ARS | Publication request: Persistent efficacy and blood sera analysis of a long-acting (LA) formulation of moxidectin against Rhipicephalus (Boophilus) microplus on treated cattle

Submitted to: Livestock Insect Worker's Conference Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: June 17, 2010
Publication Date: N/A

Interpretive Summary: The persistent efficacy of a single subcutaneous injection of a 10% long-acting (LA) injectable formulation of moxidectin administered at a concentration of 1 mg per kg of body weight was determined against Rhipicephalus (Boophilus) microplus (Canestrini). In addition, the concentration-time sera profile was determined in treated cattle. The engorgement weight, egg mass weight, and IF (reproductive capacity) of engorged female ticks recovered from treated animals infested at weekly (7-day) intervals between 14 and 63 day post-treatment were significantly lower than for ticks on untreated animals, while the number of ticks per animal recovered from treated cattle remained significantly lower than that of untreated cattle for up to 49 day post-treatment. The percentage control remained > 99% against larvae infested on treated cattle at weekly intervals between 14 and 49 day post-treatment, which is the required level of control for an acaricide to be considered for use in the U.S. Cattle Fever Tick Eradication Program. The sera concentration of moxidectin in treated cattle increased to 25.6 ppb within 1 day after treatment, and peaked at 47.3 ppb at 8 day post-treatment. Moxidectin sera levels remained above the estimated 100% threshold level for elimination of feeding ticks (8 ppb) for 44 day after treatment. The control and sera concentration data obtained in the study supported the label claim of the product of 50 day of prevention against re-infestation. Based on the results obtained in the study, cattle could be treated at 66 day intervals with minimal risk of viable ticks detaching from treated animals. This treatment interval would be 4.5-fold longer than the presently required treatment interval of 14 day, thereby reducing gathering and handling costs associated with the treatment of cattle, which is normally incurred by producers, by approximately 75%.

Technical Abstract: The therapeutic and persistent efficacy of a single subcutaneous injection of a long-acting (LA) formulation of moxidectin at a concentration of 1 mg per kg of body weight were determined against Rhipicephalus (Boophilus) microplus (Canestrini), along with the concentration-time blood sera profile in treated cattle. The therapeutic efficacy against ticks of all parasitic stages on the cattle at the time of treatment was > 99.9%, and the mean tick number, index of fecundity (IF), engorgement weight, and egg mass weight of ticks recovered from treated animals were all significantly lower than ticks from untreated animals. The IF (reproductive capacity), engorgement weight of females, and egg mass weight of ticks recovered from treated animals infested at weekly (7-day) intervals between 14 and 63 day post-treatment were significantly lower than for ticks on untreated animals, while the number of ticks per animal recovered from treated cattle remained lower than that of untreated cattle for up to 49 day post-treatment. The percentage control remained > 99% at weekly intervals between 14 and 49 day post-treatment, which is the level of efficacy required for use in the U.S. Cattle Fever Tick Eradication Program. The serum concentration of moxidectin in treated cattle increased to 25.6 ppb within 1 day after treatment, and peaked at 47.3 ppb at 8 day post-treatment. Moxidectin sera levels remained above the estimated 100% threshold level for elimination of feeding ticks (5-8 ppb) for 44-53 day after treatment. The label claim of 50 day of prevention against re-infestation for the LA moxidectin formulation used in the study was supported by the control and sera concentration data obtained. Based on these results, cattle could be treated at 66 day intervals with minimal risk of viable ticks detaching from treated animals. This treatment interval would be 4.5-fold longer than the presently required treatment interval of 14 day, thus reducing gathering and handling costs, incurred by producers, by approximately 75%.