INTERMEDIATE HOST POPULATIONS AND SEASONAL TRANSMISSION OF FASCIOLA-GIGANTICA TO CALVES IN CENTRAL MALI, WITH OBSERVATIONS ON NEMATODE POPULATIONS

To assess the seasonal transmission of Fasciola gigantica to cattle in the inland delta of central Mali, 24 yearling zebu calves were purcha sed, used as sentinels and released onto pasture in November 1991. The calves were allowed to graze freely with a local indigenous herd for a period of 45-225 days. Every 6 weeks following exposure, three senti nels were selected at random, slaughtered and examined for the presenc e of liver flukes and gastrointestinal nematodes. Adult and immature f lukes ranging from 20 to 639 in number were recovered from animals at necropsy with a peak observed in July. Differential worm counts of gas trointestinal nematodes indicated the presence of the following nemato de species in order of predominance: Cooperia spp. (53.7%), Haemonchus placei (38.3%), Oesophagostomum radiatum (6.7%), Trichostrongylus col ubriformis (0.9%), Bunostomum phlebotomum (0.1%). During the course of the experiment, ten sentinel calves died from subacute fasciolosis ca using a disruption of the study. Previous and concurrent snail populat ion studies showed that Lymnea natalensis, the snail intermediate host for F. gigantica, begins emerging in early March and reaches maturity by late April. On both occasions the peak was observed in April with a drastic decline in number in June. Control strategies are discussed in relation to the season and herd management.