African Trypanosomiasis (Sleeping Sickness) – Characteristics and History
African trypanosomiasis, or “sleeping sickness,” is a fatal disease caused by a protozoan hemoflagellate parasite, the trypanosome. It is transmitted through the bite of a tsetse fly, a member of the genus Glossina. Sleeping sick-ness is endemic, sometimes epidemic, across a wide band of sub-Saharan Africa, the so-called tsetse belt that covers some 11 million square kilometers. Although the disease was not scientifically understood until the first decade of the twentieth century, it had been recognized in West Africa as early as the fourteenth century.
Chemotherapy to combat trypanosomiasis has remained archaic, with no significant advances made and, indeed, very little research done between the 1930s and the 1980s. How-ever, in the mid-1980s field trials of a promising new drug demonstrated its efficacy in late-stage disease when there is central nervous system involvement. In addition, there have been ex-citing recent developments in the field of tsetse eradication with the combined use of fly traps and odor attractants.
An acute form of sleeping sickness caused by Trypanosoma brucei rhodesiense with a short incubation period of 5–7 days occurs in eastern and southern Africa. A chronic form (Try-panosoma brucei gambiense) of western and central Africa can take from several weeks to months or even years to manifest itself. There are many species of tsetse flies, but only six act as vectors for the human disease. The Glossina palpalis group, or riverine tsetse, is responsible for the transmission of T. b. gambiense disease. The Glossina morsitans group, or savanna tsetse, is the vector for T. b. rhodesiense, the cause of the rhodesiense form of sleeping sick-ness. Although tsetse flies are not easily infected with trypanosomes, once infected they remain vectors of the disease for life.
After being bitten by an infected fly, most victims experience local inflammation, or the trypanosomal chancre; parasites migrate from this site to multiply in blood, lymph, tissue fluids, and eventually the cerebrospinal fluid. The blood trypanosome count oscillates cyclically, with each successive wave, manifesting different surface antigens. In this manner, trypanosomes evade the antibodies raised against them by the host. Eventually, all organs are invaded, with central nervous system involvement, ultimately leading to death.
The epidemiological pattern of sleeping sick-ness varies considerably from place to place, but two features are well recognized. First, trypanosomiasis is exceptionally focal, occur-ring at or around specific geographic locations; and second, the number of tsetse flies is apparently not as important for disease incidence as is the nature of the human-fly contact.
The focal nature of sleeping sickness means that the ecological settings in which it occurs are of vital importance for understanding its epidemiology. Seemingly impossible to destroy, many historical foci tend to flare up in spite of concentrated eradication efforts since the 1930s. Very often, villages and regions that were affected decades ago remain problem areas to-day. The disease involves humans, parasites, tsetse flies, and wild and domesticated animals, and increasing population movements have complicated the epidemiology. Tsetse species have varying food preferences, ranging from the blood of wild and domestic animals to that of humans, but they require a daily blood meal, thereby making a single fly potentially highly infective.
Gambiense sleeping sickness is classically a disease of the frontier of human environments, where human-created habitat meets sylvan biotope. Humans are the principal reservoir of T. b. gambiense, and they maintain the typical endemic cycle of the disease. It is now known, however, that some animals, including domestic pigs, cattle, sheep, and even chickens, can act as reservoirs. The key to understanding the gambiense form is its chronicity and the fact that there are usually very low numbers of parasites present in the lymph and other tissue fluids. Gambiense disease can be maintained by a mere handful of peridomestic flies – that is, those that have invaded bush or cultivations near human settlements. This is known as close human-fly contact.
Riverine G. palpalis are most commonly found near waterways and pools; during dry seasons, when humans and flies are brought together through their shared need for water, the flies become particularly infective. Other common foci for the disease are sacred groves, which are often small clearings in the forest where the high humidity allows the flies to venture farther from water sources.
The virulent rhodesiense sleeping sickness is a true zoonosis maintained in wild animal reservoirs in the eastern African savannas. In the case of T. b. rhodesiense, the usual mammalian hosts are wild ungulates, with humans as adventitious hosts. Transmission of rhodesiense disease is more haphazard and directly relates to occupations such as searching for firewood, hunting, fishing, honey gathering, poaching, cultivation, cattle keeping, and being a game warden or a tourist. Whereas the gambiense form of the dis-ease is site related, the rhodesiense form is occupation related, which helps to explain why the latter characteristically affects many more men and boys than women and girls. However, when a community moves near bush infested with infected flies, the entire population is at risk.
