A comparison of type O foot and mouth disease virus field isolates from northern Thailand.

A survey of type O foot and mouth disease (FMD) virus isolates from northern Thailand was undertaken to determine the relationship between field viruses and the vaccine in use, and to gauge the range of antigenic variation among field viruses. Isolates were collected from the two most recent epizootics, 1986-1987 and 1989-1990, and assessed using a two-dimensional neutralisation test to determine their relationship to FMD type O1 Bangkok 1960 (O BKK/60) reference (vaccine challenge) virus. The critical r value for the survey was 0.259 and all isolates tested were found to have an r value considerably greater than this (range 0.66 to 0.80). The results showed close antigenic relationships between the isolates and the reference virus, and indicated a relatively small range of antigenic variation between the isolates.

Establishment of a typing enzyme-linked immunosorbent assay for foot and mouth disease antigen, using reagents against viruses endemic in Thailand.

Antisera were produced at a central laboratory in Thailand against the endemic serotypes (O, A and Asia 1) of foot and mouth disease (FMD) virus. At a regional veterinary laboratory, these antisera were used in an indirect sandwich enzyme-linked immunosorbent assay (ELISA) for the detection and serotyping of FMD virus (FMDV) antigen. ELISA readings of < 0.10 optical density (OD) units were considered negative. This was verified using fifty tissue samples which were known to be negative for FMDV. The highest mean sample value for three different dilutions was 0.02 OD units. Of a total of 93 samples submitted for antigen typing, 80 (86%) tested positive by ELISA and 13 (14%) were negative. No FMDV was detected in ELISA-negative samples following attempted tissue-culture virus isolation.