The leech as a vector of a fish piroplasm

Abstract

A piroplasm, Haemohormidium beckeri, is redescribed from two marine fish, Lycodes lavalaei and Lycodes vahlii (Zoarcidae). The parasite divided by both binary fission and schizogony. In the latter process, up to eight merozoites were produced and these developed within mature erythrocytes. Infections were prevalent among fish from areas off the Labrador coast. Parasitemias, which varied from light infections to estimates of 60 parasites/1000 erythrocytes, were recorded in 15 fish for about 6 months. Subinoculation of infected blood initiated infections in two perciform fish, Myoxocephalus octodecemspinosus and Anarhichas lupus, but not in a pleuronectiform, Pseudopleuronectes americanus, or a gadiform, Gadus morhua. Natural infections were present in three leeches, Platybdella olriki, that had fed on an infected L. lavalaei. Piroplasms were also observed in the gastrointestinal content of all 94 laboratory-reared leeches, Johanssonia arctica, dissected 7 through 109 days after engorgement on infected fish blood. Inoculations of gut contents from leeches after digestion of a blood meal produced infections in uninfected fish. Natural transmission occurred when leeches were fed again on susceptible fish, whereas pipetting entire leeches into the stomach of fish did not initiate infections. This is the first evidence that leeches transmit piroplasms in nature to fish.