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The efficacy of long-lasting nets with declining physical integrity may be compromised in areas with high levels of pyrethroid resistance.

Ochomo EO, Bayoh NM, Walker ED, Abongo BO, Ombok MO, Ouma C, Githeko AK, Vulule J, Yan G, Gimnig JE - Malar. J. (2013)

Bottom Line: However, emergence of insecticide resistance threatens the effectiveness of LLINs.No anopheline and five Culex spp. mosquitoes were found resting inside nets in Gem regardless of the number and size of holes, while 552 Anopheles gambiae s.l., five Anopheles funestus s.l. and 137 Culex spp. were in nets in Bungoma.LLIN formulations develop large holes within three years of use, diminishing their presupposed lifetime effectiveness.

View Article: PubMed Central - HTML - PubMed

Affiliation: KEMRI/CDC Research and Public Health Collaboration, PO Box 1578, Kisumu 40100, Kenya. ericochomo@yahoo.com.

ABSTRACT

Background: Long-lasting insecticide-treated mosquito nets (LLINs) are a primary malaria prevention strategy in sub-Saharan Africa. However, emergence of insecticide resistance threatens the effectiveness of LLINs.

Methods: Cross-sectional surveys of LLINs were conducted in houses of seven and four villages in Gem and Bungoma Districts in western Kenya, respectively. Condition (number and area of holes in the nets), number and species of mosquitoes resting inside them, and insecticidal activity of nets were quantified. Mosquitoes collected inside nets were allowed to lay eggs and progeny tested for susceptibility to deltamethrin and permethrin, pyrethoids commonly deployed in LLINs in western Kenya.

Results: In Gem, 83.3% of nets were less than three years old and 32.4% had at least one hole of any size; while in Bungoma, 92% were less than three years old and 48% had at least one hole. No anopheline and five Culex spp. mosquitoes were found resting inside nets in Gem regardless of the number and size of holes, while 552 Anopheles gambiae s.l., five Anopheles funestus s.l. and 137 Culex spp. were in nets in Bungoma. The number of mosquitoes resting inside nets increased with hole areas >50 cm in Bungoma. In WHO resistance assays, f1 offspring of samples collected in nets in Bungoma were 94 and 65% resistant to deltamethrin and permethrin, respectively. Nets from Bungoma retained strong activity against a susceptible laboratory strain, but not against f1 offspring of field-collected An. gambiae s.s. All An. gambiae s.s. samples collected in nets were homozygous for the kdr genotype L1014S.

Conclusions: In areas with pyrethroid resistant vectors, LLINs with modest hole areas permit mosquito entry and feeding, providing little protection against the vectors. LLIN formulations develop large holes within three years of use, diminishing their presupposed lifetime effectiveness.

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Susceptibility status of mosquito populations. Mortality of An. gambiae s.l. mosquito samples when exposed to deltamethrin and permethrin. Bungoma_Nets represents mortality of f1 offspring of mosquitoes collected resting inside nets in Bungoma, Bungoma_larvae represents mortality of samples collected as larvae in Bungoma and reared to adults for exposure while Gem_larvae mortality represents mortality of samples collected as larvae in Gem and reared to adults for exposure.
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Figure 1: Susceptibility status of mosquito populations. Mortality of An. gambiae s.l. mosquito samples when exposed to deltamethrin and permethrin. Bungoma_Nets represents mortality of f1 offspring of mosquitoes collected resting inside nets in Bungoma, Bungoma_larvae represents mortality of samples collected as larvae in Bungoma and reared to adults for exposure while Gem_larvae mortality represents mortality of samples collected as larvae in Gem and reared to adults for exposure.

Mentions: Within Bungoma, mosquitoes reared from females collected inside nets had lower susceptibility (5% to deltamethrin and 34% to permethrin) compared to those from larval collections (43% to deltamethrin and 53% to permethrin). Mosquitoes from Bungoma, whether collected from inside nets or as larvae generally showed lower susceptibility compared to mosquitoes collected as larvae from Gem (75% to deltamethrin and 65% to permethrin). In Gem, there were no mosquitoes collected from inside nets (FigureĀ 1). Based on the current WHO insecticide susceptibility guidelines, populations from Bungoma and Gem would be classified as resistant to the two insecticides [32].


