In Chapter 1, we learnt that some vector-borne diseases, such as malaria, are transmitted by mosquitoes. One of the most effective ways to prevent transmission, and hence the disease, is to stop people being bitten by infectious mosquitoes.

One of the best ways to prevent people from being bitten by mosquitoes is the use of insecticide-based interventions. However, the use of the insecticides can eventually lead to the selection of mosquito populations that can survive interaction with the insecticide.

An insecticide, and other insecticides from the same mode of action group, will have less impact on mosquito populations that are resistant to them, which in turn may lead to a reduced ability to control malaria. If we want to control the mosquitoes now and in the future, we need to do something to minimise, or mitigate, the selection of insecticide-resistant mosquito populations.

A dilemma?

This leads to a dilemma. The purpose of vector control is not to maintain a susceptible mosquito population, but to prevent vector-borne disease. Having a susceptible mosquito population enables us to use the insecticides effectively. However, the best way to prevent resistance developing, is to not use the insecticide. Can we say to the villagers of Nsuhyia that we are not going to undertake any insecticide-based vector control this year, just to help maintain a susceptible mosquito population in the region?

Large-scale vector control programmes are expensive undertakings, and the cost of the insecticide-based products can be a significant proportion of the total expenditure. If one insecticide intervention becomes less effective, it may need to be replaced. The alternative interventions may be more expensive, which, unless the budget increases, may mean that the total coverage needs to be reduced. The same challenge will apply if more expensive interventions are recommended as part of a resistance management programme.

The villagers of Nsuhyia will probably have little influence over which vector control interventions are undertaken in their region. Decisions on the design of vector control programmes are often made at regional, national, and even international levels.

Can anything be done at the local level? Who should be responsible for ensuring that the vector control programmes are taking a longer-term view and including Insecticide Resistance Management in their plans and activities? How can people at all scales of a vector control programme support activities that encourage the maintenance of an insecticide-susceptible mosquito population?

Is there a dilemma between the need for vector control today and the need to be able to undertake effective vector control in the future? If so, how do we address it?

Malaria and other vector-borne diseases don’t exist in isolation; they are part of a wider health system. Likewise, mosquito populations are influenced not only by vector control activities, but also by the wider environment in which they live, which may include agriculture, mineral extraction, water storage and management, climatic change, urbanisation, waste management, etc.

To what extent should these factors also be included in vector control and Insecticide Resistance Management? With potentially so many factors involved, which ones should be included when considering Insecticide Resistance Management?

Bear these questions in mind as we go into more detail about the development, mechanisms, and impact of insecticide resistance in Chapter 2.

Author: Mark Hoppé