Detection of Toxigenic Pasteurella Multocida Infections in Swine Herds by Assaying Antibodies in Sow Colostrum

Toxigenic Pasteurella multocida is the causative agent of progressive atrophic rhinitis (PAR), a serious respiratory infection of swine. Diagnosis of the disease has hitherto been based on clinical signs, pathologic findings, and subsequent isolation of the agent. The best Finnish pig breeding herds participating in the Finnish Pig Health Scheme have been surveyed for PAR since 1963, and the disease has been eradicated from these herds. In this study, a total of 5,650 colostrum samples from 188 Finnish Pig Health Scheme herds were analyzed with a new serologic screening method: an enzyme-linked immunosorbent assay (ELISA) able to detect antibodies to the toxin of P. multocida (PMT). Although the herds had been continuously controlled for PAR, 1 herd with PMT antibodies was found. The positive reactions in the ELISA were confirmed by isolating the causative organism. The origin of the infection also appeared to be obvious. The serologic ELISA is a suitable method for the detection and screening of toxigenic P. multocida-infected pig herds.

A Specific and Sensitive PCR Assay Suitable for Large-Scale Detection of Toxigenic Pasteurella Multocida in Nasal and Tonsillar Swabs Specimens of Pigs

A polymerase chain reaction (PCR) assay for the detection of toxigenic Pasteurella multocida in nasal and tonsillar swab specimens collected from pigs was developed. Target DNA was isolated with guanidine thiocyanate and diatomite, and 2 primer sets derived from sequences in the gene that encodes the dermonecrotic toxin-of P. multocida were used simultaneously. The method was adapted to microtiter plate format allowing large-scale use of the PCR assay. To identify false-negative test results caused by failure of amplification, a positive control template was constructed that was spiked to each DNA sample. The PCR assay was evaluated with clinical samples and compared with 2 routinely used methods for detection of toxigenic P. multocida: isolation from a selective agar and direct detection of the toxin in extracts of primary cultures by an enzyme-linked immunosorbent assay (ELISA). The sensitivity of the PCR assay was tested with 346 nasal and tonsillar swabs specimens collected from pigs of 9 herds known to be infected with toxigenic P. multocida. Toxigenic P. multocida was isolated from 22 specimens, only 28 specimens tested positive in ELISA, but 40 tested positive in the PCR assay; thus the PCR assay is the most sensitive of the 3 methods. The specificity of the PCR assay was tested with 372 swab specimens collected from pigs of 6 herds certificated to be free from toxigenic P. multocida. Toxigenic P. multocida was not isolated from any of these specimens, all tested negative in ELISA, and 370 tested negative in PCR. The 2 positive specimens came from 2 pigs of 1 litter and tested only weakly positive in the PCR assay. From these results, it was concluded that the PCR assay is not only highly sensitive but also highly specific.