SEASONAL TRENDS IN INTESTINAL NEMATODE INFECTION AND MEDICINAL PLANT USE AMONG CHIMPANZEES IN THE MAHALE MOUNTAINS, TANZANIA

A longitudinal study of nematode infection in chimpanzees was conducte d between 1989 and 1994 on the M group chimpanzees of the Mahale Mount ains National Park, Tanzania during two annual dry and rainy season pe riods and a third rainy season. Chemical and physical antiparasite pro perties of medicinal plant use against the strongyle nematode Oesophag ostomum stephanostomum have recently been reported at Mahale. Here, th e incidence of nematode infections were analyzed for seasonal trends t o elucidate the possible influence of parasite infection on previously reported seasonality of medicinal plant use and to test the hypothesi s that the use of these plants is stimulated by O. stephanostomum. The number of chimpanzees infected by O. stephanostomum was significantly higher in the rainy season than in the dry season of both 1989-1990 a nd 1991-1992. However, the incidence of Trichuris trichiura and Strong yloides fuelleborni showed no seasonality. Reinfection of individuals by O. stephanostomum occurred in synchrony with annual variation in ra infall: there was a sharp rise in the occurrence of new infections per individual within one to two months after the beginning of the first heavy rains of the season. This pattern coincides with the reproductiv e cycle of this nematode species. O. stephanostomum (95%) infections w ere associated significantly more frequently with medicinal plant use than either T. trichiura (50%) or S. fuelleborni (40%) infections. The se observations are consistent with previous reports for the increased use of these plants during the rainy season and are consistent the hy pothesis that medicinal plant use is stimulated by O. stephanostomum i nfection.