Topotype determination and genetic comparison of Foot and mouth disease viruses from infected pigs and vaccine

Abstract

The occurrence of FMD in pigs in Viet Nam is mainly caused by FMD virus serotype O. The
effectiveness of vaccines against FMD depends not only on the serotype, but also influence of topotype
of the FMDV strains. In 2019, many pig farms have been vaccinated with FMD vaccine, but the pig
herds were still suffered seriously with FMD. This study was conducted with 15 FMDV strains obtaining
from the pig farms in some southern provinces, and FMDV strains from 3 commercial FMD vaccines.
The genetic analysis showed that 15/15 field FMDV strains in this study belonged to the Mya-98/SEA
topotype, it was completely different compared to the topotype of the FMDV strains from the vaccines
(ME-SA or Euro-SA). The similarity level of nucleotide sequence of 15 field FMDV strains and 3 vaccine
FMDV strains was low (78.9 - 82.5%). The studied result showed that FMD was still occurred in the pig
farms in Viet Nam after the pigs were vaccinated with FMD vaccines. This may be related to antigen
nonconformity/mismatch between field FMDV strain and vaccine FMDV strain. This issue needs to be
studied further so that the strategy of using FMD vaccines will be considered appropriately.