The leech as a tool for studying comparative haematology

Abstract

The bite of the North American leech Macrobdella decora results in much less prolonged bleeding in fish (8 min; control = 1 min) and amphibians (11.5 min; control = 1.5 min) than in mammals (humans) (73 min; control = 6 min). Coagulation of blood flowing from leech bite wounds is initially prolonged in frogs (4.3 min; control = 2 min) and humans (5.8 min; control = 2.5 min), but gradually returns to normal during the first 10 min after the termination of feeding. Although duration of feeding is similar in fish (mean = 62 min), amphibian (mean = 79 min) and human (mean = 68 min) hosts, the gain in body weight of leeches feeding on fish (mean = 11%) and amphibians (mean = 14%) is much less than those feeding on humans (mean = 58%). Bleeding in a frog heavily infected with the intrathrombocytic yeast Thrombocytozoons ranarum was abnormal from control incisions (>20 min) and from a leech bite wound (>140 min) suggesting impairment of thrombocyte function. This comparative approach to leech — host haematology offers a methodology into understanding the biological context in which the leech antithrombin (hirudin) evolved, as well as the evolution of vertebrate haemostatic mechanisms.