Mumps 

Mumps is an acute, self-limited, systemic viral illness characterized by the swelling of one or more of the salivary glands, typically the parotid glands. The illness is caused by a specific RNA virus, known as Rubulavirus. Rubulavirus is in the genus Paramyxovirus and is a member of the family Paramyxoviridae. The virus contains a single-stranded, negative-sense RNA surrounded by a glycoprotein envelope. One of the 2 glycoproteins on the surface of the viral envelope mediates neuraminidase and hemagglutination activity, whereas the other is responsible for lipid membrane fusion to the host cell. Rubulavirus may be isolated in viral culture from saliva, urine, and cerebrospinal fluid (CSF). Serologic assays can determine the presence of an antibody response and assess differences between acute and convalescent titers. Affected salivary glands show edema and lymphocytic infiltration. (See the image below.) (See Workup.)

Even though the mumps virus, Rubulavirus, shares similar morphologic features to the human parainfluenza viruses (as part of the Paramyxovirus genus), no cross-immunity between these viruses is known. The mumps virus also shares various epidemiologic characteristics with other well-known viral pediatric diseases, such as measles (RNA virus, of the genus Morbillivirus, in the Paramyxoviridae family) and rubella (RNA virus, of the genus Rubivirus, in the Togaviridae family).

Mumps occurs worldwide. Humans are the only known natural hosts. This Paramyxovirus is highly infectious to nonimmune individuals and is the only cause of epidemic parotitis. (See Epidemiology.)

The mumps virus is inactivated by chemical agents (ie, ether, formalin, chloroform), heat, and ultraviolet light.

Also see Management of Acute Presentation of Mumps.

Vaccination

The monovalent live, attenuated mumps vaccine was licensed in the United States in December 1967, and the Advisory Committee on Immunization Practices (ACIP) recommended that its use be considered for children nearing puberty, for adolescents, and for adults. At that time, the public health community placed mumps control as a low priority; as such, the stance of the ACIP was that mumps immunization should not compromise the effectiveness of established public health programs. However, in 1972, the ACIP recommendations were strengthened to indicate that mumps vaccination was particularly important for the initially targeted age groups. Hence, in 1977, routine vaccination was recommended for all children aged 12 months or older. (See Treatment.)

In 1980, stronger recommendations called for mumps vaccination of susceptible children, adolescents, and adults, unless such vaccination was medically contraindicated. Following these increasingly comprehensive recommendations and the enactment of state laws requiring mumps vaccination for school entry and attendance, the reported incidence of mumps steadily declined.

However, in 1986 and 1987, large outbreaks of mumps occurred among under-immunized cohorts of persons born between 1967 and 1977, as based on a single-dose vaccine regimen. This resulted in a shift in peak incidence from persons aged 5-9 years to those aged 10-19 years.^[1] In 1989, the ACIP recommended that a second dose of mumps-containing vaccine be administered to children aged 4-6 years (at time of entry to kindergarten or first grade) and designated MMR as the vaccine of choice.^{[1, 2]}

Over the next decade (1988-1998), the incidence of mumps decreased among all age groups. The greatest decrease occurred among persons aged 10-19 years. This age group had reversed the trend seen in 1986 and 1987, when a resurgence of outbreaks had occurred among susceptible adolescents and young adults.

Subsequent outbreaks have occurred among highly vaccinated populations. During 1989-1990, a large outbreak occurred among students in a primary and a secondary school. Most of the students in these schools had been vaccinated, suggesting that a vaccination failure, in addition to failure to vaccinate, might have contributed to the outbreak. In 1991, another mumps outbreak occurred in a secondary school where most of the students had been vaccinated; this outbreak was also mostly attributed to primary vaccination failure.

The shift in higher risk for mumps to these other age groups (ie, from younger school-aged children to older children, adolescents, and young adults), which occurred after the routine use of the mumps vaccine was initiated, has persisted despite minimal fluctuations in disease incidence that have occurred among the various age groups.

Mumps and SARS

During the 2003 epidemic of severe acute respiratory syndrome (SARS), it was thought that the SARS-causing virus belonged to the Paramyxoviridae family. However, current case criteria have determined that SARS follows the clinical, laboratory, and transmission characteristics of an RNA coronavirus named SARS-associated coronavirus (SARS-CoV).^{[3, 4]}

Transmission, course, and symptoms

Humans are the sole reservoir for the mumps virus. The transmission mode is person to person via respiratory droplets and saliva, direct contact, or fomites. (See Etiology.) The presence of maternal antibodies typically protects infants younger than 1 year from the disease. Infections can be asymptomatic in up to 20-30% of persons. Of those with symptomatic infection, adults tend to be more severely affected when compared to children.

