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The use of cotton ropes has been recently proposed to collect oral fluids from pigs as a method to detect and monitor viral infections in swine populations. However, its use for detection and monitoring of swine bacterial pathogens by polymerase chain reaction (PCR) has not been assessed. In this study, oral-fluid testing for diagnosis of Actinobacillus pleuropneumoniae was evaluated over time, utilizing samples from experimentally infected pigs.
Eighty six-week-old pigs were randomly divided into eight groups of 10 pigs each. Pigs from Groups 1 to 7 were inoculated intranasally (1 mL per nostril) with 1 × 106 colony-forming units per mL of the following A. pleuropneumoniae serovars: 1, 3, 5, 7, 10, 12, or 15. Pigs in Group 8 were not inoculated and remained as negative controls.
One-meter rope segments were placed in a clean area of the pen and away from water and feed. Pigs were allowed to chew on the ropes for 20 to 30 minutes just prior to inoculation (Day 0), Day 1, and weekly thereafter (Days 7, 14, 28, 35, 42, and 49). Blood samples were collected on Day 0 and weekly thereafter. All pigs were euthanized 49 days post infection, and postmortem examinations were conducted to evaluate the presence and severity of A pleuropneumoniae lesions. Detection of H parasuis and S suis in oral fluids collected from all groups at all time points was used as a control for sample processing, DNA extraction, and potential presence of PCR inhibitors in oral fluids.
An average of 5 mL of oral fluids was recovered from each rope at each collection. Actinobacillus pleuropneumoniae was detected by PCR in samples collected at Day 1 in the group inoculated with serovar 3, and at Day 7 in the groups inoculated with serovars 7 and 10. Actinobacillus pleuropneumoniae was not detected by PCR at any time point in samples from pigs inoculated with serovars 1, 5, 12, or 15. Actinobacillus pleuropneumoniae was not cultured from oral-fluid samples collected throughout the experiment. Pigs inoculated with serovars 5 (n = 1), 7 (n = 4), 10 (n = 4), and 15 (n = 2) showed mild focal fibrous adhesions between the surface of the lungs and the parietal pleura at necropsy performed 49 days post inoculation. Pigs inoculated with serovars 7 and 10 also showed lung lesions. No APP-specific lesions were observed in pigs inoculated with serovars 1, 3, or 12.
These results indicate that oral-fluid testing has the potential to be a screening tool for detection of swine bacterial pathogens. Field studies are indicated to explore this potential further.
Costa G, Oliveira S, Torrison J. Detection of Actinobacillus pleuropneumoniae in oral-fluid samples obtained from experimentally infected pigs. J Swine Health Prod. 2012;20(2):78?81.