The efficacy of long-lasting nets with declining physical integrity may be compromised in areas with high levels of pyrethroid resistance.

Ochomo EO, Bayoh NM, Walker ED, Abongo BO, Ombok MO, Ouma C, Githeko AK, Vulule J, Yan G, Gimnig JE - Malar. J. (2013)

Susceptibility status of mosquito populations. Mortality of An. gambiae s.l. mosquito samples when exposed to deltamethrin and permethrin. Bungoma_Nets represents mortality of f1 offspring of mosquitoes collected resting inside nets in Bungoma, Bungoma_larvae represents mortality of samples collected as larvae in Bungoma and reared to adults for exposure while Gem_larvae mortality represents mortality of samples collected as larvae in Gem and reared to adults for exposure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4016513&req=5

Figure 1: Susceptibility status of mosquito populations. Mortality of An. gambiae s.l. mosquito samples when exposed to deltamethrin and permethrin. Bungoma_Nets represents mortality of f1 offspring of mosquitoes collected resting inside nets in Bungoma, Bungoma_larvae represents mortality of samples collected as larvae in Bungoma and reared to adults for exposure while Gem_larvae mortality represents mortality of samples collected as larvae in Gem and reared to adults for exposure.
Mentions: Within Bungoma, mosquitoes reared from females collected inside nets had lower susceptibility (5% to deltamethrin and 34% to permethrin) compared to those from larval collections (43% to deltamethrin and 53% to permethrin). Mosquitoes from Bungoma, whether collected from inside nets or as larvae generally showed lower susceptibility compared to mosquitoes collected as larvae from Gem (75% to deltamethrin and 65% to permethrin). In Gem, there were no mosquitoes collected from inside nets (FigureĀ 1). Based on the current WHO insecticide susceptibility guidelines, populations from Bungoma and Gem would be classified as resistant to the two insecticides [32].

Bottom Line: However, emergence of insecticide resistance threatens the effectiveness of LLINs.No anopheline and five Culex spp. mosquitoes were found resting inside nets in Gem regardless of the number and size of holes, while 552 Anopheles gambiae s.l., five Anopheles funestus s.l. and 137 Culex spp. were in nets in Bungoma.LLIN formulations develop large holes within three years of use, diminishing their presupposed lifetime effectiveness.

View Article: PubMed Central - HTML - PubMed

Affiliation: KEMRI/CDC Research and Public Health Collaboration, PO Box 1578, Kisumu 40100, Kenya. ericochomo@yahoo.com.

ABSTRACT

Background: Long-lasting insecticide-treated mosquito nets (LLINs) are a primary malaria prevention strategy in sub-Saharan Africa. However, emergence of insecticide resistance threatens the effectiveness of LLINs.

Methods: Cross-sectional surveys of LLINs were conducted in houses of seven and four villages in Gem and Bungoma Districts in western Kenya, respectively. Condition (number and area of holes in the nets), number and species of mosquitoes resting inside them, and insecticidal activity of nets were quantified. Mosquitoes collected inside nets were allowed to lay eggs and progeny tested for susceptibility to deltamethrin and permethrin, pyrethoids commonly deployed in LLINs in western Kenya.

Results: In Gem, 83.3% of nets were less than three years old and 32.4% had at least one hole of any size; while in Bungoma, 92% were less than three years old and 48% had at least one hole. No anopheline and five Culex spp. mosquitoes were found resting inside nets in Gem regardless of the number and size of holes, while 552 Anopheles gambiae s.l., five Anopheles funestus s.l. and 137 Culex spp. were in nets in Bungoma. The number of mosquitoes resting inside nets increased with hole areas >50 cm in Bungoma. In WHO resistance assays, f1 offspring of samples collected in nets in Bungoma were 94 and 65% resistant to deltamethrin and permethrin, respectively. Nets from Bungoma retained strong activity against a susceptible laboratory strain, but not against f1 offspring of field-collected An. gambiae s.s. All An. gambiae s.s. samples collected in nets were homozygous for the kdr genotype L1014S.

Conclusions: In areas with pyrethroid resistant vectors, LLINs with modest hole areas permit mosquito entry and feeding, providing little protection against the vectors. LLIN formulations develop large holes within three years of use, diminishing their presupposed lifetime effectiveness.

Show MeSH
Related in: MedlinePlus