Experiences with the ELISA for detection of the E. coli K99 antigen in calf faeces

This paper summarizes experiences with the use of an enzyme-linked immunosorbent assay (ELISA) for the detection of K99+ E. coli in calf faeces. ELISA results were compared with those of conventional bacteriological examination (BE) using a total of 1668 faecal samples of calves in the field, collected during aetiological and epidemiological studies. In addition, faecal samples obtained from four experimentally inoculated calves were examined with ELISA, BE and quantitative BE i.e. determination of the number of viable K99+ ETEC organisms per gram of faeces. The ELISA proved to be very useful, though slightly less sensitive than BE, when dealing with large numbers of faecal samples of calves of less than 6 days of age. Clinical ETEC-induced diarrhoea cases appeared to be diagnosed particularly reliably. In calves of over five days of age, however, positive BE-results were usually not confirmed by ELISA, most likely due to the presence of specific copro-antibodies. This last conclusion was suggested by the observation that in experimentally inoculated calves. ELISA results became negative abruptly after day 6 post-infection. The quantitative BE showed no significant decrease of the number of ETEC organisms at that time. In some faecal samples after day 6 post-infection an excess of K99 antibodies was demonstrated. It is concluded that ELISA is of no value in epidemiological studies on the spread and persistence of K99+ ETEC organisms in older calves and cows. However, ELISA is a very reliable diagnostic tool for use in large-scale field surveys on the aetiology of neonatal calf diarrhoea.