Changes in Behaviour in the Intermediate Hosts of Trematodes

Abstract

Dr. Lewis and Dr. Wright (see previous communication) are to be congratulated on emphasizing an extremely interesting point which has hitherto attracted little, if any, attention—namely, that infestation with larval trematodes can alter the behaviour of the intermediate hosts. Dr. Lewis found that whereas a large percentage of the Simuliumhe reared from pupæ collected in the Rio Guarapiche were infested with larval trematodes, those he collected in the same area biting man were uninfested. The authors suggest that the parasites may affect the brain (on which they often press) in such a way that these flies are no longer able to bite man. It is also possible that the presence of these relatively large parasites near the brain renders them sluggish and unwary, so that they fall an easy prey to predators in general and the definitive host in particular.