Infestation of tracer lambs by Fasciola hepatica in Tunisia: determining periods for strategic anthelmintic treatments.

Ovine fasciolosis causes high morbidity and mortality rates, resulting in large economic losses to the sheep industry in northern Tunisia. The authors surveyed ovine fasciolosis (Fasciola hepatica infestation) in a Barbarine sheep flock in the humid region of Tunisia (Sejnane, Governorate of Bizerte) over two consecutive years, 2004 to 2005. To assess the dynamics of fluke infestation, a total of 36 tracer lambs were introduced into the flock successively, in groups of three, every two months, and their infestations were monitored by coproscopy and necropsy. Coproscopic analysis revealed high mean percentages of infestation of 60% and 65% for flock lambs and ewes, respectively. Similarly, a high percentage of infestations was recorded in the tracer lambs (more than 70%) post mortem. Significant fluctuations in infestation dynamics were observed in the tracer lambs, and three distinct infestation periods were identified: a period of very low, non-constant infestation risk during the warm period (from July to October); a high-risk period from March to June, and a third period with a variable but constant infestation risk (from November to February). Based on these results, the authors propose strategic flukicide treatments with triclabendazole, aimed at reducing mollusc infestation and subsequent pasture contamination by metacercariae, during two main periods: in September and in February, just before the reactivation of the molluscs from aestivation and hibernation, respectively.