Vector Management is the control of an organism that transmits a disease. In the case of malaria, it would be the control of the larval and adult mosquitoes in the genus Anopheles that transmit malaria to people.
Currently Vector Management is being used in Sub-Sahara Africa to varying degrees of implementation.
Insect bed nets are a form of Vector Management. They act as a barrier, where the net is over the bed and the mesh is small enough to prevent mosquitoes from entering the sleeping area. Variations of the bed net include insecticide treated bed nets (ITN's) and long-lasting insecticide treated bed nets (LLITN's). Both are impregnated with insecticide, ITN's have insecticides with limited residual activity and LLITN's have insecticides with longer lasting residual activity. These insecticides are intended to repel or kill mosquitoes that land on them. Permethrin is commonly used. So these types of bed nets are more than just a barrier but also have insecticidal action.
A great deal of effort and resources have been invested in supplying insect bed nets, free of charge, to sub-Saharan countries, specifically for use by pregnant women and children under 5 years of age. Others are available for purchase to protect older children and adults.
The other form of Vector Management which is increasing in usage in Africa is indoor residual sprays (IRS) and the insecticide of choice is DDT. More countries are entertaining the idea of increasing the indoor residual spraying with DDT even though it is not supported by the World Health Organization. These countries concluded that too many children are still dying and suffering from cerebral malaria with the sole reliance on bed nets and medications. DDT is inexpensive; environmental concerns are minimal because it is applied to the inside of homes; and it will save more lives.
I am a proponent of Integrated Vector Management (IVM) for the control of malaria. IVM is a decision making process and once the control strategy is developed, it could include ITN's, LLITN's, IRS's, larval mosquito management and adult mosquito management. It is the selection from the array of tools (control techniques) that are efficacious and environmentally appropriate based on the types of larval habitats, on surveillance of standing water sites, on monitoring of mosquito larval and adult populations and on monitoring the incidence of malaria.
In developed countries of Europe and the America's we do not see households using insect nets over their beds or using residual indoor sprays to reduce the impact of vector or nuisance mosquitoes at the community level. We rely almost exclusively on the control of mosquitoes by larviciding and/or adulticiding.
Larviciding, the killing of mosquito larvae, may be accomplished with environmental management techniques including removal of artificial larval habitats such as discarded tires and plastic bottles, frequent emptying containers used to store drinking water, flood control, drainage of standing water areas, and the list goes on.
However, environment modification is not always feasible or desired. In such situations, larvicides are a solution. These are insecticides that kill mosquito larvae. Several in use in developed countries have the active ingredient that is generically known as B.t.i. (which stands for Bacillus thuringiensis israeliensis). This is a natural bacterium that is a disease of mosquitoes. The specificity for mosquito larvae makes it a preferred control material. Another group of larvicides contain insect growth regulators (IGR's). These prevent mosquitoes from developing into biting adults. IGR's are restricted to water habitats such as road side catch basins and other man-made artificial larval habitats that contain almost exclusively mosquito larvae.
Mosquito adulticides kill adult mosquitoes. I have made reference to the adulticides permethrin and DDT. I am now writing about insecticides that are applied to the air to kill flying mosquitoes or to foliage to kill resting mosquitoes. A common mosquito adulticide is malathion.
These are but a few examples of larvicides and adulticides. They are all closely scrutinized and have been approved by government agencies in developed countries where vector and nuisance mosquitoes are a major concern. They are restricted on how and where they are applied. They have been proven safe and will not impact negatively on the environment when applied to mosquito larval and adult habitats according to label directions.
In many jurisdictions, mosquito larviciding is preferred to adulticiding because larviciding targets mosquito larvae in defined habitats which can be relatively easily found, mapped, surveyed and treated. Larviciding is considered more effective and environmentally friendly. Therefore adulticiding is not usually on the first line of action but can be implemented if mosquito adults emerge.
To summarize, Integrated Vector Management as we know it in developed countries is a decision making process that uses a combination of techniques to suppress a vector population. Activities include but are not necessarily limited to:
• planning and managing ecosystems to prevent vectors from impacting on people;
• identifying the potential vectors and their larval and adult habitats;
• monitoring larval and adult populations of vectors as well as beneficial organisms and non-target organisms, environmental conditions and incidence of the disease in people;
• using disease incidence thresholds in making vector control decisions;
• reducing vector populations to acceptable levels using strategies that may
include a combination of biological, physical, cultural, mechanical,
behavioral and chemical controls; and
• evaluating the effectiveness of those strategies.
I have concluded based on my experiences in pest management that silver bullet solutions are rare. The current bed net and indoor residual spray strategies along with prophylactic and reactive treatments are not sufficient to bring this disease to heel.
The malaria problem is complex. The solution will be equally complex .... Malaria Vector Free Zones at the community level achieved by the application of Integrated Vector Management.
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