Mumps is an infection with a virus that causes swelling of the parotid glands in front of each ear. The parotid glands make saliva. Mumps is caused by the mumps virus, a type of paramyxovirus that spreads from person to person through coughs, sneezes and saliva, as well as through contact with contaminated items and surfaces (used tissues, shared drinking glasses, dirty hands that touched a runny nose). Once the mumps virus enters the body, it passes into the bloodstream and can spread to many different glands and to the brain:
Salivary glands — Mumps causes pain and swelling in the parotid gland and in other salivary glands located under the tongue and jaw.
Testes — In the testes, mumps infection can cause swelling, pain, tenderness and, sometimes, permanent shrinkage (atrophy), although it rarely causes sterility.
Ovaries — In women, mumps infection of the ovaries can cause pain in the lower abdomen but doesn't lead to infertility.
Pancreas — The mumps virus may cause inflammation and infection of the pancreas and abdominal pain.
Brain — Once it enters the bloodstream, the mumps virus also can travel to the brain, where it may cause meningitis (inflammation and infection of membranes covering of the brain) and encephalitis (brain infection). This brain involvement (which is very rare) sometimes leads to long-term complications, such as deafness, paralysis (weakness, especially of facial muscles), hydrocephalus and seizures.
Rarely, the mumps virus can affect other parts of the body, such as the joints, thyroid gland or lungs.
When a pregnant woman develops mumps, there may be some increased risk of fetal death and miscarriage if the mother is in her first trimester. However, the infection probably does not increase the risk of birth defects.
People with mumps are contagious during a period that begins 48 hours before and ends 6 to 9 days after the beginning of the mumps symptoms. Before an effective vaccine became available in the late 1960s, there were almost 190,000 reported cases of mumps each year in the United States. Now, thanks to the mumps vaccine, the number of annual cases has decreased by more than 99%, so that only 1 out of 1 million people in the United States gets mumps.