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Increasing role of Anopheles funestus and Anopheles arabiensis in malaria transmission in the Kilombero Valley, Tanzania.

Lwetoijera DW, Harris C, Kiware SS, Dongus S, Devine GJ, McCall PJ, Majambere S - Malar. J. (2014)

Bottom Line: Insecticide susceptibility tests indicated high levels of resistance in An. funestus against deltamethrin (87%), permethrin (65%), lambda cyhalothrin (74%), bendiocarb (65%), and DDT (66%).Similarly, An. arabiensis showed insecticide resistance to deltamethrin (64%), permethrin (77%) and lambda cyhalothrin (42%) in 2014.Complementary vector control and surveillance tools are needed that target the ecology, behaviour and insecticide resistance management of these vector species, in order to preserve the efficacy of LLINs.

View Article: PubMed Central - PubMed

Affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania. dwilson@ihi.or.tz.

ABSTRACT

Background: In order to sustain the gains achieved by current malaria control strategies, robust surveillance systems that monitor dynamics of vectors and their roles in malaria transmission over time are essential. This longitudinal study demonstrates the trends in malaria vector dynamics and their relative contribution to malaria transmission in hyperendemic transmission settings in Tanzania.

Methods: The study was conducted in two villages within the Kilombero Valley, in rural Tanzania for five consecutive years (2008-2012). Seventy-two houses were selected per village and each house was sampled for mosquitoes monthly using a CDC light trap. Collected mosquitoes were assessed for species identity and sporozoite infection status using PCR and ELISA, respectively. Anopheles funestus and Anopheles arabiensis susceptibility to insecticides was assessed using WHO guidelines.

Results: A total of 100,810 malaria vectors were collected, of which 76% were Anopheles gambiae s. l. and 24% were An. funestus. Of all An. funestus samples that amplified with PCR (n = 2,737), 97% were An. funestus s.s., 2% were Anopheles rivorulum and 1% Anopheles leesoni. Whereas for An. gambiae s.l. (n = 8,117), 93% were An. arabiensis and 7% were Anopheles gambiae s.s. The proportion of An. gambiae s.s. identified by PCR (2,924) declined from 0.2% in the year 2008 to undetectable levels in 2012. Malaria transmission intensity significantly decreased from an EIR of 78.14 infectious bites/person/year in 2008 to 35 ib/p/yr in 2011 but rebounded to 226 ib/p/yr in 2012 coinciding with an increased role of An. funestus in malaria transmission. Insecticide susceptibility tests indicated high levels of resistance in An. funestus against deltamethrin (87%), permethrin (65%), lambda cyhalothrin (74%), bendiocarb (65%), and DDT (66%). Similarly, An. arabiensis showed insecticide resistance to deltamethrin (64%), permethrin (77%) and lambda cyhalothrin (42%) in 2014.

Conclusion: The results indicate the continuing role of An. arabiensis and the increasing importance of An. funestus in malaria transmission, and pyrethroid resistance development in both species. Complementary vector control and surveillance tools are needed that target the ecology, behaviour and insecticide resistance management of these vector species, in order to preserve the efficacy of LLINs.

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Related in: MedlinePlus

Results of WHO bioassay test for insecticide susceptibility status of wild femaleAnopheles funestus(white bars) andAnopheles arabiensis(grey bars) from the study sites in the Kilombero Valley, Tanzania, in January 2013 and June 2014. The graph shows percentage 24 hours mortality rate after a one-hour exposure to the WHO diagnostic doses of insecticide. The minimum sample size for these assays was 100.
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Fig3: Results of WHO bioassay test for insecticide susceptibility status of wild femaleAnopheles funestus(white bars) andAnopheles arabiensis(grey bars) from the study sites in the Kilombero Valley, Tanzania, in January 2013 and June 2014. The graph shows percentage 24 hours mortality rate after a one-hour exposure to the WHO diagnostic doses of insecticide. The minimum sample size for these assays was 100.

Mentions: In the WHO bioassay testing, as the results indicated (Figure 3), An. funestus was fully susceptible to deltamethrin (100% mortality) with reduced susceptibility to permethrin (93%), and lambda cyhalothrin (91%) and confirmed resistance to DDT (86%) in year 2013. In 2014, An. funestus was resistant to permethrin (65%), lambda cyhalothrin (74%), bendiocarb (65%), and even to deltamethrin (87%) to which it was fully susceptible in 2013. Mortality in control tubes was 4% in both testing rounds. All tested mosquitoes were amplified as An. funestus, using PCR.Figure 3


Increasing role of Anopheles funestus and Anopheles arabiensis in malaria transmission in the Kilombero Valley, Tanzania.

