Introduction
Mumps is an acute, systemic, and highly contagious viral infection that is self-limiting as the immune system of the body fights and clears it. It is typically characterized by swelling of one or more parotid salivary glands, which become edematous and infiltrated by lymphocyte cells.
Mumps virus (MuV) is a single-stranded RNA virus, Rubulavirus within the genus Paramyxovirus, and is a member of the family Paramyxoviridae.
The epidemiologic characteristics of the mumps virus are similar to the measles and rubella viruses.
Mumps is a worldwide disease and as in measles, humans are the only known natural hosts. The mumps virus is highly infectious and more so to non-immune individuals. Mumps is less infectious than measles.
These non-immune individuals are those who have not had the disease earlier or have not been vaccinated. An infection of mumps can give life-long immunity, so a repeat infection is rare.
Due to the widespread vaccination programs, the incidence of mumps has substantially decreased. With the introduction of the mumps vaccine (MMR vaccine) in 1967, the incidence of mumps in the United States has dropped by 99%.
In non-vaccinated people, infection with mumps can occur at any age but is unusual in children below 2 years, and more particularly those below 1 year. It is normally observed in childhood, most often between the ages of 5–9 years.
With routine vaccination programs for preschool and school-going children, mumps now mostly affects adolescents and young adults.
While the effectiveness of two doses of MMR is high, studies suggest this effectiveness decreases with time. After 2 doses of the MMR vaccine, about 99% of people will gain immunity against measles and rubella, but only 88% of people will be protected against mumps.
However, vaccinated people who get mumps usually have milder symptoms and less complications. Recent outbreaks among college students who were fully vaccinated have cast a shadow over the vaccine offering life-long immunity and suggests that immunity to mumps after vaccination may wane over time.
You can get mumps at any time of year, though increasing cases are noted during late winter and early spring in temperate climates, whereas no such occurrence is observed in tropical regions
Though the initial symptoms are nonspecific, (fever, headache, malaise, muscle pain, and loss of appetite), mumps is particularly famous for causing painful and swollen salivary glands. It is usually mild in children and sometimes the child may not have any symptoms.
If you are infected with mumps after puberty, you are at a greater risk of developing complications such as testicular and ovarian inflammation, loss of hearing and life-threatening meningitis and encephalitis. Otherwise, most people recover completely within 2 weeks.
About one-third of people with a mumps infection do not develop any symptoms but they are still contagious. When symptoms do set in, they typically occur 16 to 18 days after exposure to the virus.
Causes, Risks, and Transmission
You get mumps when you catch its virus. The mumps virus is found only in humans. It is present in your nasal secretions, saliva, blood, and urine, and in the cerebrospinal fluid (CSF) if the central nervous system (CNS) is affected.
You can catch the virus in several ways.
Risk factors for mumps include:
- If you are immunodeficient
- You are a frequent international traveler to places where mumps is endemic
- You live in crowded places where there is a lack of vaccination
- You have not taken the mumps vaccine
Mumps has become endemic worldwide with epidemics occurring approximately every 5 years in unvaccinated regions. This shows how highly infectious the mumps virus is and how easily it spreads.
The virus is primarily transmitted by respiratory secretions such as droplets and saliva released into the air by the infected individual when he coughs or sneezes. It can also spread by direct contact with the infected person.
The virus typically enters your body through the nose or mouth. It stays present in saliva for 7 days before salivary gland swelling appears, and transmissibility is highest just before the inflammation of the parotid salivary glands.
Mumps is highly contagious and spreads easily causing outbreaks in thickly populated areas such as schools and dormitories.
The infectious duration of the mumps virus is long. An infected individual can pass on the infection from one week before the symptoms develop to eight days after they have developed and the infectious nature is at its most when the parotid salivary glands begin to get inflamed.
Even asymptomatic individuals can be infectious because the mumps virus is present in their saliva.
You can catch the mumps virus and get infected in the following ways:
- Being in close proximity with an infected individual when he coughs, sneezes, or talks
- Sharing utensils, water bottles, glasses, cups and towels
- Kissing or shaking hands
- Participating in activities that bring you in close contact with the infected person such as playing sports, or dancing
- Touching an object that has been infected with nasal secretions or saliva of the infected person.
- Traveling in a vehicle together
In susceptible populations, a single case can cause up to twelve new ones, though the average is 4 to 7 new cases.
Asymptomatic people infected with MUV can also transmit the virus. Furthermore, reinfection can occur even after an individual has had a natural infection or has taken the vaccine, indicating that lifelong immunity is not guaranteed after infection or vaccination.
This is possibly due to antigen drift. Some attribute this to primary vaccine failure and waning immunity offered by the vaccine.
These factors are thought to be reasons why controlling the spread of this disease is difficult. Vaccinated individuals who are infected are less contagious than the unvaccinated and the infection is not severe.
Outbreaks continue to occur in places where the vaccination rates have exceeded 90%. This possibly suggests that there may be other factors responsible that may influence disease transmission. Such outbreaks among the vaccinated population typically occur in highly crowded areas and close-knit communities.
Symptoms
During infection, the mumps virus first lodges in and infects the upper respiratory tract. It then spreads to the salivary glands and lymph nodes. From the lymph nodes, it gains access to the blood and then the virus spreads throughout the body and causes systemic symptoms and complications.
