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Fecal to oral transmission of proliferative enteropathy (PE) is considered to be a major factor in the spread of a Lawsonia infection. A seeder pig model, designed to show the effect of introducing an infected animal into a population of susceptible contact animals, allows characterization of natural transmission of Lawsonia and determination of the effect of an antibiotic intervention upon detecting fecal excretion in the susceptible contact animals and finally, by examining the practical utility of using the PCR as a tool to decide when to initiate ileitis control.
At 3 weeks of age, 60 pigs reared by seronegative dams were randomly allocated to 6 pens with 10 pigs per pen. After 3 additional weeks of acclimation, on Day 0, one seeder pig was randomly selected from each pen and inoculated with virulent pure culture of Lawsonia intracellularis. All pigs were observed 3 times per week and scored for attitude, abdominal appearance and fecal consistency. All pigs were weighed weekly. The spread of Lawsonia infection to the contact animals was monitored by thrice weekly qualitative conventional PCR and IPMA from fecal and blood samples, respectively. Three pens were randomly selected to be treated with Tiamulin 10 (35 g/ton) in the feed which was initiated on Day 9 when 30% of contact pigs were detected positive for fecal Lawsonia shedding and 10% of contact pigs were exhibiting clinical signs consistent with PE while three pens remained untreated to serve as positive Control pens.
The seeder pig in one Control pen died on Day 37. By that point in time, all contact pigs in that pen had been positive for Lawsonia shedding, while the seeder pig in one Tiamulin pen, for unknown reasons, shed much fewer Lawsonia than other seeder pigs and thus apparently failed to transmit the disease to contacts consistent with the pattern seen in other pens. The infected pigs were shedding >105 copies Lawsonia per gram feces as determined by qPCR from Day 2 through Day 25, 16 days after Tiamulin treatment was initiated. Overall, the pattern of Lawsonia shedding was quite similar between seeder pigs placed in Control pens and those placed in Tiamulin pens. Regarding abdominal appearance, the score was significantly lower in Tiamulin pens, compared to Control pens just as with the average fecal consistency score, which was also significantly lower than those treated with the antibiotic. Average body weight was the same for Control and Tiamulin pens.
The seeder pig model utilized in this trial was a useful tool in evaluating an intervention designed to reduce transmission of Lawsonia to contact pigs. The results of this trial show that it is practical to use PCR on feces to properly time interventions designed to control ileitis. Also, measuring shedding of Lawsonia by penmates in contact with seeder pigs using qPCR allowed comparison of the duration and amount of Lawsonia shedding in response to treatment. In this trial, compared to Controls, Tiamulin appeared to reduce the amounts of Lawsonia shed in feces of pigs in direct contact with an infected seeder pig, beginning 7 days after treatment was initiated. In addition, the duration of shedding at >105 copies per gram of feces was reduced in Tiamulin -treated contact pigs. As a result, Tiamulin -treated contact pigs were probably infective for a shorter period than untreated contact pigs.
D. Beckler, J. Hammer, P. Pitcher, C. Gebhart, L. Roycroft. Spread of Lawsonia intracellularis in a pure culture seeder pig challenge study. 2011 AASV Annual Meeting: 51.