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Do holes in long-lasting insecticidal nets compromise their efficacy against pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus? Results from a release-recapture study in experimental huts.

Randriamaherijaona S, Briët OJ, Boyer S, Bouraima A, N'Guessan R, Rogier C, Corbel V - Malar. J. (2015)

Bottom Line: Personal protection by both LLINs and untreated nets decreased exponentially with increasing holed surface area, without evidence for a specific threshold beyond which LLINs could be considered as ineffective.LLINs with 22,500 cm(2) holed surface area and target insecticide content provided a personal protection of 0.60 (95 % CI 0.44-0.73) and a low insecticidal effect of 0.20 (95 % CI 0.12-0.30) against resistant An. gambiae.Even though personal protection by LLINs against feeding mosquitoes is strongly reduced by holes, the insecticidal effect of LLINs is independent of the holed surface area, but strongly dependent on insecticide resistance.

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur de Madagascar, Antananarivo, Madagascar. sanji@pasteur.mg.

ABSTRACT

Background: Resistance of malaria vectors to pyrethroids threatens the effectiveness of long-lasting insecticidal nets (LLINs) as a tool for malaria control. Recent experimental hut and observational studies in Benin show that pyrethroid resistance reduces the insecticidal effect and personal protection of LLINs especially when they become torn. The World Health Organization has proposed a threshold for when nets are "too torn" at 1,000 cm(2) for rectangular holes and 790 cm(2) for round holes. This study examines whether there is a threshold above which LLINs no longer reduce malaria transmission.

Methods: Intact and artificially-holed LLINs under three months old and untreated nets were tested by releasing mosquitoes from a susceptible Anopheles gambiae colony, a pyrethroid-resistant An. gambiae population and a resistant Culex quinquefasciatus population in closed experimental huts in Southern Benin, West Africa. The efficacy of LLINs and untreated nets was evaluated in terms of protection against blood feeding, insecticidal effect and potential effect on malaria transmission.

Results: Personal protection by both LLINs and untreated nets decreased exponentially with increasing holed surface area, without evidence for a specific threshold beyond which LLINs could be considered as ineffective. The insecticidal effect of LLINs was lower in resistant mosquitoes than in susceptible mosquitoes, but holed surface area had little or no impact on the insecticidal effect of LLINs. LLINs with 22,500 cm(2) holed surface area and target insecticide content provided a personal protection of 0.60 (95 % CI 0.44-0.73) and a low insecticidal effect of 0.20 (95 % CI 0.12-0.30) against resistant An. gambiae. Nevertheless, mathematical models suggested that if 80 % of the population uses such nets, they could still prevent 94 % (95 % CI 89-97 %) of transmission by pyrethroid-resistant An. gambiae.

Conclusions: Even though personal protection by LLINs against feeding mosquitoes is strongly reduced by holes, the insecticidal effect of LLINs is independent of the holed surface area, but strongly dependent on insecticide resistance. Badly torn nets that still contain insecticide have potential to reduce malaria transmission. The relationship between LLIN integrity and efficacy needs to be understood in order to guide LLIN distribution policy.

No MeSH data available.


Related in: MedlinePlus

Direct bednet effects depending on the holed surface area on three mosquito species. The first column of panelsa, b is for An. gambiae KISUMU strain, the second column of panelsc, d is for An. gambiae collected in Akron, and the third column of panelse, f is for Cx. quinquefasciatus collected in Cotonou. The first row of panelsa, c, e shows the personal protection against feeding (see "Appendix"), the second row of panelsb, d, f shows the overall insecticidal effect of a bed net used by an individual. Symbols show median values with grey squares representing intact LLINs; cyan squares LLINs with holes of 3 cm2; magenta squares LLINs with holes of 30 cm2; yellow squares LLINs with holes of 300 cm2; black circles intact untreated nets; red circles untreated nets with holes of 3 cm2; lime green circles untreated nets with holes of 30 cm2; dark blue circles untreated nets with holes of 300 cm2. Vertical lines show 95 % confidence intervals.
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Fig3: Direct bednet effects depending on the holed surface area on three mosquito species. The first column of panelsa, b is for An. gambiae KISUMU strain, the second column of panelsc, d is for An. gambiae collected in Akron, and the third column of panelse, f is for Cx. quinquefasciatus collected in Cotonou. The first row of panelsa, c, e shows the personal protection against feeding (see "Appendix"), the second row of panelsb, d, f shows the overall insecticidal effect of a bed net used by an individual. Symbols show median values with grey squares representing intact LLINs; cyan squares LLINs with holes of 3 cm2; magenta squares LLINs with holes of 30 cm2; yellow squares LLINs with holes of 300 cm2; black circles intact untreated nets; red circles untreated nets with holes of 3 cm2; lime green circles untreated nets with holes of 30 cm2; dark blue circles untreated nets with holes of 300 cm2. Vertical lines show 95 % confidence intervals.

