Mumps is an important childhood disease that was historically widespread but now occurs very infrequently. It is an acute viral infection characterized by painful enlargement of the salivary glands, chiefly the parotids, as the usual presenting sign.
Mumps virus, the cause of mumps, is an RNA virus of the genus Paramyxovirus in the family Paramyxoviridae, which also includes the parainfluenza viruses. Only one serotype is known.
Mumps is endemic in most unvaccinated populations; the virus is spread from human reservoir by direct contact, airborne droplets, fomites contaminated by saliva, and possibly by urine. It is distributed worldwide and affects both sexes equally. Before introduction of the vaccine in 1967, the peak incidence of the disease occurred in children 5–9 yr of age; 85% of infections occurred in children younger than 15 yr of age. Now most cases occur in young adults, producing outbreaks in colleges or in the workplace. Outbreaks appear to be primarily related to a lack of immunization, especially in an underimmunized cohort of children born from 1967–1977, rather than to waning to immunity. Epidemics occur at all seasons but are slightly more frequent in late winter and spring.
There has been a dramatic decrease in the incidence of mumps since the introduction of the mumps vaccine in 1968. Except for a small increase in 1987, the incidence of mumps has steadily decreased in the United States. In 2001 there were 226 reported cases of mumps, a greater than 99% reduction from the 152,209 cases reported in 1968.
Virus has been isolated from saliva as long as 6 days before and up to 9 days after appearance of salivary gland swelling. Transmission does not seem to occur more than 24?hr before the appearance of the swelling or later than 3 days after it has subsided. Virus has been isolated from urine from the 1st–14th day after the onset of salivary gland swelling.
After entry into the last and initial multiplication in the cells of the respiratory tract, the virus is bloodborne to many tissues, among which the salivary and other glands are the most susceptible.
The incubation period ranges from 14–24 days, with a peak at 17–18 days. Approximately 30–40% of infections are subclinical. In children, prodromal manifestations are rare but may be manifest by fever, muscular pain (especially in the neck), headache, and malaise.
The onset is usually characterized by pain and swelling in one or both parotid glands. The parotid swells characteristically; it first fills the space between the posterior border of the mandible and the mastoid and then extends in a series of crescents downward and forward, being limited above by the zygoma. Edema of the skin and soft tissues usually extends further and obscures the limit of the glandular swelling, so that the swelling is more readily appreciated by sight than by palpation. Swelling may proceed extremely rapidly, reaching a maximum within a few hours, although it usually peaks in 1–3 days. The swollen tissues push the earlobe upward and outward, and the angle of the mandible is no longer visible. Swelling slowly subsides within 3–7 days but occasionally lasts longer. One parotid gland usually swells a day or two before the other, but in approximately one quarter of cases the disease remains unilateral. The swollen area is tender and painful, pain being elicited especially by tasting sour liquids such as lemon juice or vinegar. Redness and swelling about the opening of the Stensen duct are common. Edema of the homolateral pharynx and soft palate accompanies the parotid swelling and displaces the tonsil medially; acute edema of the larynx has also been described. Edema over the manubrium and upper chest wall may occur, probably because of lymphatic obstruction. The parotid swelling is usually accompanied by low-grade fever, but this may be absent.
Although the parotid glands alone are affected in the majority of patients, swelling of the submandibular glands occurs frequently and usually accompanies or closely follows that of the parotid glands. In 10–15% of patients only the submandibular gland(s) may be swollen. Little pain is associated with the submandibular infection, but the swelling subsides more slowly than that of the parotids. Redness and swelling at the orifice of the Wharton duct frequently accompany swelling of the gland. Least commonly, the sublingual glands are infected, usually bilaterally; the swelling is evident in the submental region and in the floor of the mouth.
The diagnosis of mumps parotitis is usually apparent from the clinical symptoms and physical examination. When the clinical manifestations are limited to less common lesions, the diagnosis is less clear but may be suspected during an outbreak.
Routine laboratory tests are nonspecific; usually leukopenia is present with relative lymphocytosis. An elevation in serum amylase levels is common; the rise tends to parallel the parotid swelling and then to return to normal within 2 wk.
The microbiologic diagnosis is by serology or virus culture. Enzyme immunoassay for mumps immunoglobulin (Ig) G and IgM antibodies are most commonly used for diagnosis. IgM antibodies are detectable in the first few days of illness and are considered diagnostic. They may remain elevated for weeks to months. IgG antibodies are directed primarily against the fusion (F) protein; cross reactions with parainfluenza viruses may occur. Seroconversion, or a fourfold increase in IgG titer, is diagnostic.
Mumps virus can be cultured from the saliva, cerebrospinal fluid, blood, urine, brain, and other infected tissues. Primary cultures of human or monkey kidney cells are used for viral isolation. Cytopathic effect is occasionally observed, but hemadsorption is the most sensitive indicator of infection.
The mumps skin test is unreliable for diagnosis of mumps and for determination of susceptibility to infection.
Other viral causes of parotitis include HIV infection, influenza, parainfluenza viruses 1 and 3, cytomegalovirus, and coxsackieviruses. Acute suppurative parotitis is a bacterial infection usually caused by Staphylococcus aureus in which pus can often be expressed from the duct. A salivary calculus obstructing either a parotid or, more commonly, a submandibular duct causes intermittent swelling. Preauricular or anterior cervical lymphadenitis can be differentiated by the well-defined borders of the lymph node and a location that is completely posterior to the angle of the mandible. Orchitis may also be caused by coxsackieviruses.
