Malaria Vector Control in Africa: Strategies and Challenges

Yeya Touré

Introduction

Vector control is an important part of the global malaria control strategy. There are four basic technical elements to the strategy. The first element is to provide drugs and treatment to those infected. Second, to implement sustainable and effective preventive measures, including vector control, knowing that these measures are difficult and costly, so it is important to be quite selective. The third one is to prevent or detect and contain epidemics in high-risk areas. Fourth is to strengthen local capacities in research and development.

The aim of the WHO global malaria control strategy is to halve the number of annual deaths from malaria by 2010. We have had the heads of states of African countries, who met in April 2000, and committed themselves to malaria control. They committed themselves to an intensive effort to reach our malaria objectives.

The idea behind vector control is to reduce levels of mortality and morbidity by reducing transmission of the disease. To do this we need effective vector control, which is defined as the application of targeted site-specific activities that are cost-effective. It is not an easy task. There are some concerns about the environment, which need to be taken into account, so what we need is an environmentally sustainable method for vector control aimed at reducing reliance on chemical insecticides and involving intersectoral collaboration.

From surveys of countries in Africa we were able to get an idea of the current situation of vector control. Basically, there are many efforts focused on preventing man-vector contact by large-scale implementation of bed nets. Earlier we had huge uses of DDT treatment during the eradication period, now we have basically a kind of reliance on use of bed nets and curtains. There are also some insecticide-spraying activities still conducted, mainly in urban areas, and particularly in high-risk areas.

About research and training activities, in most African countries we have research activities on malaria epidemiology and transmission, vector biology, ecology, behavior, and genetics, and environmental factors. Training activities are mostly conducted in universities and research institutions, including both short-term and long-term training in medical entomology. Very few training activities are provided by the Ministry of Health. We have a few minor resources for technicians and high-level specialists in medical entomology and health engineering. The control activities are mainly undertaken under the auspices of the Ministry of Health, and sometimes also under agencies responsible for industry, agriculture, and water management. NGOs are also sometimes involved.

Monitoring and evaluation occur under the responsibility of the national malaria control programs. Mostly we get task forces to act as a scientific and technical advisory board, but the board is not really representative of the different levels of authority and has limited decision-making power, so it is not really adequate in terms of obtaining resources and implementing useful activities.

Funding sources are mainly from government, WHO, UNICEF, UNDP, and World Bank.

Constraints

We find that in general the efforts in strategic planning and implementation are quite insufficient. So we just have a few activities that are not well organized, properly planned, or adapted to local conditions. Control activities and resources are mainly available at provincial level, where they need to be more decentralized and controlled at the sub-district level. So activities and resources are not well distributed across the country.

With implementation of bed nets, it seems that the coverage is really not more than 4 percent. So still we find that while this is the most-used vector control tool, the implementation is just not very great. And the other control methods are also not explored or used enough. There is also not always monitoring of insecticide resistance. When it comes to the use of bed nets, it's quite important to follow over time and space the development of insecticide resistance.

Training of staff and personnel is inadequate at all levels. There is not enough done to ensure that there is a career path for young people in this area. Many of our best-trained people are getting older and nearing retirement, and no measures have been taken to ensure that they will be replaced. There are not enough schools for training of technicians. Financial resources are insufficient.

Policies and Regulations: Most countries have some policies and regulations but they are not properly applied. Several sectors are involved, particularly agricultural, industry, water management, but again responsibilities are not well defined and we find that there is considerable overlapping of activities and waste of resources by lack of coordination of activities. The interaction between the researchers and the control agencies is not always optimal, we have some people making an effort in this direction, but most often it is on an individual to individual basis. It is not a well-organized or well-structured approach at the country level.

Supervision of activities is difficult to achieve because of lack of personnel, and also we don't have always the competencies that are needed.

Vector Control Strategies

We have a few vector control strategies. Indoor spraying of insecticides, personal protection measures, larval control, and environmental control. Indoor spraying has been relied on as a vector control strategy in the past, and showed clearly if it is properly implemented you can get very good results. It faces difficulties due to sustainability and cost-effectiveness, but it can still be a good choice under certain circumstances, like in high-mortality endemic areas and in drug-resistant areas. So it is a matter of being quite selective, having a very good target and understanding where to apply the method.

