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Title: Efficacy and blood sera analysis of a long-acting formulation of moxidectin against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)on treated cattle

Author
item Davey, Ronald
item Pound, Joe
item Klavons, Jerome
item Lohmeyer, Kimberly - Kim
item Freeman, Jeanne
item Perez De Leon, Adalberto - Beto
item Miller, Robert

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2010
Publication Date: 3/2/2011
Citation: Davey, R.B., Pound, J.M., Klavons, J.A., Lohmeyer, K.H., Freeman, J.M., Perez De Leon, A.A., Miller, R. 2011. Efficacy and blood sera analysis of a long-acting formulation of moxidectin against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) on treated cattle. Journal of Medical Entomology. 48(2):314-321.

Interpretive Summary: When cattle fever ticks are detected on premises in the U.S. most producers choose to vacate the premises rather than maintain and treat the cattle on the premises every 14 days for 6-9 months, as required by law, because of the excessive costs associated with gathering and handling animals. However, the increased involvement of white-tailed deer in maintaining and dispersing cattle fever ticks in infested pastures where cattle have been removed has caused an impediment to the eradication of these pests. To provide incentive to producers to maintain and treat cattle on infested premises, there is a critical need for treatment strategies that provide persistent activity against cattle fever ticks so that the interval between treatments can be extended, while still achieving eradication of the ticks. A long-acting moxidectin formulation was tested and found to provide >99% effective against ticks on the treated cattle at the time of treatment and against ticks infested on the cattle for up to 49 days after treatment. Moxidectin levels remained above the estimated 100% kill rate of ticks for 45 days after treatment. These results demonstrated that intervals between treatments with this product could be extended to 63 days apart without risk of having viable ticks detach from treated cattle. This treatment interval would reduce gathering and handling costs associated with treatment of animals by 75%, as compared to the presently require 14 day treatment interval.

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 week y 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 resu~ts, 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%.