Measles is a highly communicable acute viral disease charac-terized by fever, conjunctivitis, and pathognomonic Koplik’s spots. It is one of the five classic exanthematous diseases of the childhood; others being chickenpox, rubella, roseola, and fifth disease.
Measles virus shows following features:
· Measles virus is spherical, but is often pleomorphic, measur-ing 120–250 nm in diameter.
· It contains a negative-sense RNA genome.
· The helical nucleocapsid is surrounded by an envelope carrying H and F protein on its surface. The virus causes hemagglutination of monkey erythrocytes, but it is not followed by elution as the virus does not produce any neuraminidase activity.
Measles virus replicates in the cell cytoplasm. The virus first adsorbs cell surface by its hemagglutinin, then enters the cell, and uncoats inside the cytoplasm of the cell. The viral RNA polymerase transcribes the negative-strand genome into mRNA. Multiple copies of mRNAs are produced, each of which is translated into specific viral proteins. This is followed by the assembly of nucleocapsid, and the virus is released by budding from the cell membrane.
The measles virus has only one serotype and infects only humans, not any other mammals. The virus is antigenically uniform; it shares antigens with canine distemper virus.
The measles virus is heat labile. It is readily inactivated by ether, formaldehyde, high temperature, and ultraviolet light. The virus is stabilized by molar MgSO4 following which the virus resists heating at 50°C for 1 hour.