Mumps has an incubation period of 16-18 days; however, cases can occur from 12-25 days after exposure. After this period, prodromal symptoms (including low-grade fever, malaise, myalgias, headache, and anorexia) occur; these symptoms can last 3-5 days. After this prodromal period (about 48 h), the clinical path of the virus depends on which organ is affected. The most common presentation is a parotitis, which occurs in 30-40% of all patients and in 95% of those who are symptomatic. Parotitis is caused by the direct viral infection of the ductal epithelium and presents with localized inflammation. Other reported sites of infection are the testes, pancreas, eyes, ovaries, central nervous system (CNS), joints, and kidneys.

Given that mumps is the only cause reported for epidemic parotitis, parotitis can be used as a clinical parameter of maximum communicability of this virus. A patient is considered infectious from about 3 days before the onset of and up to 4 days after the start of active parotitis (although it has been suggested that the communicable period is actually longer, lasting from 6 d before to 9 d after facial swelling is apparent).

After the prodromal period, one or both parotid glands begin to enlarge. Initially, local parotid tenderness and same-sided earache can occur. Ordinarily, the parotid glands are not palpable; but in patients with mumps, parotid swelling increases rapidly over several days. Seventy to 80% of symptomatic cases are bilateral with unilateral swelling occurring first, followed by bilateral parotid involvement. Occasionally, simultaneous involvement of both glands occurs. Edema over the parotid gland presents with nondiscrete borders, pain with pressure, and the angle of the mandible obscured. The orifice of the Stensen duct also appears erythematous and enlarged. Parotid swelling can last for 10 days. Serologically, this inflammatory process can be confirmed with an elevated salivary amylase level.

Despite the classic correlation of mumps and parotitis, mumps is no longer the most common cause of parotid swelling. Other viral causes include cytomegalovirus, parainfluenza virus 1 and 3, influenza A, and HIV. Bacterial infections, drug reactions, and metabolic disorders also can cause parotitis. Refer to the Medscape article on Parotitis for further information.

Approximately one third of postpubertal male patients develop unilateral orchitis. Orchitis is considered the most common complication of mumps infection in the adult male. This inflammation usually follows parotitis but may precede or occur in the absence of parotid gland swelling. Orchitis usually appears during the first week of parotitis, but it can occur in the second or third week. Bilateral orchitis occurs much less frequently (about 10% of cases). Gonadal atrophy may follow orchitis, posing a greater risk with bilateral involvement; however, sterility is rare.^[5] Prepubertal boys may develop orchitis, but it is uncommon in boys younger than 10 years.

Orchitis presents with high fevers (39-41°C), severe testicular pain accompanied by swelling, and erythema of the scrotum. Nausea, vomiting, and abdominal pain are not uncommon. Fever and gonadal swelling usually resolve in 1 week, but tenderness may persist.

Retrospective case studies have investigated a possible link between mumps orchitis and the subsequent development of testicular cancer; no increased risk has been shown to date.^{[6, 7]}

Another clinical manifestations of mumps is acute pancreatitis. Pancreatitis presents with abdominal distention and pain, fever (typically low grade), nausea, and vomiting. An elevated serum lipase value supports this diagnosis. In postpubertal females, oophoritis occurs in about 7% of patients. Thyroiditis and mastitis have also been reported.

CNS involvement is the most common extrasalivary complication of this viral illness. Its presentation is most often as aseptic meningitis rather than as a true encephalitis. This complication occurs up to 3 times more frequently in males compared with females.^[8] It may precede parotitis or occur in its absence, but it usually presents within the first week after parotid swelling.

Aseptic meningitis has been seen in up to 10% of patients with history of parotitis. This percentage increases to as high as 50% in those patients without parotid gland swelling. Salient clinical indicators of CNS involvement include headache, fever, nausea, vomiting, and nuchal rigidity. Marked changes in sensorium, convulsions, paresis, and/or paralysis present in patients with encephalitis.

In clinically diagnosed aseptic meningitis or encephalitis, the CSF profile is similar. A CSF mononuclear pleocytosis occurs, as does normal glucose; although hypoglycorrhachia has been reported. Pleocytosis has a wide range of WBCs per microliter (10-2000 WBCs/µL), with a lymphocytic predominance, although an early polymorphonuclear predominance has been reported. CSF total protein is usually normal or can be mildly elevated.^[9] In addition, the mumps virus can be isolated from CSF early in the illness. Pleocytosis of the CSF has also been shown to occur in persons without clinical signs of CNS involvement.

