Serological response of chickens naturally infected with Salmonella typhimurium detected by ELISA.
Four laying flocks of chickens in Britain, each with a history of Salmonella typhimurium infection, were investigated serologically and bacteriologically. Blood samples were taken from identified birds from a single house on each site and sent to the Central Veterinary Laboratory, Weybridge for serological examination using enzyme-linked immunosorbent assays (ELISA) and rapid slide agglutination test (RST) using stained S. pullorum. The identified birds were taken to the local Veterinary Investigation Centre for bacteriological examination. On site A no salmonellae were recovered from birds in the house chosen for serological examination. Of these birds approximately 20% had antibodies to S. typhimurium in ELISA which used either a lipopolysaccharide (LPS) or heat-extract (HE) antigen from S. typhimurium. S. typhimurium was recovered from birds in one other of the four houses on the same site; these birds were not tested serologically. On site B, S. typhimurium was isolated from 8% of the birds examined. Of the total tested serologically, a third to half were seropositive by S. typhimurium ELISA using the LPS and HE antigen respectively. A small proportion of birds was seropositive by S. enteritidis ELISA and RST. No salmonellae were isolated from the other two sites although about 10% of birds tested on site C were seropositive in S. typhimurium ELISA. Cross-reactions were seen between S. typhimurium antigens in the ELISA and experimentally prepared antiserum to S. enteritidis. The S. enteritidis ELISA was generally more specific although cross-reacting antibodies were detected in sera from birds on sites A and B.