Lwetoijera DW, Harris C, Kiware SS, Dongus S, Devine GJ, McCall PJ, Majambere S - Malar. J. (2014)

Results of WHO bioassay test for insecticide susceptibility status of wild femaleAnopheles funestus(white bars) andAnopheles arabiensis(grey bars) from the study sites in the Kilombero Valley, Tanzania, in January 2013 and June 2014. The graph shows percentage 24 hours mortality rate after a one-hour exposure to the WHO diagnostic doses of insecticide. The minimum sample size for these assays was 100.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4150941&req=5

Fig3: Results of WHO bioassay test for insecticide susceptibility status of wild femaleAnopheles funestus(white bars) andAnopheles arabiensis(grey bars) from the study sites in the Kilombero Valley, Tanzania, in January 2013 and June 2014. The graph shows percentage 24 hours mortality rate after a one-hour exposure to the WHO diagnostic doses of insecticide. The minimum sample size for these assays was 100.
Mentions: In the WHO bioassay testing, as the results indicated (Figure 3), An. funestus was fully susceptible to deltamethrin (100% mortality) with reduced susceptibility to permethrin (93%), and lambda cyhalothrin (91%) and confirmed resistance to DDT (86%) in year 2013. In 2014, An. funestus was resistant to permethrin (65%), lambda cyhalothrin (74%), bendiocarb (65%), and even to deltamethrin (87%) to which it was fully susceptible in 2013. Mortality in control tubes was 4% in both testing rounds. All tested mosquitoes were amplified as An. funestus, using PCR.Figure 3

Bottom Line: Insecticide susceptibility tests indicated high levels of resistance in An. funestus against deltamethrin (87%), permethrin (65%), lambda cyhalothrin (74%), bendiocarb (65%), and DDT (66%).Similarly, An. arabiensis showed insecticide resistance to deltamethrin (64%), permethrin (77%) and lambda cyhalothrin (42%) in 2014.Complementary vector control and surveillance tools are needed that target the ecology, behaviour and insecticide resistance management of these vector species, in order to preserve the efficacy of LLINs.

View Article: PubMed Central - PubMed

Affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Tanzania. dwilson@ihi.or.tz.

ABSTRACT

Background: In order to sustain the gains achieved by current malaria control strategies, robust surveillance systems that monitor dynamics of vectors and their roles in malaria transmission over time are essential. This longitudinal study demonstrates the trends in malaria vector dynamics and their relative contribution to malaria transmission in hyperendemic transmission settings in Tanzania.

Methods: The study was conducted in two villages within the Kilombero Valley, in rural Tanzania for five consecutive years (2008-2012). Seventy-two houses were selected per village and each house was sampled for mosquitoes monthly using a CDC light trap. Collected mosquitoes were assessed for species identity and sporozoite infection status using PCR and ELISA, respectively. Anopheles funestus and Anopheles arabiensis susceptibility to insecticides was assessed using WHO guidelines.

Results: A total of 100,810 malaria vectors were collected, of which 76% were Anopheles gambiae s. l. and 24% were An. funestus. Of all An. funestus samples that amplified with PCR (n = 2,737), 97% were An. funestus s.s., 2% were Anopheles rivorulum and 1% Anopheles leesoni. Whereas for An. gambiae s.l. (n = 8,117), 93% were An. arabiensis and 7% were Anopheles gambiae s.s. The proportion of An. gambiae s.s. identified by PCR (2,924) declined from 0.2% in the year 2008 to undetectable levels in 2012. Malaria transmission intensity significantly decreased from an EIR of 78.14 infectious bites/person/year in 2008 to 35 ib/p/yr in 2011 but rebounded to 226 ib/p/yr in 2012 coinciding with an increased role of An. funestus in malaria transmission. Insecticide susceptibility tests indicated high levels of resistance in An. funestus against deltamethrin (87%), permethrin (65%), lambda cyhalothrin (74%), bendiocarb (65%), and DDT (66%). Similarly, An. arabiensis showed insecticide resistance to deltamethrin (64%), permethrin (77%) and lambda cyhalothrin (42%) in 2014.

Conclusion: The results indicate the continuing role of An. arabiensis and the increasing importance of An. funestus in malaria transmission, and pyrethroid resistance development in both species. Complementary vector control and surveillance tools are needed that target the ecology, behaviour and insecticide resistance management of these vector species, in order to preserve the efficacy of LLINs.

Show MeSH
Related in: MedlinePlus