Effect of repeated anthelmintic treatment on ability to detect predisposition of mice to Heligmosomoides polygyrus and Aspiculuris tetraptera (Nematoda) infections.

Abstract

Several recent studies have demonstrated predisposition of certain humans to heavy gastro-intestinal nematode infections. This finding has been used to support the concept of community control of nematodes based on selective treatment of the few heavily infected individuals in the community. A mouse model has been used in this study to determine whether those individuals found to be 'predisposed' to heavy infection continue to regain heavy nematode infections following repeated anthelmintic treatments. Re-infection was examined over 3 intervals of 8 weeks in 52 mice and individual worm burdens attained following drug-induced expulsion were analysed. In the case of Heligmosomoides polygyrus, parasite numbers obtained after first treatment were only significantly correlated with those obtained after the second treatment. Re-infection levels in mice during the second and third re-infection periods did not correlate with parasite loads at the beginning of the study. In the case of Aspiculuris tetraptera, correlations after each re-infection period remained significant, although the magnitude of the correlation coefficient decreased with successive re-infection intervals. The data suggest that a selective control programme based on repeated screening to identify heavily infected individuals prior to each treatment would reduce the number of H. polygyrus in the host population 17.6% more than a single screening at the beginning of the control programme, and would reduce the number of A. tetraptera by 14% more than a single screening. Re-infection rates for H. polygyrus were shown to decrease with increasing mouse age whereas re-infection rates for A. tetraptera increased with increasing mouse age.