Mentions: The results of the analysis of outcome measures are shown in Figs. 3 and 4. Consistent with the results for the crude proportion blood fed, personal protection against blood feeding (Fig. 3 panels a, c and e) decreased roughly linearly with the holed surface area on a logarithmic scale. Thus, protection decreased roughly exponentially with holed surface area on a linear scale. For An. gambiae KISUMU, the relationship was somewhat flat at a small holed surface area for LLINs. The (imaginary) curve describing the relationship for untreated nets was higher for An. gambiae AKRON than for An. gambiae KISUMU, suggesting that untreated nets consistently provided less protection against An. gambiae KISUMU. In contrast, LLINs appeared to protect relatively better against An. gambiae KISUMU than against An. gambiae AKRON as the holed surface area increased (Fig. 3 panels a, c). This was expected, as An. gambiae KISUMU is more susceptible to pyrethroids. Compared to An. gambiae, protection of untreated nets against feeding by Cx. quinquefasciatus quickly dropped as the holed surface area increased (Fig. 3 panel e), suggesting that Cx. quinquefasciatus was more capable of finding holes in nets than An. gambiae. With LLINs, protection against feeding dropped less quickly with increasing holed surface area (despite Cx. quinquefasciatus being highly pyrethroid resistant) than with untreated nets, but still faster than with An. gambiae.Fig. 3


Do holes in long-lasting insecticidal nets compromise their efficacy against pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus? Results from a release-recapture study in experimental huts.

Randriamaherijaona S, Briët OJ, Boyer S, Bouraima A, N'Guessan R, Rogier C, Corbel V - Malar. J. (2015)

Direct bednet effects depending on the holed surface area on three mosquito species. The first column of panelsa, b is for An. gambiae KISUMU strain, the second column of panelsc, d is for An. gambiae collected in Akron, and the third column of panelse, f is for Cx. quinquefasciatus collected in Cotonou. The first row of panelsa, c, e shows the personal protection against feeding (see "Appendix"), the second row of panelsb, d, f shows the overall insecticidal effect of a bed net used by an individual. Symbols show median values with grey squares representing intact LLINs; cyan squares LLINs with holes of 3 cm2; magenta squares LLINs with holes of 30 cm2; yellow squares LLINs with holes of 300 cm2; black circles intact untreated nets; red circles untreated nets with holes of 3 cm2; lime green circles untreated nets with holes of 30 cm2; dark blue circles untreated nets with holes of 300 cm2. Vertical lines show 95 % confidence intervals.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4551388&req=5

