Epidemiology in the strategies for malaria control

A rapid overview is presented of the evolution of the main orientations of malaria control, since the discovery of mosquito transmission. Stated control objectives appear to have oscillated between expectations to eradicate the vector, or at least the disease, and more modest approaches to minimise the effects of the infection. High optimism was raised when a new control measure, or new combination of existing measures, appeared to be highly effective and was expected to have universal applicability. The implementation of large scale campaigns eventually found the limits of applicability of the proposed strategy and the exaggerated expectations soon gave way to disillusion and, eventually, to a revival of research. The longest and most impacting period of exaggerated expectations was the global malaria eradication campaign of the 1950s and 1960s, which completely disregarded the study of local epidemiology, considering that all it was needed was to know if an area was "malarious" or not. Research was practically abandoned and, even when reinstated after the recognised failure of the campaign, it has retained an almost exclusive orientation towards the development of control tools, drugs or eventually vaccines. One of the earliest victims of the eradication campaign was the study of epidemic malaria and its determinants in different epidemic prone areas. In spite of an extremely long period of disillusion, lasting for almost two decades, the reality of the malaria problem led WHO and member countries to agree on a global strategy of control, aiming at a realistic use of existing tools, to at least reduce or prevent mortality. An essential element of this strategy is the prevention or control of malaria epidemics and the selective use of vector control, both of which have to be based on a solid knowledge of local epidemiology, the study of which has to rejoin the path abandoned fifty years ago.     

Implementation of malaria control

Global trends of infant and child mortality have decreased over the last 30 years, while the proportion of malaria deaths has progressively increased due to the deteriorating situation in sub-Saharan Africa. The Global Malaria Control Strategy promoted by WHO has encountered several obstacles to its implementation. Early diagnosis and prompt treatment can reduce malaria mortality, but there is still low investment on safe and effective modalities of care delivery at the periphery, where most of the malaria burden exists. Selective vector control (indoor residual spraying and insecticide-treated nets) plays a significant role outside Africa, but its wider use is limited by cost/affordability problems and operational issues (supply, delivery and logistics). Alternative methods such as environmental management and biological control are cost-effective only under very specific epidemiological situations. In most countries forecasting, early detection and containment of malaria epidemics is deficient, and there is separation between the research and control communities, particularly in Africa. Involvement of the internal agencies, strategic investments in capacity building and institutional networking are needed to strengthen capacity for malaria and research in the countries. The major responsibility is to guide the expenditure made by the communities (which far out-weigh the limited share of national health budgets) towards the most cost-effective approaches to reduce malaria mortality and morbidity.     

Social sciences in malaria control

The second annual meeting of the Partnership for Social Sciences in Malaria Control was held at the London School of Hygiene and Tropical Medicine, UK, from 8 to 10 January 2002.     

Community-based malaria control in India

India launched its National Malaria Eradication Programme (NMEP) in 1958, designed to interrupt transmission with residual insecticide spraying coupled with chemotherapy and anti-larval methods in urban areas. The strategy produced spectacular results. By 1965 malaria was reduced from around 75 million cases annually (with 800 000 deaths) to about 100 000 cases per year. Unfortunately, even under the subsequent maintenance phase, malaria began to resurge in many foci, and in 1976 the NMEP reported 6.4 million parasite positive cases. In this article, V.P. Sharma looks at some of the problems faced by the NMEP strategy, and discusses the alternative community-based approach now being evaluated in the northwestern state of Gujarat.     

Coconuts in the Americas

It has been clearly established that the Portuguese introduced coconuts to the Cape Verde islands in 1499, and these supplied the Atlantic coasts and the Caribbean in the 1500s. By contrast, early 16th century reports of coconuts on the Pacific coast of Panama are controversial. Recent DNA analysis of modern coconut populations there shows them to be similar to Philippine varieties, agreeing with morphometric analysis. Hence, coconuts must have been brought by boat from the western Pacific, but no archaeological, ethnobotanical or linguistic evidence for pre-Columbian coconuts has been found. Thus, the most parsimonious explanation is that coconuts were introduced to Panama after Spanish conquest, as supported by DNA analysis and historical records of Spanish voyages. New collections along the Pacific coast, from Mexico to Colombia, are increasing the sampling for genetic analysis, and further work in the Philippines is suggested to test probable origins. Unless new archaeological discoveries prove otherwise, the strong hypothesis of Philippine origin should direct future research on the sources of American Pacific coast coconuts.     