The animal reservoir of trypanosomes is an important factor in the epidemiology and his-tory of sleeping sickness. It is well established that the trypanosomiases are ancient in Africa. Indeed, it is conjectured that the presence of sleeping sickness may explain why the ungulate herds of the African savanna have survived human predators for so long; the wild-animal reservoir of trypanosomes firmly restricted the boundaries of early human settlement. Al-though the wild ungulate herds became trypo-tolerant, domestic cattle still succumb to the disease, and the vast majority of research and funding has been aimed at solving the problem of animal – not human – sleeping sickness.
In evolutionary terms, the presence of trypanosomes in Africa may have precluded the development of some ground-dwelling faunas, thus encouraging certain resistant primates, including the early ancestors of humankind, to fill the empty ecological niches. If so, then humans were exposed to trypanosomal infection at the time of their very remote origin. The parasites are on the whole poorly adapted to humans, which accounts for the variety of clinical symptoms and ever-changing epidemiological patterns. A perfectly adapted parasite does not kill its host – at least in the short run.
An estimated 50 million people in 42 countries are at risk for trypanosomal infection, while it is estimated that only about 5 million to 10 million people have access to some form of protection against or treatment for the disease. Sleeping sickness is endemic across the wide band of sub-Saharan Africa known as the “tsetse belt” lying roughly between 20◦ north and 20◦ south of the equator, where it also can attain epidemic proportions.
The actual number of cases will never be known, as it is a disease of remote rural areas, and even today people in such places of-ten die undiagnosed and uncounted. Most national statistics are grossly underreported, with the World Health Organization being notified of about only 10 percent of new cases. The cur-rent estimate of incidence is 20,000 to 25,000 cases annually. Most of the victims are concentrated in Zaire, Uganda, and southern Sudan. Some villages had infection rates of up to 25 percent. In the late 1970s and 1980s, severe outbreaks occurred in Cameroon, Angola, the Central African Republic, the Ivory Coast, and Tanzania, as well as in Sudan, Zambia, Uganda, and Zaire.
Although trypanosomiasis has been studied for more than 80 years, much is still unknown about the pathology of the disease. Three phases follow the bite of an infected fly: first the chancre itself; then the hemolymphatic or “pri-mary stage”; and finally the meningocephalitic or “secondary stage.” On average, people in-fected with T. b. gambiense live 2–3 years before succumbing, although there are recorded cases of infection spanning as much as 2 decades. In contrast, infection with the more virulent T. b. rhodesiense, if untreated, usually leads to death within 6–18 weeks.
The disease manifests a bewildering array of clinical symptoms, which can vary from place to place. Progressing through the two stages, there is increasing parasitemia with eventual involvement of the central nervous system. clinical symptoms can include fever, headache, and psychiatric disorders such as nervousness, irascibility, emotionalism, melancholia, and insomnia, which reflect neuronal degeneration. Other symptoms include loss of appetite, gross emaciation, sleep abnormalities, stupor, and the characteristic coma from which sleeping sickness derives its name. Some of the initial symptoms of sleeping sickness are also characteristic of early malaria, which can make differentiation between the two diseases difficult in the field. A common, easily recognizable symptom is swelling of lymph nodes. An-other common symptom is called “moon face,” an edema caused by leaking of small blood vessels. A most common complication during trypanosomiasis is pneumonia, which is a frequent cause of death. The chronic ambience form can take as long as 15 years to develop after the victim has left an endemic area.
The prospect of a vaccine for human trypanosomiasis is bleak. The phenomenon of “antigenic variation” greatly reduces the prospect of producing an effective vaccine, and at present very little research is under way on vaccine development.
The history of sleeping sickness in Africa is long and complex, and its complicated ecology has dramatically affected demographic patterns in sub-Saharan Africa. The parameters and density of human settlement have been limited in many regions until the present time, while cattle-keeping has been prevented across vast regions of the continent, thereby seriously affecting the nutrition of entire populations.
The “African lethargy,” or “sleepy distemper,” as trypanosomiasis has been called, was well known to Europeans in West Africa from as early as the fourteenth century, through good descriptions given by Portuguese and Arab writ-ers. For centuries slave traders rejected Africans with the characteristic swollen cervical glands, for it was common knowledge that those with this symptom sooner or later died in the New World or North Africa. As European exploration and trade along the West African coast increased between 1785 and 1840, the disease was reported in Gambia, Sierra Leone, and western Liberia, whereas between 1820 and 1870 it was also commonly noted along the Liberian coast.
