A 42-year-old man spends two weeks in Africa, working with an international relief group that interacts with young children. Two days after returning to the U.S., he develops a low-grade fever that is accompanied by myalgias, anorexia, and malaise. The following day, he notices a distinct swelling and tenderness in the area between his ear lobe and the angle of his jawbone, initially on one side of his face and later on both sides. The pain and swelling worsen over the next 36 hours or so, and the man finds it increasingly difficult to eat, swallow, or talk. On the fourth day of his illness, he develops severe pain, swelling, and tenderness in his left testis, along with a more obvious fever and a slight earache in both ears. At this point, the man seeks medical attention. Vital signs are normal except for fever (39ºC). On physical examination, he is found to have pronounced bilateral swelling and tenderness in the parotid area, and the orifices of the Stensen's ducts are red and swollen. His left testis is swollen to at least two times its normal size and is extremely tender, and there is obvious scrotal erythema. The man is pretty sure that he has never experienced symptoms like these before. When asked about his immunization history, he says that he never received the various childhood vaccinations that are routinely administered in the U.S. because his parents did not believe that they were safe.

Question 1.1: What is the most likely diagnosis?

The swelling and tenderness in the parotid areas suggests a form of bilateral parotitis (inflammation of the parotid glands). The painful swelling of the left testis and scrotal erythema indicate a unilateral orchitis (inflammation of a testis). The combination of symptoms suggests mumps because orchitis is a common complication of mumps in adult males (occurring in (30% of cases). The man's immunization history (or, actually, lack thereof) and recent travel to a region where mumps is endemic are also consistent with this diagnosis.

NOTE: Several other viruses can cause parotitis, including cytomegalovirus (CMV), Coxsackie viruses, influenza A, and parainfluenza types 1 and 3. Several viruses (Coxsackie B, filoviruses, coltiviruses, etc.) and several bacteria (Salmonella, Mycobacterium spp., Coxiella burnetii, etc.) can occasionally cause orchitis. However, the ability to cause both conditions simultaneously is largely limited to the mumps virus.

Question 1.2: How typical is this case?

In areas where mumps is endemic, it is primarily a disease of children. It confers lifetime immunity, so adult cases are relatively infrequent. An adult infection occurred in this case because the victim had not been exposed to the virus earlier (in the U.S.) and had not been immunized.

Mumps infections, especially those in young children, are often asymptomatic. Acute parotitis is the most frequently seen manifestation in symptomatic cases. It usually appears within 24 hrs of the onset of prodromal symptoms, but can be delayed for as long as a week. The onset is usually unilateral, but 75% of cases become bilateral within a short period of time. Parotid swelling typically progresses over 2-3 days and then resolves within 1 week.

Orchitis is the most common complication of mumps in adult males (appearing in about 30% of cases), but it seldom occurs in children. Orchitis sometimes precedes parotitis, but it usually appears during the first week of parotitis. In a few cases, orchitis is the only noticeable manifestation of the disease. Most infections are unilateral; only about 17% become bilateral.

Question 1.3: What other complications are possible?

CNS involvement occurs in 1-10% of people with mumps parotitis. The symptoms include vomiting, headaches, nuchal rigidity, and fever. Patients usually make a full recovery without noticeable sequelae. Encephalitis may develop early or late in the disease, in which case the symptoms may include fever, alterations in level of consciousness, seizures, paresis, and aphasia. This condition can lead to permanent sequelae or death. Some degree of testicular atrophy occurs in 50% of orchitis cases, months to years after recovery from the acute symptoms. Bilateral orchitis can lead to sterility, but this is rare. Oophoritis occurs in 5% of post-pubertal women. This presents with fever, nausea, vomiting, and lower abdominal pain. Other possible complications of mumps include transient renal impairment, joint involvement, pancreatitis, and deafness.

Question 1.4: What are the basic characteristics of the causative agent?

The mumps virus is a member of the Paromyxoviridae family. All members of this family have negative-sense single-stranded RNA genomes. The viron consists of a helical nucleocapsid surrounded by a pleomorphic envelope. Other medically important viruses in the Paramyxoviridae include the measles virus, parainfluenza viruses, and the respiratory syncytial virus (RSV).

Question 1.5: How is this disease transmitted?

This virus is spread via direct person-to-person contact and respiratory droplets. Mumps is highly contagious and spreads rapidly among susceptible populations. The virus infects the epithelial cells of the upper respiratory tract and spread to the parotid gland either by way of Stensen's duct or by means of a viremia. Viremia serves to spread the virus to the testes and other organs.

Question 1.6: How is this disease treated?

There is no effective antiviral drug for this disease. Analgesics and antipyretics may be utilized to reduce pain and fever. Narcotic analgesics, bed rest, ice packs, and a testicular bridge can be used to relieve pain associated with orchitis. IV fluids are given to patients with frequent vomiting as a result of pancreatitis or meningitis. Most patients recover without incident.

Question 1.7: How is this disease prevented?

An attenuated live mumps vaccine has been available since 1967. It is usually given in combination with the measles and rubella vaccines (MMR vaccine). The vaccine has proven to be quite effective in those countries that use it. In the U.S., the annual number of cases has dropped from 185,000 to fewer than 1,000.