Fig3: Direct bednet effects depending on the holed surface area on three mosquito species. The first column of panelsa, b is for An. gambiae KISUMU strain, the second column of panelsc, d is for An. gambiae collected in Akron, and the third column of panelse, f is for Cx. quinquefasciatus collected in Cotonou. The first row of panelsa, c, e shows the personal protection against feeding (see "Appendix"), the second row of panelsb, d, f shows the overall insecticidal effect of a bed net used by an individual. Symbols show median values with grey squares representing intact LLINs; cyan squares LLINs with holes of 3 cm2; magenta squares LLINs with holes of 30 cm2; yellow squares LLINs with holes of 300 cm2; black circles intact untreated nets; red circles untreated nets with holes of 3 cm2; lime green circles untreated nets with holes of 30 cm2; dark blue circles untreated nets with holes of 300 cm2. Vertical lines show 95 % confidence intervals.
Mentions: The results of the analysis of outcome measures are shown in Figs. 3 and 4. Consistent with the results for the crude proportion blood fed, personal protection against blood feeding (Fig. 3 panels a, c and e) decreased roughly linearly with the holed surface area on a logarithmic scale. Thus, protection decreased roughly exponentially with holed surface area on a linear scale. For An. gambiae KISUMU, the relationship was somewhat flat at a small holed surface area for LLINs. The (imaginary) curve describing the relationship for untreated nets was higher for An. gambiae AKRON than for An. gambiae KISUMU, suggesting that untreated nets consistently provided less protection against An. gambiae KISUMU. In contrast, LLINs appeared to protect relatively better against An. gambiae KISUMU than against An. gambiae AKRON as the holed surface area increased (Fig. 3 panels a, c). This was expected, as An. gambiae KISUMU is more susceptible to pyrethroids. Compared to An. gambiae, protection of untreated nets against feeding by Cx. quinquefasciatus quickly dropped as the holed surface area increased (Fig. 3 panel e), suggesting that Cx. quinquefasciatus was more capable of finding holes in nets than An. gambiae. With LLINs, protection against feeding dropped less quickly with increasing holed surface area (despite Cx. quinquefasciatus being highly pyrethroid resistant) than with untreated nets, but still faster than with An. gambiae.Fig. 3

Bottom Line: Personal protection by both LLINs and untreated nets decreased exponentially with increasing holed surface area, without evidence for a specific threshold beyond which LLINs could be considered as ineffective.LLINs with 22,500 cm(2) holed surface area and target insecticide content provided a personal protection of 0.60 (95 % CI 0.44-0.73) and a low insecticidal effect of 0.20 (95 % CI 0.12-0.30) against resistant An. gambiae.Even though personal protection by LLINs against feeding mosquitoes is strongly reduced by holes, the insecticidal effect of LLINs is independent of the holed surface area, but strongly dependent on insecticide resistance.

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur de Madagascar, Antananarivo, Madagascar. sanji@pasteur.mg.

ABSTRACT

Background: Resistance of malaria vectors to pyrethroids threatens the effectiveness of long-lasting insecticidal nets (LLINs) as a tool for malaria control. Recent experimental hut and observational studies in Benin show that pyrethroid resistance reduces the insecticidal effect and personal protection of LLINs especially when they become torn. The World Health Organization has proposed a threshold for when nets are "too torn" at 1,000 cm(2) for rectangular holes and 790 cm(2) for round holes. This study examines whether there is a threshold above which LLINs no longer reduce malaria transmission.

Methods: Intact and artificially-holed LLINs under three months old and untreated nets were tested by releasing mosquitoes from a susceptible Anopheles gambiae colony, a pyrethroid-resistant An. gambiae population and a resistant Culex quinquefasciatus population in closed experimental huts in Southern Benin, West Africa. The efficacy of LLINs and untreated nets was evaluated in terms of protection against blood feeding, insecticidal effect and potential effect on malaria transmission.

Results: Personal protection by both LLINs and untreated nets decreased exponentially with increasing holed surface area, without evidence for a specific threshold beyond which LLINs could be considered as ineffective. The insecticidal effect of LLINs was lower in resistant mosquitoes than in susceptible mosquitoes, but holed surface area had little or no impact on the insecticidal effect of LLINs. LLINs with 22,500 cm(2) holed surface area and target insecticide content provided a personal protection of 0.60 (95 % CI 0.44-0.73) and a low insecticidal effect of 0.20 (95 % CI 0.12-0.30) against resistant An. gambiae. Nevertheless, mathematical models suggested that if 80 % of the population uses such nets, they could still prevent 94 % (95 % CI 89-97 %) of transmission by pyrethroid-resistant An. gambiae.

Conclusions: Even though personal protection by LLINs against feeding mosquitoes is strongly reduced by holes, the insecticidal effect of LLINs is independent of the holed surface area, but strongly dependent on insecticide resistance. Badly torn nets that still contain insecticide have potential to reduce malaria transmission. The relationship between LLIN integrity and efficacy needs to be understood in order to guide LLIN distribution policy.

No MeSH data available.


Related in: MedlinePlus