A comparison of different challenge methods for induction of atrophic rhinitis in pigs

Transmission and development of atrophic rhinitis (AR) was studied in 5- to 15-week-old pigs (Groups 2-7) originating from a herd free of AR, and compared to unexposed healthy pigs (Group 1), and pigs from a herd with endemic AR (Group 8). At the start of the trial, pigs in Groups 2-5 were challenged intranasally twice a week for 3 weeks with pure cultures of bacteria originating from the endemic AR herd: Nontoxigenic Pasteurella multocida type A (PmA) plus Bordetella bronchiseptica phase I (Bb) (Group 2); PmA + toxigenic Pm type D (PmD) (Group 3); PmD only (Group 4); and PmD + Bb (Group 5). Group 6 pigs were challenged with nasal wash of pigs from the endemic AR herd, and Group 7 pigs were challenged by being housed together in the same pen with Group 8 pigs throughout the study. Nasal swabs of all pigs were cultured 5 times during the study. Serum was collected at 6 weeks post challenge. Average daily gain (ADG) and turbinate lesions (turbinate gross lesions by visual scoring and by Turbinate Perimeter Ratio, TPR, scoring, and histopathological lesions) were measured at the time of slaughter at 15 weeks of age. Mean TPR value for the Group 1 pigs was 1.64, which was significantly (P less than 0.05) different from the mean TPR value of 0.58 for the pigs from the endemic AR herd (Group 8), the 0.79 value for Group 6 pigs, and 1.03 value for Group 7 pigs. Of pigs challenged with pure bacterial cultures, only Group 5 (PmD + Bb) developed significant AR (mean TPR = 1.24). Only one pig in each of Groups 2 and 3, and two pigs in Group 4 showed TPR values indicative of AR (TPR less than 1.30). However, histopathological examination showed that those pigs were recovering from the infection 7 weeks post challenge. Constant exposure to certain bacteria or other factors in nasal washings, stress of crowding or poor environmental conditions might be required to experimentally produce AR in 5-week and older pigs similar to that in naturally infected pigs. There was no relationship between turbinate lesions and the isolation frequency or quantity of PmA, PmD, or Bb. Antibody levels against PmA or PmD had moderate to high correlation with TPR values (r = -0.694 and -0.503 respectively). ELISA values also corresponded well with the type of bacteria inoculated in each group of pigs and appeared to be a sensitive test for PmA, PmD, and Bb infections in pigs.(ABSTRACT TRUNCATED AT 400 WORDS)