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  Section: Medical Microbiology » Virology
 
 
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Measles, mumps and rubella

 
     
 
Content
Virus structure, classification and antiviral therapy
Herpesviruses I
Herpesviruses II
DNA viruses: adenovirus, parvovirus and poxvirus
Measles, mumps and rubella
Influenza viruses
Parainfluenza and other respiratory viruses
Enterovirus and viruses that infect the gastrointestinal tract
Hepatitis viruses
Tropical, exotic or arbovirus infections

Medicinal Microbiology Bacteriology, Virology, Mycology, Biocyclopedia.com
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Measles
Measles is due to an enveloped RNA virus, known as a Morbillivirus, with a single serotype. The virus encodes six structural proteins that facilitate attachment to the host cell and viral entry, which includes two transmembrane glycoproteins: fusion (F) and haemagglutinin (H). Antibodies to F and H are protective.

Pathogenesis and Epidemiology
  • Initially the virus infects epithelial cells of the upper respiratory tract.
  • It then invades neighbouring lymphoid tissue, which results in primary viraemia and involvement of the reticuloendothelial system.
  • This is followed by a secondary viraemia and dissemination throughout the body, which coincides with the onset of clinical symptoms.
  • It is transmitted by the airborne route, with a high attack rate.
  • The incubation period is 9-12 days - individuals are infectious for 3 days before the rash emerges.
  • Natural infection is followed by lifelong immunity.
  • Mortality is rare except in patients who have HIV infection, are immunocompromised or malnourished (especially those with vitamin A deficiency); mortality rates are highest in children under 2 years of age.
  • Measles is rare in countries with a vaccination programme but 90% coverage is required to ensure the disease does not re-emerge.

Clinical features
  • A prodromal 2 to 4-day coryzal illness occurs, during which small white papules (Koplik's spots) are found on the buccal mucosa near the first premolars.
  • A morbilliform rash appears, first behind the ears, then spreading centrifugally and becoming brownish.
  • Secondary pneumonia, otitis media and croup are common complications.
  • Acute postinfectious encephalitis is a rare and serious complication.
  • Subacute encephalitis, a chronic progressive disease, occurs mainly in children with leukaemia.
  • Subacute sclerosing panencephalitis (SSPE) is a rare, progressive, fatal encephalitis that develops more than 6 years after infection.

Diagnosis
  • Diagnosis is usually clinical, but may be confirmed by salivary IgM-specific enzyme immunoassay (EIA).
  • SSPE is diagnosed by detection of virus-specific antibody that is being synthesized in the CSF (e.g. specific IgM).
  • A nucleic acid amplification test (NAAT) and molecular characterization of the virus by sequencing are also available.


Mumps
A member of the Paramyxovirus genus, the mumps virus is a pleomorphic, enveloped, antisense RNA virus with one serotype.

Epidemiology
  • Mumps usually occurs in childhood but many adults are susceptible as it has a relatively low attack rate.
  • The incubation period is 14-24 days.
  • Subclinical infection is common, especially in children.
  • It is transmitted readily by the aerial route.
  • Infection creates lifelong immunity.
  • Epidemics can re-emerge if vaccination coverage falls.

Clinical features
  • Common features include fever, malaise, myalgia and parotid gland inflammation.
  • Meningitis occurs in up to 15% of patients with parotitis.
  • Complete recovery is almost invariable, although rare fatal forms and postmeningitis deafness may occur.
  • Complications include orchitis (20%), oophoritis (5%) or pancreatitis (5%) usually in older individuals.

Diagnosis
  • Diagnosis is usually clinical, but may be confirmed by specific salivary or serum IgM.
  • NAAT for diagnosis is also available.


Rubella
Rubella (rubivirus), which is a member of the Togaviridae family, is an icosahedral, pleomorphic, enveloped, positive-strand RNA virus with a single serotype.

Epidemiology
  • Rubella is rare in countries with a vaccination programme.
  • Transmission is by aerial droplets.
  • Patients are infectious from 7 days before the rash appears until 14 days after the rash.
  • Natural infection is followed by solid immunity.

Clinical features
Rubella is associated with fever, a fine, red, maculopapular rash and lymphadenopathy. During the prodrome red pinpoint lesions occur on the soft palate. Arthritis (more common in females) and self-limiting encephalitis are complications. Maternal infection may cause fetal death or severe abnormalities, such as deafness, central nervous system deficit, cataract, neonatal purpura and cardiac defects, in up to 60% of cases; the risk being highest during the first trimester.

Diagnosis
  • Diagnosis is by detection of IgM and IgG antibodies in serum or saliva.
  • Congenital disease is diagnosed by finding specific IgM persistent antibodies (>6 months) in an infant, or viral detection by culture or NAAT.


Prevention of measles, mumps and rubella
  • A live attenuated combined vaccine (the MMR) is given between 13 and 15 months, with a booster dose given at school entry.
  • Further booster doses of measles vaccine may be required.
  • The rapid antibody response to measles vaccine can be used to protect susceptible individuals exposed to measles.
  • Women attending for contraceptive advice should be screened for rubella antibodies and vaccinated if not pregnant.
  • MMR should not be given to immunocompromised individuals.

 
     
 
 
     



     
 
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