Facts about mumps

Mumps is a viral infection, which in its classical form causes acute parotitis (inflammation of the parotid salivary glands) and less frequently, orchitis, meningitis and pneumonia. Complications include sensorineuronal deafness, oligospermia, subfertility (rarely) and occasionally death from encephalitis. In the pre-vaccine area, mumps was primarily a childhood illness but epidemics among military recruits were not uncommon. The viral aetiology of the disease was identified in 1934 and live attenuated mumps vaccines have been available since the 1960s. Most European countries have had routine childhood mumps immunisation since the 1980s. Vaccination is now administered as a combination vaccination together with the measles and rubella attenuated virus components.

Name and nature of infecting organism

• The mumps virus is a RNA virus of the genus Rubulavirus in the family Paramyxoviridae;

• Several different genotypes of the mumps virus have been recognised, although the significance of this genotypic variation with regards to vaccine response remains unclear.

Clinical features and sequelae

• Mumps is primarily a respiratory infection and as such transmitted by aerosol and respiratory droplets. The invasion of the respiratory tract is frequently accompanied by viremia that results in organ involvement with a preference for the salivary glands.
• The most common and characteristic clinical presentation of mumps is an acute and tender parotid swelling which develops 16–18 days after exposure in up to 70% of cases. The swelling may be unilateral or bilateral (30–40% of cases), and the inflamed swollen parotid gland lifts the earlobe up and out in a characteristic fashion. The submandibular and sublingual glands may also be involved and swollen. 
• Parotitis may be preceded by non-specific prodromal symptoms lasting 3–5 days including malaise, fever, headache, myalgia and arthralgia. 
• Mumps may present as a lower respiratory tract infection, particularly in young children.
• Asymptomatic and subclinical mumps virus infections are common and may represent up to 20% of all infections. 
• Serious complications, including encephalitis, may precede or follow the parotitis and can also occur without any apparent involvement of the salivary glands. 
• Central nervous system (CNS) infection is common with mumps and up to 50% of patients have been shown to have asymptomatic pleocytosis in the cerebrospinal fluid (CSF).
• Mumps meningitis is a mild and often asymptomatic disease with complete recovery. Clinical signs and symptoms of meningism are associated with finding the virus in CSF in up to 15% of cases. The wide variation in the reported proportion of CNS involvement in mumps cases are likely to reflect differences in clinical practice and the likelihood of having a lumbar puncture performed. 
• Encephalitis is a rare but serious complication that affects 0.02–0.3% of cases and is responsible for most mumps-associated deaths.
• Orchitis is the most common complication in postpubertal males and is reported to occur in 25–50% of mumps infections. In about 30% of cases the orchitis is bilateral and may lead to oligospermia, subfertility and decreased testosterone production but only rarely sterility. 
• Mumps can cause pancreatitis, which may be associated with transient hyperglycaemia. 
• Oophoritis occurs in 5% of post-pubertal women with mumps infection.
• Sensorineural deafness may occur from one in 3400 to one in 20 000 cases, and is unilateral in 80% of cases.
• Arthropathy, myocarditis, mastitis, thyroiditis, uveitis and nephritis have been reported. 
• The incidence of myocarditis is reported to be up to 15%, but it is usually asymptomatic although deaths have been reported.
• The risk of foetal death is increased in women who contract mumps in the first trimester. 
• A morbilliform rash can occur.

Epidemiology

• The following is the clinical definition of mumps for the purpose of epidemiological surveillance: Any person with fever and at least one of the following: 
  (1) sudden onset of unilateral or bilateral tender swelling of the parotid gland or other salivary glands without other apparent cause, (2) orchitis; or (3) meningitis.

• About 200 000 cases of mumps were reported in Europe from 2006 to 2015, with the highest incidence in young children and adolescents.
• Europe-wide mumps incidence rates can be found in  ECDC’s Annual epidemiological report  on communicable diseases in Europe.
• In 2015, the hospitalisation rate was 9% in countries that reported these data (n=6 834) and complications were more frequently reported in adolescents and young adults than in children.

• Immunisation against mumps has been associated with a marked decline in the incidence of mumps disease in many European countries as well as in the United States. Mumps outbreaks have been reported in vaccinated communities, particularly in close-contact settings such as schools, colleges, and camps. However, high and sustained vaccination coverage helps limit the size, length, and spread of outbreaks.

• There is large variation in the reported incidence of mumps across Europe. Several factors may explain the observed differences in the epidemiology between Member States, including differences in surveillance systems, historical or current vaccination policies, and vaccination coverage levels.
• The current epidemiology of mumps in Europe is likely to be a consequence of a combination of incomplete vaccine coverage and waning immunity to the measles-mumps-rubella (MMR) vaccine among those that have been vaccinated in the absence of natural boosting.

• Only a fraction of the reported cases are laboratory confirmed (41% in 2015), and many lack information on immunisation status making it difficult to evaluate vaccine effectiveness.

Transmission

• Humans are the only known host of the mumps virus.
• Spread is from person to person by airborne or droplet transmission. 
• Individuals should be considered infectious from 12–25 days after exposure.
• The mean incubation period is 19 days with a range of 14–25 days.

Prevention

• Immunisation is the only effective method of prevention. 
• Mumps vaccine is given in the form of the combined trivalent MMR vaccine in all European countries with a first dose traditionally in the second year of life. The timing of the second dose varies across countries. View the vaccination schedules for countries in Europe; and for more recent updates please refer to national vaccination websites.
• The mumps component of the MMR vaccine is about 88% (range: 31−95%) effective when two doses are given; one dose is about 78% (range: 49%−92%) effective.
• Mathematical models indicate that 85–90% immunisation coverage is required to achieve herd immunity and the elimination of mumps transmission.
• Vaccine efficacy and safety are dependent on the vaccine strain. The Urabe and Leningrad-Zagreb strains have been associated with an increased risk of aseptic meningitis. 
• The strains currently used in MMR vaccines by European manufacturers are Jeryl Lynn (Merck), Leningrad-3 and RIT4385 (GlaxoSmithKline). Pavivac, BBM18 (a successor of the Rubini strain) and Sophia-6 strains are used occasionally.

Management and treatment

• Mumps virus can be isolated in cell culture or detected by PCR from nasopharyngeal swabs, urine, blood and fluid from the buccal cavity, typically from seven days before up until nine days after the onset of parotitis. Genotyping of isolated strains is recommended if breakthrough infections in vaccinated individuals are identified.
• Detection of mumps-specific IgM in saliva samples taken between one and six weeks after the onset of rash or parotid swelling is a sensitive and specific means of confirming the diagnosis. 
• A significant rise in mumps specific IgG antibodies between acute and convalescent titres or a positive mumps IgM titer confirms the diagnosis.
• The risks of further transmission can be mitigated by isolation of mumps patients for five days from the onset of swollen glands.
• Antibiotics are required only if there is secondary bacterial infection of the parotid glands. 
• Prompt notification to the local public health agency, based on clinical suspicion, rather than waiting for confirmatory laboratory results before notifying, is essential to mitigate the risks of further transmission.
• Recording and reporting of immunisation history for all cases is important. 
• Confirmation requires laboratory investigation unless a case is epidemiologically linked to a confirmed case.  

Note: The information contained in this factsheet is intended for the purpose of general information and should not be used as a substitute for the individual expertise and judgement of healthcare professionals.

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