Efficacy of ivermectin in hookworms as examined in Ancylostoma caninum infections.

Single oral doses of ivermectin were given to dogs with moderate or heavy infections ofAncylostoma caninum (egg counts ranging from 7,100 to 41,700 eggs/g feces) at 100, 50, 30, or 10 ,g/kg body weight. Each of these dosages was effective in clearing the infection completely, so that numerous worms were passed in the feces on days 1-3, but no worm was recovered from the intestinal tract at necropsy on day 4 after treatment. In contrast, an average of 178 worms per dog was recovered at necropsy from the vehicle-treated control and the untreated animals. Albendazole, a known anti-hookworm agent, even in a dose of 400 mg, eliminated only 21-65% of the worms harbored by the infected animals. No untoward reaction to ivermectin or significant pathological change was noted in the experimental animals. In vitro experiments demonstrated that ivermectin: (1) was highly detrimental to actively motile adult worms in concentrations greater than 5.60 Ag/ml; (2) was detrimental to eggs inside the uterine tissue of female worms in dosages at or greater than 10 ,ug/kg body weight; and (3) killed infected larvae in concentrations as low as 0.0025 ,ug/ml. Hookworm infections are prevalent in many African, South American, and Asian countries (Anonymous, 1981), and the number of people afflicted in China is estimated to reach 250 million (Wang, 1987). The anthelmintics commonly employed at present, including albendazole and pyrantal pamoate, are not efficient, as repeated dosages or courses of treatment are usually required to clear infections. Furthermore, untoward side-reactions are not uncommon. Ivermectin is a derivative of avermectin Bl, one of a group of naturally occurring substances produced by an actinomycete, Streptomyces avermitilis. This anti-parasitic agent has been found effective against a variety of nematode infections of animals, including those caused by Toxocara canis, Toxocara leonina, Trichuris vulpis (Anderson and Roberson, 1982), and Dirofilaria immitis (Campbell and Blair, 1978). Aziz et al. (1982) found it highly effective against human onchocerciasis. Reports concerning the effect of ivermectin in hookworm infections were contradictory. Anderson and Roberson (1982) reported satisfactory results in animal ancylostomiasis. However, Rajasekariah et al. (1986) found it unsatisfactory for Necator americanus in hamsters, and Aziz et al. (1982) and Diallo et al. (1985) found it either ineffective or not fully effective in human neReceived 25 May 1988; revised 28 December 1988; accepted 13 January 1989. * Institute of Antiparasitic Diseases, Sichuan Academy of Medical Sciences, Sichuan Province, People's Republic of China. catoriasis. Further studies concerning this agent in hookworm infections are thus indicated. The present communication reports the efficacy of ivermectin in experimental hookworm infections of Ancylostoma caninum in dogs and its detrimental effects in vitro on living adult worms, eggs, and infective larvae. MATERIALS AND METHODS Ivermectin preparation Ivermectin used in this study was IVOMEC? (manufactured by MSD AGVET, Inc., Barceloneda, Puerto Rico, lot 41262, date of expiration May 1987) and was supplied by Drs. C. E. Courtney and Q. Y. Zeng of the University of Florida, Gainesville. It was a clear solution containing 1% ivermectin, 40% glyceroformol, and propylene glycol, q.s. ad 100%, and was for use in cattle by subcutaneous injection. It was freshly diluted with gum tragacanth to appropriate concentrations before use.