Bio-efficacy and physical integrity of piperonylbutoxide coated combination net (PermaNet 3.0) against pyrethroid resistant population of Anopheles gambiae s.l. and Culex quinquefasciatus mosquitoes in Ethiopia.

BACKGROUND

PermaNet 3.0 is a deltamethrin-treated combination long-lasting insecticidal net with the addition of synergist piperonylbutoxide (PBO) on its roof section. It is designed to overcome the challenge posed by pyrethroid resistant vector populations against mainstream long-lasting insecticidal nets impregnated with pyrethroids only. The objective of this study was to determine insecticide resistance status of Anopheline and Culicine mosquitoes, to evaluate the bio-efficacy of PermaNet 3.0 nets and to assess household factors affecting the physical integrity of PermaNet 3.0 after 3 years of use.

METHODS

Insecticide susceptibility test was conducted using the WHO tube test. Bio-activity of PermaNet 3.0 samples was evaluated using the WHO cone bioassay. Cross-sectional survey was conducted on 150 randomly selected households from two districts to determine household factors affecting net utilization. One hundred fifty PermaNet 3.0 nets were randomly collected from the community with replacement after 3 years of deployment and physical integrity of each net was assessed.

RESULTS

Both Anopheles gambiae sensu lato and Culex quinquefasciatus developed resistance against permethrin and deltamethrin. However, following pre-exposure to synergist PBO the susceptibility of mosquito population increased to both permethrin (from 39% without to 92% with PBO against An. gambiae and from 28% without to 94% with PBO against Culex quinquefasciatus) and deltamethrin (from 52% without to 99% with PBO against An. gambiae and from 43% without to 98% with PBO against Culex quinquefasciatus). Eighty percent (80%) mortality was recorded in wild population of An. gambiae s.l. exposed to unused PermaNet 3.0, but its bioactivity subsequently declined as washing frequency increased from 0 to 20. The PBO coated roof section of unused PermaNet 3.0 resulted in higher mosquito mortality (100%) compared to the side panels without PBO (85%). House structure, cooking and washing habits, and damage due to household pests were cited as determinants associated with bed net deterioration. Bed net proportionate hole index (pHI) was ranged from 0 to 6064. Of the 150 PermaNet 3.0 nets assessed 80, 29 and 41 were considered as 'good', 'acceptable' and 'too torn', respectively.

CONCLUSIONS

The bio-efficacy evaluation of PermaNet 3.0 from Jimma area, southwestern Ethiopia showed moderate efficacy against pyrethroid resistant population of An. gambiae and Culex quinquefasciatus. Thus, NMCPs in parallel to deployment of LLINs, should implement timely insecticide resistance management and integrated vector management strategies to slowdown the evolution and further spread of insecticide resistance. Household factors such as, housing conditions, open flame fire used for cooking and rodent attack were identified as factors contributing to the observed reduced bed net physical integrity in the study area. Universal coverage of bed nets should be accompanied with community awareness creation and training on net utilization and handling.