According to the current status by World Health Organization (WHO), measles virus strains are divided into 8 clades (designated as A through H) and 24 genotypes. Genotyping is based on the sequence variation of COOH terminal 450 nucleotide coding for 150 amino acids of nucleoprotein (N-150) or entire coding region of H. Difference in nucleotide by >2.5% in N protein or 2% in H from the closest reference strain is considered as a separate genotype. Within a genotype, there may be multiple lineages. Each lineage includes a group of viruses that have identical N-450 nucleotide sequence. Viruses of same lineage indicates single chain transmission.

Clade A includes all the measles vaccine strains: Moraten, Edmonston, Zagreb. It has not been found till date in any endemic transmission and the wild virus types of clade A are considered to be extinct. Clades A, E and F consist of single genotype each. During the period 2005 to 2015, 11 wild type genotypes were found. In 2017, 5 wild type genotypes belonging to 3 clades—B3, D4, D8, D9 and H1 were detected. In India during 2011 to 2015, D8 and D4 were the predominantly circulating genotypes along with a few B3 from Kerala state. Table 12.2 describes the genotypes and their geographic distribution.

Importance of Genotyping

1. It helps in tracking the transmission path ways of measles virus.

2. To monitor the status of endemic virus transmission as absence of endemic virus is a criterion for verifying the measles elimination in a particular region.

 3. Genotyping helps to differentiate between natural infections or vaccine-related adverse events (as all measles virus vaccine strains belong to genotype A).

Pattern of Genotype Circulation

Three patterns of genotype circulation have been described.

1. Regions with endemic circulation: In countries where endemic transmission still persists, majority of measles cases occur due to the circulating endemic strains. Multiple co circulating lineages are detected.

 2. Countries where measles is eliminated: Small number of cases due to imported viruses with various genotypes.

3. Countries with good measles control but increase in number of susceptible individuals due to poor maintenance of high vaccination coverage: Reintroduction of virus usually leads to outbreak due to single genotype.

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مواضيع ذات صلة

Complications of Measles Virus

Clinical Features of Measles Virus

Diagnosis of Respiratory Virus Infection

Human metapneumovirus (HMPV)

Human respiratory syncytial virus (HRSV)

Chemical Composition of Viruses

Survey of RNA-Containing Viruses

Survey of DNA-Containing Virus Families

Universal System of Virus Taxonomy

Human parainfluenza viruses (HPIV)

Complications of Influenza virus

Influenza virus