Enteric Infections in Man and Animals: Standardization of Immunological Procedures

The protective effect of a combined rotavirus/enterotoxigenic E. coli K99 vac­ cine against naturally occurring neonatal diarrhoea was evaluated in two dairy and two beef herds. Before vaccination, frequency of diarrhoea in these herds was 46% up to 60% with losses of 7% to 20%. After vaccination of pregnant cows and heifers mild diarrhoea occurred in 14% to 20% of their calves, one out of 144 calves died with enteric symptoms. In 13 out of 26 calves of nonvaccinated controls where diarrhoea was noted, one of them died. K99-positive enterotoxigenic E. coli were not detected in any of the faeces tested. Rotavirus was found in one of the beef herds. Neonatal diarrhoea is still one of the most serious problems in calfbreeding, especially in its modern form with large numbers of animals. The eco­ nomic losses due to diarrhoeal disease during the first two weeks of life are enor­ mous. They result from the loss of calves, retarded growth rates and — last but not least — from the cost of the treatment of affected animals. A number of infectious agents can be recovered from the faeces of such diseased calves, including viruses, e.g. rota-, coronaor parvoviruses, bacteria like enterotoxigenic E. coli and protozooa, e.g. Cryptosporidia (8). Recent results indicate that mixed infections with two or more of these agents are the rule rather than the exception. Furthermore, it can be supposed that the severe forms of diarrhoeal disease seen in the field are always caused by mixed infections. Evi­ dence from experimental infections confirms this hypothesis. The clinical course of the disease after mixed infection with rotavirus and enterotoxigenic E. coli or Coronavirus is more severe and results in higher mortality rates than monoinfec­ tions usually do. For instance, it has been shown that colostrum-deprived calves survived an infection with 10 enterotoxigenic E. coli whereas after mixed infec­ tion with rotavirus and the same doses E. coli, all of the animals died (15). Fur­ ther evidence comes from other investigations (21, 17) in colostrum-deprived and conventional calves. The results indicate that adhesion, colonization and growth of enterotoxigenic E. coli in the small intestine is enhanced by a preceeding or simultaneous infection with rotaviruses. Moreover it seems that such mixed infections cause severe disease even in older calves. Taken together, these data 238 W. Eichhorn et al. indicate a probable synergism of the pathogens involved, although up to now a possible interference cannot be excluded. However, for the development of an effective immunoprophylaxis, it can be deduced that only combined vaccines containing two or more of the pathogens described will be successful. Former recommendations for the prophylaxis of neonatal enteric disease included the improvement of sanitary conditions, feeding of preserved colostrum for at least one week and active local immunization or newborn calves (3). This strategy, however, proved to be unsatisfactory. Early publications on the effect of a commercially produced rotaviral vaccine seemed to be promising (19), but following studies could not confirm these results (1, 9, 12). On the other hand, oral immunization against enterotoxigenic E. coli is reported to be very effective (7). One of the draw-backs of this kind of vaccine is its strict O-antigen specifity. Considering the broad spectrum of O-antigens of enterotoxigenic E. coli, it is obvious that a specific vaccine must be prepared for each herd. Finally, it seems to be impossible to achieve any amelioration of the hygie­ nic conditions in the majority of the farms and most of the farmers usually neglect the advice to preserve colostrum and feed it to the calves for at least one week. Because of this failure of the hitherto recommended prophylactic measu­ res, interest is now focussed on passive immunization of calves by vaccinations of their dams (3, 14, 16, 22). We have developed a combined rotavirus/enterotoxigenic E. coli K99 vac­ cine. This report describes its effects in the field. MATERIALS AND METHODS