Etiology
Measles is caused by a spherical RNA virus of the genus Morbillivirus and family Paramyxoviridae. It is relatively large, with an RNA genome. It is related to canine distemper and rinderpest viruses, but measles differs from these 2 viruses because it does not possess specific neuraminidases, and it hemagglutinates while the others do not.
Measles virus is heat labile. Humans are the natural host but monkeys can become infected. Laboratory strains can infect mice and hamsters.[Figure caption and citation for the preceding image starts]: Transmission electron micrograph shows the ultrastructural appearance of a single measles virusCenters for Disease Control and Prevention [Citation ends].
Pathophysiology
Measles virus is transmitted via person to person contact or via airborne spread of droplets. Virus infects epithelial cells of the nose and conjunctivae, multiplies in these cells, and then extends to the regional lymph nodes. Primary viremia occurs 2 to 3 days after infection, and measles virus continues to replicate in epithelial and reticuloendothelial system tissue over the next few days. Secondary viremia occurs on days 5 to 7, and infection becomes established in the skin and other tissues including the respiratory tract on days 7 to 11. The prodromal phase, which lasts 2 to 4 days, occurs at this time with fever, malaise, cough, coryza, and conjunctivitis. Koplik spots may develop on the buccal mucosa about 1 to 2 days before the rash and may be apparent for 1 to 2 days after rash onset. The rash then develops at about 14 days after infection; at this time virus can be found in blood, skin, respiratory tract, and other organs. Over the next few days, viremia gradually decreases as the rash coalesces and gradually resolves along with the other signs and symptoms. Measles-specific immunoglobulin M antibodies appear at the time of the rash and can be detected up to 2 months after the onset of the rash.[12]
Classification
Classification of viruses
Genus Morbillivirus, family Paramyxoviridae.
Related to canine distemper and rinderpest viruses.
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