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Twenty-five Ayrshire/Friesian cows were vaccinated once with a new combined vaccine against rotavirus, coronavirus and Escherichia coli F5 (K99) or given a saline placebo 31 days before the first expected calving date. Blood samples were taken from the cows at intervals from vaccination until seven days after calving and from their calves up to 28 days after birth, and colostrum and milk samples were collected from the cows at intervals for 28 days after calving. There was a significant increase in the mean specific antibody titre against all three antigens in the serum of the vaccinated animals (even in the presence of pre-existing antibody) which was accompanied by increased levels of protective antibodies to rotavirus, coronavirus and E coli F5 (K99) in their colostrum and milk for at least 28 days.

In order to investigate the ability of an oil adjuvanted vaccine containing bovine coronavirus antigen to enhance lactogenic immunity in the calf, pregnant cows and heifers were vaccinated and specific virus neutralising antibody levels determined in serum, colostrum and milk. Pre-existing antibody titres (as a result of natural infection) in the serum of these animals were found to be significantly increased as a result of a single shot vaccination carried out between 2 and 12 weeks before calving. This was reflected in a similar increase in the titre and duration of specific antibody in milk and colostrum that was passed on to the calves. The overall response observed was highly dependent on an adequate antigen payload being incorporated within the single dose vaccine. No abnormal local or systemic reactions were observed as a result of vaccination. It is hoped that this approach will lead to the production of a superior commercial vaccine for the protection of neonatal calves against enteric coronavirus infection.

AIMS--To evaluate the clinical performance of enzyme immunoassays for IgG and IgM antibodies to Toxoplasma gondii based on enhanced chemiluminescence. METHODS--Classification of routine clinical samples from the originating laboratories was compared with that obtained using the chemiluminescence based assays. Resolution of discordant results was achieved by testing in alternative enzyme immunoassays (IgM) or by an independent laboratory using the dye test (IgG). RESULTS--Compared with resolved data, the IgM assay was found to be highly specific (100%) with a cut off selected to give optimal performance with respect to both the early detection of specific IgM and the detection of persistent levels of specific IgM (sensitivity 98%). Compared with resolved data, the IgG assay was shown to have a sensitivity and a specificity of 99.4%. CONCLUSIONS--The Amerlite Toxo IgM assay possesses high levels of sensitivity and specificity. Assay interference due to rheumatoid factor like substances is not a problem. The Amerlite Toxo IgG assay possesses good sensitivity and specificity, but is less sensitive for the detection of seroconversion than methods detecting both IgG and IgM.

SUMMARY Using an ELISA for the detection of virus-specific immune complexes, ten cows were found to be shedding bovine enteric coronavirus. The shedding patterns from five of these animals were followed for a period of 12 weeks, and all were found to be chronically shedding virus. Despite the presence of both faecal and serum antibody the infection was not cleared; therefore, the role of cell-mediated immunity (CMI) was investigated by immunosuppressing the chronically shedding cows with dexametha- sone. No major role for CMI in maintaining the chronic infection could be determined, although immunosuppression did result in a temporary reduction in the shedding of virus-specific immune complexes. INTRODUCTION Coronaviruses are associated with a wide variety of diseases in both humans and animals (Tyrrell et al., 1978) and many members of the coronavirus family appear to be capable of establishing chronic infections in their hosts. These infections include chronic central nervous system disease in mice (Bailey et al., 1949) and pigs (Mengeling & Cutlip, 1976), chronic nephritis in chickens (Alexander et al., 1978) and chronic disease of the eye in rats (Lai et al., 1976). The detection of coronaviruses associated with enteritis for several months after infection has also been reported in both humans (Moore et al., 1977) and pigs (Underdahl et al., 1975). Bovine enteric coronavirus (BEC) has been shown to be a primary pathogen in neonatal calf diarrhoea (Mebus et al., 1973). The incidence of BEC-associated enteritis in naturally occurring outbreaks of diarrhoea in young calves has been reported to vary from 15 to 70% (Crouch et al., 1984; Langpap et al., 1979; Marsolais et al., 1978; Morin et al., 1976) and serological evidence indicates that the virus may be widespread (Rodak et al., 1982), at least in Western Canada. Little information is available concerning the infection of cows by BEC, and the possible role they may play in the epidemiology of infection. We have previously shown that the virus can be detected in the faeces from over 70% of clinically normal cows from a single herd (Crouch & Acres, 1984). This report describes the shedding pattern and immune responses of clinically normal cows chronically shedding BEC in their faeces over a period of several months. METHODS Virus. The P.Q isolate of BEC (originally obtained from S. Dea, Department of Pathology and Microbiology, Faculty of Veterinary Medicine, University of Montreal, St Hyacinthe, Quebec, Canada) grown in Madin-Darby bovine kidney (MDBK) cells as described previously (Crouch & Raybould, 1983) was used throughout this study. Preparation oJJaecal samples. Faecal samples were collected and stored at 4 °C until diluted 1 in 3 (w/v) in 0.01 M- phosphate-buffered saline pH 7-2 (PBS) containing 0.05 % Tween 20. Following low-speed centrifugation at 3000 r.p.m. (MSE Chilspin) for 20 min, the partially clarified supernatants were removed and stored at -20 °C until tested. 0000-6410 © 1985 SGM

Monoclonal antibodies reactive with three different viral polypeptides were evaluated singly and in combination as the capture antibody(s) in an enzyme-linked immunosorbent assay system for the detection of bovine enteric coronavirus. Similar levels of sensitivity were found for all combinations tested. A sensitive, highly specific, and reproducible assay for the detection of bovine enteric coronavirus was developed, using a mixture of two of these monoclonal antibodies reactive with antigenic components either external or internal to the virion. These monoclonal antibodies were bound indirectly to 96-well plates via rabbit anti-mouse immunoglobulin. After sample application and incubation, virus was detected by using rabbit anti-coronavirus peroxidase conjugate followed by enzyme substrate and chromagen. Fecal samples from a single herd of cows were screened for the presence of coronavirus by this assay. Five percent of clinically normal cows were found to be shedding coronavirus.

SUMMARY A serial study of rotavirus infection in gnotobiotic piglets is described. They were infected when 7 days old and the course of infection was followed for 21 days, by immunofluorescence and histological examinations of the intestinal epithelium and by titration of the virus content of the gut lumen. There appeared to be two stages of recovery of the intestinal wall, the earlier stage involving non-immune mechanisms and the later involving antibody.

Purified coronavirus, detergent extracts of purified coronavirus, and virus-infected Madin-Darby bovine kidney cells were evaluated as antigen substrates in enzyme-linked immunosorbent assay (ELISA) and passive hemagglutination systems. Only detergent-extracted and -unextracted, purified viruses were reactive as antigen substrates in ELISA, whereas all three antigen preparations could be used for sensitization of erythrocytes in the passive hemagglutination assay. The passive hemagglutination system with infected cell extracts exhibited a similar level of sensitivity and specificity to the ELISA system employing purified coronavirus but enabled 300 times more tests to be performed per volume of virus-infected cell culture.