Certainly the disease was an important factor in the history of colonial Africa. In the beginning, colonial administrators were concerned mainly with the health of Europeans and those few Africans in their service. But the threat of epidemics of sleeping sickness eventually forced colonial authorities to take much more seriously the health of entire African populations.
In those colonies affected by sleeping sickness, medical services often developed in direct response to this one disease, which resulted in the development of “vertical” health service – programs aimed at controlling a specific disease while neglecting other crucial public health issues. As recently as the 1970s, the World Health Organization urged developing countries to move toward “hori-zontal” health services that take into ac-count the multifactoral nature of disease and health.
Sleeping sickness, along with malaria and yellow fever, played an important role in the development of the new specialties of parasitology and tropical medicine. In 1898, Patrick Manson, the “father of tropical medicine,” published the first cogent discussion of the new scientific discipline. He explained that tropical diseases were very often insect-borne parasitical diseases, the chief example being trypanosomiasis.
Trypanosomiasis at the time was very much on the minds of colonial officials. In the decade between 1896 and 1906, devastating epidemics killed more than 250,000 Africans in the new British protectorate of Uganda, as well as an estimated 500,000 residents of the Congo basin. Understandably, the new colonial powers, including Britain, France, Germany, Portugal, and King L´eopold’s Congo Free State, perceived sleeping sickness to be a grave threat to African laborers and taxpayers, which in turn could dramatically reduce the utility of the new territories. Moreover, the fears were not limited to the continent of Africa; the British also speculated that sleeping sickness might spread to India, the “jewel” of their empire.
Thus ensued one of the most dramatic campaigns in the history of medicine, as scientific research teams were dispatched to study sleeping sickness. They began with the Liver-pool School of Tropical Medicine’s expedition to Senegambia in 1901 and the Royal Society’s ex-pedition to Uganda in 1902; other expeditions followed until World War II.
Many of these were sent by new institutions especially designed to investigate the exotic dis-eases of warm climates. The British, for example, opened schools of tropical medicine at Liverpool and London in 1899, while other such schools came into being in Germany, Belgium, France, Portugal, and the United States. This new field of scientific endeavor offered the opportunity for bright young men to gain international acclaim and a place in the history of medicine.
It should be noted that sleeping sickness was not the only disease to receive such attention as Europeans sought to establish themselves permanently in regions of the globe where health conditions were difficult and mortality was high. There were major discoveries by Man-son, who was the first to demonstrate insects as vectors of human disease (filariasis); and by Ronald Ross, who found that the malaria para-site was transmitted by the Anopheles mosquito. Yet, despite the fact that endemic malaria was probably the cause of far more morbidity, the trypanosomiases attracted much attention in the new field of tropical medicine for the next 2 or 3 decades.
International meetings were convened to dis-cuss sleeping sickness, beginning with one at the British Foreign Office in 1907. As the number of “tryps” specialists increased, sleeping sickness became a key factor in the international exchange of research findings in tropical medicine. The Sleeping Sickness Bureau was opened in London in 1908 to facilitate communication of research findings on all aspects of the disease. Its work continues to the present time.
After World War I and the formation of the League of Nations’ Health Organization (the antecedent of the World Health organization), two major conferences in 1925 and 1928 were convened to focus on African sleeping sickness. These conferences, following the pat-tern of the nineteenth-century sanitation and hygiene conferences, sought international collaboration and cooperation in implementing public-health solutions. In Africa, special re-search centers on tsetse flies and sleeping sickness appeared in many colonies including Uganda, Kenya, Tanganyika (now Tanzania), Belgian Congo (Zaire), Nigeria, Ghana, and French Equatorial Africa (Chad, Central African Republic, Congo-Brazzaville, and Gabon). Sleep-ing sickness thus became an important catalyst for cooperation among the colonial powers in Africa, which in turn aided the rapid growth of tropical medicine as a field. In fact, sleeping sickness early in the twentieth century attracted international attention to Africa with an urgency that was repeated in the early 1980s with AIDS.
