Measles (Rubeola) Virus: Description and Pathogenesis

In this article we will discuss about Measles (Rubeola) Virus:- 1. Meaning of Measles (Rubeola) Virus 2. Description of Measles Virus 3. Pathogenesis 4. Complication 5. Immunity 6. Laboratory Diagnosis 7. Epidemiology 8. Control.

Contents:

1. Meaning of Measles (Rubeola) Virus
2. Description of Measles Virus
3. Pathogenesis of Measles Virus
4. Complication of Measles Virus
5. Immunity from Measles Virus
6. Laboratory Diagnosis of Measles Virus
7. Epidemiology of Measles Virus
8. Control of Measles Virus

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1. Meaning of Measles (Rubeola) Virus:

Measles is the most common cause of childhood fevers and is highly infectious in nature.

2. Description of Measles Virus:

Measles virus is antigenically related to canine distemper virus (CDV) in dog and rinder­pest virus in cattle. Spikes on envelope contain only haemagglutinin but not neuraminidase. Besides, Matrix M protein is located below the envelope lipid bilayer and F protein is also a projection (spike).

3. Pathogenesis of Measles Virus:

Inhalation is the mode of entry. The incubation period is 9-12 days. The virus multiplies in lymphoid tissues of respiratory tract and invades the blood circulation (primary viraemia) and localizes in the reticulo-endothelial system. Secondary viraemia is characterised by flu-like high fever, cough, conjunctivitis.

Koplik’s spots (red spots with a bluish white centre on the buccal mucosa) appear in the prodromal phase. After secondary viraemia the virus settles in epithelial surfaces of skin, respiratory tract and conjunctiva. As the acute symptoms decline in 1-2 days maculopapular rash appears on skin, mucous membrane and conjunctiva.

Rash is due to interaction of immune T cells with virus infected cells in small blood vessels. The rash fades out in a week. Immuno-competent patients recover in 10-14 days.

4. Complication of Measles Virus:

1. Giant cell pneumonia, otitis media, post-measles encephalitis may occur in smaller number.

2. Mortality is high in malnourished and immuno-compromised children.

3. Sub-acute sclerosing pan-encephalitis (SSPE) is a complication of measles and is considered to be a slow form of measles virus encephalitis due to a defective form of measles virus in infected cell. Patient’s condition deteriorates over several years and finally develop CNS symptoms.

5. Immunity from Measles Virus:

There is only one serotype of measles virus and an infection confers lifelong immunity.

6. Laboratory Diagnosis of Measles Virus:

1. Direct smear stained by Giemsa’s stain show giant cells and inclusion bodies (Cowdry type A). Immuno-fluorescence test can detect virus particles in exfoliated respiratory cells.

2. Isolation: Specimens collected during febrile period can be used to cultivate in human fibroblasts, monkey or human kidney cells. Growth is slow with CPE.

Serology:

HI, CF and NI tests can detect measles-specific Ig M antibody.

7. Epidemiology of Measles Virus:

The disease is endemic throughout the world and epidemics occur in late winter and early spring. Man is the only natural host of measles and monkeys acquire the infection from man. Transmission is through respiratory route, conjunctivitis may be the source.

8. Control of Measles Virus:

1. Active immunization:

Live vaccine in use is 90% effective. It is administrated in one dose subcutaneously.

2. Passive immunization:

Pooled sera containing antibody against measles virus confer passive immunity to infants.