Taura Syndrome - Variants of The Virus

Variants of The Virus

RNA viruses such as TSV have high rates of spontaneous mutation. These very high rates might be due to the lack of proofreading function of the RNA-dependent RNA polymerase and have resulted in the emergence of several genetic variants of the virus. As of May 2009, four genetic clusters are recognized: Belize (TSV-BZ), America (TSV-HI), Southeast Asia and Venezuela. The Belize strain is considered the most virulent. Point mutations in TSV capsid proteins might provide specific isolates with selective advantages such as host adaptability, increased virulence or increased replication ability. Even small variations in the TSV genome can result in substantial differences in virulence.

All TSV variants are similar in shape and size, with light variations. The average size of TSV-BZ virus particles is 32.693+/- 1.834 nm compared to TSV-HI with a size of 31.485 +/- 1.187 nm. The region of highest genetic difference is within the capsid protein CP2, with pairwise comparison of nucleotide showing a 0 to 3.5% difference amongst isolates. The most variations in CP2 occur at the 3'-terminal sequence; this may be because it is less constrained by structural requirements and more exposed than other regions of the protein.