A new enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against foot-and-mouth disease virus. I. Development and method of ELISA.

A liquid-phase blocking sandwich ELISA has been developed for the quantification of antibodies against foot-and-mouth disease virus which may replace the virus neutralisation (VN) test. This test employs the incubation of a constant amount of antigen with a range of test serum dilutions in the liquid-phase before being assayed using a trapping ELISA. Thus it does not rely on the availability or growth of tissue culture cells. The assay is rapid and relatively simple to perform, reagents are used economically and results may be recorded within 24 h. The ELISA is sensitive and results are more specific and more reproducible than those obtained by VN. Results are expressed as reciprocal antibody titres which are analogous and of a similar order to those recorded by VN. Individual titres, therefore, may be easily assessed by workers in the field who are already familiar with VN.

Foot-and-mouth disease and the African buffalo (Syncerus caffer). 1. Carriers as a source of infection for cattle.

Ten pregnant buffalo cows, six of which were subsequently shown to be carriers of SAT 1, 2 and 3 viruses, were captured in the Kruger National Park (KNP) and allowed to calve in captivity. The buffalo cows and calves were separated by a fence from 6 FMD susceptible cattle but the buffalo and cattle were obliged to use common drinking troughs and hay racks. Over a period of 15 months, during which the buffalo calves lost their maternally-derived immunity, neither the buffalo calves nor the susceptible cattle became infected with FMD virus. By the end of the observation period, however, only 1 buffalo cow still had detectable virus in its oesophageal/pharyngeal specimens.

Simultaneous vaccination of cattle against foot-and-mouth disease and rinderpest.

A total of 118 local cattle in the Sultanate of Oman were divided into three groups, one which received a trivalent inactivated foot-and-mouth disease vaccine, another which received attenuated tissue culture rinderpest vaccine and a third which received both vaccines simultaneously at separate sites on opposite sides of the neck. The serological response to vaccination was monitored at day 0, 21 and 42 in virus neutralisation tests. The simultaneous administration of the two vaccines produced no ill effects and the serological responses did not differ significantly from the response to either vaccine given separately.

A study of antigenic variants of foot-and-mouth disease virus by polyacrylamide gel electrophoresis of their structural polypeptides.

Twenty-nine foot-and-mouth disease (FMD) type A virus strains, previously classified serologically as distinct subtypes were analysed by polyacrylamide gel electrophoresis (PAGE) to determine the extent of variation in the pattern of the structural polypeptides and to evaluate the technique as an aid to existing subtyping techniques. The majority of the subtypes examined had distinct polypeptide patterns, however, some variation also occurred between strains within a subtype. The position of VP2(1B) and VP3(1C) was often unchanged in different strains within a subtype and between geographically related subtypes over long periods of time. Changes in the position of VP1(1D) were also observed within a subtype. The technique was considered to be of value for the screening of isolates prior to conventional serological subtyping procedures and in the tracing of the possible origin of FMD outbreaks.

The duration of the foot-and-mouth disease virus carrier state in African buffalo (i) in the individual animal and (ii) in a free-living herd.

The maintenance of a virus depends on a number of factors, including the duration of infectivity and the size of the available host population. In this work, foot-and-mouth disease virus was shown to persist in individual African buffalo (Syncerus caffer) for up to at least five years; thus, the duration of infectivity is more than adequate to cover the normal periods between calving peaks. In a small isolated free-living population which varied from 30 to 100 buffalo, two immunological types of foot-and-mouth disease virus were maintained for at least 24 years and through several generations.

A rapid enzyme-linked immunosorbent assay for the detection of foot-and-mouth disease virus in epithelial tissues.

A rapid double sandwich enzyme-linked immunosorbent assay (ELISA) has been used for the identification and type differentiation of foot-and-mouth disease (FMD) viruses in epithelial tissue samples submitted for diagnosis from the field. No difficulty was experienced in the direct typing of freshly harvested epithelium from recently ruptured vesicles by the complement fixation (CF) test or ELISA. The ELISA was more sensitive and specific, but proved no more efficient than the traditional CF test in the direct typing of samples of poorer quality from many countries overseas where communications are often difficult. However, when both tests were used concurrently, FMD virus typings were confirmed in 27 more samples. Some possible reasons for the failure of ELISA to detect virus in certain cases are discussed.

Serological response of cattle to simultaneous vaccinations against foot-and-mouth disease and haemorrhagic septicaemia.

In Malaysia, where vaccination campaigns against foot-and-mouth disease and haemorrhagic septicaemia are routinely carried out, it was desirable to determine whether it was safe and efficacious to administer both vaccines simultaneously. A trial group of 104 cattle was divided into three groups; group 1 animals received both vaccines simultaneously, group 2 animals received only foot-and-mouth disease vaccine and group 3 animals received only haemorrhagic septicaemia vaccine. The serological response to vaccinations was monitored at 0, 21 and 35 days by the virus neutralisation test for foot-and-mouth disease and the mouse-protection and indirect haemagglutination tests for haemorrhagic septicaemia. The simultaneous administration of the two inactivated vaccines produced no adverse effects and the serological response did not differ from the response to either vaccine given separately, thus indicating that cattle may be safely and effectively vaccinated simultaneously in this way.

