Resistance

Mosquito resistance to insecticides is reported in 68 countries. At least 57 reported resistance to 2 or more insecticide classes.

Insecticide resistance is caused by genetic changes in an insect. These increase the insect’s ability to overcome the effects of different chemicals. This means that certain species of mosquito are becoming resistant to some of the substances designed to kill them

Since 2000, progress in malaria control has resulted primarily from expanded access to vector control interventions, particularly in sub-Saharan Africa. However, these gains are threatened by emerging resistance to insecticides among Anopheles mosquitoes.  According to the latest World malaria report, 68 countries reported mosquito resistance to at least 1 of the 5 commonly-used insecticide classes in the period 2010-2017; among these countries, 57 reported resistance to 2 or more insecticide classes.

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Resistance Mechanisms

Physiological resistance and behavioural avoidance of mosquitoes to insecticides are two integral responses ascribed to the intensified implementations of chemical-based control programmes.

The extensive use of pyrethroids inevitably elicit different levels of resistance to numerous populations, despite the presence of geographical isolation. The most common mechanisms of pyrethroid resistance that have been identified in Ae. aegypti includes mutations in the sensitive sodium channel and metabolic-mediated insecticide resistance.

Aedes aegypti develops resistance to pyrethroids by acquisition of one or several amino acid ande enzymes involved in metabolic-mediated detoxification have been reported to be related to pyrethroid resistance.

Increasing Resistance

Mosquitoes have developed resistance by using two methods.Physiological resistance and behavioral avoidance of insecticides are ascribed to the intensified implementations of chemical-based control programmes

Behavioural Avoidance

A change in mosquitoes’ feeding or resting behaviour to minimise exposure to insecticides, . Direct contact excitation (irritancy) is a phenomenon when mosquitoes escape from insecticide-exposed environment upon physical contact.

Cuticular resistance

Cuticle thickening is implicated in insecticide resistance by reducing the uptake of the insecticide that reaches the target site in response to the modification of chemical composition of the cuticle. A recent study revealed that this mechanism may play a major role in the development of resistance where it normally happens simultaneously with other mechanism(s).

Knockdown Resistance

Target site resistance in mosquitoes is related to either single or multiple mutations in target genes; for example, the Vssc gene which leads to mutations in the GABA receptors. The most well-studied target site resistance for Ae. aegypti is kdr because it confers resistance against pyrethroids.
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WHO Critical Need For New Technologies

The World Health Organisation has made urgent requests for new technologies and methods that may overcome resistance
  • Resistance is a major concern globally
  • Mosquitoes resistance is increasing
  • They have developed enzymes to prevent intake of insecticide
  • They have increased thickness in their cuticle to prevent absorption
  • WHO signals urgent need for new technologies
  • Overuse of insecticides has and is accelerating resistance
  • Standard IRS methods are not working as well now
  • PBO in IRS is now not as effective