Limits...
Preventive effect of permethrin-impregnated long-lasting insecticidal nets on the blood feeding of three major pyrethroid-resistant malaria vectors in western Kenya.

Kawada H, Ohashi K, Dida GO, Sonye G, Njenga SM, Mwandawiro C, Minakawa N - Parasit Vectors (2014)

Bottom Line: ITNs and LLINs are still used as effective self-protection measures, but there have been few studies on the effectiveness of ITNs and LLINs in areas where vector mosquitoes are pyrethroid-resistant.However, during the hours when people were beneath LLINs, these provided protective efficacy as indicated by reduced human blood feeding rates.Such limitation of LLINs will need to be intensively addressed in African countries in the near future.

View Article: PubMed Central - PubMed

Affiliation: Department of Vector Ecology & Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan. vergiss@nagasaki-u.ac.jp.

ABSTRACT

Background: Since the World Health Organization (WHO) adopted the use of long-lasting insecticidal nets (LLINs) as a principal strategy for effective malaria prevention and control, pyrethroids have been the only class of insecticides used for LLINs. The dramatic success of insecticide-treated nets (ITNs) and LLINs in African countries, however, has been threatened by the rapid development of pyrethroid resistance in vector mosquitoes. ITNs and LLINs are still used as effective self-protection measures, but there have been few studies on the effectiveness of ITNs and LLINs in areas where vector mosquitoes are pyrethroid-resistant.

Methods: To investigate the behavioral pattern of mosquitoes in the houses where LLINs were used, indoor mosquito trappings of Anopheles gambiae s.s., An. arabiensis, and An. funestus s.s. were performed with Centers for Disease Control and Prevention (CDC) miniature light trap equipped with a collection bottle rotator at 2-hour intervals between 4:00 pm and 8:00 am. The trapped female mosquitoes were identified and classified as unfed, blood fed, and gravid. The abdominal contents of fed female mosquitoes were used for DNA extractions to identify the blood source.

Results: A large proportion of human blood feeding of An. arabiensis and An. funestus s.s. (but not An. gambiae s.s.) took place during the time people were active outside LLINs. However, during the hours when people were beneath LLINs, these provided protective efficacy as indicated by reduced human blood feeding rates.

Conclusion: LLINs provided effective protection against pyrethroid-resistant malaria vector populations during bedtime hours. However, protection of LLINs was insufficient during the hours when people were active outside of the bed nets. Such limitation of LLINs will need to be intensively addressed in African countries in the near future.

Show MeSH

Related in: MedlinePlus

Indoor activity pattern ofAn. gambiaes.s.,An. arabiensis, andAn. funestuss.s. female mosquitoes trapped by CDC miniature traps equipped with a collection bottle rotator in houses in which LLINs were used. Different letters indicate the significant difference (Tukey honestly significant difference test, p < 0.05), and bars indicate the 95% confidence limits for the total number of mosquitoes collected at each time period.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4150967&req=5

Fig3: Indoor activity pattern ofAn. gambiaes.s.,An. arabiensis, andAn. funestuss.s. female mosquitoes trapped by CDC miniature traps equipped with a collection bottle rotator in houses in which LLINs were used. Different letters indicate the significant difference (Tukey honestly significant difference test, p < 0.05), and bars indicate the 95% confidence limits for the total number of mosquitoes collected at each time period.

Mentions: The indoor activity patterns of the 3 major malaria vectors in western Kenya are shown in Figure 3. The number of trapped female An. gambiae s.s. (fed and unfed) significantly rose at night (10:00 pm to 2:00 am), falling before and after this period (ANOVA, df = 7, χ2 = 84.9, p < 0.0001). The number of human blood–fed mosquitoes also peaked during this period (ANOVA, df = 7, χ2 = 26.7, p < 0.001), but there was no significant peak in the number of animal blood–fed mosquitoes (ANOVA, df = 7, χ2 = 7.20, p = 0.41). The allelic frequency of the point mutation in the voltage-gated sodium channel (L1014S) in the collected mosquitoes was 98.4% (n = 96, Accession AB776705, AB776706). Among the 283 female An. gambiae s.s. collected (13.4 ± 0.70/house per a night), 195 were unfed (68.9%, 9.3 ± 0.81/house per a night), 45 contained blood from a human source (15.9%, 2.0 ± 0.26/house per a night), and 43 had fed from an animal source (15.2%, 2.0 ± 0.26/house per a night). Among the 45 female mosquitoes engorged with human blood, 22 (48.9%) were trapped from 10:00 pm to 2:00 am. There was no significant difference in the ratio of human blood–fed mosquitoes to unfed plus animal blood–fed mosquitoes between bedtime (10:00 pm to 6:00 am), when most residents were assumed to sleep under bed nets, and active time (4:00–10:00 pm and 6:00–8:00 am), when most residents were active outside bed nets (χ2 = 0.03, p = 0.73, Figure 4).Figure 3


Preventive effect of permethrin-impregnated long-lasting insecticidal nets on the blood feeding of three major pyrethroid-resistant malaria vectors in western Kenya.

