Mumps Virus: Pathogenesis, Clinical Findings, Lab Diagnosis

  • Mumps virus causes nonsuppurative enlargement of one or both salivary glands.
  • It causes a mild childhood disease; complications including meningitis and orchitis are common in adults.
  • >1/3rd of all mumps infections are asymptomatic.
  • A berring- bone or zipper-like RNP frequently leaks from the virions in preparation examined by electron microscope (typical to all paramyxoviruses).

Pathogenesis

  • humans are the only natural hosts.
  • 10- replication occurs in nasal or upper respiratory tract epithelial cells; viremia disseminates virus to salivary glands (involvement of parotid glands not obligatory).
  • The incubation period ranges from 2 weeks to 4 weeks (typically 16-18 days); the virus is shed in saliva from about 2 to 9 days after the onset of swelling.
  • Mumps is a systemic viral disease.
  • Frequently infects the kidneys; viruria persists for up to 14 days after onset of symptoms.
  • CNS is also commonly infected.

Clinical Findings

  • mumps is an iceberg disease, often subclinical, although common as a childhood infection ( at least one-third of all conditions).
  • After an incubation period of 14-18 days; a prodromal period of ‘ flu-like illness ( fever, malaise, anorexia) is seen, which is followed by developing pain in parotids, which then swell rapidly (due to blockage of the efferent duct), sucking off a lemon in front of a sufferer is a refined form of torture!
  • Parotitis resolves in 1 week.
  • CNS involvement is common ( about 50 % of infection), the majority are clinically inapparent; meningitis in 15% of cases and encephalitis in 0.3%.
  • 20-50% of men develop orchitis (often unilateral); complication is painful, and atrophy of testis may occur, but only rarely does sterility result.
  • Oophoritis in about 5% of girls develops after parotitis resolves.

Immunity

  • immunity is permanent after a single infection; even subclinical infections generate lifelong immunity.
  • there is only one antigenic type, and it doesn’t exhibit significant antigen (Ag) variation.
  • Ab to HN gp (V-Ag), the F-gp and internal nucleocapsid protein (S-Ag) develop in serum following natural infection; CMI response also develops.
  • Passive immunity from mothers confers immunity in infants for six months.
  • Ab to S-Ag appear earlier (3-7 days after onset of symptoms) but disappear within six months;
  • Ab to V-Ag develop after four weeks of onset but persists for years.

Laboratory Diagnosis

Lab studies are not required to establish the diagnosis of typical cases. However, they may sometimes be confused with enlargement of parotids due to suppuration, drug sensitivity, tumors, etc.

Isolation and identification of virus

  • saliva, CSF, and urine collected within a few days after onset of illness
  • monkey kidney cells preferred for viral isolation; samples should be inoculated shortly after collection.
  • For rapid diagnosis, IFT to detect viral Ag in 2-3 day cell culture.
  • the virus produces little CPE (cell rounding, giant cell formation)
  • Haemadsorption test to demonstrate the presence of haemadsorbing agent.

Serology

  • Ab- rise detected using paired sera; ELISA or HI test commonly used.
  • Mumps IgM presents early in the illness and lasts for 60 days; the heterotypic Ab induced by parainfluenza virus infection doesn’t cross-react in mumps IgM, ELISA.
  • CFT using S- and V- Ag is also performed.

Epidemiology

  • endemic worldwide; disease incidence highest in children aged 5-9 yrs.
  • Humans are the only natural hosts; transmission by direct contact, airborne droplets, or contaminated fomites.
  • Subclinical cases can transmit the virus.

Treatment, Prevention, and Control

  • no specific therapy
  • immunization with attenuated live mumps vaccine (made in chick embryo culture) produces a subclinical, non-communicable infection; it is available in monovalent form (mumps only) or in combination with measles and rubella (MMR vaccine) and given as a single subcutaneous injection; provides protection for at least 10 yrs.
  • The vaccine contains the Jeryl Lynn or Urabe strains.
  • Contraindications are pregnancy, immunodeficiency, and hypersensitivity to neomycin and egg protein.
  • Passive immunization is not very reliable.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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