Prevalence of trypanosome infections in the marine leech Johanssonia arctica off eastern Newfoundland

Abstract

A study was conducted to determine the prevalence of trypanosomal stages, indistinguishable from Trypanosoma murmanensis, in the marine leech Johanssonia arctica off eastern Newfoundland, Canada, from 1972 to 1990. Prevalence of the infection was highest between May and October, with a peak in July, and lowest during winter. The highest prevalences were also associated with a high percentage of engorged leeches in summer–autumn. Prevalence of infection in recently emerged leeches, following their first blood meal, was greater in July than at other times of the year. Similarly, the percentage of infection increased with age of the leech and was greater in summer than in winter. The number of leeches, as well as the prevalence of infection, decreased offshore. Prevalence of infection was observed to be substantially lower in saliva than in gut contents. A study of host preference on J. arctica indicated that a greater percentage of blood meals was taken from flatfish in summer; in winter, as the latter became submerged in sediment, there was a shift in feeding to eelpouts and wolffish. The prevalence of the infection was greater in fish, especially flatfish, closer to shore than in offshore areas and corresponds to the abundance of the vector. Results from the present study suggest that infections in the leech reach a peak during summer–autumn and are acquired mainly from flatfish, in which prevalence of the infection adjacent to the coast is highest.