The South of Mozambique is a Hot-spot for Mosquito Resistance to Pyrethroids

A research team composed researchers from ISGlobal and the Manhiça Health Research Center (CISM), Mozambique, has shown that the Anopheles funestus population in Manhiça is extremely resistant to the pyrethroid insecticides used to treat mosquito nets and perform indoor spraying. 

Chemical insecticides have been a key tool in malaria control and elimination strategies and, according to WHO estimates, have contributed to saving more than one million lives between 2000 and 2012. However, they also impose a strong selective pressure on mosquito populations and to date, no malaria-affected country in Africa is free of insecticide-resistant mosquitoes.  A study performed in 2009 in Manhiça, Mozambique, revealed the appearance of pyrethroid-resistant mosquitoes, but since then no other resistance study had been performed in the region. 

The aim of this new study that has just been published in Malaria Journal was to evaluate the current levels of resistance to pyrethroids and the impact of such resistance in the efficacy of two commonly used long-lasting mosquito nets (LLIN).   For this, the authors captured more than 700 Anopheles mosquitoes, identified them and evaluated their resistance when exposed to three different pyrethroids or to pyrethroid-treated LLIN. The predominant species in the region was An. funestus, of which 75% to 95% were resistant to the tested pyrethroids. In addition, six hours of exposure to LLINs were necessary to eliminate 50% of the mosquitoes. These results indicate that pyrethroid-based interventions are no longer efficient in killing the main malaria vector in the South of Mozambique. 

Even though mosquito nets still provide a physical barrier between mosquitoes and humans, alternative LLINs that include other compounds with antivectorial activity will have to be tested.  For indoor residual spraying, the chemical arsenal is more limited due to the high level of resistance to other insecticides such as carbamates and DDT. The authors conclude that vector control programmes in Manhiça will have to include multiple control strategies in order to achieve malaria elimination in the region. 

Reference:

Long-lasting insecticidal nets no longer effectively kill the highly resistant Anopheles funestus of southern Mozambique
Katey D Glunt, Ana Paula Abílio, Quique Bassat, Helder Bulo, Allison E Gilbert, Silvie Huijben, Maria Nélia Manaca, Eusebio Macete, Pedro Alonso and Krijn P Paaijmans

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