CNS involvement (meningitis or encephalitis) carries a good prognosis and is usually associated with an uneventful and complete recovery.

Neuritis of the auditory nerve may result in sensorineural deafness.^[10] A sudden onset of tinnitus, ataxia, and vomiting is followed by permanent deafness. Other neurologic complications include facial nerve neuritis and myelitis. A more complete list of complications appears below. (See also Prognosis.)

Lifelong immunity usually follows clinical or subclinical mumps infection, although second infections have been documented.

Complications

Potential complications of mumps include the following:

• Meningitis/encephalitis
• Sensorineural hearing loss/deafness^[10]
• Transverse myelitis
• Polyneuritis
• Guillain-Barr é syndrome
• Cerebellar ataxia (with encephalitis)
• Keratouveitis
• Thyroiditis
• Myocarditis
• Mastitis
• Pneumonia
• Pancreatitis
• Nephritis
• Orchitis
• Oophoritis
• Arthritis
• Thrombocytopenia purpura

Mumps in infancy

Maternal transplacental antibodies are protective of infants up to age 12 months. Infants born to mothers who have mumps a week prior to delivery may have clinically apparent mumps at birth or develop illness in the neonatal period.

After the initial entry into the respiratory system, the virus replicates locally. Viremic dissemination then occurs to target tissues, such as the salivary glands (parotid glands) and extrasalivary locations (CNS). These findings are based on experimentally induced mumps infection by Henly et al in 1948.

A secondary phase of viremia, occurring before the immune response, is the result of replication of the virus at the target organs. Viruria is also common, via blood transmission of the virus into the kidneys, where active replication occurs. Therefore, impairment of renal function (glomerulonephritis) may occur.

Cell necrosis and inflammation with mononuclear cell infiltration is the tissue response. Salivary glands show edema and desquamation of necrotic epithelial cells lining the ducts. Focal hemorrhage and destruction of germinal epithelium may occur, leading to duct plugging.

Risk factors

Lack of immunization, international travel, and immune deficiencies can make a child more prone to infection by the Paramyxovirus mumps virus.

Incidence and prevalence in the United States

After licensure of the mumps vaccine in the United States in December 1967 and subsequent introduction of state immunization laws in an increasing number of states, the reported incidence of mumps substantially decreased. There were 666 cases of mumps reported in 1998, for example, in contrast to 152,209 cases reported in 1968 (30 y earlier).

Although incidence decreased in all age groups, the largest decreases (>50% reduction in incidence rate per 100,000 population) occurred in persons aged 10 years or older. Overall, the incidence of mumps was lowest in states with comprehensive school immunization laws requiring mumps vaccination for entry and was highest in states without such requirements.

Presently, the prevalence of mumps is at record low levels because of the recommendation of 2 doses of MMR vaccine and its high coverage rate in the United States. During the 1990s, mumps cases continued to substantially decline, from 5,292 reported cases in 1990 to 266 reported cases in 2001, meeting the Healthy People 2000 Objective of less than 500 cases per year. In 2003, the Centers for Disease Control and Prevention (CDC) reported a total of 231 cases.^[11]

However, in July 2005, an epidemic occurred in Sullivan County, New York at a summer camp.^[12] An investigation conducted by the New York State Department of Health (NYSDOH) identified 31 cases of mumps, likely introduced by a camp counselor who had traveled from the United Kingdom and had not been vaccinated for mumps. Even though 96% of the participants at the summer camp had been vaccinated for mumps, a mumps outbreak can result from exposure to virus imported from a country with an ongoing mumps epidemic. The likelihood of disease in US residents caused by imported virus from areas with mumps epidemics remains high.

International status

Because the virus is present throughout the world, risk of exposure to mumps outside the United States may be high. In many countries throughout the world, mumps remains endemic. The mumps vaccine is in use in only 57% of countries belonging to the World Health Organization (WHO), predominantly those countries with more developed economies.^[13]

The variations in the number of persons who receive the mumps vaccination worldwide make it difficult to estimate the numbers affected. The incidence varies markedly from region to region.

The United Kingdom reported an epidemic of mumps in 2005, with 56,390 cases reported in persons aged 15-24 years who were not vaccinated.^[14]

Race predilection

During 1990-1998, race and ethnicity were reported for approximately two thirds of cases in each of 28 states and the District of Columbia. Mumps incidence decreased for people of all races during this 4-year period. For each year, incidence was highest among black persons, ranging from 1.2-8.2 times the incidence of any other racial group. Moreover, a higher incidence in blacks was found to occur in every age group; this relationship was most notable for persons aged 5-19 years.

