Summary auto-generated
Researchers analyzed the nucleocapsid gene sequences of 20 measles virus isolates from South Africa collected between 1986 and 1995 to characterize genetic variation and identify new genotypes. Using PCR amplification and phylogenetic analysis of a 590 base pair fragment, they compared South African strains with previously described measles virus sequences. The study identified three distinct groups: three vaccine-like viruses closely related to the Edmonston strain; four wild-type viruses forming a new subgroup (D5) within genotype D; and multiple recent isolates from the Johannesburg area forming an entirely new genotype (I) with characteristic amino acid substitutions. By analyzing 100 measles virus strains total and establishing new criteria for genotype classification (sequences differing by no more than 15 nucleotides belong to one genotype), the researchers expanded the known number of measles virus genotypes from seven or eight to nine. Their findings demonstrate significant genetic drift in circulating wild-type measles virus and reveal geographic variation in strain distribution, with genotypes D and I being dominant in recent isolates from South Africa, Europe, and the USA. The identification of new genotypes raises questions about potential vaccine effectiveness against emerging viral variants.
Key findings
- A new measles virus genotype (I) was identified from South African isolates collected in 1994-1995, characterized by three distinctive amino acid substitutions in the nucleocapsid protein
- Four earlier South African isolates (1986-1995) formed a new subgroup (D5) within genotype D, sharing characteristic mutations with a 1983 Cameroon strain
- Three vaccine-like measles viruses with sequences similar to the Edmonston and Schwarz vaccine strains were identified among South African isolates
- Phylogenetic analysis of 100 measles virus strains established new classification criteria and expanded the total number of known genotypes from 7-8 to 9, indicating significant global genetic variation
- Genotype I displays a higher mutation rate (7.3% amino acid divergence) compared to subgroup D5 (4.6%), suggesting ongoing genetic drift in circulating wild-type measles virus
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Abstract
Sequence analysis was performed on 20 measles virus (MV) isolates from South Africa, five of which were obtained between 1986 and 1989 and 15 isolates collected during the 1994/95 measles season. A 590 bp fragment of the carboxyl terminus of the nucleocapsid (N) was amplified by PCR and subjected to sequence and phylogenetic analysis. Comparison of the South African MV strains with those previously described revealed that at least two distinct groups of wild-type (wt) MV exist, one of which has been circulating since 1986. The major genotype (I) was represented by the more recent isolates which showed three characteristic amino acid substitutions. Furthermore, three vaccine-like viruses with sequences very similar to the Edmonston wt strain were identified. Phylogenetic analysis of 100 MV strains allowed the assignment of new definitions for MV genotypes and subgroups. Employing these definitions, the majority of South African isolates analysed here formed a new genotype.