Personal protection measures are based on insecticide-impregnated materials such as bed nets and curtains mainly, but clearly we are facing implementation problems. It has been demonstrated that if they are properly applied they can provide a 30 to 60 percent reduction in malaria morbidity, and can be useful in terms of preventing drug resistance.

Larval control, given the nature of the vectors, which tend basically to breed everywhere in a small amount of water on the surface of the ground, this approach can be acceptable only under suitable mapping and characterization of breeding sites, and will work mainly in urban and peri-urban areas. Larval control can be attained through environmental management, large space coverage, and community participation, and can be done through chemical or biological control.

Environmental control is used to prevent breeding, nesting, and feeding of vectors by source reduction and even through better housing, windows, doors, screening. Environmental changes from road, dam, or pipeline construction, deforestation, agriculture, and irrigation can generate larval breeding sites. Environmental control can mostly be used in urban and peri-urban areas, and mostly require community participation and intersectoral collaboration.

Transmission occurs mainly during the rainy season, which peaks in October, but also there is transmission during the dry season. Why do we have transmission during the dry season? We find that during the dry season we have this river, which has a sandy bed, and you get a reduction of the river bed, and with the sand you get small spots of water which are perfect breeding sites for mosquito larva. So this is what creates the development of mosquitoes during the dry season and a certain level of transmission. So in this case, although you might need to undertake a kind of operational research to see the real efficacy and cost-effectiveness of such an approach, it will be acceptable to reduce the bed of the river such that there are no longer such spots to be the breeding sites during the dry season. In this way you will be able to eliminate the dry season transmission.

In the peak rainy season it will be acceptable to use an insecticide that will last for two or three months, and use it in August for example, and you will eliminate almost 90 percent of the transmission which occurs during August, September, and October.

Again, now, about the issues of strengthening vector control. We think there is need for better information management in most of these countries, to identify potential sources of information, like research institutions and control services, because we think it is important that control strategies are adapted to local conditions. It becomes crucial to find ways to gather the information. And knowing the information, we can fill the gaps in knowledge and update previous information. In most cases in these countries we will find information that is at best ten years old. At the same time we need to develop information dissemination abilities, so that the information can get to those who are supposed to use it.

Strategic planning has to be based on information -- epidemiology of transmission of malaria, vector biology, ecology, behavior, genetics, environmental, socioeconomic -- but also taking into account resources available, including health centers, bed nets, and so on. Once you have this information you go to stratify the control areas in time and space using GPS-based mapping, and set your priorities.

So, to summarize some recommendations, we need:

to build capacity, by improving initial and continuing training and infrastructure and training facilities;
to assess the cost effectiveness and implementation issues of control measures in well-defined settings;
to ensure joint collaborative work between researchers and control services;
to continue monitoring vector resistance and insecticide development;
new and innovative methods for implementing existing methods;
research on transmission blocking vaccines, engineering of malaria vectors and parasites;
new ways of using multiple methods either simultaneously or consecutively to target the same vectors, which will increase efficacy and cost effectiveness;
direct community involvement at different implementation steps, particularly in environmental management, vector control, for use of bed nets and curtains, and for primary detection of loss of efficacy;
health education for knowledge and skill development and social mobilization;
involvement of other sectors, to coordinate, share resources rationally, set standards, and avoid duplication; and
increased donor contributions to consolidate governmental efforts.

Countries need to undertake vector control strategy situation analysis, develop mechanisms of information mangement, capacity development, regulations and operations, promote more the implementation materials, improve decentralization and coordination, improve coordination among interested parties, and develop community participation and intersectoral collaboration in vector management.

Yeya Touré is Manager of the Molecular Entomology Committee for Basic and Strategic Research within the Special Programme for Research and Training in Tropical Diseases (TDR) at the World Health Organization. He also remains Professor of Biology and Genetics, Department of Parasitic Diseases, Faculty of Medicine, Pharmacy and Odonto-stomatology and Head of the Malaria Research and Training Center, Department of Epidemiology of Parasitic Diseases, at the University of Mali.

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