Search

From December 1998 to March 2000, caecum and ascendant colon of 42 horses naturally infected with cyathostomes were collected during routine necropsy or from a local slaughterhouse. Changes in the numbers of mucosal and submucosal mast cells (MMC and SMMC), intraepithelial, mucosal and submucosal eosinophils (IE, ME and SME) in the large intestine were investigated by histochemical techniques in relation to the worm burdens. The effect of age was examined in three subgroups: 6-24-month-old horses (group 1), 2-10-year-old horses (group 2) and horses more than 10 years of age (group 3). No globule leucocytes were detected in any sections. No significant variations with breed or sex were observed in cell counts. The main variations were higher eosinophil counts in groups 2 and 3 and a marked increase of the MMC counts in the oldest horses (group 3). For each cell type, the infiltration was homogeneous and generalised along the large intestine. In the whole horse sample, the IE numbers were the only parameters that correlated with the MMC and SMMC counts. Very few significant relationships were found between mast cells and eosinophils in groups 1 and 3, whereas numerous positive correlations were recorded in group 2. In the whole horse sample, several correlations were found between different cell counts and cyathostome burdens. The numbers of larvae, adult worms, and the total worm burdens were related to some of the tissular eosinophil counts while the percentage of early third stage larvae (EL3) was linked to mast cell densities. These relations between cells and worm populations showed variations with age. In group 1, most of the significant associations were found between eosinophil counts (IE and SME) and the total numbers of larvae and worms; in group 2, they were noticed between the three eosinophil types and the total cyathostome burdens. In group 3, a MMC hyperplasia was observed and correlations were mostly recorded between these MMC and the total numbers of adult worms or the percentage of EL3. Several associations were also detected between eosinophils (mainly ME and/or IE) and different cyathostome burdens. These variations in the relationship between inflammatory cells and cyathostomes seemed to be consistent with the cellular changes observed among the three age groups. These results suggest that eosinophil and mast cell infiltrations quantified in the large intestine wall might be associated with cyathostome infection.

Forty-two horses from Normandy (France) were examined post-mortem for small strongyle infections from October to March. In the positive horses, total worm numbers ranged from 234 to 90,247 (mean 11,297). Encysted larvae represented the major part of the total cyathostome burdens with a high percentage (83%) being early third stage larvae. They were mostly recovered from the caecum (48%) and ventral colon (40%) and were less present in the dorsal colon (12%). Adult cyathostomes were mainly located in the ventral colon (64%) and less frequently in the dorsal colon (27%) and caecum (9%). Twenty species of Cyathostominae were identified. The 10 most prevalent species (in sequence of prevalence) were Cyathostomum coronatum, Cylicocyclus nassatus, Cylicocyclus insigne, Cyathostomum catinatum, Cylicostephanus goldi, Poteriostomum imparidentatum, Cyathostomum labiatum, Cylicocyclus ultrajectinus, Cylicostephanus calicatus and Cylicostephanus minutus which comprised 84% of the total adult population. Twelve species showed a site preference in the ventral colon, five in the dorsal colon and only one in the caecum while two species were collected in nearly equal numbers from the ventral and dorsal colon. The number of species per horse ranged from 1 to 12 with a median of 5. Infections with singletons occurred in 12.5% of the positive horses while multiple infections were encountered in 87.5%. A positive correlation was found between the intensity of cyathostome infection and its diversity, measured either by the number of occurring species or Shanon indexes.

Summary The efficacy of orally administered moxidectin was evaluated against benzimidazole-resistant populations of cyathostomes. The mares used belonged to a herd in which the presence of benzimidazole-resistant small strongyles had been previously demonstrated. First, the mares harboring resistant cyathostomes were identified by fenbendazole treatment and egg hatch assays. The fecal samples containing the small strongly population with the highest LC50 (0.375μg/ml) were cultured in order to prepare infective doses. Thirty-six (36) mares were each experimentally infected with 10,000 resistant third stage larvae. Fifty-seven (57) days later, 30 mares were selected and randomly allocated to three groups of ten according to their fecal epg counts. One group remained untreated, one group received fenbendazole (7.5 mg/kg of body weight) and one group was treated with moxidectin 2% equine gel (0.4 mg/kg). Samples of feces were taken just before treatment and ten days after. Fenbendazole reduced the average number of cyathostome eggs by 40.7%; moxidectin reduced this number by 100%. Compared to the control group, the efficacies were 100% and 0% for moxidectin and fenbendazole, respectively. No adverse reactions to either of the drugs were observed.