Invasive Species Compendium

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Abstract

The life-cycle of Trypanosoma cobitis Mitrophanow 1883.

Abstract

The morphology and development of Trypanosoma cobitis during its life-cycle in the blood of 6 species of fish from the river Lee, UK, and also in its invertebrate vector, the leech Hemiclepsis marginata, are described. After entry into the crop of H. marginata during feeding on infected fish, the trypanosomes underwent morphological changes: epimastigotes predominated in the middle period of blood digestion and the appearance of long slender metacyclics in the crop coincided with the final digestion of the blood. The metacyclic trypomastigotes, which were first seen in the proboscis sheath 5 days after feeding, did not divide and were maintained by division of the epimastigote crop forms. In fish, the slender trypomastigotes increased in length from 11.5 mu m 24 hours after infection, to a maximum of 32 mu m after 7 months. The course of infection was an initial high parasitaemia, followed by a gradual decrease in numbers, although trypanosomes were still detectable 10 months after infection. The absence of pleomorphism in infections resulting from a single leech feed indicates that the occurrence of this phenomenon in wild-caught infected fish is a result of several infections of various durations.