Single dilution ELISA for detection of serum antibody to foot-and-mouth disease virus in cattle.

A single dilution blocking ELISA was developed and evaluated for measuring serum antibody to foot-and-mouth disease virus (FMDV). Basic parameters of the assay were established and a positive-negative threshold determined from testing 176 specific antibody negative sera from Australian cattle. Sera collected from immunised animals in Thailand were tested by ELISA and virus-neutralisation (VN) tests and the results compared. A positive correlation between ELISA and VN titres was recorded for each of the 3 FMDV serotypes endemic in Thailand, with the overall correlation coefficient being r = 0.8990. A positive correlation for each of the serotypes was also found between ELISA titre and the degree of blocking (percentage inhibition) of each test serum at a dilution of 1:16, with the overall correlation being r = 0.8704. This simplified ELISA was sensitive, specific and gave reproducible results, and had the potential to test quickly and efficiently a considerable number of sera.

A comparison of enzyme-linked immunosorbent assay, complement fixation and virus isolation for foot and mouth disease diagnosis.

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.

Serological comparison of type Asia 1 foot and mouth disease virus isolates from Thailand.

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.

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.

The pathogenicity of bovine strains of foot and mouth disease virus for impala and wildebeest.

Impala (Aepyceros melampus) and wildebeest (Connochaetes taurinus) were infected with bovine strains of foot and mouth disease virus by intradermolingual inoculation. No clinical signs developed in the impala but mild atypical lesions developed in the tongues of the wildebeest with generalized spread to one foot in two of the eight animals exposed. All the impala but only some of the wildebeest developed viraemia. No virus could be isolated from any tissues in either species after the 7th day following virus inoculation. Immune response occurred in both species. A field survey revealed few animals of either species with significant antibody titers and no virus 'carriers' were found.

The pathogenicity of an avian influenza virus isolated in Victoria.

An influenza virus (H7N7) isolated from an outbreak of disease in chickens in Victoria, was examined for its ability to cause disease in inoculated chickens, turkeys and ducks. The virus was highly pathogenic in chickens and turkeys but produced no clinical disease in ducks. Transmission of infection occurred from inoculated chickens to those in direct contact but other chickens separated by a distance of 3m directly downwind developed neither clinical disease nor antibody to the virus.

A national serological survey to verify Australia's freedom from porcine reproductive and respiratory syndrome.

OBJECTIVE: To provide serological data to support Australia's claim of freedom from porcine reproductive and respiratory syndrome. DESIGN: A national serological survey was designed to provide 99% confidence of detecting at least one infected pig herd in Australia, assuming that at least 5% of herds would have been exposed to porcine reproductive and respiratory syndrome virus and that at least 25% of the 'finisher' pigs in these herds would have antibodies to the virus. PROCEDURE: A two-stage testing regime was used. All samples were tested with a commercially available enzyme-linked immunosorbent assay. If assay reactions were found, all samples from the herd were to be tested using the indirect immunofluorescence antibody assay. RESULTS: Of the 875 samples from 163 herds from all States in Australia, there was some evidence of reactivity in only four samples from four herds on the enzyme-linked immunosorbent assay. Further testing using the indirect immunofluorescence antibody assay according to the study protocol demonstrated that the reactions were not due to the presence of specific porcine reproductive and respiratory syndrome virus antibodies in the sera. CONCLUSION: The results of this study support the view that Australian pigs are free of porcine reproductive and respiratory syndrome virus.

The effect of repeated vaccination in an enzootic foot-and-mouth disease area on the incidence of virus carrier cattle.

A comparison was made of the incidence of foot-and-mouth disease virus ;carrier' cattle in an unvaccinated enzootic area and an area where routine 6-monthly vaccination with an inactivated vaccine had been carried out for 3-4 years. The incidence of carriers in the vaccinated area was 0.49% as compared to 3.34% in the non-vaccinated area. The results indicate that, provided the immune status of the vaccinated herd is maintained at a level sufficient to prevent outbreaks of clinical disease and the re-introduction of virus is prevented through livestock movement controls, it should be possible to eradicate the disease from an enzootic area through vaccination.

The foot-and-mouth disease virus subtype variants in Kenya.

The subtype variants found in Kenya in the past ten years have been studied. The type O and type SAT 2 subtypes have a distinct geographical distribution which appears to be associated with livestock movement patterns. The type A viruses have a greater tendency to antigenic variation and their geographical distribution is less distinct. In type C only minor differences exist between the three viruses studied.

Observations on the stability of foot and mouth disease vaccine antigens.

The 146S particle of the foot and mouth disease virus which is used as a vaccine antigen was found to be relatively stable when stored for prolonged periods at 4 degrees C. However, stored antigens of virus strains of the SAT serotypes but not of a virus strain of the type O serotype became less thermostable at 37 degrees C following 4 degrees C storage. Vaccines returned from the field 10 months after they were made were shown to contain significant amounts of 146S antigen of the O, A, SAT 1 and SAT 2 serotypes. Vaccine containing antigens at least 6 months old was shown to stimulate an acceptable immune response.

The role of sheep and goats in the epizootiology of foot-and-mouth disease in Kenya.

The pathogenicity of two bovine field strains of virus for indigenous goats was examined in the laboratory. The goats failed to develop clinical disease or become virus carriers although the majority showed a definite immune response. A field survey in a foot-and-mouth disease enzootic area showed that the indigenous sheep and goat populations were frequently exposed to infection as evidenced by a high proportion of sero-positive animals but the incidence of virus carriers was very low in goats and no carriers were detected in sheep.

In vitro comparison of foot-and-mouth disease virus subtype variants causing disease in vaccinated cattle.

Foot-and-mouth disease virus isolates of types O, A and SAT 2, from diseased animals in herds routinely vaccinated twice a year were compared antigenically with the vaccine strains in the complement-fixation, neutralization and radial immunodiffusion tests. It was found that strains which had readily infected vaccinated cattle had R values against the vaccine strain in the complementfixation and radial immunodiffusion tests of 30 or less, while strains causing primary outbreaks with little spread had R values of 30-40. Threefold differences in humoral neutralizing antibody concentration between the field variant and the vaccine strain in sera from vaccinated animals were likely to be significant in terms of protection.