The initial symptoms are general and do not indicate anything specific. The usual incubation period for mumps is between 12 and 25 days. This is the time between exposure to the virus and the appearance of the first symptoms.
You are contagious from two days before symptoms begin until five days after the salivary gland swelling begins. Some individuals develop no symptoms but they are still contagious.
The first symptoms to develop are non-specific and flu-like and they are seen in most mumps patients. They include:
Common symptoms include:
- A headache
- Fever that is low-grade initially but can rise up to 1030F (39°C)
- Pain, tenderness, and swelling of one or more of the parotid salivary glands situated in front of the ear. These are the most commonly affected glands. The infection is mostly bilateral but is unilateral in 25% of the cases. The glandular swelling starts 7 days after the mumps virus is present in saliva and transmissibility is highest just before the development of parotitis (inflammation of the parotid salivary glands). Swelling usually peaks in 1 to 3 days and then subsides during the next week.
- Pain on chewing and swallowing
- Loss of appetite
- Muscle aches
- Tiredness
The general symptoms of low-grade fever, malaise, and headache last for several days before you develop the swollen salivary glands.
About 70% of the infected people develop swollen and painful glands. The rest have only very mild generalized symptoms (low-grade fever, malaise) or respiratory symptoms.
Rarely, the symptoms can be more severe, possibly due to complications. They include:
- High fever with shivering chill
- Nausea and vomiting
- Abdominal pain
- Neck pain or stiffness
- Severe headaches due to meningitis or encephalitis
- Confusion or disorientation
Complications
Studies have time and again reported lower rates of complications compared to those that developed during the pre-vaccine era, which suggests vaccination may protect you against serious mumps infections and its complications.
Studies also showed that the rates of complications and hospitalization among the mumps-infected vaccinated people were significantly much lower compared to unvaccinated cases.
However, complications can occur in vaccinated people but the severity of them is much lower.
There are several complications that mumps can cause. The symptoms can make one worry, but they’re rarely serious and usually resolve as the infection passes. They are more common in male adolescents and adults.
They include:
- Swollen testicle/s (orchitis). Orchitis is the most common complication of mumps infection in adult males. There is severe testicular pain. One or both testicles can get inflamed and swollen. Orchitis is seen to develop in 20 to 25% of mumps-infected males and 80% of these cases occur in those below 10 years. One or both testicles can be swollen and painful. Two-thirds of cases are unilateral and one-third bilateral. Testicular atrophy and reduced fertility (reduced sperm count) develop in one-half of those affected. Rarely, it can cause sterility. It’s more common in those post-puberty male patients, who have had mumps infection after puberty. Pain and swelling of the testicles accompanied by a high fever usually begins seven to 10 days after the salivary glands swell. Occasionally there may also be abdominal pain, which goes away in three to seven days.
- Swollen ovaries (oophoritis). Oophoritis is inflammation of one or both ovaries. It is seen to develop in 5–10% of post-pubertal women who were infected with mumps. It causes pelvic pain and abdominal tenderness accompanied by fever, vomiting, and an upset stomach. It can rarely cause irregular and inconsistent menstrual blood flow, premature menopause, and makes it difficult for a woman to become pregnant.
- Mastitis. Mastitis is an infection or inflammation of breast tissue. It is seen in up to about 30% of post-pubertal women. Symptoms include pain and tenderness in the breast area. It gets resolved with time
- Encephalitis. Encephalitis is inflammation and damage of the brain tissue. Symptoms include changes in consciousness, seizures, loss of muscle control, and paralysis. It is the most dangerous complication of mumps that can cause death, which is rarely attributed to mumps.
- Meningitis. Aseptic meningitis, a central nervous system complication, is inflammation of the membranes covering the brain and spinal cord. Symptoms include fever, headache, vomiting, neck stiffness, and sensitivity to light. Meningitis caused by mumps rarely causes long-term problems. It can develop in 25% of people and resolves within 14 days. Since it is viral meningitis the cerebral spinal fluid test result is negative with routine bacterial cultures.
- Hearing loss. This complication can develop suddenly or gradually. Hearing loss is a rare complication of mumps seen in less than 1 percent of cases. It is usually seen in one ear only and usually gets better after the illness. However, very rarely hearing loss can be of sudden onset and be permanent. Mumps is the most frequent cause of this one-sided deafness in children wherein the inner ear could be damaged. It’s estimated that permanent hearing loss occurs in around 1 in 20,000 cases of mumps.
- Pancreatitis. Mumps can cause inflammation and damage to the pancreas, resulting in its swelling. Symptoms may include sudden abdominal (epigastric) pain and tenderness, an upset stomach, vomiting, and high fever. Rarely, jaundice may develop. This complication of mumps is rare and only short-term. About 1 in 25 cases develop this acute condition.
- Miscarriage. Although mumps has not been linked to birth defects or premature births, getting mumps during the first trimester of pregnancy can increase the risk of miscarriage. The risk is higher in a non-immune woman who has not been vaccinated or didn’t have an earlier mumps infection.
- Other rare complications of mumps include:
- Myocarditis (inflammation of the heart)
- Thyroiditis (inflammation of the thyroid gland)
- Nephritis (inflammation of the kidney)
- Hepatitis (inflammation of the liver)
- Arthritis (inflammation of a joint)
- Keratitis (inflammation of the cornea)
- Thrombocytopenia (low platelet count)
