Efficacy and Blood Sera Analysis of a Long-Acting Formulation of Moxidectin Against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) on Treated Cattle

Abstract

The therapeutic and persistent efficacy of a single subcutaneous injection of a long-acting formulation of moxidectin at a concentration of 1 mg/kg body weight was 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 cattle at the time of treatment was >99.9%, and the mean tick number, index of fecundity, engorgement weight, and egg mass weight of ticks recovered from treated animals were all significantly lower than ticks from untreated animals. The index of fecundity, engorgement weight of females, and egg mass weight of ticks recovered from treated animals infested at weekly (7-d) intervals between 14 and 63 d posttreatment were significantly lower than for ticks on untreated animals, whereas the number of ticks per animal recovered from treated cattle remained lower than that of untreated cattle for up to 49 d posttreatment. The percentage control remained >99% at weekly intervals between 14 and 49 d posttreatment, which is the minimum level of efficacy considered acceptable for use in the United States Cattle Fever Tick Eradication Program. The serum concentration of moxidectin in treated cattle increased to 25.6 ppb (parts per billion) within 1 d after treatment, and peaked at 47.3 ppb at 8 d posttreatment. Moxidectin sera levels remained above the estimated 100% threshold level for elimination of feeding ticks (5-8 ppb) for 44-53 d after treatment. The label claim of 50 d of prevention against reinfestation for the long-acting moxidectin formulation used in the study was supported by the efficacy and sera concentration data obtained. Based on these results, cattle could be treated at 63-d 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 d, thus leading to approximately 75% reduction in gathering and handling costs of cattle incurred by producers.

Experimental oral delivery of the systemic acaricide moxidectin to free-ranging white-tailed deer (Artiodactyla: Cervidae) parasitized byAmblyomma americanum(Ixodida: Ixodidae)

“…Moxidectin was not detected in one animal captured on 3 June 2021 (15 days exposed) and in 2 on 3 July 2021 (45 days exposed), likely new arrivals to the site around the time of capture. Our capture success was lower in 2022 (15 captures) and mean moxidectin sera levels lower than in 2021, but 100% of 11 sera samples from white-tailed deer captures at the time of treated corn distribution were within or above the 5-8 ppb threshold reported to be the minimum ivermectin level required for control of feeding ticks on cattle (Nolan et al 1985, Miller et al 1999) and white-tailed deer (Pound et al 1996), and for moxidectin in cattle (Davey et al 2011) (Table 1). For both years combined, 24 of 29 (83%) white-tailed deer captures that occurred during the time of moxidectin-treated corn distribution were at or well above the 5-8 ppb threshold.…”

“…Avermectins have been delivered to cattle to treat endo- and ectoparasites for decades (Drummond et al 1981, Davey et al 2011). Because these efforts were successful, oral acaricide delivery to white-tailed deer was evaluated since they act as secondary hosts for cattle parasites and often range adjacent to and within pastures, a potential source of live tick reintroduction.…”