Response to the disease occurred within the private sector as well. Concerned at the possible loss of increasingly important African markets, the European business community encouraged and sometimes initiated research into tropical diseases. For example, the principal founder of the Liverpool School of Tropical Medicine in 1899 was the influential and powerful capital-ist Alfred Lewis Jones, chairman of a Liverpool-based shipping line that plied a lucrative trade along the West African coast. The businessman shared the imperialist’s dismay at the potential devastation that could be caused by sleeping sickness, and together they were keen to support attempts to prevent the decimation of African populations.
The politics of colonialism often reflected contemporaneous perceptions of the epidemiology of sleeping sickness. By 1900, for example, it was widely accepted that the disease had been endemic in West Africa for centuries but had only recently begun spreading into the Congo basin and eastward.
From the earliest days of colonial settlement, it was not uncommon to blame sleeping sick-ness for the abandoned villages and depopulated regions that Europeans encountered during their push into the interior. It usually did not occur to the intruders that in many cases Africans were withdrawing from areas because of the brutal nature of colonial conquest. Half a century would pass before researchers began to examine the deeper socioeconomic and political causes of the dramatic changes in the African disease environment that had resulted in the spread and increased incidence of sleeping sickness.
Medical experts at the turn of the nineteenth century tended to favor the theory of circumstantial epidemiology, which held that diseases were spread mainly through human agency within specific sets of circumstances. Because of a lack of effective treatments, the principal methods of control of epidemic dis-ease consisted of segregation or isolation and disinfection with acrid smoke or strong fumes such as sulfur and vinegar. Disease was perceived as an invader to be demolished. This view accounts for much of the imagery and idiom of war used in early public-health campaigns. A major adjunct to this theory was the belief that once the circumstances had been identified, most diseases in Africa could and would be controlled, even eliminated, with techniques and technology developed in Europe. The European colonials assumed they would succeed where Africans had failed and that they would transform the continent by conquering the problems of tsetse and the Trypanosoma, among others. Most colonists believed that much of the backwardness they saw in African society was attributable, at least in part, to endemic diseases such as sleeping sickness.
Powerful notions of the potential of Western technology for solving health problems in Africa, sleeping sickness among them, have survived until quite recently. Rarely, if ever, did colonial authorities consider the possibility that Africans not only possessed some ideas about the ecology of sleeping sickness but had gained fairly effective control of their environment. An example of one such African strategy was the warnings to early European travelers not to travel through certain regions during daylight hours when tsetse flies were active and might infect their transport animals. Moreover, throughout the tsetse-infested regions, there were instances of African residence patterns that allowed coexistence with the ubiquitous tsetse flies yet avoided population concentrations conducive to epidemic outbreaks. European colonizers, by contrast, often disrupted – or destroyed – indigenous practices and survival strategies with the result that endemic sleeping sickness spread and sometimes became epidemic with disastrous effects.
The colonial powers, however, held their own version of the history of sleeping sickness and its evolution. Prior to their arrival, ancient, in-tractable foci of the disease had existed in West Africa and in the Congo basin around which, from time to time, the disease would flare into epidemic proportions. Colonials believed that it really began to spread only after the European newcomers had suppressed local wars and slave raiding among African peoples and established law and order. This in turn allowed many Africans, for the first time ever, to move freely and safely away from their home regions. protected by Pax Brittannica, Pax Belgica, and the like, the increased movements of Africans carried sleeping sickness from old endemic foci to new populations. There was some basis for this hypothesis, especially in West Africa such as in Ghana and Rukuber of Nigeria. This widely accepted notion of the spread of sleeping sickness had an important consequence in the enormous effect expended by the Europeans in trying to regulate African life at every level, and especially to limit strictly any freedom of movement.
John Ford, a British entomologist who spent more than 25 years researching sleeping sick-ness, was one of the first to challenge this “classical view” of the pacification of Africa and the spread of the disease. He argued that it was not the pacific character of European colonization but, on the contrary, its brutal nature, that greatly disrupted and stressed African populations. In particular, the balanced ecological relationships among humans, tsetse flies, and trypanosomes were disrupted by European activities with the result that endemic sleeping sickness flared into epidemic proportions. Vivid examples of the results of such ecological upheaval were the sleeping sickness epidemics in Uganda and the Congo basin that had killed hundreds of thousands.
Epidemics continued throughout much of the colonial period, especially prior to World War II, when there were serious outbreaks in both West and East Africa. Public-health regulations to control the disease affected other areas of administration. In some colonies, sleeping sick-ness programs became so extensive and bureaucratic that they came into conflict with other departments, exacerbating competition for scarce staffing and financial resources within colonial administrations. In addition, sleeping sickness regulations were often responsible for confrontations between the private and public sectors as members of the former were increasingly hindered in their attempts to exploit the people and resources of Africa.
