Determining Treatment to Control Two Multidrug-Resistant Parasites on a Texas Horse Farm

A study was undertaken at the Texas A&M Horse Center to evaluate and compare the effectiveness of three anthelmintics—ivermectin, fenbendazole, and a combination of ivermectin and pyrantel pamoate—on fecal egg count reductions of cyathostomes and Parascaris equorum in 30 naturally infected foals. The foals were randomized into three treatment groups, with individuals being rerandomized after each 8-week observation period. The treatments of ivermectin and fenbendazole were given at the manufacturer's recommended doses, and the pyrantel treatment was given at two times the manufacturer's recommended dose. Fecal egg counts were performed at the time of treatment and at 2-week intervals after treatment for a total of 8 weeks. Each foal received a total of three treatments during the course of the study. Fecal egg counts were performed by a modified McMaster's test, with a sensitivity of 25 eggs per gram of feces, and by the modified Wisconsin double centrifugal flotation technique, with a sensitivity of 0.2 eggs per gram of feces. Fecal egg reduction percentages were calculated. Analysis of the results showed that ivermectin, either used alone or with pyrantel, was a more effective anthelmintic for cyathostome (small strongyle) control than fenbendazole. Fenbendazole and pyrantel showed a higher initial reduction in Parascaris egg counts when compared with the ivermectin-only-treated group, but this difference lessened over time. The use of the combination treatment showed the best results for controlling both parasites, indicating that a combination of anthelmintics may be necessary to control parasites on some equine farms.     

Occurrence of anthelmintic resistant equine cyathostome populations in central and southern Italy

In the present survey, 276 horses bred on 16 farms located in central and southern Italy were investigated for the presence of drug resistant cyathostomes by a Fecal Egg Count Reduction Test (FECRT). Sixteen to 20 animals were selected on each farm and randomly assigned to one of four equally sized treatment groups. Groups were treated with fenbendazole, pyrantel pamoate, ivermectin or moxidectin. Resistance to fenbendazole was declared on six farms (37.5%) and suspected in two farms (12.5%), with FECR values ranging from 41% to 88.3%. Resistance to pyrantel was found in two farms (12.5%) and was suspected in one case (6.2%), with FECR values ranging from 43% to 85.4%. Macrocyclic lactones remained effective on all farms. Only cyathostome third stage larvae (L3) were found in fecal cultures after treatment. This paper reports the first wide survey conducted in Italy for anthelmintic resistance in equine cyathostomes. The results indicate that multiple drug resistant equine cyathostomes are present in the central and southern regions of Italy. These data call for a geographically and numerically broader investigation of horse farms in all regions and for the development and implementation -among veterinarians, owners and managers of a plan to reduce the expansion of these anthelmintic resistant populations and control these important parasites.