Sleeping sickness - Trypanosomiasis
Sleeping Sickness is a serious parasitic disease occurring in African countries lying between latitudes 150 north & 200 south. An increase in the number of cases has been noted in recent years notably in the southern Sudan. The parasites are known as trypanosomes hence the medical term for the infection is TRYPANOSOMIASIS. There are two forms of the disease each caused by a different sub-species of the parasite Trypanasoma brucei. One form (caused by the rhodesiense sub-species & therefore called the Rhodesian or eastern form) is an acute illness lasting up to a few weeks & occurs in eastern & southern regions, whilst the other western or Gambian form, occurring in western & central Africa, produces a long lasting, chronic disease which causes symptoms over a period of many years. If untreated most patients with either form of the disease will die or be left with irreversible brain damage.
HOW THE DISEASE IS TRANSMITTED
The parasites are transmitted to man (and other animals, notably cattle) by the bite of the tsetse fly. Sub-species of this biting fly transmit the separate sub-species of parasite; thus the tsetse fly transmitting the acute illness of eastern & southern Africa lives in vast, relatively sparsely populated savannah regions, whereas the fly transmitting chronic Sleeping Sickness lives in the humid forest areas near river banks. People are liable to be infected where they cross rivers or gather on the forested banks of rivers, watercourses or lakes to wash or collect water. Tsetse flies live on the blood of the animals they bite. They are relatively resistant to standard insect repellants & can bite through light clothing. They are attracted to bright & also very dark colours & to clouds of dust such as that kicked up by a travelling horde of animals – & moving vehicles! They tend to rest on bushes during the hottest part of the day. Fortunately for travellers they inhabit rural areas & it is most unusual for a single bite to convey infection. Trypanosomiasis is very rare in non-residents
Once inoculated by an infected fly the parasites proliferate in the blood. Fortunately most are destroyed by the host’s natural defenses, but some may manage to evade the immune system & gradually invade body organs & eventually the brain. In the acute form the bite sites becomes inflamed about a fortnight after the bite & fever develops. Scattered areas of painful skin blotches may occur & there are painful lymph gland enlargements. As the illness progresses the person becomes depressed, has trembling of the limbs, weakness, & difficulty in speaking. Drowsiness progresses to sleepiness & eventually sleep is almost constant. In the Gambian form symptoms develop only slowly starting months or even some years after the bite of the tsetse fly. Such symptoms include vague ill-health, non-specific gland swellings, personality or intellectual changes & speech problems or weakness & co-ordination difficulties suggesting nervous system disease. Diagnosis may be long delayed. Examination of blood or spinal fluid will be needed to demonstrate the presence of typanosome parasites.
PREVENTION & CURE
If treatment is started early in either form the outlook is good, but the drugs used are dangerous in themselves so very careful & skilled medical monitoring is needed. Prevention of the tsetse fly bite depends more on protective clothing, which should be of moderately heavy material & of drab colour such as khaki, than on insect repellents. Insecticide spraying of tents & camp sites may be useful as well as using permethrin impregnated mosquito nets & outer clothing. Resting under a bush from the hot sun in scrub country is asking for trouble. but in general tourist travellers are not much at risk.
There is currently no vaccine & preventive drugs remain too toxic for general use.