Rhodnius prolixus

Abstract

A study was undertaken to determine whether T. congolense was strictly a plasma parasite as had been concluded by HORNBY (1952). Recent investigations by GOODWIN (1970) and Losos and IKEDE (1970) have shown that T. brucei leaves the blood vessels and invades various tissues of laboratory and domestic animals, where it causes extensive mononuclear inflammatory cell reaction. If Hornby's conclusions are valid it would mean that the pathogenesis of the disease caused by T. congolense differs significantly from that produced by T. brucei. 24 East African Zebu cattle were infected intravenously with metacyclic forms of trypanosomes. 19 animals were killed in extremis after an average course of disease of 78 days SD ~ 20. Post mortem examination was carried out immediately after death. 5 animals were examined during chronic stages of disease at 129 and 169 days after infection. In the 19 animals examined in extrernis large numbers of trypanosomes were found only in the blood vessels, particularly in the capillaries and venules of the brain, heart, and skeletal muscles. In 2 of the 5 chronic cases were trypanosomes occasionally found in the blood vessels of the brain. It appears that T. congolense is a strict plasma parasite which localizes in the microcirculation of certain tissues. Anaemia, emaciation, and cachexia were the changes observed. In 60 % of the animals a focal polioencephalomalacia developed affecting the most dorsal cerebral gyri. It was postulated that this lesion was due to the accumulation of trypanosomes in the cerebral circulation. The myocarditis, encephalitis, cellulitis, and lymphadenitis, which are commonly observed in the disease caused by T. brucei, were not observed.