An extravascular site of development of Trypanosoma congolense

Abstract

TSETSE-TRANSMITTED African pathogenic trypanosomes are thought to be divisible into two groups because of their distribution in the mammalian host and the characteristic lesions they produce during infection¹. Trypanosoma brucei brucei and related subspecies have a wide distribution in the body, parasitising the intercellular fluids, connective tissue and parenchymatous tissues, and the fluids of body cavities^2–4, whereas T. vivax and T. congolense are considered to be strictly plasma parasites, confined to the circulatory system^5,6. It has been shown, however, that local skin reactions develop at the sites of bites of tsetse flies infected with T. congolense, and fluid expressed from reaction sites contains trypanosomes several days before they can be detected in the peripheral blood^7–9. We have recently examined the development of T. congolense in local reactions and give evidence here from light and electron microscopy that the trypanosomes develop in connective tissue. The multiplication and persistence of trypanosomes at the site of infection have important implications in relation to immunogenesis and might also play a part in the pathogenesis of the ensuing disease and the efficiency of chemotherapy.