ITN mixtures of chlorfenapyr (Pyrrole) and alphacypermethrin (Pyrethroid) for control of pyrethroid resistant Anopheles arabiensis and Culex quinquefasciatus.

Pyrethroid resistant Anopheles gambiae malaria vectors are widespread throughout sub-Saharan Africa and continued efficacy of pyrethroid ITNs is under threat. Chlorfenapyr is a promising pyrrole insecticide with a unique mechanism of action conferring no cross-resistance to existing public health insecticides. Mixtures of chlorfenapyr (CFP) and alphacypermethrin (alpha) may provide additional benefits over chlorfenapyr or alphacypermethrin used alone. An ITN mixture of CFP 100 mg/m(2)+alpha 25 mg/m(2) was compared with CFP 100 mg/m(2) and alpha 25 mg/m(2) in a small-scale experimental hut trial in an area of wild An. arabiensis. The same treatments were evaluated in tunnel tests against insectary-reared pyrethroid susceptible and resistant Culex quinquefasciatus. Performance was measured in terms of insecticide-induced mortality, and blood-feeding inhibition. Tunnel tests showed that mixtures of CFP 100+ alpha 25 were 1.2 and 1.5 times more effective at killing susceptible Cx. quinquefasciatus than either Alpha 25 (P = 0.001) or CFP 100 (P = 0.001) ITNs. Mixtures of CFP100+ alpha 25 were 2.2 and 1.2 times more effective against resistant Cx. quinquefasciatus than either alpha 25 (P = 0.001) or CFP100 (P = 0.003) ITNs. CFP 100+ alpha 25 produced higher levels of blood-feeding inhibition than CFP alone for susceptible (94 vs 46%, P = 0.001) and resistant (84 vs 53%, P = 0.001) strains. In experimental huts the mixture of CFP 100+ Alpha 25 killed 58% of An. arabiensis, compared with 50% for alpha and 49% for CFP, though the differences were not significant. Blood-feeding inhibition was highest in the mixture with a 76% reduction compared to the untreated net (P = 0.001). ITN mixtures of chlorfenapyr and alphacypermethrin should restore effective control of resistant populations of An. gambiae malaria vectors, provide protection from blood-feeding, and may have benefits for resistance management, particularly in areas with low or moderate frequency of pyrethroid resistance. A wash-resistant mixture should be developed urgently

Percentage response of pyrethroid susceptible <i>Cx. quinquefasciatus</i> in tunnel tests.

<p>Percentage response for parameters related to repellency and blood-feeding for ITNs treated with CFP alone (100–200), alpha alone (25), and mixtures of CFP (100/200)+Alpha (25). If the superscript in a time period (0 h, 24 h, 48 h, 72 h) is the same there was no significant difference between treatments (P>0.05) (n = 350 p/treatment).</p

Experimental hut results for <i>An. arabiensis</i>.

<p>Comparison of <i>An. arabiensis</i> results for ITNs treated with CFP 100, alpha 25, and mixture of CFP 100+ alpha 25. If the superscript in a column is the same there was no significant difference between treatments (P>0.05).</p

Percentage mortality of pyrethroid resistant <i>Cx. quinquefasciatus</i> in tunnel tests.

<p>Percentage mortality for ITNs treated with CFP alone (100 and 200), alpha alone (25), and mixtures of CFP (100/200)+alpha (25). If the superscript in a time period (0 h, 24 h, 48 h, 72 h) is the same there was no significant difference between treatments (P>0.05) (n = 350 p/treatment).</p

Resistance status of <i>Cx. quinquefasciatus</i> Muheza strain.

<p>Percentage mortality of <i>Cx. quinquefasciatus</i> Muheza strain after exposure in World Health Organization (WHO) resistance tests lined with treated papers at diagnostic concentrations.</p

Resistance status of <i>Anopheles arabiensis</i> F1 strain.

<p>Percentage mortality of <i>An. arabiensis</i> F1 wild strain after exposure in cylinder bioassays lined with treated papers at diagnostic concentrations.</p

Ball Bioassay results for <i>An. arabiensis</i> using 3 and 30 minutes exposure.

<p>Results of ball bioassay (% mortality after 72 h holding) for mixture of CFP 100+ Alpha 25, CFP 100, and alpha 25 with <i>An. arabiensis F1 wild</i> and exposure time of 3 and 30 minutes.</p