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Efficacy of Bacillus thuringiensis var. israelensis against malaria mosquitoes in northwestern Burkina Faso.

Dambach P, Louis VR, Kaiser A, Ouedraogo S, Sié A, Sauerborn R, Becker N - Parasit Vectors (2014)

Bottom Line: All used concentrations successfully killed 100 percent of the larvae within 24 hours, while the higher concentrations showed a slightly prolonged residual effect.For the higher concentrations, up to three days no new larvae were found, implicating that the residual effect of WDG in tropical conditions is approximately one to two days.The overall pupae reduction in treated tubs was 98.5%.

View Article: PubMed Central - PubMed

Affiliation: Institute of Public Health, University of Heidelberg, Heidelberg, Germany. peter.dambach@web.de.

ABSTRACT

Background: In Sub Saharan Africa malaria remains one of the major health problems and its control represents an important public health measure. Integrated malaria control comprises the use of impregnated mosquito nets and indoor residual spraying. The use of drugs to treat patients can create additional pressure on the equation of malaria transmission. Vector control may target the adult mosquitoes or their aquatic larval stages. Biological larvicides such as Bacillus thuringiensis israelensis (Bti) represent a promising approach to support malaria control programs by creating additional pressure on the equation of malaria transmission.

Methods: In this study we examined the efficacy of a water-dispersible granule formulation (WDG) of the biological larvicide Bti (VectoBac®) against wild Anopheles spp. larvae. Different concentrations of the larvicide were tested in standardized plastic tubs in the field against untreated controls. In weekly intervals tubs were treated with fixed concentrations of larvicide and the percentage reduction of larvae and pupae was calculated.

Results: All used concentrations successfully killed 100 percent of the larvae within 24 hours, while the higher concentrations showed a slightly prolonged residual effect. Natural reconolization of larvae took place after two and three days respectively, late instar larvae were not found before 5 days after treatment. For the higher concentrations, up to three days no new larvae were found, implicating that the residual effect of WDG in tropical conditions is approximately one to two days. The overall pupae reduction in treated tubs was 98.5%.

Conclusions: Biological larviciding with Bti can be a promising, additional tool in the fight against malaria in Africa. Environmental particularities in tropical Africa, first and foremost the rapid development of mosquitoes from oviposition to imago have to be taken into account before implementing such counter measures in national or international vector control programs. Nonetheless biological larviciding seems to be an appropriate measure for selected conditions, offering a significant contribution to the future of malaria control.

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Related in: MedlinePlus

Population dynamics of early larval instars, late instars and pupae ofAnopheles spp. in open field trials exposed to water-dispersible granule (WDG) ofBti. Arrows indicate the date of treatment. Trial period from December 26th 2012 to January 23rd 2013. White horizontal bars indicate no significant difference between treatment and control tubs, blue bars do (dark blue: α = 0,05; light blue α = 0,10). Days with precipitations are indicated and amount of rainfall is given in millimeters.
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Fig2: Population dynamics of early larval instars, late instars and pupae ofAnopheles spp. in open field trials exposed to water-dispersible granule (WDG) ofBti. Arrows indicate the date of treatment. Trial period from December 26th 2012 to January 23rd 2013. White horizontal bars indicate no significant difference between treatment and control tubs, blue bars do (dark blue: α = 0,05; light blue α = 0,10). Days with precipitations are indicated and amount of rainfall is given in millimeters.

Mentions: All concentrations tested showed a 100% reduction of larvae within the first 24 hours after application. Over time in both rounds (October/November 2012 and December/January 2012/13) and all sample cycles, natural declines and increases of larval densities were observed in the control and treatment groups. The first round of larvicide application showed reoccurrence of early instars after one to two days. In round two, early instar larvae were found after two days in the lowest concentration of 0.2 mg/l, and after three days in the higher concentrations. After five to six days in rounds one and two respectively, all concentrations showed late instar larvae. Pupae were only found in a small number of cases, mostly towards the end of each assay. During the first 21 days of each round virtually no pupae were found in the treated tubs. Despite the low residual effect of all WDG Bti concentrations of approximately two days and the fast recolonization with Anopheles larvae, the absence of pupae was significant. The overall pupal reduction in treated tubs averaged over both rounds was 98.5%, which is a proxy for the efficacy in reducing the emergence of adult mosquitoes. The second round of open field trials (from December 26th 2012 on) showed generally higher reduction rates and slightly longer residual effects. The lowest concentration showed in both rounds a shortened residual effect, which can be observed particularly amongst early instar larvae in the first and second application run. The detailed results are shown in Figure 1, Figure 2, and Table 1, Table 2.Figure 1


Efficacy of Bacillus thuringiensis var. israelensis against malaria mosquitoes in northwestern Burkina Faso.

