Mumps overview

# Overview
Mumps virus (MuV) is an enveloped, non-segmented, negative-sense RNA virus belonging to the Paramyxovirus family that causes mumps. Humans are the only natural host for mumps virus (MuV). MuV is transmitted through respiratory droplets (saliva or mucus), direct contact, or contact with surfaces carrying MuV. MuV infects the upper respiratory tract epithelium and disseminates through the lymphatic system to cause systemic infection. Replication in the parotid gland (or other salivary gland) causes mononuclear cell infiltration, hemorrhage, edema, and necrosis. The average incubation period for MuV is 16-18 days. Nonspecific prodromal symptoms develop and last 3-4 days. Several days after onset of prodrome, one or both of the parotid salivary glands begin to swell (parotitis). One parotid may swell before the other, and in 25% of patients, only one side swells. Complications include: orchitis in post-pubertal males, Oophoritis and/or mastitis in post-pubertal females, transient sensorineural hearing loss, Meningitis, Encephalitis, Pancreatitis, and Spontaneous abortion during the first trimester of pregnancy. Mumps is self-limiting and prognosis is excellent for uncomplicated mumps. The characteristic presentation of mumps is tender, swollen parotid glands. Inflammation of submandibular and sublingual salivary glands is palpable in 10% of patients. Sialoadenitits is usually preceded by a low-grade fever. The jawbone is often not palpable and swelling pushes the angle of the ear out and up. Mumps must be differentiated from other diseases or pathogens that cause upper respiratory infection, prodromal symptoms, swelling of salivary glands (sialadenitis), particularly parotitis. Etiologic agents that cause similar symptoms include: parainfluenza virus, adenovirus, Epstein-Barr virus, coxsackievirus, influenza A, parvovirus B19, human herpesvirus 6. Non-infectious causes include: salivary calculi, tumor, sarcoid, Sjogrens syndrome, thiazide drug reaction, iodine sensitivity. Laboratory findings for the mumps virus can be useful, and may include virus isolation from swabs of affected salivary ducts, urine, or serum samples. Serologic testing for IgM antibody or detecting a significant rise in IgG antibody confirms a mumps diagnosis.  Antigen detection by polymerase chain reaction (PCR) is an efficient and rapid method to determine mumps as a diagnosis. umps can be prevented with the MMR vaccine. The United States is replacing MMR with the MMRV vaccine, which also protects against chickenpox. A single dose is on average 78% effective at preventing mumps while 2 doses is on average 88% effective. Since the initiation of the MMR vaccination program in the United States in 1967, the incidence of mumps has declined by 99%.

# Historical Perspective
Mumps may have first been described by Hippocrates as a disease causing parotitis and orchitis in the 5th century. Prior to the vaccination program, which started in the United States in 1967, approximately 186,000 cases occurred each year. Implementation of the vaccination program resulted in an approximate 99% decrease in incidence rates. Outbreaks in 2006 and 2009 in the United States resulted in 6,584 and over 3,000 affected people, respectively.

# Pathophysiology
Humans are the only natural host for mumps virus (MuV). MuV is transmitted through respiratory droplets (saliva or mucus), direct contact, or contact with surfaces carrying MuV. MuV infects the upper respiratory tract epithelium by binding to extracellular sialic acid via the hemagglutinin-neuraminidase (HN) glycoprotein. MuV is able to evade an immune response with small hydrophobic (SH) protein, which blocks TNF-mediated apoptosis, and with the V proteins, which inhibit IFN production and signaling. MuV disseminates through the lymphatic system to cause systemic infection. Replication in the parotid gland (or other salivary gland) causes mononuclear cell infiltration, hemorrhage, edema, and necrosis.

# Causes
Mumps virus (MuV) is an enveloped, non-segmented, negative-sense RNA virus that causes mumps. MuV belongs to the genus Rubulavirus and family Paramyxovirus. Humans are the only natural host of MuV. MuV is transmitted through respiratory droplets (saliva or mucus), direct contact, or contact with surfaces carrying MuV. MuV is able to bind to host epithelial cells via haemagglutinin-neuraminidase (HN) and fusion (F) glycoproteins. Small hydrophobic (SH) protein is presumed to block TNF-mediated apoptosis. Non-structural proteins NS1 and NS2 (V proteins) inhibit IFN production and signaling.

# Differential Diagnosis
Mumps must be differentiated from other diseases or pathogens that cause upper respiratory infection, prodromal symptoms, swelling of salivary glands (sialadenitis), particularly parotitis. Etiologic agents that cause similar symptoms include: parainfluenza virus, adenovirus, Epstein-Barr virus, coxsackievirus, influenza A, parvovirus B19, human herpesvirus 6. Non-infectious causes include: salivary calculi, tumor, sarcoid, Sjogrens syndrome, thiazide drug reaction, iodine sensitivity.

# Epidemiology and Demographics
Since the initiation of the MMR vaccination program in the United States, the incidence of mumps has declined by 99%. Currently, the number of cases per year ranges from a couple hundred to a couple thousand. Mumps predominantly occurs in school-age children (5-14 years) but outbreaks have occurred in adolescents and adults. There is currently no significant difference in mumps incidence between sexes and races. Mumps is uncommon in the United States and other developed countries. However sporadic outbreaks have occurred, predominantly in environments that involve close contact or high level of social interaction. Only 57% of countries belonging to the World Health Organization use a mumps vaccine. Most of these countries are developing and mumps remains endemic in these regions.