Kawada H, Ohashi K, Dida GO, Sonye G, Njenga SM, Mwandawiro C, Minakawa N - Parasit Vectors (2014)

Indoor activity pattern ofAn. gambiaes.s.,An. arabiensis, andAn. funestuss.s. female mosquitoes trapped by CDC miniature traps equipped with a collection bottle rotator in houses in which LLINs were used. Different letters indicate the significant difference (Tukey honestly significant difference test, p < 0.05), and bars indicate the 95% confidence limits for the total number of mosquitoes collected at each time period.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4150967&req=5

Fig3: Indoor activity pattern ofAn. gambiaes.s.,An. arabiensis, andAn. funestuss.s. female mosquitoes trapped by CDC miniature traps equipped with a collection bottle rotator in houses in which LLINs were used. Different letters indicate the significant difference (Tukey honestly significant difference test, p < 0.05), and bars indicate the 95% confidence limits for the total number of mosquitoes collected at each time period.
Mentions: The indoor activity patterns of the 3 major malaria vectors in western Kenya are shown in Figure 3. The number of trapped female An. gambiae s.s. (fed and unfed) significantly rose at night (10:00 pm to 2:00 am), falling before and after this period (ANOVA, df = 7, χ2 = 84.9, p < 0.0001). The number of human blood–fed mosquitoes also peaked during this period (ANOVA, df = 7, χ2 = 26.7, p < 0.001), but there was no significant peak in the number of animal blood–fed mosquitoes (ANOVA, df = 7, χ2 = 7.20, p = 0.41). The allelic frequency of the point mutation in the voltage-gated sodium channel (L1014S) in the collected mosquitoes was 98.4% (n = 96, Accession AB776705, AB776706). Among the 283 female An. gambiae s.s. collected (13.4 ± 0.70/house per a night), 195 were unfed (68.9%, 9.3 ± 0.81/house per a night), 45 contained blood from a human source (15.9%, 2.0 ± 0.26/house per a night), and 43 had fed from an animal source (15.2%, 2.0 ± 0.26/house per a night). Among the 45 female mosquitoes engorged with human blood, 22 (48.9%) were trapped from 10:00 pm to 2:00 am. There was no significant difference in the ratio of human blood–fed mosquitoes to unfed plus animal blood–fed mosquitoes between bedtime (10:00 pm to 6:00 am), when most residents were assumed to sleep under bed nets, and active time (4:00–10:00 pm and 6:00–8:00 am), when most residents were active outside bed nets (χ2 = 0.03, p = 0.73, Figure 4).Figure 3

Bottom Line: ITNs and LLINs are still used as effective self-protection measures, but there have been few studies on the effectiveness of ITNs and LLINs in areas where vector mosquitoes are pyrethroid-resistant.However, during the hours when people were beneath LLINs, these provided protective efficacy as indicated by reduced human blood feeding rates.Such limitation of LLINs will need to be intensively addressed in African countries in the near future.

View Article: PubMed Central - PubMed

Affiliation: Department of Vector Ecology & Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan. vergiss@nagasaki-u.ac.jp.

ABSTRACT

Background: Since the World Health Organization (WHO) adopted the use of long-lasting insecticidal nets (LLINs) as a principal strategy for effective malaria prevention and control, pyrethroids have been the only class of insecticides used for LLINs. The dramatic success of insecticide-treated nets (ITNs) and LLINs in African countries, however, has been threatened by the rapid development of pyrethroid resistance in vector mosquitoes. ITNs and LLINs are still used as effective self-protection measures, but there have been few studies on the effectiveness of ITNs and LLINs in areas where vector mosquitoes are pyrethroid-resistant.

Methods: To investigate the behavioral pattern of mosquitoes in the houses where LLINs were used, indoor mosquito trappings of Anopheles gambiae s.s., An. arabiensis, and An. funestus s.s. were performed with Centers for Disease Control and Prevention (CDC) miniature light trap equipped with a collection bottle rotator at 2-hour intervals between 4:00 pm and 8:00 am. The trapped female mosquitoes were identified and classified as unfed, blood fed, and gravid. The abdominal contents of fed female mosquitoes were used for DNA extractions to identify the blood source.

Results: A large proportion of human blood feeding of An. arabiensis and An. funestus s.s. (but not An. gambiae s.s.) took place during the time people were active outside LLINs. However, during the hours when people were beneath LLINs, these provided protective efficacy as indicated by reduced human blood feeding rates.

Conclusion: LLINs provided effective protection against pyrethroid-resistant malaria vector populations during bedtime hours. However, protection of LLINs was insufficient during the hours when people were active outside of the bed nets. Such limitation of LLINs will need to be intensively addressed in African countries in the near future.

Show MeSH
Related in: MedlinePlus