Effects of milbemycin D on adult Angiostrongylus cantonensis in rats.

Effects of milbemycin D against adult Angiostrongylus cantonensis in rats were examined. The first-stage larval counts in rat faeces (larvae per gram of faeces per female worm recovered, LPG/female) were most conspicuously reduced in the group treated with nine consecutive weekly doses of 5.0 mg/kg. The effect was more marked in the group treated with five or ten successive daily doses of 5.0 mg/kg than the group treated with a single dose of 25.0 or 5.0 mg/kg. Host lung-body weight ratio and number of recovered worms were reduced significantly only in the group treated with five or ten successive daily doses of 5.0 mg/kg. These results suggest that the action of milbemycin D on the reproductive system of the worms might be differentiated from its killing action. The in vitro motility of females recovered from rats medicated with nine consecutive weekly doses of 5.0 mg/kg was inhibited, and almost all females and males were semitransparent and colourless. Results obtained from sectioned worms showed little content in their digestive tracts and uteri. In addition, there were few eggs and first-stage larvae in the lung tissues of treated rats. These suggest that milbemycin D affects the reproductive functions of the worms through an indirect mode of action including paralysis and inhibition in food intake and energy and/or synthetic metabolism.