Control of sleeping sickness due to Trypanosoma brucei gambiense*

Bulletin of the World Health Organization, 60 (6): 821-825 (1982) Control of sleeping sickness due to Trypanosoma brucei gambiense* A UNDP/WORLD BANK/WHO CONSULTATION' Sleeping sickness due to Trypanosoma brucei gambiense is endemic in 23 African countries and an estimated 45 million people are exposed to infection. The relatively low incidence of the disease (about 10 000 new cases each year) is mainly a result of50years of regular medical surveillance and treatment in combination with tsetse control where indicated and possible. The present article considers the significant developments in research in the field and assesses the impact of these findings on techniques used in the control of the disease. The World Health Organization has recently established an action programme for sleeping sickness control to organize and coordinate medical surveillance, treatment of infected individuals, and vector control activities. Among its objectives, the programme aims to provide support for national control services in the form of technical expertise, training of staff, and provision of newly developed equipment for diagnosis and treatment. The programme is also closely associated with the research activities supported by the UNDP/ World Bank/WHO Special Programme for Research and Training in Tropical Diseases. Sleeping sickness due to Trypanosoma brucei gambiense is endemic in 23 African coun- tries (Fig. 1) and an estimated 45 million people are at risk of infection. With approxi- mately 10 000 new infections a year, the disease may appear to be a health problem of only moderate importance, but this low incidence is the result of 50 years of regular medical surveillance and treatment, in combination with tsetse control where indicated and possible. Despite many pressing health problems, national health services continue to give priority to trypanosomiasis control. It is estimateda that US$ 5 million are spent annually on sleeping sickness surveillance and vector control operations. Nevertheless, only 6 million people are covered by medical surveillance programmes. Lack of funds and skilled personnel are major constraining factors at both national and international levels and the high costs of surveillance and tsetse control operations are beyond the financial resources of most health departments. Long-term solutions, involving permanent removal of tsetse habitats by appropriate use of land, require economic invest- ment and technical skills, which, as yet, can be mobilized only in exceptional circum- stances. DISTRIBUTION AND PREVALENCE The prevalence of sleeping sickness and the priority accorded to it vary considerably in the different endemic countries. The occurrence of the disease is unpredictable and is not restricted to any particular region. In some countries, resurgence of the disease in several * Requests for reprints should be addressed to Chief, Trypanosomiases and Leishmaniases, World Health Organization, 1211 Geneva 27, Switzerland. A French translation will be published in a later issue of the Bulletin. ' This article is based on the report of a Consultation held in Brazzaville, 1-4 July 1980, under the sponsorship of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases. I WHO Technical Report Series, No. 635, 1979 (The African trypanosomiases: report of a joint WHO Expert Committee and FAO Expert Consultation) pp. 89-92. 4234 -821- UNDP /WORLD BANK /WHO CONSULTATION Fig. 1. Principal foci of sleeping sickness in Africa. foci has been reported. All foci, whether stable or expanding, represent a threat to adjacent areas, where conditions are often favourable for transmission. Many of the foci are located in moist savanna, preforest, and forest areas, where climatic and geographical conditions may hamper systematic surveillance, early treatment of the population, and vector control operations. The sahelian drought which occurred on the northern limits of Glossina distribution may have reduced the number of reported cases, while the tsetse control measures in Nigeria, directed at controlling animal trypanosomiasis by spraying of riverine habitats, had a marked effect also in reducing human disease. MEDICAL SURVEILLANCE AND TREATMENT Sleeping sickness control relies on either "passive" case detection in health centres as part of their routine tasks, or "active" case detection by mobile teams specially trained to diagnose sleeping sickness by clinical and parasitological techniques. Throughout the region, staff formerly occupied solely with sleeping sickness are being incorporated into polyvalent mobile teams. In spite of the accepted need for constant vigilance in surveillance, even in the low endemic areas, logistic constraints, in particular vehicle maintenance and the high cost of fuel, have meant that a number of residual foci have not been surveyed for many years. Diagnosis Parasitological diagnosis has been improved by the use of the microhaematocrit technique, particularly when the buffy coat is examined with dark ground illumination using a special microscope objective. The most sensitive parasitological technique is the recently developed miniature anion exchange centrifugation method, which involves 822 SLEEPING SICKNESS DUE TO T. B. GAMBIENSE separation of the parasites from the red blood cells by filtration and subsequent centrifu- gation. Serological methods of diagnosis are not widely used in surveillance, but countries with access to centres with serodiagnostic facilities do apply, to a limited extent, indirect fluor- escent antibody test procedures. Two new serological tests have been developed recently: the indirect haemagglutination test, which is now produced commercially, and the card agglutination test for trypano- somiasis, which is still in the experimental phase. These tests have been designed as rapid, sensitive, and simple diagnostic tools for use in the field by relatively untrained personnel. The techniques are now undergoing large-scale field trials to assess their suitability for wide application by public health services. Treatment As yet, no major progress has been made in research on treatment. Systematic chemo- prophylaxis with pentamidine is used in only a few countries, and resistance to the drug has been reported in some areas; in two countries, clinical evidence has suggested resistance to melarsoprol. Detailed clinical studies on the pharmacodynamics and incidence of side- effects are being undertaken, which should lead to more rational use of currently available drugs. VECTOR CONTROL In general, it is not practicable to eradicate the vectors of gambiense sleeping sickness since areas cleared of the fly are rapidly reinvaded from nearby infested areas. Vector control, therefore, should aim to reduce man-fly contact and hence transmission of the disease. Efficient insecticide campaigns are difficult and expensive to organize and execute, and cheaper methods, such as the use of traps and clearing of vegetation by local people are preferable. The ecology of Glossina spp. varies from place to place and extensive surveys should be carried out in the particular area where control is envisaged before