There is no specific antiviral therapy; treatment is entirely supportive. Antipyretics (acetaminophen or ibuprofen) are indicated for fever. Bed rest should be guided by the patient's needs, but no evidence indicates that it prevents complications. The diet should be adjusted to the patient's ability to chew. Orchitis should be treated with local support and bed rest. Mumps arthritis may respond to a 2-wk course of a nonsteroidal anti-inflammatory agent or corticosteroids. Salicylates do not appear to be effective.
Viremia early in the infection probably accounts for the widespread complications. There is no firm evidence that maternal infection is damaging to the fetus; a possible relationship to endocardial fibroelastosis has not been firmly established. Mumps in early pregnancy does increase the chance of abortion.
This is the most frequent complication in childhood. Its true incidence is hard to estimate
because subclinical infection of the central nervous system, as evidenced by cerebrospinal fluid pleocytosis, has been reported in more than 65% of patients with mumps parotitis. Clinical manifestations occur in more than 10% of patients. The incidence of mumps meningoencephalitis is approximately 250/ 100,000 cases; 10% of these cases occurred in patients older than 20 yr of age. The mortality rate is about 2%. Males are affected three to five times as frequently as females.
The pathogenesis of mumps meningoencephalitis may be either a primary infection of neurons or a postinfectious encephalitis with demyelination. In the first type, parotitis frequently appears at the same time or following the onset of encephalitis. In the latter type, encephalitis follows parotitis by an average of 10 days. Parotitis may in some cases be absent. Aqueductal stenosis and hydrocephalus have been associated with mumps infection. Injecting mumps virus into suckling hamsters has produced similar lesions.
Mumps meningoencephalitis is clinically indistinguishable from meningoencephalitis of other origins (see Chapter 174.2 ). Moderate stiffness of the neck is seen, but the remaining findings on neurologic examination are usually normal. The cerebrospinal fluid may show a lymphocytic pleocytosis of less than 500 cells/ mm3 , although occasionally the count may exceed 2,000 cells/mm3 .
ORCHITIS AND EPIDIDYMITIS.
These complications rarely occur in prepubescent boys but are common (14–35%) in adolescents and adults. The testis is most often infected with or without epididymitis; epididymitis may also occur alone. Bilateral orchitis occurs in approximately 30% of patients. Rarely, there is a hydrocele. The orchitis usually follows parotitis within 8 days. Orchitis may also occur without evidence of salivary gland infection. The onset is usually abrupt, with a rise in temperature, chills, headache, nausea, and lower abdominal pain; when the right testis is implicated, appendicitis may be suggested as a diagnostic possibility. The affected testis becomes tender and swollen, and the adjacent skin is edematous and red. The average duration of illness is 4 days. Approximately 30–40% of affected testes atrophy, leaving a cosmetic imbalance. Infertility is rare even with bilateral orchitis.
Pelvic pain and tenderness are noted in about 7% of postpubertal female patients. There is no evidence of impairment of fertility.
Mild or subclinical pancreatic involvement is common, but severe pancreatitis is rare. It may be unassociated with salivary gland manifestations and may be misdiagnosed as gastroenteritis. Epigastric pain and tenderness, which are suggestive, may be accompanied by fever, chills, vomiting, and prostration. An elevated serum amylase value is characteristically present in patients with mumps, with or without clinical manifestations of pancreatitis.
Serious cardiac manifestations are extremely rare, but mild infection of the myocardium may be more common than is recognized. Electrocardiographic tracings revealed changes, mostly depression of the ST segment, in 13% of adults in one series. Such involvement may explain the precordial pain, bradycardia, and fatigue sometimes noted among adolescents and adults with mumps.
Migratory polyarthralgia and even arthritis are occasionally seen in adults with mumps but are rare in children. The knees, ankles, shoulders, and wrists are most commonly affected. The symptoms last from a few days to 3 mo, with a median duration of 2 wk.
Although it is uncommon in children, a diffuse, tender swelling of the thyroid may occur about 1 wk after the onset of parotitis; antithyroid antibodies subsequently develop.
Unilateral, rarely bilateral, nerve deafness may occur; although the incidence is low (1/15,000 cases), mumps was historically a leading cause of unilateral nerve deafness. The hearing loss may be transient or permanent.
Dacryoadenitis may occur with painful swelling, usually bilateral, of the lacrimal glands. Optic neuritis (papillitis) may occur; symptoms vary from loss of vision to mild blurring, with recovery in 10–20 days.
The prognosis of rubella in childhood is excellent. Infection usually confers permanent immunity, although reinfections have been documented.
Mumps vaccine is derived from the Jeryl Lynn strain of mumps virus, which is attenuated by serial passage in embryonated hens' eggs and chick embryo cell culture. The vaccine induces antibody in 96% of seronegative recipients and has 97% protective efficacy.
The initial mumps immunization, usually as measles-mumps-rubella (MMR) vaccine, is recommended at 12–15 mo of age. A second immunization, also as MMR, is recommended routinely at 4–6 yr of age but may be administered at any time during childhood provided at least 4 wk have elapsed since the first dose. Children who have not previously received the second dose should be immunized by 11–12 yr of age. Women should avoid becoming pregnant for 30 days after monovalent mumps vaccination (3 mo if vaccination was performed with rubella vaccine). Other contraindications to vaccination include allergy to a vaccine component (anaphylaxis to neomycin), moderate or severe acute illnesses with or without fever, immunodeficiency (primary immunodeficiencies, cancer and cancer therapy, long-term high-dose corticosteroid therapy, severely immunocompromised, including those with HIV infection), and recent immune globulin administration (see Chapter 282 ). Rarely, parotitis and low-grade fever can develop 10–14 days after vaccination. Vaccinees do not shed virus.
Persons born before 1957 can be considered immune to mumps. Maternal antibody is protective in the infant in the first 6 mo of life.