Dynamics of infestation of tracers lambs by gastrointestinal helminths under a traditional management system in the North of Tunisia

The authors present a survey of gastrointestinal helminths of sheep on permanent pastures in the extreme north region of Tunisia (Mediterranean climate). Dynamic infestation of animals has been monitored by using batches of three tracer lambs introduced each two months during 2004 and 2005. These lambs were kept in the pens of veterinary school of Sidi Thabet (Tunisia) during three months and then necropsied. Faecal and blood samples were took from tracer lambs each two months during the whole period, and from animal flock only during 2004. The main helminth genera encountered were Trichostrongylus spp., Teladorsagia spp., Strongyloides papillosus and Anoplocephalidea; occasionaly were found Nematodirus, Oesophagostomum, Chabertia, Cooperia, Trichuris and Paramphistomum. The egg count of the ewes and lambs in the flock showed two peaks. For both ewes and lambs there is a gradual increase from January with a peak in May-June. This first peak is considered to be due to acquisition of infective larvae during the rainy and cold season, as evident from the worm burdens of tracer lambs. The second peak was exclusively observed in ewes during late autumn-early winter (November-December); it has two origins: infestation by third larvae stage and the periparturient rise. The worm burdens of tracer lambs showed that there was a gradual accumulation of nematodes from September- October, reaching a peak in March-April; a very low or naught infection is reported during the dry period (July-August). Infection by Anoplocephalidea was higher during the dry season. This study is primordial for a comprehensive control programme implementation against gastrointestinal helminths. Les auteurs présentent une étude quantitative et qualitative des helminthes gastro-intestinaux des ovins dans le nord de la Tunisie (climat méditerranéen). La dynamique d’infestation des animaux a été contrôlée en utilisant des lots de trois agneaux traceurs introduits tous les deux mois durant une période qui s’est étalée sur deux années, 2004 et 2005. Après leur retrait du pâturage, les agneaux traceurs ont été gardés à l’École vétérinaire de Sidi Thabet (Tunisie) durant trois mois, puis autopsiés. Des échantillons de matière fécale et de sang ont été pris sur des agneaux traceurs à chaque période de pâture et aussi sur des animaux d’un troupeau de la région d’étude durant l’année 2004. Les principaux helminthes rencontrés étaient Trichostrongylus spp., Teladorsagia spp., Strongyloides papillosus e