Efficacy of doramectin against eyeworms (Thelazia spp.) in naturally and experimentally infected cattle.

The anthelmintic efficacy of doramectin was assessed for the control of Thelazia spp. in two studies using 44 naturally or experimentally infected calves. Cattle were randomly assigned based on weight to either a doramectin treatment group or a saline control group. Treated animals received doramectin at a dosage of 200 micrograms kg-1, subcutaneously in the lateral midline of the neck. Control animals received an equivalent dosage of 0.9% sterile saline. Animals were slaughtered 13-16 days after treatment and all eyes and associated tissues (including the lacrymal glands and ducts) were removed and examined for total number, species and viability of eyeworms. Two species of eyeworms, Thelazia skrjabini and Thelazia gulosa were found in the control group of naturally infected calves. Only T. skrjabini was found in the control group of experimentally infected calves. No eyeworms were found in any doramectin-treated animal. The efficacy of doramectin against Thelazia spp. in both naturally and experimentally infected calves was 100%.