Ijumba J N, Lindsay S W
Tropical Pesticides Research Institute, Arusha, Tanzania.
Med Vet Entomol. 2001 Mar;15(1):1-11. doi: 10.1046/j.1365-2915.2001.00279.x.
The high population growth rate of the African continent has led to an increased demand for food and is in danger of outstripping agricultural production. In order to meet this need, many governments have sought ways of improving food production by initiating large-scale irrigation projects, involving reclamation of arid and semi-arid areas for the cultivation of crops. Although crop irrigation promises one solution to alleviating hunger and encourages economic growth, irrigation has often been blamed for aggravating disease in local communities. Malaria is one of the major tropical diseases associated with irrigation schemes, and changes in the transmission pattern of this disease following irrigation development have been a perennial subject of debate. It has often been assumed that high numbers of malaria vector Anopheles mosquitoes (Diptera: Culicidae) resulting from irrigation schemes lead inevitably to increased malaria in local communities. However, recent studies in Africa have revealed a more complex picture. Increased numbers of vectors following irrigation can lead to increased malaria in areas of unstable transmission, where people have little or no immunity to malaria parasites, such as the African highlands and desert fringes. But for most of sub-Saharan Africa, where malaria is stable, the introduction of crop irrigation has little impact on malaria transmission. Indeed, there is growing evidence that for many sites there is less malaria in irrigated communities than surrounding areas. The explanation for this finding is still unresolved but, in some cases at least, can be attributed to displacement of the most endophilic and anthropophilic malaria vector Anopheles funestus Giles by An. arabiensis Patton with lower vectorial capacity, as the latter thrives more than the former in ricefields. Similarly, among members of the An. gambiae complex, some cytotypes of An. gambiae sensu stricto are more vectorial than others. For example, the Mopti form has high vectorial capacity and breeds perennially in irrigated sites, whereas the savanna form is often sympatric but more seasonal. Also we suggest that many communities near irrigation schemes benefit from the greater wealth created by these schemes. Consequently irrigation communities often have greater use of bednets, better access to improved healthcare and receive fewer infective bites compared with those outside such development schemes. Thus, in most cases, irrigation schemes in Africa do not appear to increase malaria risk, except in areas of unstable transmission. However, developers should take the opportunity to improve health-care facilities for local communities when planning irrigation schemes wherever they occur.
非洲大陆的高人口增长率导致对粮食的需求增加，并有超过农业生产的危险。为了满足这一需求，许多政府已设法通过启动大规模灌溉项目来提高粮食产量，这些项目包括开垦干旱和半干旱地区用于种植作物。尽管作物灌溉有望成为缓解饥饿的一种解决方案并促进经济增长，但灌溉常常被指责加剧了当地社区的疾病。疟疾是与灌溉计划相关的主要热带疾病之一，灌溉发展后这种疾病传播模式的变化一直是长期争论的话题。人们常常认为，灌溉计划导致大量疟蚊（双翅目：蚊科）必然会使当地社区的疟疾增加。然而，非洲最近的研究揭示了一幅更为复杂的图景。灌溉后媒介数量增加会导致疟疾在传播不稳定地区增加，在这些地区人们对疟原虫几乎没有或没有免疫力，如非洲高地和沙漠边缘地区。但对于撒哈拉以南非洲的大部分地区，疟疾传播稳定，引入作物灌溉对疟疾传播影响不大。事实上，越来越多的证据表明，对于许多地方来说，灌溉社区的疟疾比周边地区少。这一发现的解释仍未解决，但至少在某些情况下，可以归因于最嗜内和嗜人的疟疾媒介冈比亚按蚊被传播能力较低的阿拉伯按蚊取代，因为后者在稻田中比前者更易繁殖。同样，在冈比亚按蚊复合体成员中，冈比亚按蚊指名亚种的一些细胞型比其他细胞型更具传播能力。例如，莫普提型传播能力强，常年在灌溉地区繁殖，而稀树草原型通常与之共存但繁殖更具季节性。我们还认为，灌溉计划附近的许多社区受益于这些计划创造的更多财富。因此，与这些发展计划之外的社区相比，灌溉社区通常更多地使用蚊帐，更容易获得改善的医疗保健，并且受到的感染叮咬更少。因此，在大多数情况下，非洲的灌溉计划似乎不会增加疟疾风险，不稳定传播地区除外。然而，开发者在规划灌溉计划时，无论在何处，都应利用这个机会改善当地社区的医疗保健设施。
