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London School of Hygiene & Tropical Medicine Malaria Centre

Malaria research in vector studies

Combining Indoor Residual Spraying (IRS) with chlorfenapyr and Long-Lasting Insecticide Nets (LLINs) for improved control of pyrethroidresistant Anopheles gambiae: an experimental hut trial in Benin.

LSHTM investigators:
Corine Ngufor, Raphael N’Guessan & Mark Rowland.
External collaborators:
Pelagie Boko, Abibatou Odjo, Estelle Vigninou, Alex Asidi & Martin Akogbeto (Centre de Recherches Entomologiques de Cotonou, Benin).
Funding body:
The Bill & Melinda Gates Foundation through the Innovative Vector Control Consortium.

Neither indoor residual spraying (IRS) nor long-lasting insecticidal nets (LLINs) are able to fully interrupt transmission in holoendemic Africa as single interventions.

The combining of IRS and LLINs presents an opportunity for improved control and management of pyrethroid resistance through the simultaneous presentation of unrelated insecticides. Chlorfenapyr IRS and a pyrethroid-impregnated polyester LLIN (WHO approved) were tested separately and together in experimental huts in southern Benin against pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus. Anopheles gambiae were genotyped for the kdr gene to assess the combination’s potential to prevent the selection of pyrethroid resistance.

The frequency of kdr was 84%. The overall mortality rates of An. gambiae were 37% and 49% with the six- hole and 80-hole LLINs, respectively, and reached 57% with chlorfenapyr IRS. Overall mortality rates were significantly higher with the combination treatments (82-83%) than with the LLIN or IRS individual treatments. Blood feeding (biting) rates and repellency of mosquitoes with the combination of LLIN and chlorfenapyr IRS showed significant improvement compared to the IRS treatment but did not differ from the LLIN treatments indicating that the LLINs were the primary agents of personal protection. The combination killed significantly higher proportions of Cx. quinquefasciatus (51%, 41%) than the LLIN (15%, 13%) or IRS (32%) treatments.

The chlorfenapyr IRS component was largely responsible for controlling pyrethroid-resistant mosquitoes and the LLIN component was largely responsible for blood feeding inhibition and personal protection. Together, the combination shows potential to provide additional levels of transmission control and personal protection against pyrethroid-resistant mosquitoes, thereby justifying the additional resources required. Chlorfenapyr has potential to manage pyrethroid resistance in the context of an expanding LLIN/IRS strategy.