Lymphoreticular and Hematopoetic Infections
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MUMPS

General Goal: To know the cause of this disease, the most common modes of transmission, the major manifestations, and the major complications of this disease.

Specific Educational Objectives: The student should be able to:

1. recite the common means of transmission and identify the major disease manifestations.

2. identify the cell-types in which the virus infects.

3. explain what is in the vaccine and why it is important to give the vaccine to children.

Reading: MEDICAL MICROBIOLOGY by P.R. Murray, K.S. Rosenthal, G.S. Kobayashi and M.A. Pfaller, 3rd Edition. pp. 468-469.

Mosby's Color Atlas and Text of Infectious Diseases by Christopher P. Conlon and David R. Snydman. pp. 60-61.

Lecture: Dr. Neal R. Chamberlain

References:

OVERVIEW

A common childhood inflammatory disease of the salivary glands with occasional serious complications. Although infection of the parotid glands is the most common manifestation, many other organs can be involved. The incidence of mumps has shown a dramatic decrease since the introduction of the mumps vaccine in 1967.

ETIOLOGY

"Mumps" virus (paramyxovirus; RNA virus). also called benign viral parotitis.

EPIDEMIOLOGY

Distribution: Worldwide distribution with man as the only known reservoir. Prior to the vaccine, about 50% of children contracted mumps. Except for an outbreak in 1986-87, the incidence has been low. About 1500 cases are reported each year, down from the almost 150,000 reported cases per year before the vaccine

Transmission: Viral transmission occurs through inhalation of respiratory droplets, or by direct person to person contact.

Infective period: 2-3 days before symptoms until 9 days after symptoms disappear. One third of cases are subclinical.

Incidence: Mumps is primarily a childhood disease with about 95% of all cases occurring in children under 15 years of age. This virus is highly contagious.

Neonates receive passive immunity from the mother and the high incidence of childhood mumps infections makes adult cases rare.

PATHOGENESIS

The virus usually enters the body through the upper respiratory tract and infects regional lymph nodes.

A viremia results from spread of the virus from the lymph nodes to the bloodstream. The viremia disseminates the virus to the meninges, salivary glands (necrosis, interstitial edema, inflammation, and lymphocytic infiltration), testes, pancreas, ovaries, kidneys (virtually every case shows impaired renal function), thyroid, eyes, and mammary glands (occasionally). The mumps virus has a tropism for glandular tissue and also is neurotropic, resulting in meningitis, encephalitis, myelitis, polyneuritis, polyradiculitis, and cranial neuritis. There also is frequent renal involvement.

MANIFESTATIONS Mumps is often asymptomatic. A clinically nondescript, febrile upper-respiratory disease is also common in infants and preschoolers.

Classical mumps: The male to female ratio is 1:1.

Incubation period: 14-25 d with average of 18 d.
Prodrome: myalgia, anorexia, malaise, and a low grade fever.
Swollen and tender salivary glands (example 2)(most commonly the parotid; parotitis), also earache; swelling lasts about 1 week and usually involves both sides.

Orifices of Wharton's and/or Stensen's ducts become red and swollen with pinpoint petechial hemorrhages.
Obstruction of these inflamed ducts by edema or cellular debris make chewing or drinking very painful.

Mumps virus also infects and can cause swelling of the pancreas, thyroid, prostrate, and lacrimal glands.

OTHER MANIFESTATIONS

Epididymoorchitis. This occurs in about 20% of postpubertal males that contract mumps. The symptoms occur abruptly and include bilateral testicular swelling (3 - 4- fold), tenderness, nausea, vomiting, elevation of temperature, and chills. Surprisingly, sterility due to mumps orchitis is rare. This condition is usually seen in adolescent patients.

Aseptic meningitis. Mumps virus infects the CNS in about 50% of patients. Symptoms are seen in 10% of cases, usually males, and are similar to those of benign viral meningitis, e.g., fever, headache, nausea, vomiting, and lethargy. Symptoms usually subside completely 3-10 days after onset. For meningitis, the male to female ratio is 3:1. A severe encephalitis may occur if the brain is involved. The encephalitis from mumps occurs in 2.6/1000 cases, but it is fatal in 1.4% of those cases.

Deafness. Before the availability of vaccine, mumps was one of the leading causes of childhood deafness (1:15,000 mumps cases). This hearing loss due to nerve destruction was complete and permanent, but was unilateral in 75% of cases.

Oophoritis. Ovarian mumps involvement occurs in 5% of post-pubertal females. Symptoms include tenderness and pain, and can mimic appendicitis if the right ovary is involved. There is no evidence that mumps oophoritis causes impaired fertility in females.

Mortality: Mortality is rare and usually occurs in patients older than 19 years.

Mumps in pregnancy. (Intrauterine mumps infection)

First trimester: increased fetal death and abortion.
Second and third trimesters: little risk of congenital disease.
Neonatal mumps infection is extremely rare.

DIAGNOSIS

Clinical picture usually suffices for mumps parotitis. The gland feels jellylike. The overlying skin is not usually warm to the touch is it is in bacterial parotitis.

Blood analysis: Orchitis, pancreatitis, or aseptic meningitis is often associated with high total white cell counts (above 20,000 with a high number of PMN's).

Rapid diagnosis can be made directly on pharyngeal cells or on urine sediment using an immunofluorescence assay for viral antigen.

THERAPY

Treat the symptoms.

PREVENTION A live, attenuated live mumps vaccine is available for 15-month-old infants and older; singly or in combination with measles and rubella (MMR). A booster shot should be given at 4-6 yrs. In most states MMR is required for admission to school.

Immunity is long-lasting; a mild parotitis may occur.

Vaccine should not be given during pregnancy since the virus can cross the placenta.