Indoor collections of the Anopheles funestus group (Diptera: Culicidae) in sprayed houses in northern KwaZulu-Natal, South Africa.

BACKGROUND

Insecticide resistance in malaria vector mosquitoes presents a serious problem for those involved in control of this disease. South Africa experienced a severe malaria epidemic during 1999/2000 due to pyrethroid resistance in the major vector Anopheles funestus. Subsequent monitoring and surveillance of mosquito populations were conducted as part of the malaria vector control programme.

METHODS

A sample of 269 Anopheles funestus s.l. was collected in Mamfene, northern KwaZulu-Natal, using exit window traps in pyrethroid sprayed houses between May and June 2005. Mosquitoes were identified to species level, assayed for insecticide susceptibility, analysed for Plasmodium falciparum infectivity and blood meal source.

RESULTS

Of the 220 mosquitoes identified using the rDNA PCR method, two (0.9%) were An. funestus s.s. and 218 (99.1%) Anopheles parensis. Standard WHO insecticide susceptibility tests were performed on F1 progeny from wild caught An. parensis females and a significant survival 24 h post exposure was detected in 40% of families exposed to 0.05% deltamethrin. Biochemical analysis of F1 An. parensis showed no elevation in levels/activity of the detoxifying enzyme systems when compared with an insecticide susceptible An. funestus laboratory strain. Among the 149 female An. parensis tested for P. falciparum circumsporozoite infections, 13.4% were positive. All ELISA positive specimens (n = 20) were re-examined for P. falciparum infections using a PCR assay and none were found to be positive. Direct ELISA analysis of 169 blood meal positive specimens showed > 75% of blood meals were taken from animals. All blood fed, false positive mosquito samples for the detection of sporozoites of P. falciparum were zoophilic.

CONCLUSION

The combination of pyrethroid resistance and P. falciparum false-positivity in An. parensis poses a problem for vector control. If accurate species identification had not been carried out, scarce resources would have been wasted in the unnecessary changing of control strategies to combat a non-vector species.