Samples of rectal faeces were collected immediately after slaughter from 400 cattle each month for a 1-year period and from 1000 each of sheep, pigs and poultry over the same period. Samples were examined for Escherichia coli O157 by enrichment culture in buffered peptone water with vancomycin, cefixime and cefsulodin followed by immunomagnetic separation and culture of magnetic particles onto cefixime tellurite sorbitol MacConkey agar. E. coli O157 was isolated from 752 (15.7%) of 4800 cattle, 22 (2.2%) of 1000 sheep and from 4 (0.4%) of 1000 pigs, but not from any of 1000 chickens. Of the cattle sampled. 1840 (38.4%) were prime beef animals, 1661 (34.6%) were dairy animals being culled and the status could not be determined for the other 1299 (27%) animals. E. coli O157 was found in 246 (13.4%) of the 1840 beef cattle and 268 (16.1%) of the 1661 dairy cattle. The monthly prevalence of E. coli O157 in cattle was 4.8-36.8% and was at its highest in spring and late summer. Seventeen of the 22 isolates from sheep were also made over the summer period. All E. coli O157 isolates from sheep and 749 (99.6%) of the 752 E. coli O157 isolates from cattle were verocytotoxigenic as determined by Vero cell assay and DNA hybridization, eaeA gene positive, contained a 92 kb plasmid and were thus typical of strains causing infections in man. In contrast isolates from pigs were non-toxigenic, eaeA gene negative and did not contain a 92 kb plasmid and would, therefore, be unlikely to be a source of infection for man.

Fifteen isolations of infectious bronchitis (IB) virus were made from a total of 126 Brazilian poultry flocks of all ages that were examined. These flocks (14 chicken and 1 quail) were experiencing a variety of IB-like conditions including respiratory disease, digestive and kidney problems, and drops in egg production. One of the isolates was of the Massachusetts serotype. The remainder were examined by means of cross-neutralization tests in tracheal organ cultures and were shown to belong to at least four antigenic groups, all different from ones described previously in other countries. Some, but not all, of the flocks from which they were isolated had been vaccinated against IB with vaccines of the Massachusetts serotype. In vivo protection studies showed that the MA5 vaccine (of the Massachusetts serotype) protected well against challenge with four of these isolates, representing the different serotypes reported in this study.

No abstract

Outbreaks of infectious coryza have been reported in vaccinated flocks in different countries, indicating that new serotype(s) of Haemophilus paragallinarum may have evolved. Several field isolates from vaccinated flocks in the US, Ecuador, Argentina and Zimbabwe were examined and, apart from one serotype C strain, all were typed as serotype B. An inactivated commercial trivalent vaccine, containing serotypes A, B and C, protected against challenge with the serotype C isolate but protection against challenge with serotype B isolates was weaker, suggesting that they might represent a new variant immunotype. An experimental tetravalent oil adjuvant vaccine, containing one of the serotype B isolates, appeared immunogenic against all isolates after one vaccination. Its efficacy and safety were further tested in layer chickens housed under field conditions. Chickens were vaccinated at 8 and 16 weeks of age while controls were unvaccinated. Vaccinates and controls were challenged with type A, B, C and variant type B at 25, 45 or 65 weeks of age. There was good protection (PB/ 0.05) against all four immunotypes after all challenges. No systemic reactions were observed and local reactions were similar to those found with the commercial trivalent vaccine. The tetravalent vaccine may therefore be a good choice for control of new field isolates.

The work reported here is an initial attempt to find an alternative method by which the safety of live-attenuated Newcastle disease virus (NDV) vaccines for the respiratory tract of young chickens can be assessed. The current recommended methods involve either the subjective assessment of respiratory signs, or raise ethical concerns, as in the case of the intracerebral pathogenicity index. The two methods considered here were the use of tracheal organ cultures to assess the level of ciliostasis which the vaccines caused to the ciliated epithelium of the trachea and the incorporation of a pathogenic strain of in the inoculum in order to induce colibacillosis. Both methods were successful in confirming the safety of the two vaccines. However, these results are only preliminary and more studies need to be performed to determine whether one or both methods have potential, either to replace the existing statutory tests, or provide a test which might be useful during the development stages of a new live-attenuated NDV vaccine.