Death from a Fly

Posted by Patrick Patton on November 23, 2012 at 12:13 pm | Filled Under: Flies| Comments Off

PERCHED precariously astride a flying buttress of rock jutting out from the edge of the Muchinga Escarpment in Northern Rhodesia, I gazed out over the Luano Valley to the Mwepwe Hills, while the evening sun threw great shadows across the folds and contours of what is virtually a southern continuation of the Great Rift Valley which runs the length of the African continent. My companion handed me the binoculars and pointed out away in the distance the small bare brown patches, hand-cleared out of the bush, that told their own story. This was tsetse country and the strips of open ground were tiny areas laboriously reclaimed from the surrounding tsetse-ridden thickets. This vast sweep of thickly forested valley was only an infinitesimal part of an afflicted landscape denied to man simply because of the presence of a small brown fly.

In spite of advances in science, bio-chemistry, surgery and medicine, the problems of disease and starvation remain, and the most elusive of all man’s foes are the insects that carry the disease and cause the starvation. Insects, of which there are more than 700,000 known species, are respon­sible for one half of all human deaths; and there are 100,000 different species in Africa south of the Sahara, the most abundant of all living things inhabiting this great continent. More destructive than the elephant, more dreaded than the beasts of prey, the tsetse fly ranges over an area equal to twice that of the United States, and in Northern Rhodesia alone inhabits 85,000 square miles, roughly one third of her territory.

Great Rift Valley

Appalled by the extent of the problem and fascinated by the variety and ingenuity of the counter-measures in force, I had committed myself to a journey of over 5000 miles through Northern Rhodesia to learn more of this little-publicized campaign. Thanks to the kindness and co­operation of the Department of Veterinary Services and Tsetse Control and the unfailing patience of the tsetse supervisors them­selves, I was able to see for myself what was being done.

Principally known and feared as the carrier of trypanosomiasis or `sleeping sickness’ in man and of bovine trypanosomiasis or `tryps’, as it is commonly called, in cattle, horses and dogs, there are, as I discovered, twenty-two kinds of tsetse fly. Here in Northern Rhodesia four species have been found, but the main infestation is caused by two varieties, Glossina morsitans, the most widespread, and Glossina pallidipes, each favouring a different terrain, al­though in suitable localities the latter can be found superimposed on the former. It was a long time before entomologists and scientists established the fact that the dis­ease borne by the fly was not due merely to its bite, but to the introduction of a parasite from the fly to the man or animal bitten. The tsetse fly cannot drink water and can take no other food than blood. In feeding, it sometimes in­gests small parasitic animalcules, called trypanosomes, which com­plete their life cycle inside the body of the fly, so that after some weeks the tsetse becomes infective to other host animals, whose resist­ance to the trypanosomes varies greatly: some, like the baboon, cannot be infected at all; many, like the croco­dile, are tolerant to the only trypanosomes that can infect them; and some, like man, are immune to most kinds of trypanosomes but are killed by others.

male_tsetse_fly

Once seen, the tsetse is comparatively easy to recognize. It is little bigger than the average house-fly, with unmistakeable scissor-like wings and a neat triangle or hatchet cell formed by the veins on either wing. Unique among insects, it does not lay eggs but hatches out a living larva.

A veterinary assistant charges his syringe with a trypanocidal drug. Most inoculation is done by Africans under European supervision

Although its dangers have long been known, it is only within the last decade or so that any really effective measures have been evolved to eradicate the fly. A hundred years ago, when David Livingstone was making his epic journey along the course of the Zambesi, a trader might lose every ox in his team to the tsetse fly, while at the turn of the century in Uganda 200,000 people died from sleeping sickness in five years.

From the human standpoint, the presence of tsetse is of vital importance, because where there are human beings there are also cattle, and in most fly-belts it is these domestic animals that succumb; in an increasing number of fly-belts too the man-killing trypanosomes occur. They are not nearly so deadly today as they once were, because with increased medical knowledge and new drugs, sleeping sickness can almost always be cured if it is treated sufficiently early; it is also usually possible to break much of the contact between man and fly so that no new cases occur, as only one in several hundred flies normally carries the trypanosomes of human sleeping sickness.

tsetse fly

I learnt that tryps can be spread in various ways. Cattle may stray into a tsetse area and be bitten by infected flies. Traffic from tsetse areas into clean areas can bring a few flies onto a farm; before they die, which they will do, as tsetse can­not live in unsuitable conditions, they will infect several beasts. Human settlement in itself is of the greatest value in the fight against the fly, not only as an aid to its ultimate elimination, but also to consolidate gains already made. Uninhabited country is liable to be invaded by tsetse from neighbouring populated areas. In land that is being used for agricultural purposes, however, the ecological conditions are generally so changed that tsetse are unable to exist and the danger is lessened. Tsetse can also be found on meat, dried fish, tobacco, blankets and even on the backs of cyclists. They will also attach them­selves readily to moving objects such as cars or lorries, as I found to my cost, and be carried many miles from their usual haunts. Cattle already infected will sometimes stray from one farm to another and spread tryps, while game, especially elephant, moving about the country or disturbed from its normal haunts, sometimes wanders from fly-belts onto farms carrying with it a few tsetse.



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