Trichuris suis population dynamics following a primary experimental infection.

Trichuris suis population kinetics was studied by experimentally infecting 40 pigs with 5000 T. suis infective eggs. Six pigs were sacrificed every 2 weeks from 1 to 9 weeks post-inoculation (p.i.) and the remaining 10 pigs were sacrificed 11 weeks p.i. to estimate worm burdens. An equal number of uninfected control pigs were sacrificed at the same time points for comparison. Egg excretions from each pig were evaluated every week from 5 to 11 weeks p.i. Peripheral blood eosinophilia and basophilia were also evaluated every 2 weeks throughout the experimental period. After an initial almost 100% establishment of T. suis an expulsion phase followed approximately 9 weeks p.i., resulting in an aggregated distribution of the worms in the pig population, as it is characteristic for most helminth infections. By 11 weeks p.i. almost all worms had been expelled. Egg excretion peaked 7 weeks p.i. and a significant non-linear relationship between worm burdens and egg excretion was found. The predilection site for T. suis was the caecum and proximal colon and the relative distribution of worms in the large intestine did not change over time until expulsion. Peaking peripheral blood eosinophil and basophil levels were observed in the T. suis infected pigs 5 and 7 weeks p.i., respectively, reflecting the host activated immune response against the parasite. We here describe the course of a primary T. suis infection in pigs by detailed worm counts, demonstrating an effective expulsion that results in an almost 100% clearance of infection as previously indicated by monitoring faecal egg excretion.