Semifield study on prophylactic efficacy of ivermectin by intermittent medication against Dirofilaria immitis infection in dogs.

Abstract

Prophylactic efficacy of ivermectin by monthly interval medication against Dirofilaria immitis natural infection was evaluated. Thirty five mongrel dogs were used and divided into three groups of Group A, B and C in this study. All dogs were exposed to D. immitis natural infection through mosquitos for three months from July 1 to September 30 in 1984. Dogs of Group A and B were experimentally inoculated three times with every 10 of infective larvae of D. immitis, 30 of the larvae in total, per dog in July and August. Fifteen dogs of Group A were orally given ivermectin at 6 μg/kg on the first days of August, September, October and November. Fifteen dogs of Group B were given placebo on the same days as ivermectin. Five dogs of Group C were kept nontreated. Average 49.1 worms were recovered from all dogs of Group B, and the average recovery ratio of the worms recovered for the infective larvae inoculated was 163.7%. Average 33.6 worms were recovered from all dogs of Group C. The recovery numbers of Group B and C suggest that severe D. immitis natural infection occurred to dogs in this study. No worms were recovered from dogs of Group A which were given ivermectin. The results of this study showed that ivermectin prevented migration of the larvae to the right ventricle, and caused no toxic findings in this study. It is proven that monthly interval medication of ivermectin at 6 μg/kg during the period from one month after the first infection to one month after the last infection of D. immitis prevents dogs from D. immitis infection completely.