Mumps is an acute infectious disease caused by the mumps virus. It is characterized by the swelling of one or more of the salivary glands, typically the parotid glands. Although generally mild, infection can result in complications such viral meningitis and orchitis /oophoritis.
With the introduction of routine mumps vaccination programs in Canada, mumps has transitioned from being a common childhood infection to a relatively rare disease. Nonetheless, outbreaks of mumps continue to occur in Canada with an increasing proportion of cases occurring in young adults. The National Advisory Committee on Immunization (NACI) recommends immunization against mumps.
The mumps virus is an enveloped, negative-sense, single stranded RNA virus which belongs to the Rubulavirus genus in the Paramyxoviridae family.
The average incubation period for mumps is 16 to 18 days, but can range from 12 to 25 days. Mumps most commonly presents as unilateral or bilateral parotitis (30% to 40% of all patients) that is preceded by fever, headache, malaise, myalgia, or anorexia.
Systemic symptoms usually resolve within 3 to 5 days, and parotid swelling subsides within 7 to 10 days. Approximately 20% of infections are asymptomatic and 40% to 50% manifest as nonspecific or respiratory symptoms.
Although complications are relatively frequent, permanent sequelae are rare. Cerebrospinal fluid pleocytosis (inflammatory cells in cerebrospinal fluid) is found in about half of all infected individuals and 1% to 10 % of cases will have symptoms of viral meningitis, typically lasting 3 to 4 days and resolving without sequelae. Orchitis is reported in 20% to 30% of post-pubertal males and approximately 5% of post-pubertal females experience oophoritis. Because involvement of the reproductive organs is commonly unilateral, sterility is rare.
Mumps in pregnancy has not been associated with congenital malformations, but mumps infection during the first trimester of pregnancy has been associated with spontaneous abortion.
Other less commonly reported complications include thyroiditis, myocarditis, mastitis, pneumonia, pancreatitis, nephritis and arthritis. Infection occurring in unimmunized adults is more likely to result in complications.
Child with unilateral parotitis. Source: US Centers for Disease Control and Prevention.
Mumps virus is spread through contact with respiratory droplets from an infected person, direct contact with the saliva of an infected person, and contact with a contaminated surface. Although the mumps virus has been isolated from the saliva of persons infected with mumps 7 days before symptom onset to 9 days after, persons infected with mumps are most infectious between 2 days before to 5 days after symptom onset.
Individuals infected with mumps who are asymptomatic can transmit the disease to others.
Mumps occurs worldwide with cases reported throughout the year and epidemics occurring every 2 to 5 years. Mumps remains endemic in many countries, and mumps vaccine is used in national immunization programs in only 62% of World Health Organization (WHO) member states as of 2012.
In general, individuals of all ages who have not had mumps or who have not been immunized according to the recommended immunization schedule are at risk of being infected. In Canada, adults born before 1970 are presumed to have acquired natural immunity to mumps. Adolescents and adults born in 1970 or after who are at the greatest risk of exposure to mumps include:
Mumps can be prevented by immunization. Routine immunization of children is recommended with two doses of a combined measles, mumps and rubella (MMR) or measles, mumps, rubella and varicella (MMRV) vaccine beginning at 12 to 15 months of age, with a second dose provided at 18 months of age or any time thereafter before a child enters kindergarten or first grade.
Two doses of MMR vaccine are also recommended for:
One dose of MMR vaccine is recommended for:
For detailed information about the MMR and MMRV vaccines and their use please refer to the Canadian Immunization Guide.
Since the approval of mumps vaccine in 1969, the number of reported mumps cases has decreased by more than 99%, from an average of nearly 33,000 cases reported per year from 1951 to 1955 to approximately 180 cases per year from 2011 to 2013 (Figure 1).
The average annual incidence during the period 2011 to 2013 was 0.40 cases per 100,000 person-years, with the highest incidence rates observed among 20 to 24 year olds (1.25 cases per 100,000), followed by 15 to 19 year olds (0.86 cases per 100,000) and 25 to 29 year olds (0.73 cases per 100,000). A change in the age distribution of mumps cases since the introduction of a routine second dose of MMR vaccine in 1996/1997 has been observed. While the proportion of reported cases aged 1 to 9 years has decreased from an average of 58% from 1991 to 1995 to an average of 7% from 2011 to 2013, the proportion of reported cases aged 20 years and older has increased from an average of 16% to an average of 67% during the same period.
With the introduction of routine immunization programs, cases of mumps have become sporadic and are often associated with outbreaks. From 2007 to 2010, large mumps outbreaks were reported in several Canadian provinces, including British Columbia, Alberta, Ontario, Quebec, Nova Scotia, and New Brunswick. In several of the outbreaks, the majority of cases occurred in persons aged 20 to 29 years, many of whom were college or university students who had received only one dose of a mumps-containing vaccine. Other outbreaks occurred in communities that were largely unimmunized due to religious or philosophical reasons. These outbreaks tended to have a younger age distribution, more in keeping with outbreaks that were seen in the pre-vaccine era.
Figure 1. Reported casesFootnote 1 and incidence (per 100,000 person-years) of mumps in Canada by year, 1924 to 2013.
Health professionals in Canada play a critical role in identifying and reporting cases of mumps. See the Surveillance section for more information in mumps surveillance in Canada, including national mumps case definitions.