Immunological studies of Pasteurella anatipestifer infection in the white Pekin duck (Anas platyrhnchos) using an enzyme linked immunosorbent assay.

An enzyme-linked immunosorbent assay was developed for the detection of antibodies to Pasteurella antipestifer in duck sera. The assay was shown to be sensitive, specific and reproducible. Its superiority over rapid slide agglutination and agar gel precipitin tests for detecting early antibody responses to the organism was demonstrated. Serum antibody titres were shown to correlate with protection against virulent intramuscular challenge. Moreover, the formation of the antigen/antibody complex in vivo was shown to effect an immunological memory to the organism. The protection afforded by different pre-formed preparations of antigen/antibody complex to intramuscular challenge was investigated and their efficacy discussed. Epidemiological studies indicated that ducklings were most susceptible to infection given intramuscularly; those infected orally neither died nor showed clinical signs of the disease. Intranasal instillation caused no deaths, but signs of infection were occasionally observed in the treated birds. In the orally challenged group, specific antibodies were detected in the tracheal washings of five of nine birds examined, but circulating antibodies to the organism were found in only one individual. Specific antibodies were also shown to be present in the tracheal washings of nine of twelve birds infected intranasally, whilst serum antibodies were detected in four of these individuals. It was further shown that antibodies present on the tracheal surface could also be derived from those administered intraperitoneally. Experiments were conducted to evaluate the efficacy of an experimental combined P. anatipestifer - E. coli vaccine in the field. A single injection of vaccine given at 10 or 14 days of age effected significant reductions in mortalities caused by these diseases. Immunological data indicated that the vaccine effected a priming of the neonatal humoral immune function, thus increasing the efficacy of the antibody response following exposure to the organism