Haycraft’s seminal discovery of hirudin was followed a
century later by the discovery of other antihemostatic
agents in leech saliva: platelet-aggregation inhibitors,
coagulation inhibitors and destabilase. It is doubtful,
however, whether the known antihemostatic armamentarium
of H. medicinalis saliva can account for the prolonged
bleeding observed after a leech feed. Munro et
a196 examined the blood oozing from a leech bite.
During the first minute after the leech had dropped off,
whole blood clotting time, thrombin clotting time, and
prothrombin time were elevated, and ADP- and thrombin-
induced aggregation were inhibited. Coagulation
parameters and aggregation reverted to normal within
15 min. In our work, we found that hirudin and the PAF antagonist were washed away in the blood oozing
from a leech bite in the course of 20 min, and that activated
partial thromboplastin time, which was elevated
at first, reverted to normal (Rigbi et al manuscript in
preparation). Nonetheless, bleeding continued for
hours. It has been suggested that vasodilation in the
vicinity of a leech bite97*98a nd calin may contribute to
this phenomenon. Notwithstanding the important role
of known antihemostatic agents, most of which are
unavailable commercially, the prolonged bleeding from
a leech wound, i.e. delayed clot formation, makes a
strong case for leech therapy in situations such as those
mentioned here. Indeed, the use of leeches in both the
lay and medical communities is growing.