Mumps is an acute, systemic, communicable viral infection whose most distinctive feature is swelling of one or both parotid glands
Mumps is an acute, systemic, communicable viral infection whose most distinctive feature is swelling of one or both parotid glands. Involvement of other salivary glands, the meninges, the pancreas, and the gonads is also common.
Mumps virus, a paramyxovirus, is pleomorphic and has a diameter ranging from 100 to 600 nm. The virion is composed of RNA and five proteins. The RNA is surrounded by an envelope with glycoprotein projections. There are two envelope glycoproteins¾a hemagglutinin-neuraminidase (HN) and a hemolysis cell fusion antigen (F)¾as well as a matrix envelope protein (M). There are two internal components: a nucleocapsid protein (NP) and an RNA polymerase protein. There is only one antigenic type of mumps virus.
After the introduction of mumps vaccine in 1967, the incidence of clinical mumps declined significantly in the United States. In 1968 (before widespread immunization), 185,691 cases of mumps were reported in this country. The 906 cases reported in 1995 represent a reduction in the number of cases by >99% from prevaccine levels; this is the lowest number of cases ever reported in a year. Before widespread vaccination, the incidence of mumps was highest in the winter and spring, with epidemics every 2 to 5 years. At that time, mumps was principally a disease of childhood, although today more than 50% of cases occur in young adults. Epidemics tended to occur in confined populations, such as those in schools and the military services.
The incubation period of mumps generally ranges from 14 to 18 days, with extremes of 7 and 23 days. However, because a contact may be shedding virus before the onset of clinical disease or (like one-third of patients) may have subclinical infection, the incubation period in individual cases is often uncertain. One attack of mumps usually confers lifelong immunity. Long-term immunity is also associated with immunization.
Mumps virus is transmitted by droplet nuclei, saliva, and fomites. Replication of the virus in the epithelium of the upper respiratory tract leads to viremia, which is followed by infection of glandular tissues and/or the central nervous system (CNS).
Little is known of the pathology of mumps since the disease is rarely fatal. The affected glands contain perivascular and interstitial mononuclear cell infiltrates with prominent edema. Necrosis of acinar and epithelial duct cells is evident in the salivary glands and in the germinal epithelium of the seminiferous tubules.
The prodrome of mumps consists of fever, malaise, myalgia, and anorexia. Parotitis, if it develops, usually does so within the next 24 h but may be delayed for as long as a week; it is generally bilateral, although the onset on the two sides may not be synchronous and at times only one side is affected. The submaxillary and sublingual glands are involved less often than the parotid and are almost never involved alone. Swelling of the parotid is accompanied by tenderness and obliteration of the space between the ear lobe and the angle of the mandible. The patient frequently reports an earache and finds it difficult to eat, swallow, or talk. Glandular swelling increases for a few days and then gradually subsides, disappearing within a week. The orifice of Stensen’s duct is commonly red and swollen. Presternal pitting edema has been described in about 5% of mumps cases, often in association with submandibular adenitis.
Other than parotitis, orchitis is the most common manifestation of mumps among postpubertal males, developing in about 20% of cases. The testis is painful and tender and is enlarged to several times its normal size; accompanying fever is common. Later, testicular atrophy develops in half of the affected men. Since orchitis is bilateral in fewer than 15% of cases, sterility after mumps is rare. Oophoritis in women¾far less common than orchitis in men¾may cause lower abdominal pain but does not lead to sterility.
Aseptic meningitis, which may develop before, during, after, or in the absence of parotitis, is a common manifestation of mumps in both children and adults. Symptoms include stiff neck, headache, and drowsiness. Pleocytosis of the cerebrospinal fluid (CSF), with up to 1000 cells/uL, may develop in up to 50% of cases of clinical mumps, but clinical signs of meningeal irritation are documented in only 5 to 25% of cases. Within the first 24 h, polymorphonuclear leukocytes may predominate in CSF, but by the second day nearly all the cells are lymphocytes. The glucose level in CSF may be abnormally low, and this finding may arouse suspicion of bacterial meningitis. Aseptic meningitis due to mumps without parotitis is indistinguishable clinically from that caused by other viruses. Mumps meningitis is almost invariably self-limited, although cranial nerve palsies have occasionally led to permanent sequelae, particularly deafness. More rarely, mumps virus may cause encephalitis, which presents as high fever with marked changes in the level of consciousness and frequently results in permanent sequelae in survivors. Other CNS problems occasionally associated with mumps include cerebellar ataxia, facial palsy, transverse myelitis, Guillain-Barre syndrome, and aqueductal stenosis leading to hydrocephalus.
