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Insecticide resistance – a case study from Tanzania

Read Prisca Kweyamba illustrate the context in which insecticide resistance can develop in malaria mosquitoes, in a case study from Tanzania.

Resistance to different classes of insecticides used in public health has been widely reported throughout Tanzania. Resistance to pyrethroid and carbamate insecticides has been detected throughout the country, prompting fears of disruption to national malaria control programmes.

The loss of insecticide susceptibility by mosquitoes in communities can be influenced by repeated exposure of mosquito larvae to insecticide-contaminated aquatic habitats, and sporadic use of consumer insecticide sprays. Such sprays are readily available on the open market and are commonly used by the population as a short-term measure against mosquitoes and to prevent mosquito bites in their homes.

The impact of farming

Our communities heavily depend on farming for their livelihood. Farming can involve the extensive use of insecticides. Most insecticides used in agriculture are from the same mode of action classes as those used in vector control. There is no doubt that regular use of insecticides in agriculture has contributed to the rapid loss of insecticide susceptibility seen among malaria mosquitoes. As well as on nets, mosquitoes are exposed to pyrethroid insecticides from use in consumer products, indoor residual spraying, livestock pest control, and agriculture.

Reports of resistance to organophosphate insecticides are of much concern. This mode of action class has been used as an alternative after mosquitoes became resistant to pyrethroid and carbamate insecticides. The use of organophosphate insecticides in agriculture is likely to be contributing to the loss of susceptibility to this class among the mosquito malaria vectors. It is probable that the same thing will happen with the recently introduced neonicotinoids that are now being used for indoor residual spraying (IRS) in the Lake Zone of Tanzania, as well as in agriculture, unless steps are taken.

Community engagement

There is no doubt that communities associate mosquitoes with a negative health outcome. As a result, they will wish for mosquitoes to be controlled. Most people are disturbed by mosquito-bites and there is a concern about mosquitoes not dying when their usual insecticide sprays are no longer effective. People may also throw away their insecticide-treated nets if they get bites after the net gets damaged. Mosquito nuisance is the common motivator for desiring that mosquitoes remain “easy to kill” by the available insecticides.

There is a major challenge to help local communities understand how the repeated use of pesticides in the wider environment is contributing towards a loss of susceptibility among mosquitoes. For example, the repeated use of weed killers and pesticides in agriculture, which is deemed important due to poor crop yields. It is also likely that insecticide resistance among other disease vectors such as ticks, which are associated with farming, is also developing due to exposure via this route.

Our communities usually lack the desire to dig into why mosquitoes are not dying, and would rather strongly prefer the “people from the science world” to fix this problem. It is time to heavily engage the Agro-Veterinary sector to sensitise farmers on how and why improper use of pesticides and insecticides is not only leading to loss of insecticide susceptibility in common agricultural-pests, but also in mosquitoes.

There is also a need for continuous community engagement and communities’ involvement in mosquito control efforts. This includes support of the national surveillance programme which monitors the susceptibility of malaria vectors to existing and new insecticide-based products.

Author: Prisca Kweyamba

© University of Basel
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The Resistant Mosquito: Staying Ahead of the Game in the Fight against Malaria

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