Serological comparison of type A foot and mouth disease virus isolates from Thailand.

Antigenic variation of type A foot and mouth disease (FMD) virus in Thailand was examined using a total of 82 field viruses isolated between 1986 and 1989. A two-dimensional serum microneutralisation test was used to compare these isolates to a reference strain, A15 Bangkok 1960 (A BKK/60). Viruses regarded as unrelated to A BKK/60 were compared to another reference strain, A22 Nakhon Pathom 1986 (A NPT/86). This approach divided the viruses into two groups. Most of the viruses shared a close antigenic relationship with A BKK/60. Only twelve viruses were regarded as unrelated to A BKK/60, and these were related to A NPT/86. All but one of these twelve isolates were from two provinces in one administrative region of the country. Future type A vaccines in Thailand will need to confer protection against both groups of viruses.