COMPARATIVE EFFICACY OF MOXIDECTIN 2-PERCENT EQUINE ORAL GEL AND IVERMECTIN 2-PERCENT EQUINE ORAL PASTE AGAINST ONCHOCERCA-CERVICALIS (RAILLIET AND HENRY, 1910) MICROFILARIAE IN HORSES WITH NATURALLY ACQUIRED INFECTIONS IN FORMOSA (ARGENTINA)

On the basis of positive skin snips for Onchocerca cervicalis microfil ariae (MF), 45 horses were chosen from 48 in a total of 257 screened o n 12 locations in the northeast Province of Formosa (Argentina), and r andomly assigned to two treatment groups of 20 horses each, and a nont reated control group of five horses. On Day 14 post-treatment (PT), sk in snip samples in the ivermectin-treated (0.2 mg/kg) group were negat ive for normal viable microfilariae (MF), while horses in the control group maintained their pretreatment level of infection. On the same Da y in the moxidectin-treated (0.4 mg/kg) group, 18 horses were negative for MF, but the remaining two had a total of 1 and 2 MF, respectively (equivalent to 10 and 20 MF/g of skin), but all three parasites showe d marked cuticular and structural damage. Both horses were negative in a repeat biopsy on Day 21. From Day 3 PT, one ivermectin-treated hors e (5%) evidenced an approximate 15 x 2 x 3 cm-sized, apparently nonpai nful, oedematous swelling on the ventral midline, 20 cm in front of th e navel, which remained unchanged on Day 14 PT. Adverse reactions were not observed in the moxidectin-treated group. Parasitaemia was found in 18.7% of sampled horses (48 of 257), and the number of MF varied be tween 10-1820/g of skin snip <((x)over bar 172)>). Similar prevalence and total counts had been described previously in 1985 and 1986 in cat tle-farm horses in the same area of Argentina. in surveys in Texas (19 74) and Louisiana (1995) in the USA, infection rates were also similar . but total counts much higher. It is concluded that moxidectin 2% equ ine oral gel and ivermectin 2% equine oral paste, were equally 100% ef fective in the control of O. cervicalis MF. Contrary to ivermectin, mo xidectin did not cause post-treatment dermal reactions. (C) 1997 Elsev ier Science B.V.