Dambach P, Louis VR, Kaiser A, Ouedraogo S, Sié A, Sauerborn R, Becker N - Parasit Vectors (2014)

Population dynamics of early larval instars, late instars and pupae ofAnopheles spp. in open field trials exposed to water-dispersible granule (WDG) ofBti. Arrows indicate the date of treatment. Trial period from December 26th 2012 to January 23rd 2013. White horizontal bars indicate no significant difference between treatment and control tubs, blue bars do (dark blue: α = 0,05; light blue α = 0,10). Days with precipitations are indicated and amount of rainfall is given in millimeters.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4262221&req=5

Fig2: Population dynamics of early larval instars, late instars and pupae ofAnopheles spp. in open field trials exposed to water-dispersible granule (WDG) ofBti. Arrows indicate the date of treatment. Trial period from December 26th 2012 to January 23rd 2013. White horizontal bars indicate no significant difference between treatment and control tubs, blue bars do (dark blue: α = 0,05; light blue α = 0,10). Days with precipitations are indicated and amount of rainfall is given in millimeters.
Mentions: All concentrations tested showed a 100% reduction of larvae within the first 24 hours after application. Over time in both rounds (October/November 2012 and December/January 2012/13) and all sample cycles, natural declines and increases of larval densities were observed in the control and treatment groups. The first round of larvicide application showed reoccurrence of early instars after one to two days. In round two, early instar larvae were found after two days in the lowest concentration of 0.2 mg/l, and after three days in the higher concentrations. After five to six days in rounds one and two respectively, all concentrations showed late instar larvae. Pupae were only found in a small number of cases, mostly towards the end of each assay. During the first 21 days of each round virtually no pupae were found in the treated tubs. Despite the low residual effect of all WDG Bti concentrations of approximately two days and the fast recolonization with Anopheles larvae, the absence of pupae was significant. The overall pupal reduction in treated tubs averaged over both rounds was 98.5%, which is a proxy for the efficacy in reducing the emergence of adult mosquitoes. The second round of open field trials (from December 26th 2012 on) showed generally higher reduction rates and slightly longer residual effects. The lowest concentration showed in both rounds a shortened residual effect, which can be observed particularly amongst early instar larvae in the first and second application run. The detailed results are shown in Figure 1, Figure 2, and Table 1, Table 2.Figure 1

Bottom Line: All used concentrations successfully killed 100 percent of the larvae within 24 hours, while the higher concentrations showed a slightly prolonged residual effect.For the higher concentrations, up to three days no new larvae were found, implicating that the residual effect of WDG in tropical conditions is approximately one to two days.The overall pupae reduction in treated tubs was 98.5%.

View Article: PubMed Central - PubMed

Affiliation: Institute of Public Health, University of Heidelberg, Heidelberg, Germany. peter.dambach@web.de.

ABSTRACT

Background: In Sub Saharan Africa malaria remains one of the major health problems and its control represents an important public health measure. Integrated malaria control comprises the use of impregnated mosquito nets and indoor residual spraying. The use of drugs to treat patients can create additional pressure on the equation of malaria transmission. Vector control may target the adult mosquitoes or their aquatic larval stages. Biological larvicides such as Bacillus thuringiensis israelensis (Bti) represent a promising approach to support malaria control programs by creating additional pressure on the equation of malaria transmission.

Methods: In this study we examined the efficacy of a water-dispersible granule formulation (WDG) of the biological larvicide Bti (VectoBac®) against wild Anopheles spp. larvae. Different concentrations of the larvicide were tested in standardized plastic tubs in the field against untreated controls. In weekly intervals tubs were treated with fixed concentrations of larvicide and the percentage reduction of larvae and pupae was calculated.

Results: All used concentrations successfully killed 100 percent of the larvae within 24 hours, while the higher concentrations showed a slightly prolonged residual effect. Natural reconolization of larvae took place after two and three days respectively, late instar larvae were not found before 5 days after treatment. For the higher concentrations, up to three days no new larvae were found, implicating that the residual effect of WDG in tropical conditions is approximately one to two days. The overall pupae reduction in treated tubs was 98.5%.

Conclusions: Biological larviciding with Bti can be a promising, additional tool in the fight against malaria in Africa. Environmental particularities in tropical Africa, first and foremost the rapid development of mosquitoes from oviposition to imago have to be taken into account before implementing such counter measures in national or international vector control programs. Nonetheless biological larviciding seems to be an appropriate measure for selected conditions, offering a significant contribution to the future of malaria control.

Show MeSH
Related in: MedlinePlus