Mumps: a resurgent disease with protean manifestations

Mumps is an infectious disease caused by a single-stranded RNA virus belonging to the genus Rubulavirus and the family Paramyxoviridae. It has no animal reservoirs and is therefore purely a human disease. There is only one serotype of the virus, which can be further divided into 10–11 genotypes.1 The term “mumps” is probably derived from a word meaning “grimace”, reflecting the impact of parotitis on facial expression.

Although mumps has generally been regarded in recent years as an uncommon and mild self-limiting illness of early childhood, Australian data for the period 2002–2005 show that 138/419 people with mumps (33%) were hospitalised, of whom three-quarters were aged over 15 years. Complications of mumps in hospitalised patients were recorded in 19/138 cases (14%), with orchitis being the most common complication (10/19), followed by pancreatitis (2/19). There was one death in a patient aged 100 years.2

As many clinicians in the developed world would have seen few, if any, cases of mumps, there needs to be an increased awareness of the infection. Here, I describe the changing epidemiology of mumps in the developed world and review modes of transmission and presentation, as well the investigation and management of the disease.

The estimated global incidence of mumps is 100–1000/100 000 population per year, with epidemic peaks every 2–5 years.3 In temperate climates, the peak incidence of mumps is in winter and spring, whereas cases can occur consistently throughout the year in tropical climates.4

Before the introduction of mass vaccination programs, mumps primarily affected 5–9-year-old children, but more recent (and large) outbreaks have mainly affected adolescents and adults.5,6 In 2004–2005 in the United Kingdom, more than 56 000 clinical cases of mumps were notified, with the majority of confirmed cases occurring in 15–24-year-olds.7 This change is clinically important, as mumps tends to be more severe in adolescents and adults than in children.8 Furthermore, some complications such as orchitis are limited to post-pubertal infection. Posters produced for mumps education campaigns in response to large Canadian outbreaks that also affected many adolescents and adults (http://www.health.alberta.ca/public/disease_conditions.html#mumps) are shown in Box 1.

In Australia, the National Notifiable Diseases Surveillance System (NNDSS) has recorded a consistent rise in mumps notifications over the past few years, with almost 600 notifications in 2007. NNDSS data show that notification rates in adolescents and young adults have increased over time, reflecting a similar pattern overseas. In 2007, 76% of mumps notifications in Australia were for people aged 20 years or older.9

The reasons for this change in mumps epidemiology are multifactorial. They include primary vaccine failure due to true immunological failure or administration of ineffective vaccine;5 secondary vaccine failure due to a loss of immunity despite initial seroconversion;10 and a lack of cross-neutralisation between vaccine strains and wild-type genotypes.1,11,12

Transmission of mumps occurs through droplet infection, fomites or direct contact. The virus enters the body through the upper respiratory tract. After the virus has multiplied within the local reticuloendothelial and lymphoid systems, there is a period of 7–10 days of viraemia, during which other organs can become infected.13

Histologically, mumps parotitis is characterised by diffuse interstitial oedema with a predominantly mononuclear serofibrinous exudate. The ductal lumina contain necrotic debris. There is relative sparing of the glandular cells. The histological appearance of mumps orchitis is fairly similar to that of parotitis.14

Mumps is highly infectious,8 with a single case generating up to 12 secondary cases in a susceptible population. The infectious period lasts from 2 days before the onset of symptoms to 9 days afterwards.15 Even asymptomatic people can transmit the virus.14 Natural infection was once thought to confer lifelong immunity, but we now know that reinfection can occur, although it tends to be milder and more atypical than in primary infection.16

The World Health Organization and the Centers for Disease Control and Prevention have the same clinical case definition for mumps:

Although mumps is probably the best known cause of bilateral parotitis, a number of differential diagnoses should be considered (Box 3). A suspected mumps infection can be confirmed by detection of antibodies to the virus, detection of viral RNA by reverse transcriptase-polymerase chain reaction (RT-PCR) techniques, or viral cultures of various clinical specimens. In Australia, mumps viral cultures are rarely performed. Serum, saliva and/or urine specimens may be useful in cases of uncomplicated mumps, but if mumps meningitis is suspected, cerebrospinal fluid (CSF) examination may be indicated.

Currently, treatment of mumps is generally supportive for both parotid and extra-parotid manifestations, including mumps meningitis. The use of local measures, such as heat or cold packs, and a combination of antipyretics and analgesics is generally recommended.14

Treatment with intramuscular mumps immune globulin may be of benefit in the early stages in certain cases, but this product is not available in Australia. Intravenous immunoglobulin therapy appears to have reduced certain complications of mumps, but this has not led to universal recommendations for its use.19

The role of subcutaneous interferon alpha-2b in preventing testicular atrophy in mumps orchitis has been examined, but there are conflicting data on outcome, presumably reflecting the small numbers of both subjects and studies.32-34

There is no effective post-exposure prophylaxis for mumps cases.35

In Australia, the measles–mumps–rubella (MMR) vaccine is currently recommended for children at the ages of 1 and 4 years. For adults who have only ever received a single dose of vaccine containing a mumps component, a second dose of MMR can be given at any age. As it is a live vaccine, its use is contraindicated for immunocompromised hosts.35 Short-term efficacy and seroconversion rates of about 90% are achieved after a single dose.4 The second dose of vaccine results in about 95% seroconversion, with a slower decline in antibody titres over time compared with subjects vaccinated only once.36 Immunogenicity and observational data tend to concur in showing that two doses of vaccine are more efficacious than one.37

In Australia, the Jeryl-Lynn strain of mumps vaccine is used.35 Despite being less efficacious and more expensive than the Urabe strain, its use is still cost-effective and less likely to cause vaccine-related aseptic meningitis.38

Apart from minor local reactions at the injection site, the major systemic reactions that may occur after mumps vaccination are low-grade fever, aseptic meningitis, meningoencephalitis and parotitis. Post-vaccine meningitis occurs 2–3 weeks after vaccination.4 The meningitis is mild to moderate in severity, and all reported cases have resolved completely within a week.39 The Jeryl-Lynn vaccine strain is associated with the lowest rate of vaccine-related aseptic meningitis, ranging from less than 1 case/525 312 doses to 0.1 cases/100 000 doses.3 Sensorineural deafness, orchitis and even post-vaccination pancreatitis have also been reported as extremely rare complications following vaccination.4,40

There has been a resurgence of mumps in recent times that is multifactorial in origin. More cases are occurring in older age groups than previously, meaning that cases of greater severity and/or with more complications, such as epididymo-orchitis and oophoritis, will be seen. Clinicians need to raise their awareness of the disease — in particular of its protean manifestations — and to be familiar with the available tools for diagnosis.

1 Posters produced for mumps education campaigns in response to large Canadian outbreaks that affected many adolescents and adults

Courtesy of the Nova Scotia Department of Health Promotion and Protection.