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In this study, 60 pigs with clinical signs of post-weaning multisystemic wasting syndrome (PMWS) from 20 different pig herds and 180 control pigs (without clinical signs of PMWS) were examined to get more insights into the frequencies of porcine circovirus 2 infections and the presence of co-infections in pigs with and without clinical signs of PMWS in the Netherlands. Porcine circovirus type 2 was detected in 100% of the pigs with clinical signs of PMWS by virus isolation and/or PCR and in 50% of the pigs from PMWS-free herds. There was an association between the levels of infectious PCV2 and/or PCV2 DNA load and the severity of clinical signs as described for PMWS. A high variation in PCV2 antibody titres was found in the clinically affected pigs, and 27% of these pigs did not mount PCV2 antibody titres higher than 1:200. A concurrent infection of PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV) was found in at least 83% of the pigs with clinical signs of PMWS and in 35% of the pigs from PMWS-free herds. Co-infections of European- and American-type PRRSV were detected only in PMWS herds and in one control herd with a history of PMWS clinical signs.

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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.