ABSTRACT
Antigenic variation of type Asia 1 foot and mouth disease (FMD) virus in Thailand was examined using a total of 50 field viruses isolated between 1986 and 1992. A two-dimensional serum neutralisation test was used to calculate r values for comparison of these isolates with a reference vaccine strain, Asia 1 Bangkok 1960 (BKK/60). Viruses were also compared to two field isolates, Asia 1 36-2/88 and Asia 1 45/88, and some were compared to another vaccine strain, Asia 1 Nakhon Pathom 1984 (NPT/84). In 80% of cases, field isolates were deemed to be significantly different from the vaccine virus Asia 1 BKK/60, and the distribution of r values indicated that there would be some advantage in selecting a new vaccine strain more closely related to contemporary field strains.
Subject(s)
Aphthovirus/immunology , Foot-and-Mouth Disease/virology , Animals , Antigenic Variation , Aphthovirus/classification , Buffaloes , Cattle , Cattle Diseases/epidemiology , Cattle Diseases/virology , Cell Line , Cricetinae , Disease Outbreaks/veterinary , Foot-and-Mouth Disease/epidemiology , Neutralization Tests/veterinary , Swine , Swine Diseases/epidemiology , Swine Diseases/virology , Thailand/epidemiologyABSTRACT
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.
Subject(s)
Antigens, Viral/analysis , Aphthovirus/immunology , Foot-and-Mouth Disease/virology , Animals , Antigenic Variation , Aphthovirus/classification , Aphthovirus/isolation & purification , Buffaloes , Cattle , Immune Sera/immunology , Neutralization Tests/veterinary , Rabbits , Sheep , Swine , ThailandABSTRACT
A total of 205 epithelial tissue samples were examined for the presence of foot and mouth disease virus by either the complement-fixation (CF) test, enzyme-linked immunosorbent assay (ELISA) and/or by virus isolation in bovine thyroid or kidney cell cultures. The virus was isolated from 134 of the 201 (67%) specimens. Samples, from which virus was isolated, were termed virus-positive samples. The CF test detected viral antigen in 30 (24%) of 123 virus-positive samples, whereas the ELISA detected it in 100 (81%) of these specimens. The ELISA was thus at least 3 times more efficient than the CF test in detecting the virus in epithelial-tissue samples. There were 5 samples from which virus was not isolated but which were positive with the ELISA procedure. The ELISA was particularly useful for testing samples from pigs and for assessing specimens from animals with resolving lesions. The ELISA gave virus type-specific results in 89% of 63 virus-positive cases compared to 40% for the CF test. The ELISA was thus a very useful, accurate and sensitive method for the direct testing of epithelial tissues of affected animals.
