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Internal Medicine

Mumps

Acute viral infection characterized by painful enlargement of the salivary glands, most characteristically the parotid glands.

Acute viral infection characterized by painful enlargement of the salivary glands, most characteristically the parotid glands.

History:

Mumps was first described by Hippocrates in the fifth century BC, in his first Book of Epidemics, but a viral aetiology was not demonstrated until the 1930s, when Johnson and Goodpasture fulfilled Koch’s postulates by transferring the disease from experimentally infected rhesus macaques (Macaca mulatta), to children in his neighbourhood, using a bacteria-free, filter-sterilized preparation of macerated monkey parotid tissue.

Microbiology

Mumps virus (MuV):

Single-stranded RNA paramyxovirus; Humans are the only natural hosts for viral mumps. The virus has a variable incubation period of 7 to 21 days. Individuals are most contagious 1 to 2 days before the onset of symptoms. Primary replication occurs in upper airway mucosal epithelium. Infection of mononuclear cells in regional lymph nodes promotes viremia which leads to systemic inflammation in the salivary glands, testes, ovaries, pancreas, mammary glands, and the central nervous system (CNS).
  • Only one serotype is known
MuV virion structure.
MuV virion structure. (A) Thin sectioned transmission electron micrograph showing a typical MuV particle alongside (B) a schematic of the particle. The enveloped particles are pleomorphic, in the size range 100–600 nm. Within this structure lies the long, coiled electron-dense ribonucleoprotein (RNP), containing the MuV genome. Small spikes can be observed on the surface of the particle, corresponding to the viral HN and F glycoproteins. The same general features of the MuV particle are shown in the schematic (B). The envelope (blue lines) is studded with the HN (purple) and F (blue) glycoproteins and encases the viral RNP, made up of the RNA genome (3′–5′) in complex with N (yellow), P (orange) and L (gold) proteins. The M protein (red) interacts with the envelope, glycoproteins and the RNP. The V, I and SH proteins are expressed in infected cells, but are not thought to be incorporated within the virion. | Photomicrograph courtesy of CDC/A Harrison and FA Murphy (http://phil.cdc.gov/phil/details.asp)

Risk factors:

  • Immunodeficiency
  • International travel
  • Lack of vaccination

Presentation

Mumps is transmitted either through droplet spread or direct contact with the saliva of an infected person. The incubation period is 15-24 days, and patients are considered to be contagious from 2 days before to 5 days after the onset of parotitis or resolution of the swelling. About one-third of infections are asymptomatic.

MuV clinical presentation and pathogenesis
MuV clinical presentation and pathogenesis: Mumps is a respiratory-spread, acute, inflammatory disease in humans, which causes a range of systemic symptoms. The incubation period is 2–4 weeks. Approximately one-third of infections are asymptomatic. The prodromal phase is characterized by non-specific, often mild symptoms, such as low-grade fever, headache and malaise. An early acute phase follows, likely representing spread of the virus from the respiratory tract and development of systemic symptoms, typically parotitis, which lasts from a few days to 1 week. During the established acute phase, orchitis, meningitis or encephalitis may appear. Symptoms usually resolve within 2 weeks, coincident with the development of a MuV-specific humoral response. Long-term complications and death are rare | Rubin, S., Eckhaus, M., Rennick, L. J., Bamford, C. G., & Duprex, W. P. (2015). Molecular biology, pathogenesis and pathology of mumps virus. The Journal of pathology, 235(2), 242–252. https://doi.org/10.1002/path.4445

Asymptomatic presentation:

Approximately one-third to one-half of MuV infections are asymptomatic or result in only mild respiratory symptoms, sometimes accompanied by fever

Prodromal symptoms:

This phase is shortly followed by parotitis in the following days
  • Nonspecific symptoms: Fever, malaise, headache, myalgias, and anorexia

Mumps parotitis:

