Operational impact of DDT reintroduction for malaria control on Anopheles arabiensis in Mozambique

ABSTRACT With the increase in indoor residual spraying in many internationally and nationally funded malaria control programs, and affirmation by World Health Organization (WHO) that DDT is appropriate for use in the absence of longer lasting insecticide formulations in some malaria endemic settings, DDT has been reintroduced as a major malaria control intervention in Africa. Indoor residual spraying with DDT was reintroduced into Mozambique for malaria control in 2005, and it is increasingly becoming the main insecticide used for malaria vector control in Mozambique. The selection of DDT in Mozambique is evidence-based, taking account of the susceptibility of Anopheles arabiensis (Patton) and Anopheles gambiae (Giles) s.s. to all the available insecticide choices, as well as relative costs of the insecticide and the logistical costs of spraying. Before this time in Mozambique, DDT was replaced by h-cyhalothrin in 1993. Resistance occurred quickly to this insecticide, and in 2000 the pyrethroid was phased out and the carbamate bendiocarb was introduced. Low-level resistance was detected by biochemical assay to bendiocarb in 1999 in both Anopheles funestus (Giles) and An. arabiensis, although this was not evident in WHO bioassays of the same population. In the 2000-2006 surveys the levels of bendiocarb resistance had been selected to a higher level in An. arabiensis, with resistance detectable by both biochemical and WHO bioassay. The insecticide resistance monitoring program includes assessment of field populations by standard WHO insecticide susceptibility assays and biochemical assays. Monitoring was established in 1999, and it was maintained as part of an operational monitoring and evaluation program thereafter.