deciding on the specific approach to be used. Trapping Promising results have recently been obtained using biconical traps (Challier/ Laveissiere) impregnated with decamethrin for the control of riverine Glossina; fly densities were reduced by over 90%. This method is cheap and easy to apply, and carries no risk of pollution or toxicity for the members of the community. Alteration of habitat Prior to the development of insecticides, the clearing of riverine vegetation played a major role in the control of gambiense sleeping sickness in several endemic areas. Even today, much could be achieved by instructing local people on the role of tsetse in the trans- mission of the disease and by encouraging them to clear the types of vegetation known to harbour the fly. 823 UNDP/ WORLD BANK/WHO CONSULTATION Ground application of residual insecticide formulations Insecticides can be applied to the resting sites of Glossina by workers with knapsack or other types of spraying equipment. Knowledge of the ecology of flies in the areas to be treated can allow highly selective treatment of the vegetation. Insecticide deposits should persist for at least two months; DDT and dieldrin have been the most widely used compounds. Aerial application of insecticides Helicopter techniques have been developed for the application of residual and non- residual insecticides to riverine foci using very low dosages, thus minimizing pollution and killing of non-target organisms. However, the technique has not been effective in wetter areas, such as the forest savanna mosaic areas of the Ivory Coast. The studies have empha- sized the need for research on meteorological variables as well as new insecticide formu- lations before embarking on large-scale trials. The sequential application of aerosols of insecticides such as endosulfan from fixed- wing aircraft has been used to control populations of savanna species of Glossina, but is not appropriate for general use against vectors of gambiense sleeping sickness, which usually occupy very humid areas. Aerial application should be reserved for emergency situations where immediate inter- ruption of the transmission cycle is needed. This technique can rapidly achieve a considerable reduction in the fly density, but only exceptionally does it provide a long-term solution. WHO ACTION PROGRAMME ON SLEEPING SICKNESS CONTROL The World Health Organization has recently established an action programme on sleep- ing sickness control to organize and coordinate medical surveillance, treatment of infected individuals, and vector control activities. Among its objectives, the programme aims to provide support for national control services, in the form of technical expertise, training of staff, and provision of equipment. The control tools currently available need to be improved and simplified for application in rural health centres. This may require a reduction in technical quality, but it is accepted that expanded surveillance should take precedence over high local detection rates. In the short term it is planned to produce manuals on medical surveillance and tsetse control, and to distribute test kits for diagnosis and treatment. A central technical service will be established to coordinate the services, to replenish the contents of the kits, and to update the manuals when necessary. Trypanosomiasis kits for diagnosis and treatment The kits are intended for use by both mobile and stationary health teams. The rate at which they will be distributed will depend on the total number and capacity of the medical units that are operational in the endemic foci. The exact figure will be obtained from a detailed analysis by the participating national health services. According to preliminary estimates, approximately 10 000 kits will eventually be distributed. There will be two types of diagnostic kit: the first is for screening purposes and is intended for use only by the peripheral medical units and mobile teams; the second 824 SLEEPING SICKNESS DUE TO T. B. GAMBIENSE contains equipment and reagents necessary for parasitological confirmation of diagnosis in the case of a positive serological result. The second kit also contains limited equipment for emergency situations and is intended for isolated rural units with limited access to hospital laboratories, and for the reinforcement of hospital laboratories and mobile teams. Any patient with a positive result in the preliminary tests should be referred to the district hospital or other designated treatment centre, where a detailed examination should be carried out. Fairly extensive laboratory facilities will be required in these centres, including a good quality microscope, equipment for examination of the cerebrospinal fluid, and an adequate supply of drugs. Treatment should be administered only in the larger district or regional hospitals under the supervision of a medical officer. Appropriate facilities, such as an isolation room and supportive equipment, should be available, particularly for patients with a reactive encephalopathy. Only when exceptional circumstances prevent transport to an appropriate hospital would the use of melarsoprol be acceptable in the rural medical centres. A small amount of melarsoprol is included in the treatment kit for use in these cases. Delivery system Since almost 80% of the population of most developing countries live in rural areas, it is necessary that an efficient delivery system be established from the outset. The delivery system should be adapted to the existing infrastructure and to the disease characteristics in the country. Where services already exist for trypanosomiasis control, they should organize the delivery of the test kits. RESEARCH IN PROGRESS Research on sleeping sickness is carried out under the auspices of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases. One aspect of this work is to try to acquire a better understanding of disease epidemiology in the different affected zones. Investigations are being carried out in two T. b. gambiense areas (the Congo and Upper Volta/Ivory Coast) and one T. b. rhodesiense area (Zambia). The studies include a search for animal reservoirs, improvement of parasite characterization techniques, and elucidation of transmission cycles. The recently developed parasite characterization techniques using isoenzyme methods have made it possible to define the characteristics of parasites in man and in potential reservoir hosts. Pigs and dogs in Liberia and Ivory Coast have been found to be infected with organisms similar to those circulating in man in the area and recent studies carried out in Upper Volta have indicated that kobs and hartebeest were also potential hosts of parasites infective for man. Moreover, this work has been aided by the discovery that Mastomys natalensis (the multimammate rat) can be used as a host for isolating stocks of the Trypanozoon subgenus. Experimental studies on transmission of Trypanozoon by Glossina have shown that physiological interference by parasites in infected flies affects their feeding behaviour. The fact that infected flies feed more frequently and more voraciously than uninfected ones may have important epidemiological implications. 825