Although incidence rates for Hispanics exceeded the rates for non-Hispanics in every age group, differences in rates were minimal for children younger than 5 years and for persons aged 20 years or older. The greatest difference in incidence rates between Hispanics and non-Hispanics was in persons aged 5-19 years.

Sex predilection

Males and females are affected equally with parotitis.

Symptomatic meningitis has a male-to-female ratio of 3:1.

Age predilection

As in the prevaccine era, most reported mumps cases still occur in school-aged children (aged 5-14 y). Almost 60% of reported cases occurred in this population from 1985-1987, compared with an average of 75% of reported cases from 1967-1971, the first 5-year period post licensure. However, for the first time since mumps became a reportable disease, the reported peak incidence rate shifted from children aged 5-9 years to older age groups for 2 consecutive years (ie, 1986, 1987).

Persons aged 15 years or older accounted for more than one third of the reported total from 1985-1987, whereas during the period 1967-1971, an average of only 8% of reported cases occurred among this population. Although reported mumps incidence increased in all age groups from 1985-1987, the most dramatic increases were among adolescents aged 10-14 years (almost a 7-fold increase) and young adults aged 15-19 years (more than an 8-fold increase).

Increased occurrence of mumps in susceptible adolescents and young adults has been demonstrated in several outbreaks in high schools, on college campuses, and in occupational settings.^[15] Nonetheless, despite this age shift in reported mumps, the overall reported risk of disease in persons aged 10-14 years and those aged 15 years or older is still lower than that in the prevaccine and early postvaccine eras.

The overall prognosis in uncomplicated mumps is excellent.

The prognosis of patients with encephalitis is generally favorable; however, neurologic damage and death can occur. Reported rates of mumps encephalitis range as high as 5 cases per 1000 reported mumps cases. Permanent sequelae are rare; the reported encephalitis case-fatality rate has averaged 1.4%. Transient myelitis or polyneuritis is rare. Approximately 10% of all infected patients develop a mild form of meningitis, which could be confused with bacterial meningitis.

Sensorineural deafness is one of the most serious of the rare complications involving the CNS.^[10] It occurs with an estimated frequency of 0.5-5 cases per 100,000 reported mumps cases. Transient sensorineural loss occurs in 4% of adults with mumps. Minor degrees of hearing loss or impairment are likely to occur with higher incidence and are probably reversible. Deafness after mumps is rare, mostly unilateral (20% bilateral), and often permanent.

Orchitis (usually unilateral) has been reported as a complication in 20-50% of clinical mumps cases in postpubertal males. Some testicular atrophy occurs in about 35% of cases of mumps orchitis. Absolute sterility sequela is rare, with impairment of fertility occurring in 13% of patients.

Oophoritis is a benign inflammation of the ovaries and occurs in about 5% of postpubertal females. Impairment of fertility has not been shown.

Pancreatitis occurs in 5% of persons infected with mumps. The hyperglycemia that results is usually transient, but a few cases of diabetes mellitus have been reported. It is not conclusive that the mumps virus has been the definitive cause.^[16] Limited experimental, clinical, and epidemiologic data suggest permanent pancreatic damage may result from injury caused by direct viral invasion.

Other rare complications include myocarditis, nephritis, arthritis, thyroiditis, thrombocytopenia purpura, mastitis, and pneumonia. These usually resolve within 2-3 weeks without sequelae.^[17] In 13% of adults with myocarditis, electrocardiographic findings are depression of ST segments and bradycardia. Deaths due to myocarditis have been reported. The incidence of this cardiac complication is reported to be up to 15%, but it is usually asymptomatic.^[17]

Mumps infection in pregnant women increases the risk of embryonic loss, spontaneous fetal loss, and fetal death, especially during the first trimester of pregnancy (reported to be as high as 27%). No association was found between mumps and congenital anomalies, and studies relating maternal mumps infection to endocardial fibroelastosis in the fetus are inconclusive. Mumps during pregnancy was rare even before immunization and is now even rarer with the widespread use of mumps immunization in childhood.

Death due to mumps is rare; the majority of the fatalities (>50 %) occur in persons older than 19 years.

Advise parents and educators to exclude the infected child from large-population facilities until 9 days after parotid swelling begins or until this swelling subsides.

Advise all children and adults to follow good handwashing practices.

For patient education information, see the Children's Health Center and the Infections Center, as well as Mumps and Immunization Schedule, Children.