Résumé
This study was carried out on 250 slaughtered cattle at Ahvaz abattoir in Khouzestan province of Iran to investigate the occurrence of Pasteurella multocida carriers and relationship with their immunity status. Nasopharyngeal swabs and 10 ml blood samples were taken immediately after slaughter. The swabs were streaked on 5% sheep blood agar plates. Cultures were incubated at 37°C for 24h and the plates were examined for colonies resembling P. multocida. Suspicious colonies were further subcultivated and examined microscopically and biochemically. The isolates were serotyped serologically and their pathogenicity in mice was carried out. Sera samples were tested for the presence of antibody against P. multocida by indirect haemagglutination [IHA] test and sera with a titer of >/= 1:16 were considered as positive. P. multocida was isolated from the nasopharynx of 6 [2.4%] out of 247 healthy cattle examined. There was no relation between infection and sex or age. All of 6 isolates belonged to type B. They were pathogenic for mice and caused death in injected mice within less than 24h after injection. Indirect haemagglutination test revealed the titers of >/= 1:16 of P. multocida antibody in 212 [84.8%] cattle. Among 6 cattle recognized as the carriers of P. multocida, 5 were positive serologically and 2, 2 and one of them had titers 1:128, 1:64, and 1:32, respectively