Measles morbillivirus
Measles morbillivirus (MeV), also called measles virus (MV), is a single-stranded, negative-sense, enveloped, non-segmented RNA virus of the genus Morbillivirus within the family Paramyxoviridae. It is the cause of measles. Humans are the natural hosts of the virus; no animal reservoirs are known to exist.
Genotypes[edit]
The measles virus genome is typically 15,894 nucleotides long and encodes eight proteins.[16] The WHO currently recognises 8 clades of measles (A–H). Subtypes are designed with numerals—A1, D2 etc. Currently, 23 subtypes are recognised. The 450 nucleotides that code for the C‐terminal 150 amino acids of N are the minimum amount of sequence data required for genotyping a measles virus isolate. The genotyping scheme was introduced in 1998 and extended in 2002 and 2003.
Despite the variety of measles genotypes, there is only one measles serotype. Antibodies to measles bind to the hemagglutinin protein. Thus, antibodies against one genotype (such as the vaccine strain) protect against all other genotypes.[17]
The major genotypes differ between countries and the status of measles circulation within that country or region. Endemic transmission of measles virus was interrupted in the United States and Australia by 2000 and the Americas by 2002.[18]
Infection[edit]
In the early stages of infection, the measles virus via CD150 (SLAMF1) receptor infects immune cells located in the host respiratory tract such as macrophages and dendritic cells.[19][20][21] They transmit the virus to the lymphoid organs, from which it spreads systemically. In the later stages of infection, the virus infects other immune cell types, including B cells[22] and T lymphocytes[23] also via SLAMF1 receptor. In addition, it infects epithelial cells located in the airways. These cells become infected via nectin-4 receptor and by cell to cell contacts with infected immune cells. The infection of epithelial cells allows the virus to be released via the airstream.[24][25]