Catching tsetse

When did we relate tsetse to trypanosomiasis?

African cattle owners learned long ago from experience, that there was a link between biting flies and the spread of trypanosomiasis or nagana in their stock. The link between the tsetse fly and trypanosomiasis was first formally established by David Bruce working in what is now KwaZulu-Natal, South Africa.

David Bruce
David Bruce was born in Melbourne, Australia, but grew up in Britain and joined the British army’s medical service. In 1894, Bruce was sent to Natal to investigate an outbreak of nagana in northern Zululand.

David Bruce gave a vivid description of nagana:

"The horse stares, he has a watery discharge from his eyes and nose. Shortly afterwards a slight swelling of the belly and puffiness of the sheath may be noticed, and the animal falls off in condition. The hind extremities also tend to become swollen; and these various swellings fluctuate, one day being less marked, or having disappeared. During this time the animal is becoming more and more emaciated, he looks dull and hangs his head, his coat becoming harsh and thin in places; the mucous membranes of the eyes and gums are pale, and probably slight cloudiness of the cornea is observable. In severe stages, a horse presents a miserable appearance. He is a mere scarecrow, covered by rough hair, which falls off in places. His hind extremities and sheath may be more or less swollen, sometimes to a great extent, and he may become blind. At last he falls to the ground and dies of exhaustion. During his illness he has shown no symptoms of pain, and up to the last days has had a good appetite."

Bruce undertook bacteriological and microscopic examinations of affected oxen and noticed motile, vibrating organisms in their blood. He demonstrated formally that these organisms caused nagana by inoculating blood from infected cattle into healthy horses and dogs. The test animals developed the symptoms of nagana and large numbers of trypanosomes could be seen in their blood.

Bruce went on to show that healthy cattle and dogs sent into tsetse-infested areas acquired this same blood parasite in their blood and became ill, suggesting that nagana was identical to the ‘tsetse fly disease’. A survey of the wild animals in the tsetse-infested area showed that the trypanosomes were in these animals too, leading Bruce to suggest that the disease could be controlled by destroying the wild hosts (Bruce, 1896).

While the link between tsetse and trypanosomiasis was elucidated rapidly, Bruce thought initially that the parasite was transmitted mechanically by tsetse. The existence of a developmental cycle within the fly followed after a further 15 years of research (Bruce et al., 1909).

Sleeping sickness
Some of the earliest descriptions of sleeping sickness come from what is now Mali. Travellers recognized the symptoms of the disease but were not aware of its link with tsetse flies. Aldo Castellani is credited with formally identifying trypanosomes as the cause of sleeping sickness (Castellani, 1903).

Trout and trypanosomes
The first description of a trypanosome was made by Gabriel Valentin from the University of Bern in Switzerland. He observed an organism in the blood of a trout and published his observations in 1841. To this day, many tsetse entomologists retain an interest in trout.

References
Bruce, D. (1896). Further report on the tsetse fly disease or nagani in Zululand. Harrision and Sons, London

Bruce, D., Hamerton, A.E., Bateman, H.R. & Mackie, F.P. (1909). The development of Trypanosoma gambiense in Glossina palpalis. Proceedings of the Royal Society (series B) 81, 405-414.

Castellani, A. (1903). On the discovery of a species of Trypanosoma in the cerebrospinal fluid of cases of sleeping sickness. Proceedings of the Royal Society 71, 501-508.