Control of Ticks Systemically with Merck MK-933, an Avermectin13

Merck MK-933 (7-\[[2,6-dideoxy-4- O -(2,6-dideoxy-3- O -methyl-α-L- arabino -hexopyranosyl)-3- O -methyl-α-L- arabino -hexopyranosyl]oxy]-3’,4’,5’6,6’,7,10,11,14,15,17a,20,20a,20b-tetradecahydro-20,20b-dihydroxy-5’,6,8,19-tetramethyl-6’-(1-methylpropyl)spiro[11,15-methano-2 H ,13 H ,17 H -furo[4,3,2- pq \]\[2,6\]benzodioxacyclooctadecin-13,2’-[2 H ]pyran]-17-one), an avermectin given orally to cattle daily by capsule, was highly effective in preventing engorgement and reproduction of adults of six species of three-host ticks—Amblyomma americanum (L.), A. cajennense (F.), A. maculatum Koch, Dermacentor andersoni Stiles, D. variabilis (Say), and Rhipicephalus sanguineus (Latreille)—and all parasitic stages of a one-host species— D. albipictus (Packard)—at dosages of >50 μg/kg per day. A daily subcutaneous injection of 10 μg/kg per day afforded complete control, but a similar injection of 5 μg/kg per day was not completely effective. MK-933 formulated as sustained-release tablets or boluses designed to release ca. 50 μg/kg per day was also effective, but the sustained-release devices eroded at rates higher or lower than those anticipated. The activity of this chemical at such low dosage levels makes it an excellent candidate as an acaricide for the control of ticks systemically.