Intemofionalloumal/ zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Purasirology Vol. 21, No. 3, pp. 307-314, 1991 002O-7519/91 s3.00 + 0.00 Printed in Great Britain Pergamon Press p/c 0 1991 Australian .Sockryfor Pruruirolcgy SEASONAL DYNAMICS OF FASCIOLA HEPATZCA BURDENS IN GRAZING TIMAHDIT SHEEP IN MOROCCO KH. KHALLAAYOUNE,*B.E.STROMBERG,I‘SA.DAKKAK*~~~J.B.MALONE§ * Dtpartement de Parasitologie et Maladies Parasitaires, Institut Agronomique et Veterinaire Hassan II, B.P. 6202, Rabat-Instituts, Morocco t Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108, U.S.A. 9 Department of Microbiology and Parasitology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, U.S.A. (Received 26 February 1990; accepted 30 November 1990) Ah&a&-KHALL.&%YOUNE KH., STROMBERG B. E., DAKKAK A. and MALONE J. B. 1991. Seasonal dynamics of Fusciola hepatica burdens in grazing Timahdit sheep in Morocco. International Journalfor Parasitology 21: 307-314. Seasonal transmission of Fusciolu heputica was observed in sentinel sheep and the dynamics of the snail intermediate host, Lymnueu truncatula, was followed over a 3-year study period in the Middle-Atlas mountains in Morocco. High fluke burdens were recorded in both lambs and ewes in the fall and winter, suggesting that transmission occurred in late spring. Fluke burdens ranged from one to 302 in ewes and from one to 345 in lambs. Infections with 200 or more flukes were always fatal. A unique feature of this study was the annual cyclical fluctuation of the fluke burdens. Burdens reached maximum levels during the winter and then declined to low numbers by late spring and summer. This suggested self-regulation which may be dependent on breed resistance or may be related to forage factors, including lack of forage (nutritional stress). Snail populations were cyclical and correlated with fluke transmission as observed in the sentinel sheep. The weather was observed to affect the snail populations which in turn limited fluke transmission. INDEX KEY WORDS: Fusciola hepatica; sheep; Timahdit breed sheep; Lymnaea truncatula; Morocco. INTRODLJCITON Fasciola hepatica is a major cause of economic loss to sheep producers in Morocco as well as in other areas of the world. In the extensive rangelands of the Middle- Atlas mountains, where sheep raising is the major source of income for rural communities, malnutrition, traditional management and parasitism represent important constraints on efficient animal production. Anthelmintics are routinely used by local farmers to treat clinical disease rather than to prevent the infect- ion. This approach has limited success in controlling fasciolosis and the establishment of more rational prophylactic programs based on regional epidemiol- ogical information are needed. Data on the bionomics of lymnaeid snail intermediate hosts and sentinel hosts can be used to evaluate the level of pasture contamin- ation and to determine the high-risk season for fasciolosis in grazing animals. The life-cycle of F. hepatica is highly dependent on variation in the prevailing temperature and soil moisture conditions (Ollerenshaw, 1959; Ollerenshaw & Rowlands, 1959; Hope-Cawdery & Moran, 1971; Meek & Morris, 1979a; Smith, 1981; Malone, Loyacano, Hugh-Jones & Corkum, 1984) and an accurate description of 1 To whom all correspondence should be addressed. seasonal transmission patterns requires long-term epidemiological investigations over several years to dilute the effects of annual weather variations. The objectives of this study were (i) to determine, using sentinel sheep, the seasonal fluctuation of fluke burdens, (ii) to evaluate the population dynamics of the snail vector and fluke transmission in relation to the climate, and (iii) to develop a control strategy that will reduce the economic impact of the infection in the Middle-Atlas region. MATERIALSANDMETHODS Monthly visits were made to a privately owned sheep operation on the open rangelands of the Middle-Atlas mountains at Timahdit in North central Morocco (altitude 1797 m) over a 3-year period (June 198%May 1988). The purpose was to evaluate fluke burdens in sentinel sheep naturally exposed to infections and to monitor the dynamics of Lymnaea truncatula intermediate-host populations for comparison with weather fluctuations. Sentinel sheep. Evaluations of sheep fluke burdens, herd prevalence and seasonal transmission were assessed using sentinel sheep. To ensure. adequate numbers of sentinel sheep for necropsy each month (three ewes, three lambs), about 46 Timahdit breed ewes (2-7 years of age; mean body weight of 27.6 f 3.2 kg) and 46 lambs (4-6 months; mean body weight of 15.4 f 3.6 kg) were purchased in June of each year from the owner of the sheep operation and retained in the same 307