Endectocides for malaria control

Systemic endectocidal drugs, used to control nematodes in humans and other vertebrates, can be toxic to Anopheles spp. mosquitoes when they take a blood meal from a host that has recently received one of these drugs. Recent laboratory and field studies have highlighted the potential of ivermectin to control malaria parasite transmission if this drug is distributed strategically and more often. There are important theoretical benefits to this strategy, as well as caveats. A better understanding of drug effects against vectors and malaria ecologies are needed. In the near future, ivermectin and other endectocides could serve as potent and novel malaria transmission control tools that are directly linked to the control of neglected tropical diseases in the same communities.     

Coadaptation and malaria control

Malaria emerges from a disequilibrium of the system 'human-plasmodium-mosquito' (HPM). If the equilibrium is maintained, malaria does not ensue and the result is asymptomatic plasmodium infection. The relationships among the components of the system involve coadaptive linkages that lead to equilibrium. A vast body of evidence supports this assumption, including the strategies involved in the relationships between plasmodium and human and mosquito immune systems, and the emergence of resistance of plasmodia to antimalarial drugs and of mosquitoes to insecticides. Coadaptive strategies for malaria control are based on the following principles: (1) the system HPM is composed of three highly complex and dynamic components, whose interplay involves coadaptive linkages that tend to maintain the equilibrium of the system; (2) human and mosquito immune systems play a central role in the coadaptive interplay with plasmodium, and hence, in the maintenance of the system's equilibrium; the under- or overfunction of human immune system may result in malaria and influence its severity; (3) coadaptation depends on genetic and epigenetic phenomena occurring at the interfaces of the components of the system, and may involve exchange of infectrons (genes or gene fragments) between the partners; (4) plasmodia and mosquitoes have been submitted to selective pressures, leading to adaptation, for an extremely long while and are, therefore, endowed with the capacity to circumvent both natural (immunity) and artificial (drugs, insecticides, vaccines) measures aiming at destroying them; (5) since malaria represents disequilibrium of the system HPM, its control should aim at maintaining or restoring this equilibrium; (6) the disequilibrium of integrated systems involves the disequilibrium of their components, therefore the maintenance or restoration of the system's equilibrium depend on the adoption of integrated and coordinated measures acting on all components, that means, panadaptive strategies. Coadaptive strategies for malaria control should consider that: (1) host immune response has to be induced, since without it, no coadaptation is attained; (2) the immune response has to be sustained and efficient enough to avoid plasmodium overgrowth; (3) the immune response should not destroy all parasites; (4) the immune response has to be well controlled in order to not harm the host. These conditions are mostly influenced by antimalarial drugs, and should also be taken into account for the development of coadaptive malaria vaccines.     

Prospects for malaria control

Malaria control strategies have to be established locally according to epidemiological situations, including socio-economic factors and to resources available for their implementation. It has been stressed that all antimalaria activities be integrated in PHC.Stratification of malaria is the introduction to malaria control and serves as a basis for the planning which should be established by a body of experts on malaria at the central level (epidemiologist, entomologist, specialists in social sciences, sanitary engineer) who later will guide, supervise and evaluate the activities.Case treatments, sometimes presumptive, are the most basic activities of control. They are cheap and they can be carried out by PHC which insures the coverage of the entire population at risk. Drug resistance of Plasmodium falciparum is a growing and threatening problem. In a number of areas cheap and harmless chloroquine has to be replaced by drugs or combinations of drugs which can only be delivered by experienced personnel. Chemoprophylaxis is recommended for pregnant women but questioned for infants and young children because the risk of side-effects and resistance selection and the difficulties of maintaining a good coverage for a long time.Vector control by house-spraying remains the best means of reducing transmission and is still the basis of malaria control in countries in Asia and America where the disease has been seriously reduced. In some areas resistance to DDT lead to the use of more expensive organophosphates and/or carbamates. Resistance to these compounds has also been reported in several countries. House-spraying is probably one of the malaria activities which is the most difficult to integrate in PHC. Some attempts have been successful.Integrated vector control with community participation is not a simple task nor a panacea. To be efficient it needs to be established on a strong scientific basis. Tools and technics have to be selected for each area according to the vector ecology and socio-cultural habits of the population. Maintaining community interest in a long lasting activity is a problem which has never been really explored. Self-protection against vectors (mainly by using impregnated mosquito nets) has shown promise and is currently being evaluated at an operational scale with community involvement. There is great hope for a vaccine but more advances are necessary before its place in malaria control can be established.Intersectorial approach is the best way to counteract undesirable effects of development schemes like irrigation. There is a need for training in the scope of interdisciplinary actions for high level personnel. PHC agents need special training whatever they are, specialized or multipurpose. Special attention must be paid to malaria in health education for communities at risk. Some researches dealing with the most immediate problems are suggested.     

