Monoclonal antibody characterization of South African field isolates of Haemophilus paragallinarum.

A total of 27 different isolates of Haemophilus paragallinarum were made from chickens between June 1991 and December 1992. All of these isolates were examined by ELISA, by means of a locally produced panel of three monoclonal antibodies (denoted F1, V1 and VF3). The isolates were all of the F1 antigenic type. Three of them showed a weak reaction with the F1 monoclonal antibody, while three other isolates reacted strongly with the F1 as well as with the VF3 Mab. A selection of stored Haemophilus isolates, dating from 1984 to 1985, were also examined with the Mabs and found to be of the F1 antigenic type. Fifteen isolates were collected before 1974, i.e. before the use of Haemophilus vaccines in this country. The majority of them were of the F1 antigenic grouping. Some showed a weak reaction with the F1 Mab; others showed a strong reaction with both the F1 and VF3 Mabs; and a few showed no significant reaction with any of the Mabs used. Strains used for the production of infectious coryza vaccine were also examined with the Mabs. Strain 0083 showed a stronger reaction with the V1 Mab than with the F1 Mab, whereas strain 0222 showed no reaction with any of the Mabs. None of the SA field isolates collected since the use of vaccines exhibits the V1 antigenicity, which is the prevalent antigen of strain 0083. Most (80%) of the SA field isolates showed a stronger reaction with the F1 Mab than did strain 0083. Antigenically silent isolates similar to 0222 (Page's serotype B) were isolated before the use of vaccines, but not since.