M/C manifestation (> 95% cases), and hallmark clinical feature. Parotitis is usually bilateral, developing 2–3 weeks after exposure and lasting for 2–3 days, but it may persist for a week or more in some cases
  • Bilateral parotid swelling: Painful inflammation between earlobe and angle of mandible
  • Mucosa of Stenson’s duct is often red and swollen along with the involvement of the submaxillary and submandibular glands.
  • Glandular inflammation most often presents but then subsides within one week
A child with mumps
A child with mumps (U.S. Centers for Disease Control and Prevention)

Case study:

Complications

Mumps during pregnancy:

  • Premature birth
  • Low birth weight
  • Fetal malformation

Epididymo-orchitis:

M/C extra-salivary gland manifestation of mumps (10–20% cases) in adults & adolescents
  • Painful swelling, enlargement, and tenderness of the testes which is most often bilateral
  • Testicular atrophy (50% cases)
  • Sterility and subfertility after mumps infection (rare, < 15% cases)

Mumps ophritis (lower abdominal pain)

  • Female sterility is almost never seen

Neurological complications:

MuV is highly neurotropic, with evidence of central nervous system (CNS) involvement in up to half of all cases of infection, based on pleocytosis of the cerebrospinal fluid. However symptomatic CNS infection is less common, but significant
  • Aseptic meningitis (1-10%)
    • M/C cause of aseptic meningitis in children
  • Meningoencephalitis (0.02-0.3% cases)
  • Unilateral sensorineural hearing loss (due to involvement of the labyrinth)
  • Others: Transverse myelitis, Guillan-Bare syndrome, cerebellar ataxia, facial palsy, and hydrocephalus
MuV infection of the rat brain
MuV infection of the rat brain: The most prominent neuropathological outcome following MuV intracranial inoculation in small animal models (hamsters, rats) is enlargement of the lateral and third ventricles, ie hydrocephalus, which has also been reported in cases in humans. The cause of hydrocephalus is postulated to be denuding of virus-infected ependymal cells lining the ventricles. (A) Sagittal section of rat brain tissue immunohistochemically stained for the MuV nucleoprotein, showing extensive infection of the ventricular ependymal cells (green foci). (B) Approximately 3 weeks later, ependymal cell loss is evident in comparison to the well-preserved ependymal cell architecture in rats injected with the Jeryl Lynn vaccine strain (C); haematoxylin and eosin (H&E) stain | Rubin, S., Eckhaus, M., Rennick, L. J., Bamford, C. G., & Duprex, W. P. (2015). Molecular biology, pathogenesis and pathology of mumps virus. The Journal of pathology, 235(2), 242–252. https://doi.org/10.1002/path.4445

Rare systemic complications:

  • Pancreatitis, myocarditis, thyroiditis, nephritis, hepatic disease, arthritis, keratitis, and thrombocytopenic purpura

Diagnosis

Lab studies:

The virus is highly neurotropic, with laboratory evidence of central nervous system (CNS) infection in approximately half of cases.
  • ELISA
    • IgM (CONFIRMATORY, indicates recent infection, in 100% cases by day 5)
    • IgG (indicates past exposure, possible immunity)
  • ↑ Serum & urinary amylase (90% cases)

Differential diagnosis

Mumps parotitis differentials
  • Suppurative parotitis
  • Submandibular lymphadenitis
    Recurrent juvenile parotitis
  • Calculus in Stensen duct
  • Other viral infections causing parotitis:
    • Coxsackie A
    • Cytomegalovirus (CMV)

Management

Symptomatic management:

Mumps is typically a benign illness that is self-resolving. Treatment is supportive care for each presenting symptom.
  • Proper hydration & rest
  • Analgesics
  • Cold/hot compresses over parotid (relieve pain)
  • Avoid food which encourages salivary flow (as they cause pain)

Orchitis:

  • Cold compresses and support to the scrotum
  • Analgesics

Trivalent measles-mumps-rubella (MMR) vaccine:

Administered in 2 doses with children most often receiving the first dose around 1 year of age and the second dose typically given between the ages of 4 to 6
  • Live attenuated vaccine
  • Jerryl Lynn strain

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