Foot and mouth disease: the future of vaccine banks.

The authors briefly review the history of vaccine banks for foot and mouth disease, their current location and their constituent serotypes and strains, together with the occasions on which they have been activated. Experimental studies on emergency vaccines are summarised and areas identified for further investigation. The future of such banks is considered, including the principal strengths and weaknesses of existing banks, and suggestions are made for potential improvements. The fact that the banks have been activated on relatively few occasions over the 25 years of their existence testifies in part to the relatively rare calls which have been made upon them, but also reflects the difficulty in deciding when and how to utilise emergency vaccination. Nevertheless, in an era of increasing global risks of the spread of foot and mouth disease, banks will most certainly continue to have strategic and tactical importance in the control of this most readily communicable of animal diseases.

Infection of pigs with transmissible gastroenteritis virus from contaminated carcases.

Sixteen 6-month-old pigs were exposed to transmissible gastroenteritis (TGE) virus by placing them in close contact with piglets infected at 1 week of age. Fourteen of the older pigs were slaughtered between 1 and 5 d after exposure to infection and their carcases dressed in simulated abattoir conditions. Samples of muscle, bone marrow and carcase lymph nodes were stored at -25 degrees C for at least 30 d and then homogenised and fed to groups of 1-week-old and 3-week-old pigs. Four of 12 one-week-old pigs died and TGE virus was isolated from intestinal contents of one of these. All pigs of both age groups developed neutralising antibody to TGE virus over the ensuing 4 w. The results indicate that carcases from pigs infected with TGE virus can represent a source of infection for susceptible pigs given access to them.

The occurrence of equine arteritis virus in Australia.

This paper reports the first isolation of equine arteritis virus (EAV) in Australia and serological evidence of exposure to EAV in Australian horses. Twelve Standardbred stallions imported from North America were found to shed EAV in semen. One hundred and seven stallions were tested for serum antibodies to EAV and 73% of Standardbred stallions tested were seropositive as compared to 8% of Thoroughbred stallions. Serum antibody was detected in 71% of Standardbred mares, 6% of Standardbred racehorses and 1% of Thoroughbred mares and racehorses. Examination of stored serums demonstrated that EAV had been present in Australia since at least 1975.

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.

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.

Interactions of porcine alveolar macrophages and bone marrow cells with African swine fever virus and virus-infected cells.

Virus yields from porcine alveolar macrophages (AM) infected with African swine fever virus (ASFV) were greater and were achieved more rapidly, when inoculated at a high multiplicity of infection (MOI) than at low MOI. The difference was related to a lower percentage of cells becoming infected after low MOI inoculation. The reduced yields after low MOI were not caused by prolongation of the culture time, by bacterial endotoxins or by production of inhibitory substances by infected AM. Virus-infected AM were not susceptible to lysis in antibody-dependent cell mediated cytotoxicity (ADCC) assays and this was apparently due to a paucity of viral antigen expressed on the cell surface. Uninfected AM did not act as effectors in ADCC. Porcine bone marrow (PBM) cells were effective in mediation of ADCC and their activity was reduced after ASFV infection. Cells separated into adherent and non-adherent populations, depleted by carbonyl iron treatment or separated by Ficoll-Hypaque centrifugation, all showed effector activity in ADCC. The effector cells were not mature neutrophils or lymphocytes and were probably granulocytic precursors.

The immunogenicity of K99 antigen in whole cell bacterins of Escherichia coli.

K99 antigen in Escherichia coli whole cell bacterins was immunogenic in rabbits and mice. Mice vaccinated subcutaneously and bled three weeks later had a serum antibody response which was dose dependent. The dose response on dilution of bacterins was shown to be mainly due to dilution of K99 antigen, rather than the reduction in adjuvant or bacterial cell concentration. The procedure appears to be a satisfactory one for immunogenicity testing of bacterins containing K99 antigen.

Effect of infectious bovine rhinotracheitis virus infection of calves on cell populations recovered by lung lavage.

Calves were challenge exposed with infectious bovine rhinotracheitis (IBR) virus, and experiments were carried out to determine the presence of virus in the lungs, virus or viral antigen in alveolar macrophages, and alterations in immune functions of alveolar macrophages. In experiment 1, calves were challenge exposed intranasally with IBR virus. Although clinical signs of IBR occurred in all challenge-exposed calves, there was minimal evidence of virus or viral antigen in cells lavaged from their lungs, and macrophage Fc- and complement-receptor activities, phagocytic activity, and ability to mediate antibody-dependent cell cytotoxicity were unaltered. In experiment 2, calves were challenge exposed intranasally or by aerosol with IBR virus strains Colorado-1 and 108, and samples were collected 4 and 6 days after challenge exposure. Virus was isolated from the lungs, and pathologic lesions of greater severity occurred in those calves challenge exposed by aerosol. Less than 0.1% of lavaged cells from challenge-exposed calves produced infectious centers on susceptible cell monolayers. In 1 sample of lavaged cells, approximately 5% of the cells, mainly macrophages, had viral antigen in the cytoplasm, as detected by immunofluorescence. Because of the small proportion of macrophages that appeared to become infected after challenge exposure of calves with IBR virus, it is believed that the effect of IBR virus in predisposing calves to pneumonic pasteurellosis is an indirect, rather than a direct, manifestation of viral infection of macrophages.

The characterisation and pathogenicity of porcine enteroviruses isolated in Victoria.

Approximately 23 viruses were isolated from healthy pigs, pigs with encephalitis, and in cases of reproductive failure. Five viruses were identified as enteroviruses and a total of 10 isolates were shown to cross-react serologically to varying degrees. Twenty viruses were neutralised by a reference antiserum of serotype 8 porcine enterovirus. Intracerebral inoculaton of colostrum-deprived piglets with 2 of the characterised viruses caused lesions of encephalomyelitis which were not induced by oral infection. Intrafoetal inoculation of 2 sows with one characterised faecal isolate caused foetal death and abortion, but no adverse effects followed oral dosage.