Measles Virus Genotypes
There are 24 recognized genotypes of measles virus, organized into eight distinct clades (A-H). 1
Genetic Classification Structure
The measles virus demonstrates significant genetic diversity despite remaining antigenically monotypic (a single serotype). The classification system is based on nucleotide sequence analysis, particularly of the C-terminal region of the nucleocapsid (N) protein gene, which represents the most variable region of the viral genome. 2, 3
- Eight major clades have been identified and designated A through H 1
- 24 distinct genotypes exist within these eight clades, each showing at least 8% nucleotide sequence divergence from other genotypes 3
- The 450-nucleotide region coding for the COOH-terminal 150 amino acids of the nucleoprotein serves as the standard "signature sequence" for genotype identification 3, 4
Geographic Distribution Patterns
While measles virus genotypes are not strictly geographically restricted, certain patterns of regional predominance exist:
- At least four genotypes co-circulate globally at any given time 3
- Some genotypes appear to be predominantly endemic in large geographic areas, though they can be imported elsewhere 3, 5
- Molecular epidemiologic tracking has proven valuable for identifying imported cases versus endemic transmission, particularly in elimination programs 5
Clinical Significance
The existence of multiple genotypes does not affect vaccine efficacy or clinical management, as all genotypes remain within a single serotype and vaccine-induced antibodies provide cross-protection. 2 However, genotyping serves critical public health functions:
- Monitoring transmission pathways and identifying outbreak sources 5
- Distinguishing imported cases from indigenous transmission 3, 5
- Evaluating measles elimination program effectiveness 5
The genetic stability of individual strains, combined with their variability between different lineages, makes genotyping an essential tool for measles surveillance and control efforts. 3