The The trypanosomiases are amongst the most serious of the so-called 'neglected tropical diseases' . In the 1980s, American trypanosomiasis (Chagas disease, due to Trypanosoma cruzi) was believed to infect over 24 million people  with another 100 million considered at risk, although these estimates have since been reduced (Fig. 1). Chagas disease can be fatal in its early acute stage, but more usually progresses to a debilitating chronic phase - affecting up to 30% of those infected - involving severe cardiac lesions and, with some strains, intestinal lesions resulting in the so-called 'mega-syndrome' of severe intestinal dilations. Because of these debilitating effects, the World Bank  ranked Chagas disease as by far the most serious of the parasitic diseases affecting Latin America, with a social and economic impact far in excess of even the combined impact of other diseases such as malaria, leishmaniasis and schistosomiasis. By contrast, African trypanosomiasis (Sleeping Sickness) is invariably fatal if untreated, with the gambiense form generally causing a chronic disease leading to fatal sequelae after some years, and the more acute rhodesiense form often leading to death in just a few months. But the suite of closely-related animal trypanosomiases transmitted by tsetse in Africa (including T. b. brucei, T. vivax, T. congolense, and T. simiae) have an even greater impact, denying livestock over vast areas, and affecting agricultural production both directly and indirectly by limiting the use of draught animals for transport and ploughing. The World Health Organization currently estimates some 300,000 cases of human Sleeping Sickness , while the economic cost of animal trypanosomiasis in Africa has been estimated at US$4.75 billion per year . American and African trypanosomiases are difficult to treat, and vaccines are unavailable. Two drugs - benznidazole and nifurtimox - can be used to treat Chagas disease, but they are currently only used in the acute stage or early chronic stage of infection, and both can cause severe side effects, sometimes life-threatening. Nifurtimox can also be used to treat gambiense Sleeping Sickness, although a range of other drugs is more widely used (Table 1). None is ideal, and the most widely used - melarsoprol (sometimes described as "a mixture of arsenic and antifreeze") - Published: 1 August 2008 Parasites & Vectors 2008, 1:24 doi:10.1186/1756-3305-1-24
Received: 2 July 2008 Accepted: 1 August 2008 This article is available from: http://www.parasitesandvectors.com/content/1/1/24 2008 Schofield and Kabayo; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Parasites & Vectors 2008, 1:24 http://www.parasitesandvectors.com/content/1/1/24 tends to be lethal for up to 10% of those treated. Other drugs are used to treat livestock, but tend to be expensive for African farmers, and show increasing problems of drug-resistance and drug-counterfeiting . In both continents therefore, vector control is of crucial importance in trypanosomiasis control.
The vectors of these trypanosomiases - Triatominae (kissing bugs) in Latin America, Glossinidae (tsetse-flies) in Africa - are very different insects, but share certain characteristics that render them highly vulnerable to available vector control methods. Both are slowly-reproducing - often described as K-strategists in the terminology of MacArthur & Wilson  - and so have a limited capacity to repopulate areas where their abundance has been reduced. Moreover, their demographic strategies tend to lead to reduced genetic variability within each vector population, limiting their capacity to respond to vector control interventions through selection of new attributes such as insecticide-resistance . No tsetse population has yet been selected for insecticide resistance, and amongst Triatominae only one focus of limited resistance was detected in Rhodnius prolixus in Venezuela during the 1970s, with some pyrethroid resistance now also being found amongst some Triatoma infestans populations in southern Bolivia and northwestern Argentina [9,10]. Control of American trypanosomiasis (Chagas disease)
Chagas disease was first described by Brasilian clinician Carlos Chagas in 1909. Remarkably, Chagas not only described the causative agent, Trypanosoma cruzi, with most of its life-cycle and clinical features, he also described its vectors and some small animal reservoirs, and was amongst the pioneers - with Jos Pellegrino and Emmanuel Dias - in attempts to control it. The parasite, and vector species of Triatominae, are widely distributed in the Americas from the Great Lakes of northern USA to southern Argentina, generally in a silvatic cycle of transmission involving small nest-building animals such as opossums, armadillos, and various species of rodent. In much of Latin America however, species of Triatominae have adapted to live in the cracks and crevices of rural dwellings, emerging at night to feed on the sleeping occupants. While feeding, they may defaecate the remains of their previous bloodmeal, so that if infected, the parasites in the bug faeces can pass to the human host - especially across the mucosa of eye, mouth, or nose. As Carlos Chagas observed, since the bugs live in the cracks of poorquality rural homes, then improving the houses should make them less suitable for the bugs, and house improvement programmes remain an important component of Chagas disease control in many areas. By the 1940s, attempts were also being made to eliminate domestic Tri-atominae by spraying kerosene over house walls, and even using military flame-throwers. But synthetic insecticides proved more effective (and less hazardous). Organochlorines such as BHC (lindane) and dieldrin were widely used until being progressively replaced by synthetic pyrethroids during the 1980s.
The human trypanosomiases - Chagas disease in Latin America, Sleeping Sickness in Africa - may be eliminated as major public health problems within the next decade or so. In Latin America, the campaigns have focused primarily on vector control - elimination of domestic vector populations by indoor insecticide spraying - although the strategy is now changing to give additional emphasis to detection and treatment of new cases that may occur as a result of adventitious silvatic Triatominae entering houses . In Africa, Sleeping Sickness control relies primarily on case detection and treatment, although it is increasingly recognised that operational advances will more likely be sustained where vector control is also carried out effectively. But for the African animal trypanosomiases, that contribute so much to poverty, underdevelopment, and food insecurity, tsetse elimination is now seen as the primary approach for the long-term. And in both continents - Latin America and Africa - accumulating experience is showing that large-scale elimination of vector populations is feasible, and more likely to be sustainable in the face of changing circumstances and priorities. Comparing the two situations, both before and after the current initiatives, may be premature in the light of ongoing interventions, but seems to reveal a series of key features that may be conducive to success. Of paramount importance is the political mandate, giving legitimacy to large-scale interventions, and greatly assisting - although by no means guaranteeing - the continuity of action required. This has been relatively weak for the Latin American initiatives, and requires constant reaffirmation as national policies change. It is stronger for the PATTEC initiative, and the mandated requirement for annual reporting to the AU Heads of State and Government provides regular opportunities for reaffirmation in the light of progress achieved. The political mandate also influences resource allocation, both in operational funds and the executive personnel who implement the control interventions. It is noteworthy that - so far - almost all funding for the current trypanosomiasis control initiatives, both in Latin America and in Africa, has come from national governments - either from national budgets or repayable loans. Of parallel importance is the academic and research community. Where this is strong in some countries of Latin America, it has greatly helped to promote continuity of control interventions, as well as assisting in problem-solving and in programme monitoring and evaluation. Where it is weak however, or disconnected from the control programmes, it can be a distraction and hindrance . The indication is that academia should be prepared to work closely with the vector control services, such that their activities will be mutually complementary, but with both working to ensure continuity of intervention and effective monitoring of progress. Of particular importance is that the research responds to the practical needs of the control programmes, rather than pursuing untried - and generally unneeded - technical innovations. The importance of the political mandate and of the academic community is perhaps equally relevant for the control of any vector-borne disease, but for the trypanosomiases one further factor is of crucial importance. For both African and American trypanosomiasis, the vectors are exquisitely vulnerable to currently available control techniques. The low reproductive rates and limited genetic variability of tsetse and of Triatominae essentially restrict their ability to respond to the changing circumstances imposed by available control interventions . This cannot be said of many other vectors, and should be a key factor heralding the long hoped for success.
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