Morphological and taxonomic studies on mammalian trypanosomes

The present revision of the morphology, taxonomy and affinities of trypanosomes causing Surra in the Old World was undertaken in order to determine the status of the diverse geographical and hostal strains, the exact relation of which toTrypanosoma evansiand allied species was hitherto a subject of controversy. The material for this study was represented by thirty strains from diverse mammalian hosts and various countries, extending from Morocco to the Philippines. One of the problems dealt with is the occurrence of polymorphism inT. evansi. When single samples of typical (monomorphic) strains from naturally infected animals were examined, only negligible numbers of stumpy forms (0·05–0·40 %) were found in a minority of cases. But in strains kept under continuous observation for several years the proportion of stumpy forms occasionally rose higher (2–25%), while one strain exhibited a remarkable and persistent degree of polymorphism in the course of 17 years, the proportion of stumpy forms—including numerous posteronuclear ( = posterior-nuclear) ones—fluctuating from 0 to 60%. It was shown that—as in the case of theBruceigroup—the length distributions in polymorphic samples ofT. evansicould be statistically resolved into distinct curves, corresponding to the three morphological components (stumpy, intermediate, slender).