Contractile activity and motility responses of the dog heartworm Dirofilaria immitis to classical anthelmintics and other compounds

A variety of compounds including classical anthelmintics and avermectin analogs were screened for their effects on movements of adult heartworms (HW) (Dirofilaria immitis). Contractile activity was measured by tension recording of spontaneous movements of intact HW coil preparations (6 min compound exposure) and motility was evaluated by observation of spontaneous, free movements in culture (3 and 7 days compound exposure). Results for female HW indicated that some compounds caused spastic paralysis of contractile activity and inhibition of motility in culture (bephenium, DL-tetramisole, and pyrantel); some caused only spastic paralysis of contractile activity (methyridine and disophenol); and some caused only inhibition of motility in culture (chlorpromazine, dithiazanine, 1-ethoxycarbonylmethyl-1-methylpyrrolidinium, and 4-methyltropolone). Effects on motility in culture appeared to be lethal. The following compounds lacked effects: amprolium, 2-amino-2-thiazoline, bithionol, bitoscanate, bitriben, hexachlorophene, ivermectin, and 10 H-phenothiazine. A group of avermectin analogs was screened for effects only on motility in culture of both adult female and male HW. Several of the analogs affected motility, but the effects appeared to be non-lethal. Microfilaria release into the culture media was suppressed by two of the analogs (an aglycone and avermectin B2). The HW maintenance system used in the present study facilitated screening of compounds for effects on this parasite.