Strategic control of Dicrocoelium dendriticum (Digenea) egg excretion by naturally infected sheep

The aim of this study was to determine the most appropriate months for applying albendazole (ABZ; oral suspension dose 20 mg/kg body weight) to sheep naturally infected with Dicrocoelium dendriticum and kept at pasture, in order to reduce parasite egg shedding to a minimum, mainly during the cold months and, as a result, decrease pasture contamination by viable eggs. Five animal groups (G), homogeneous as regards the number of eggs per gram (EPG) in faeces, were established. The treatment months were: G1, November and January; G2, November and February; G3, November and April; G4, January; and G5 (control), April. Ten samplings (S1-S10) were carried out every 35 to 45 days to collect faecal samples from the rectum of each animal in the five groups. The sedimentation technique and McMaster egg counting chambers were used to analyze the faecal samples. Due to the effect of albendazole (ABZ) treatments, the five groups behaved differently with regard to EPG reduction and the percentage of samples positive for D. dendriticum eggs. Using the Kruskal-Wallis test, statistically significant differences (P < 0.05) were observed between the EPG values obtained in G5 and the rest of the groups from November to May, but not from May onwards. The biggest reduction in egg excretion was obtained in G1, mainly in the cold period when elimination is highest and egg survival greatest, so G1 gave the best result, followed by G2, G4, G3 and finally G5 in descending order.