Mosquito nets fall into two groups: those that are not treated with insect killing or repelling chemicals, and those that are treated with such chemicals (i.e. ITNs). All mosquito nets act as a physical barrier, preventing bites by vector mosquitoes and thus providing personal protection against malaria to the individual(s) using the nets. In addition, ITNs can kill or disable mosquitoes by contact with the insecticide.

ITNs are most useful when a large proportion of biting by local mosquitoes takes place after people have gone to sleep inside houses. ITNs have three main functions:

ITNs (like all nets) reduce contact between the person and mosquito by acting as a physical barrier.
When mosquitoes are in contact with the ITN, the insecticide on the nets kills them.
The insecticide on the nets also has a repellent effect, that is, it prevents mosquitoes from coming close to a person sleeping under ITNs, and to some extent it prevents mosquitoes from entering and staying in a house. The repellent effect adds a chemical barrier to the physical one, further reducing human–vector contact and increasing the protective effect of the mosquito nets.

Individuals sleeping under ITNs have effective personal protection against malaria vectors. However, if ITN use is widespread in a village or community, it can actually increase protection against malaria vectors even for those who are not sleeping under nets.

Can you explain why widespread ITN use in a community could increase protection against malaria vectors even for people who are not sleeping under ITNs?

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ITNs can kill mosquitoes on contact. For this reason, if ITN use is widespread, the local malaria vector population will be reduced, so even people who do not have ITNs will be less likely to be bitten by a malaria vector.

Thus ITNs can be a very effective vector control intervention for reducing malaria transmission for individuals and communities.