavity, and CSF can be tested.
  • Hemagglutination inhibition (i.e. IgG, IgM)
  • Real-time RT-PCR
  • ELISA
  • Culture
• If meningitis/encephalitis is suspected, consider a lumbar puncture.

Management and Prevention

Management

• Mumps usually has a self-limiting clinical course. 
• Treatment for the infection and its complications is based on supportive care. 
• The patient is isolated to avoid further spread during the infectious period.
• Analgesic and antipiretics may be administered.
• General recommendations are given to reduce the patient’s discomfort:
  • Avoid citrus foods and drinks.
  • Warm and/or cold compresses may be placed over the parotid gland.
• Complications may require additional measures:
  • Pancreatitis with excessive vomiting → IV fluids
  • Orchitis → bed rest and ice packs to the scrotum

Prevention

• MMR triple vaccine:
  • Children should get 2 doses of the MMR vaccine.
  • The 1st dose is given at 12–15 months of age.
  • The 2nd dose is given at 4–6 years of age.
  • Can be given to all ages
• MMRV (measles, mumps, rubella, and varicella) vaccine:
  • Only approved for children who are 12 months–12 years of age 
  • The 1st dose is given at 12–15 months of age.
  • The 2nd dose is given at 4–6 years of age.

Differential Diagnosis

• Encephalitis/meningitis: infection of the brain tissue and the lining surrounding the brain, respectively. Encephalitis and meningitis can be bacterial or viral in origin. Mild cases may cause no symptoms or give rise to mild flu-like symptoms. Severe cases can result in life-threatening conditions. Immediate medical attention is needed for symptoms like confusion, hallucinations, seizures, and loss of sensation. Management is using supportive care and also requires finding and treating the underlying cause.
• Mastoiditis: an infection in the mastoid bone with the formation of pus-filled cysts starting usually from a middle-ear infection. Symptoms include redness, swelling, and tenderness around the bone as well as fever, ear pain, and discharge. Management is with antibiotics and surgery may be needed in severe cases.
• Epididymitis and orchitis: acute inflammation of the epididymis and the testis due to viral or bacterial infections. Patients present with testicular pain and scrotal swelling. Diagnosis is based on clinical findings and urinalysis with culture. Management is with empiric gram-negative coverage antibiotics and culture-directed therapy.
• Sialolithiasis: a condition in which stones in the salivary glands get infected and cause inflammation and pain. Patients present with painful parotid, submandibular, sublingual, or minor salivary glands. Management is with antibiotics and anti-inflammatory agents, hoping for a spontaneous stone expression.