Mumps pancreatitis, which may present as abdominal pain, is difficult to diagnose because an elevated serum amylase level can be associated with either parotitis or pancreatitis. Other unusual complications of mumps include myocarditis, mastitis, thyroiditis, nephritis, arthritis, and thrombocytopenic purpura. An excessive number of spontaneous abortions are associated with gestational mumps when the disease occurs during the first trimester. Mumps in pregnancy does not lead to premature birth or fetal malformations.
The diagnosis of mumps is made easily in patients with acute bilateral parotitis and a history of recent exposure. When parotitis is unilateral or absent or when sites other than the parotid gland are involved, laboratory diagnosis is required (see below).
The myriad causes of bilateral parotid swelling other than mumps virus include infection with other viruses, such as parainfluenza virus type 3, coxsackieviruses, and influenza A virus; metabolic diseases, such as diabetes mellitus and uremia; and drugs, such as phenylbutazone and thiouracil. Unilateral parotid swelling can result from a tumor, a cyst, or a ductal obstruction due to stones or strictures. Other conditions associated with chronic parotid swelling include sarcoidosis, Sjogren’s syndrome, and infection with HIV. Suppurative parotitis, usually caused by Staphylococcus aureus, is most often unilateral.
Other entities should be considered when manifestations consistent with mumps appear in organs other than the parotid. Testicular torsion may produce a painful scrotal mass resembling that seen in mumps orchitis. Other viruses (e.g., enteroviruses) may cause aseptic meningitis that is clinically indistinguishable from that due to mumps virus.
Mumps virus is readily isolated after inoculation of appropriate clinical specimens into a variety of host systems, such as rhesus monkey kidney cells and human embryonic lung fibroblasts. The virus can be rapidly identified by the use of cells grown in shell vials and of fluorescein-labeled monoclonal antibodies. Mumps virus may be recovered from saliva, throat, and urine during the first few days of illness and from the CSF of patients with mumps meningitis. Shedding of virus in the urine may persist for as long as 2 weeks. No particular peripheral blood cell count is characteristic of mumps.
Highly sensitive enzyme-linked immunosorbent assays are useful for diagnosis of mumps and for determination of susceptibility to the disease. Acute mumps can be diagnosed either by the examination of acute- and convalescent-phase sera for a significant increase in IgG antibody titer or by the demonstration of specific IgM in one serum specimen. Use of a skin-test antigen to assess immunity to mumps has been replaced by serologic testing.
Live attenuated mumps vaccine (Jeryl Lynn strain) induces antibodies that protect against infection in more than 95% of cases. The subcutaneously administered vaccine may be given to children older than 1 year but is not recommended for younger infants because of the potential for interference by passive maternal antibodies. Mumps vaccine is usually administered as part of the measles-mumps-rubella (MMR) vaccine at the age of 12 to 15 months and again at 4 to 12 years of age. This MMR vaccine is also recommended for susceptible older children, adolescents, and adults, particularly adolescent males who have not had mumps. For these patients, either MMR or monovalent mumps vaccine may be given; two doses are preferred. Inadvertent immunization of individuals who are already immune is not associated with significant adverse reactions. Mumps vaccine is not recommended for pregnant women, for patients receiving glucocorticoids, or for other immunocompromised hosts. However, children with HIV infection who are not severely immunocompromised can safely be immunized against mumps; MMR vaccine is usually used for this purpose (Chap. 194).
Therapy for parotitis and other manifestations of mumps is symptom-based. The administration of analgesics and the application of warm or cold compresses to the parotid area may be helpful. Mumps immune globulin is of no value in the prophylaxis or treatment of established disease. Testicular pain may be minimized by the local application of cold compresses and gentle support for the scrotum. Anesthetic blocks may also be used. Neither the administration of glucocorticoids nor incision of the tunica albuginea is of proven value for the treatment of severe orchitis. Anecdotal information on a small number of patients with orchitis suggests that administration of interferon a may be helpful.^
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