Mumps is a contagious disease caused by a virus that results in swelling of the parotid glands (glands located below and in front of the ears that produce saliva in the mouth).

It is considered to be as contagious as influenza and rubella (German measles), but less contagious than measles or varicella (chickenpox). It occurs throughout the year, but is most common in late winter or early spring. Most cases occur in children ages 5 to 15, although infection is possible at any age and cases among adults are usually more severe than those involving children. Children under age 2 rarely develop mumps.

An infected person passes the mumps virus through droplets in their breath or mucus or by transmitting it through objects. After the virus enters the body, it grows in the nasopharynx (the upper part of the throat behind the nose) and lymph nodes. It can spread through the bloodstream to tissues in the body such as the meninges (membranes surrounding the brain and spinal cord), pancreas, testes and ovaries.

Mumps usually begins with a general sick feeling (malaise), fever, chills and a sore throat, followed by swelling of the parotid glands that causes the cheeks to puff out.

Most people who develop mumps recover fully. Complications of the disease are rare, but they are potentially serious. They include:

• Aseptic meningitis. Illness characterized by headache, fever and inflammation of the lining of the brain that is not caused by bacteria. According to the Centers for Disease Control and Prevention (CDC), tests of fluid in the brain and spinal cord indicate that 50 to 60 percent of mumps patients develop aseptic meningitis, but most do not experience symptoms. Of that group, up to 15 percent of patients develop symptoms. Patients usually recover within several days.
  
  
• Testicular inflammation (orchitis). According to the CDC, this occurs in up to 50 percent of males who have reached puberty. Signs and symptoms include testicular swelling, tenderness, nausea, vomiting and fever. Some men may develop testicular atrophy, but sterility rarely occurs as a result of this condition.
  
  
• Ovarian inflammation (oophoritis). This occurs in 5 percent of females who have reached puberty but does not affect fertility, according to the CDC.
  
  
• Pancreatitis. A disease that causes swelling of the pancreas. It is rare, but symptoms include pain in the upper abdomen, nausea and vomiting.
  
  
• Deafness. According to the CDC, deafness occurs in approximately 1 in 20,000 cases of mumps. Onset is usually sudden and results in permanent hearing impairment.
  
  
• Miscarriage. Pregnant women who develop mumps during the first trimester of pregnancy have a greater chance of miscarriage (spontaneous termination of pregnancy).

In some rare cases, mumps causes inflammation of the brain (encephalitis), breasts (mastitis) or spinal cord (myelitis). Other complications of mumps that are even rarer include arthralgia (pain in the joints), arthritis (inflammation of the joints) and nephritis (inflammation of the kidneys). An average of one death from mumps per year was reported between 1980 through 1999, according to the CDC.

Before a vaccine was licensed in the United States in 1967, mumps was considered a routine childhood illness. There were more than 200,000 cases of mumps reported each year. Since introduction of the vaccine, the number of cases has dropped dramatically. In 2003, there were 231 cases of mumps reported in the United States, according to the CDC.

However, mumps is common in other countries and is easily contracted by those who have not been vaccinated or already had the disease.

In early 2006, the U.S. experienced its largest outbreak of mumps in two decades. Many of these cases occurred among college students. This outbreak was most likely to due to a decrease in vaccination rates among students.