Limits...
Increasing insecticide resistance in Anopheles funestus and Anopheles arabiensis in Malawi, 2011 – 2015

View Article: PubMed Central - PubMed

ABSTRACT

Background: Susceptibility of principal Anopheles malaria vectors to common insecticides was monitored over a 5-year period across Malawi to inform and guide the national malaria control programme.

Methods: Adult blood-fed Anopheles spp. and larvae were collected from multiple sites in sixteen districts across the country between 2011 and 2015. First generation (F1) progeny aged 2–5 days old were tested for susceptibility, using standard WHO procedures, against pyrethroids (permethrin and deltamethrin), carbamates (bendiocarb and propoxur), organophosphates (malathion and pirimiphos-methyl) and an organochlorine (DDT).

Results: Mortality of Anopheles funestus to deltamethrin, permethrin, bendiocarb and propoxur declined significantly over the 5-year (2011–2015) monitoring period. There was wide variation in susceptibility to DDT but it was not associated with time. In contrast, An. funestus exhibited 100% mortality to the organophosphates (malathion and pirimiphos-methyl) at all sites tested. There was reduced mortality of Anopheles arabiensis to deltamethrin over time though this was not statistically significant. However, mortality of An. arabiensis exposed to permethrin declined significantly over time. Anopheles arabiensis exposed to DDT were more likely to be killed if there was high ITN coverage in the mosquito collection area the previous year. There were no other associations between mosquito mortality in a bioassay and ITN coverage or IRS implementation. Mortality of An. funestus from four sites exposed to deltamethrin alone ranged from 2 to 31% and from 41 to 94% when pre-exposed to the synergist piperonyl butoxide followed by deltamethrin. For permethrin alone, mortality ranged from 2 to 13% while mortality ranged from 63 to 100% when pre-exposed to PBO.

Conclusion: Pyrethroid resistance was detected in An. funestus and An. arabiensis populations across Malawi and has worsened over the last 5 years. New insecticides and control strategies are urgently needed to reduce the burden of malaria in Malawi.

Electronic supplementary material: The online version of this article (doi:10.1186/s12936-016-1610-1) contains supplementary material, which is available to authorized users.

No MeSH data available.


Mortality of An. arabiensis exposed to bendiocarb over time. Each point denotes the mortality for a single population with 95% confidence limits. The X-axis represents time expressed as the year plus the day of the year divided by 365.25
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC5120501&req=5

Fig9: Mortality of An. arabiensis exposed to bendiocarb over time. Each point denotes the mortality for a single population with 95% confidence limits. The X-axis represents time expressed as the year plus the day of the year divided by 365.25

Mentions: Mortality of An. arabiensis to deltamethrin is shown in Fig 7 and Additional file 1: Table S8. Mortality ranged between 56 and 100% in 2011 and between 57 and 100% in 2015. There was no evidence for a trend that was significantly different from zero (p = 0.626). In contrast, there was a slight decline in mortality of An. arabiensis exposed to permethrin over time (Fig. 8; Additional file 1: Table S9, p = 0.021). Mortality in this species was >90% at 3 sites tested in 2011 but was <60% in all sites tested in 2015 except for one in Mwanza district where mortality was 100% (Fig. 9; Additional file 1: Table S10). There were few sites where An. arabiensis was exposed to bendiocarb but a general declining trend was observed (p = 0.007). Maps showing the distribution of resistance in An. arabiensis over time are provided in Additional file 2: Figures S4–S6.Fig. 7


Increasing insecticide resistance in Anopheles funestus and Anopheles arabiensis in Malawi, 2011 – 2015
Mortality of An. arabiensis exposed to bendiocarb over time. Each point denotes the mortality for a single population with 95% confidence limits. The X-axis represents time expressed as the year plus the day of the year divided by 365.25
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5120501&req=5

Fig9: Mortality of An. arabiensis exposed to bendiocarb over time. Each point denotes the mortality for a single population with 95% confidence limits. The X-axis represents time expressed as the year plus the day of the year divided by 365.25
Mentions: Mortality of An. arabiensis to deltamethrin is shown in Fig 7 and Additional file 1: Table S8. Mortality ranged between 56 and 100% in 2011 and between 57 and 100% in 2015. There was no evidence for a trend that was significantly different from zero (p = 0.626). In contrast, there was a slight decline in mortality of An. arabiensis exposed to permethrin over time (Fig. 8; Additional file 1: Table S9, p = 0.021). Mortality in this species was >90% at 3 sites tested in 2011 but was <60% in all sites tested in 2015 except for one in Mwanza district where mortality was 100% (Fig. 9; Additional file 1: Table S10). There were few sites where An. arabiensis was exposed to bendiocarb but a general declining trend was observed (p = 0.007). Maps showing the distribution of resistance in An. arabiensis over time are provided in Additional file 2: Figures S4–S6.Fig. 7

View Article: PubMed Central - PubMed

ABSTRACT

Background: Susceptibility of principal Anopheles malaria vectors to common insecticides was monitored over a 5-year period across Malawi to inform and guide the national malaria control programme.

Methods: Adult blood-fed Anopheles spp. and larvae were collected from multiple sites in sixteen districts across the country between 2011 and 2015. First generation (F1) progeny aged 2&ndash;5&nbsp;days old were tested for susceptibility, using standard WHO procedures, against pyrethroids (permethrin and deltamethrin), carbamates (bendiocarb and propoxur), organophosphates (malathion and pirimiphos-methyl) and an organochlorine (DDT).

Results: Mortality of Anopheles funestus to deltamethrin, permethrin, bendiocarb and propoxur declined significantly over the 5-year (2011&ndash;2015) monitoring period. There was wide variation in susceptibility to DDT but it was not associated with time. In contrast, An. funestus exhibited 100% mortality to the organophosphates (malathion and pirimiphos-methyl) at all sites tested. There was reduced mortality of Anopheles arabiensis to deltamethrin over time though this was not statistically significant. However, mortality of An. arabiensis exposed to permethrin declined significantly over time. Anopheles arabiensis exposed to DDT were more likely to be killed if there was high ITN coverage in the mosquito collection area the previous year. There were no other associations between mosquito mortality in a bioassay and ITN coverage or IRS implementation. Mortality of An. funestus from four sites exposed to deltamethrin alone ranged from 2 to 31% and from 41 to 94% when pre-exposed to the synergist piperonyl butoxide followed by deltamethrin. For permethrin alone, mortality ranged from 2 to 13% while mortality ranged from 63 to 100% when pre-exposed to PBO.

Conclusion: Pyrethroid resistance was detected in An. funestus and An. arabiensis populations across Malawi and has worsened over the last 5&nbsp;years. New insecticides and control strategies are urgently needed to reduce the burden of malaria in Malawi.

Electronic supplementary material: The online version of this article (doi:10.1186/s12936-016-1610-1) contains supplementary material, which is available to authorized users.

No MeSH data available.