Two major patterns emerged in the colonial campaigns against sleeping sickness. In one, the focus was on tsetse eradication, whereas in the other, the focus was on the medicalization of victims. Most campaigns were a combination of features from both approaches. Within this framework, national variations emerged in the colonial campaigns. The British took a more broadly ecological approach to control of the disease, whereas the French and the Belgians took a more “medical” approach to the problem of human infection. British policy was to break the chain of sleeping sickness transmission by separating people from flies. Thus, while British administrators implemented social policies aimed at protecting people from disease, the scientific community, especially the new entomologists, searched for solutions to the “tsetse fly problem” in Africa. The compulsory mass resettlement of Ugandans, which probably helped save lives, from lakeshore communities in Buganda and Busoga in 1908, and the huge Anchau (northern Nigeria) scheme begun in 1936 are good examples of breaking transmission chains. Likewise, in some regions where it was ecologically feasible, Belgians resettled groups of people such as those along the Semliki River in eastern Congo.
Unfortunately, in the context of recently conquered and colonized Africans, who had rural subsistence economies and whose culture and tradition were intricately linked to locale, compulsory relocation sometimes had calamitous effects on those it was meant to protect. In the Belgian Congo an extraordinary amount of legislation and effort was directed at the control of populations in relation to sleeping sickness. It is not surprising that many Africans regarded sleeping sickness as the colonial disease be-cause of the sometimes overwhelming amount of administrative presence it elicited.
French and Belgian efforts were directed chiefly at “sterilizing the human reservoir” of trypanosomes through mass campaigns of medicalization, or injections. To achieve this, they conducted systematic surveys of entire populations, hoping to locate, isolate, and treat all victims. Eug`ene Jamot, a French parasitologist, developed this method in Ubangui-Chari (French Equatorial Africa) and later introduced it in affected parts of Cameroon and French West Africa. In 1916, he organized an ambitious sleeping sickness campaign based on mobile teams, which systematically scoured the country for victims of the disease to be injected.
A grid system was devised to ensure complete surveys, and the mobile teams worked with true military efficiency. Between July 1917 and August 1919, more than 90,000 individuals had been examined, and 5,347 victims were identified and treated. Jamot’s design for a sleep-ing sickness service was soon adopted by the Belgians in the Congo, and by 1932 there were five such teams operating annually in northern Congo alone. Admirable as it was for its sheer scale of organization, the policy of mass medicalization did not affect the fundamental ecology of the parasites; indeed, this approach had the effect of removing the store of antibodies from humans that had been built up through long contact with the parasites.
Sterilization of the human reservoir was made possible in 1905 when the first trypanocidal drug became available in the form of an arsenical compound, atoxyl. Discovered by the German chemist Paul Ehrlich and adapted for use with sleeping sickness by Wolferstan Thomas of the Liverpool School of Tropical Medicine, atoxyl, alone or in combination with other compounds, remained the only chemotherapy for 2 decades. Atoxyl was toxic for 38 percent of patients, with dreadful side effects suffered by those whom it did not kill out-right, among them the blinding of 30 percent of those injected. Later, new drugs – suramin (1916-20), tryparsamide (1919–25), and pentamidine (early 1940s) – came into use for early-stage rhodesiense and gambiense disease. Another most problematic arsenical with serious side effects, including up to 5 percent mortality, was and is used for second-stage disease. This drug, melarsoprol (along with suramin and pentamidine), has remained the drug of choice since the 1940s.
In the early 1960s, which saw independence for many African territories, colonial rulers concurred that human sleeping sickness was under control in Africa. But political upheavals, accompanied by the breakdown of medical infrastructures and large-scale population displacements, once again seriously affected the epidemiology of the disease. Some countries – Zaire, Uganda, Sudan, and Ivory Coast, for instance – witnessed epidemics of sleeping sickness, and it has been estimated that by 1969 there were up to 1 million victims in the Congo alone.
Tsetse flies and the trypanosomes that cause sleeping sickness will continue actively to shape the future of humankind in Africa. Because the most effective means of control is continual and thorough surveillance, present-day health planners and administrators must be aware of the history of this disease and the ease with which that history can repeat itself.