Ethical dilemmas in malaria control.

Because the term "malaria control" specifies an anti-malaria activity rather than an outcome of that action, progress has been evaluated in terms of the effort expended. Plans that specify goals and time lines tend to lack irreversible endpoints. Anti-malaria interventions that are stimulated by economic considerations focus on sites in which the residents enjoy some employment advantage, while interventions based on humanitarian objectives serve the neediest residents of broad regions. Site-specific interventions are conducted by industrial or municipal agencies, while regional interventions are conducted by public agencies. Industry contributes an element of sustainability by injecting the possibility of gainful employment into the site. Efforts that distribute assets mainly to the richest-of-the-poor may fail to preserve lives that would otherwise have been preserved, while those that serve the poorest-of-the-poor may fail to create sustainable cycles of health and wealth. Progress in relieving the burden imposed by malaria requires economically motivated as well as humanitarian contributions, and both should specify realistically time-limited goals that ultimately permit deintensification.     

Strategies for malaria control in Colombia

Attempts at malaria eradication this century have been highly effective but early successes have not been sustained. This has been ascribed to the lack of community involvement in these campaigns. Colombia has put huge effort into malaria control on a number of fronts, from vaccine development to the evaluation of the integrated use of more traditional methods. William Rojas, Fernando Pe?aranda and Mouricio Echavarria describe a pilot programme for integrated malaria control in Colombia whose success they attribute to committed community participation.     

Epidemiology and control of malaria in Colombia

Malaria is currently one of the most serious public health problems in Colombia with an endemic/epidemic transmission pattern that has maintained endemic levels and an average of 105,000 annual clinical cases being reported over the last five years. Plasmodium vivax accounts for approximately 70% of reported cases with the remainder attributed almost exclusively to Plasmodium falciparum. A limited number of severe and complicated cases have resulted in mortality, which is a downward trend that has been maintained over the last few years. More than 90% of the malaria cases in Colombia are confined to 70 municipalities (about 7% of the total municipalities of Colombia), with high predominance (85%) in rural areas. The purpose of this paper is to review the progress of malaria-eradication activities and control measures over the past century within the eco-epidemiologic context of malaria transmission together with official consolidated morbidity and mortality reports. This review may contribute to the formulation of new antimalarial strategies and policies intended to achieve malaria elimination/eradication in Colombia and in the region.     

The economics of malaria control in Thailand

Economics has been variously described as the science concerned with the production, consumption and distribution of goods and services, the art of assessing values and, less flatteringly for economists, applied common sense. Irrespective of one's view, there can be little doubt about the basic issue. Resources available to a community are always scarce in relation to needs and aspirations and as a result, choices have to be made about how resources will be used, which requires economic evaluation. In addition, efforts have to be made to understand and improve the efficiency of existing operations by economic analysis.     

A theoretical approach to predicting the success of genetic manipulation of malaria mosquitoes in malaria control

Background  

Mosquitoes that have been genetically modified to better encapsulate the malaria parasite Plasmodium falciparum are being considered as a possible tool in the control of malaria. Hopes for this have been raised with the identification of genes involved in the encapsulation response and with advances in the tools required to transform mosquitoes. However, we have only very little understanding of the conditions that would allow such genes to spread in natural populations.