Neutralising antibodies to wildebeest-derived malignant catarrhal fever virus in African wildlife.

A total of 2,722 sera collected between 1963 and 1983, from 43 different species of wildlife in 11 African countries was examined for neutralising antibodies against the wildebeest-derived strain of malignant catarrhal fever (MCF) virus. Antibodies were demonstrated in 10 species of Bovidae which included eight species from the sub-family Hippotraginae and one species each from Bovinae and Antilopinae. Neutralising antibodies were also recorded in hippopotamus. It is suggested that the high prevalence of antibodies recorded in sera from waterbuck and reedbuck indicate infection with MCF. However, titres in other species may be due to antigenically related viruses.

Neutralising antibodies to lumpy skin disease virus in African wildlife.

A total of 3445 sera from 44 different wild species collected between 1963 and 1982 in 11 African countries south of the Sahara, were examined for neutralising antibodies to Lumpy Skin Diseases (LSD) Virus (prototype Neethling). Antibodies were demonstrated in six species but were of low prevalence. It was concluded from the generally negative results, that wildlife in Africa probably does not play a very important part in he perpetuation and spread of LSD Virus.

Prevalence of neutralizing antibodies to bovid herpesvirus 2 in African wildlife.

A total of 3,470 sera, collected between 1963 and 1980 from 45 different species of wildlife in nine African countries, was examined for virus neutralizing (VN) antibodies to bovid herpesvirus 2. Antibodies were demonstrated in 20 species including 15 Bovidae, two Suidae, hippopotamus (Hippopotamus amphibius), giraffe (Giraffa camelopardalis) and a green monkey (Cercopithecus aethiops); 11 of these species had not been previously recorded as sero-positive. Although the significance of neutralizing antibodies in the absence of virus isolation remains in doubt, results suggest that infection is widespread in wildlife. The highest VN titres were recorded in waterbuck (Kobus ellipsiprymnus and K. defassa), reedbuck (Redunca arundinum) and buffalo (Syncerus caffer). Infection appears to be continuous in free-living populations of buffalo and antibodies are present in the majority of animals by the age of 2 yr.

Counter immunoelectrophoresis in the diagnosis and serological surveillance of swine vesicular disease.

A comparison of the counter immunoelectrophoresis (CIEP) test for swine vesicular disease with serum neutralisation and double immunodiffusion is reported here. Two groups of sera were used in the comparison: one group (908 sera) was tested blind by CIEP and the other group (778 sera) comprised field samples from infected and suspect premises submitted routinely for swine vesicular disease confirmation. The CIEP test proved simple to perform and gave results within two hours. It was very economic in the use of reagents and its sensitivity, though less than that of the serum neutralisation test, compared favourably with the sensitivity of the double immunodiffusion test. No false positive results were detected out of the 1686 sera tested.

The response of some African wildlife species to foot-and-mouth disease vaccination.

The preservation of wildlife is of increasing importance in may countries in Africa but, due to hazards of possible transmission of disease from wild to domesticated species, the interests of the conservationist can conflict with those of the livestock owner. Foremost among transmissible diseases common to many species of both wild and domesticated animals is foot-and-mouth disease (FMD). The effects of FMD vaccination on three important wildlife species, African buffalo (Syncerus caffer), eland (Taurotragus oryx) and impala (Aepyceros melampus), are described. The pattern of response in all three species was similar to that of cattle but of a lower order. The implications are discussed and a vaccination protocol is suggested.

Some virus diseases of domestic animals in the Sultanate of Oman.

Little is known of the occurrence of animal virus diseases in the Sultanate of Oman. This paper reports the results of a countrywide survey carried out in 1978 to establish the prevalence of some important viral pathogens of domestic animals with the dual purpose of providing baselines for future investigations and guidelines for those entrusted with disease control. Foot-and-mouth disease virus type O, previously identified in Oman in 1976, was isolated from clinically affected animals. In addition, virus types A and Asia 1 were isolated from unaffected animals. Serological studies indicated that infection with all 3 types had been widespread. The presence of infectious bovine rhinotracheitis was confirmed by virus isolations and sheep and goat pox, long recognised in Oman, was confirmed by the demonstration of pox particles in dried lesion material. In serological studies antibodies were found to the viruses of peste des petits ruminants, bovine herpes mammillitis, bovine virus diarrhoea, parainfluenza 3 and African horse sickness. There were no significant antibody levels to rinderpest in unvaccinated animals and no antibody to equine infectious anaemia or vesicular stomatitis viruses.