# Risk Factors
Risk factors for mumps include: unvaccinated individuals who do not have evidence of immunity, belonging to the age group 2-12 years, international travel, especially to countries without mumps vaccination programs, working or living in close proximity to individual(s) infected with Rubulavirus, and being in states of immunodeficiency.

# Natural History, Complications and Prognosis
The average incubation period for mumps virus is 16-18 days. Nonspecific prodromal symptoms develop and last 3-4 days. Several days after onset of prodrome, one or both of the parotid salivary glands begin to swell (parotitis). One parotid may swell before the other, and in 25% of patients, only one side swells. Other salivary glands (submandibular and sublingual) under the floor of the mouth also may swell but do so less frequently (10%). Parotitis, lasts at least 2 days, but may persist longer than 10 days. Complications include: orchitis in post-pubertal males, Oophoritis and/or mastitis in post-pubertal females, transient sensorineural hearing loss, Meningitis, Encephalitis, Pancreatitis, and Spontaneous abortion during the first trimester of pregnancy. Mumps is self-limiting and prognosis is excellent for uncomplicated mumps. Adolescents and adults are more likely than children to develop complications but these are rare, and prognosis is still favorable.

# Diagnosis

## Diagnostic Criteria
Suspected mumps involves parotitis, orchitis, or oophoritis unexplained by another diagnosis OR a positive lab result with no mumps clinical symptoms. Probable mumps involves parotitis or other salivary gland swelling lasting at least 2 days, or orchitis or oophoritis unexplained by another more likely diagnosis, in a person with a positive test for serum anti-mumps immunoglobulin M (IgM) antibody OR person with epidemiologic linkage to another probable or confirmed case or linkage to a group/community defined by public health during an outbreak of mumps. Confirmed mumps involves positive mumps laboratory confirmation for mumps virus with reverse transcription polymerase chain reaction (RT-PCR) or culture in a patient any of the following symptoms: acute parotitis or other salivary gland swelling, lasting at least 2 days, aseptic meningitis, encephalitis, hearing loss, orchitis, oophoritis, mastitis, pancreatitis.

## History and Symptoms
The most common symptoms of mumps are a prodrome with low grade fever, myalgia, anorexia, malaise, and headache, followed by painful, bilateral parotitis. Less common symptoms include orchitis in post-pubertal males, oophoritis or mastitis in post-pubertal females, encephalitis, and transient sensorineural hearing loss. Approximately 15-20% of patients may be asymptomatic.

## Physical Examination
The characteristic presentation of mumps is tender, swollen parotid glands. Inflammation of submandibular and sublingual salivary glands is palpable in 10% of patients. Sialoadenitits is usually preceded by a low-grade fever. The jawbone is often not palpable and swelling pushes the angle of the ear out and up. 25% of patients present with unilateral swelling. Stensen's duct orifice may be inflamed and erythematous. Lymph node swelling can be differentiated by the well-defined borders of the lymph nodes, location behind the angle of the jawbone, and lack of the ear protrusion or obscuring of the jaw angle.

## Laboratory Findings
Laboratory findings for the mumps virus can be useful, and may include virus isolation from swabs of affected salivary ducts, urine, or serum samples. Serologic testing for IgM antibody or detecting a significant rise in IgG antibody confirms a mumps diagnosis. However, there are many important caveats to be aware of when interpreting the results. Antigen detection by polymerase chain reaction (PCR) is an efficient and rapid method to determine mumps as a diagnosis. It may be necessary to test for antibodies for other infections causing parotitis including: Epstein-Barr Virus, parainfluenza virus, parvovirus B19, adenovirus, and enterovirus.

## CT
Mumps is a clinical diagnosis. Imaging studies do not play a role in the initial diagnosis of mumps. However, imaging studies, such as a CT scan, may be helpful in patients with secondary complications.

## Ultrasound
Mumps is a clinical diagnosis. Imaging studies do not play a role in the initial diagnosis of mumps. However, imaging studies, such as an ultrasound, may be helpful in patients with secondary complications.

## Other Diagnostic Studies
Mumps is a clinical diagnosis. Further testing may be required in patients with secondary complications.

# Treatment

## Medical Therapy
No antiviral agent currently exists and therefore supportive care is indicated for patients with mumps. Supportive care includes prescribing analgesics, application of warm or cold packs to swollen areas, warm salt water gargles, and fluid intake. Patients should avoid acidic foods or juices. Patients should be isolated for at least 5 days after onset of symptoms.

## Primary Prevention
Mumps can be prevented with the MMR vaccine. The United States is replacing MMR with the MMRV vaccine, which also protects against chickenpox. A single dose is on average 78% effective at preventing mumps while 2 doses is on average 88% effective. In general all age groups should receive 2 doses of MMR or MMRV vaccine unless an individual has evidence of immunity. The vaccine is contraindicated in pregnant women, individuals with egg or neomycin allergies and immune-compromised or severely immune-suppressed individuals.