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An experimental hut study to quantify the effect of DDT and airborne pyrethroids on entomological parameters of malaria transmission.

Ogoma SB, Lorenz LM, Ngonyani H, Sangusangu R, Kitumbukile M, Kilalangongono M, Simfukwe ET, Mseka A, Mbeyela E, Roman D, Moore J, Kreppel K, Maia MF, Moore SJ - Malar. J. (2014)

Bottom Line: Outcomes were deterrence--reduction in house entry of mosquitoes; irritancy or excito-repellency--induced premature exit of mosquitoes; blood feeding inhibition and effect on mosquito fecundity.These effects are in addition to significant toxicity and reduced mosquito fecundity that affect mosquito densities and, therefore, provide community protection against diseases for both users and non-users.Airborne insecticides and freshly applied DDT had similar effects on deterrence, irritancy and feeding inhibition.

View Article: PubMed Central - HTML - PubMed

Affiliation: Ifakara Health Institute, Environmental Health and Ecological Sciences, P,O, Box 74, Bagamoyo, Tanzania. sogoma@ihi.or.tz.

ABSTRACT

Background: Current malaria vector control programmes rely on insecticides with rapid contact toxicity. However, spatial repellents can also be applied to reduce man-vector contact, which might ultimately impact malaria transmission. The aim of this study was to quantify effects of airborne pyrethroids from coils and DDT used an indoor residual spray (IRS) on entomological parameters that influence malaria transmission.

Methods: The effect of Transfluthrin and Metofluthrin coils compared to DDT on house entry, exit and indoor feeding behaviour of Anopheles gambiae sensu lato were measured in experimental huts in the field and in the semi-field. Outcomes were deterrence--reduction in house entry of mosquitoes; irritancy or excito-repellency--induced premature exit of mosquitoes; blood feeding inhibition and effect on mosquito fecundity.

Results: Transfluthrin coils, Metofluthrin coils and DDT reduced human vector contact through deterrence by 38%, 30% and 8%, respectively and induced half of the mosquitoes to leave huts before feeding (56%, 55% and 48%, respectively). Almost all mosquitoes inside huts with Metofluthrin and Transfluthrin coils and more than three quarters of mosquitoes in the DDT hut did not feed, almost none laid eggs and 67%, 72% and 70% of all mosquitoes collected from Transfluthrin, Metofluthrin and DDT huts, respectively had died after 24 hours.

Conclusion: This study highlights that airborne pyrethroids and DDT affect a range of anopheline mosquito behaviours that are important parameters in malaria transmission, namely deterrence, irritancy/excito-repellency and blood-feeding inhibition. These effects are in addition to significant toxicity and reduced mosquito fecundity that affect mosquito densities and, therefore, provide community protection against diseases for both users and non-users. Airborne insecticides and freshly applied DDT had similar effects on deterrence, irritancy and feeding inhibition. Therefore, it is suggested that airborne pyrethroids, if delivered in suitable formats, may complement existing mainstream vector control tools.

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Process of collecting mosquitoes from experimental huts. A: A coil placed on the floor 0.5 m from the volunteer B: HN collecting mosquitoes from exit traps using a mouth aspirator; C: AM collecting resting mosquitoes using a backpack aspirator; D: HN sorting mosquitoes and keeping them in individual tubes for checking oviposition.
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Figure 5: Process of collecting mosquitoes from experimental huts. A: A coil placed on the floor 0.5 m from the volunteer B: HN collecting mosquitoes from exit traps using a mouth aspirator; C: AM collecting resting mosquitoes using a backpack aspirator; D: HN sorting mosquitoes and keeping them in individual tubes for checking oviposition.

Mentions: Four Ifakara design experimental huts (Figure 2) fitted with window and eave exit traps were used inside the SFS. The huts were placed in individual compartments separated by 10 metres and a netting screen. A fully-randomized fully-balanced 4 × 4 Latin square design was performed to determine efficacy of DDT used as IRS, Transfluthrin and Metofluthrin coils in four experimental huts. The treatments were tested for four nights per week. Therefore, one balanced round of experiments was completed in 16 days. The treatments tested were: 1) standard control – DDT as IRS; 2) negative control – no insecticide used; 3) two Transfluthrin coils (0.03%) per hut each night and 4) two Metofluthrin (0.00625%) coils per hut each night. Treatments and two male volunteers were randomly allocated to each hut. The pair of volunteers was rotated between huts every fourth night while the treatments remained in the same huts during the entire study period. Equal numbers of mosquitoes were used in each compartment, hence there was no need to rotate the treatments between huts to minimize location bias as is the case in field experiment. Experiments began each evening at 1930 hours when volunteers entered respective huts. Technicians placed two lit coils on the floor 0.5 m from the volunteer inside respective huts (Figure 5A). After 10 minutes, the volunteers simultaneously released 100 female mosquitoes in each hut from netting cages. The volunteers slept on mattresses on the floor and did not use bed nets.


An experimental hut study to quantify the effect of DDT and airborne pyrethroids on entomological parameters of malaria transmission.

Ogoma SB, Lorenz LM, Ngonyani H, Sangusangu R, Kitumbukile M, Kilalangongono M, Simfukwe ET, Mseka A, Mbeyela E, Roman D, Moore J, Kreppel K, Maia MF, Moore SJ - Malar. J. (2014)

Process of collecting mosquitoes from experimental huts. A: A coil placed on the floor 0.5 m from the volunteer B: HN collecting mosquitoes from exit traps using a mouth aspirator; C: AM collecting resting mosquitoes using a backpack aspirator; D: HN sorting mosquitoes and keeping them in individual tubes for checking oviposition.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4230423&req=5

Figure 5: Process of collecting mosquitoes from experimental huts. A: A coil placed on the floor 0.5 m from the volunteer B: HN collecting mosquitoes from exit traps using a mouth aspirator; C: AM collecting resting mosquitoes using a backpack aspirator; D: HN sorting mosquitoes and keeping them in individual tubes for checking oviposition.
Mentions: Four Ifakara design experimental huts (Figure 2) fitted with window and eave exit traps were used inside the SFS. The huts were placed in individual compartments separated by 10 metres and a netting screen. A fully-randomized fully-balanced 4 × 4 Latin square design was performed to determine efficacy of DDT used as IRS, Transfluthrin and Metofluthrin coils in four experimental huts. The treatments were tested for four nights per week. Therefore, one balanced round of experiments was completed in 16 days. The treatments tested were: 1) standard control – DDT as IRS; 2) negative control – no insecticide used; 3) two Transfluthrin coils (0.03%) per hut each night and 4) two Metofluthrin (0.00625%) coils per hut each night. Treatments and two male volunteers were randomly allocated to each hut. The pair of volunteers was rotated between huts every fourth night while the treatments remained in the same huts during the entire study period. Equal numbers of mosquitoes were used in each compartment, hence there was no need to rotate the treatments between huts to minimize location bias as is the case in field experiment. Experiments began each evening at 1930 hours when volunteers entered respective huts. Technicians placed two lit coils on the floor 0.5 m from the volunteer inside respective huts (Figure 5A). After 10 minutes, the volunteers simultaneously released 100 female mosquitoes in each hut from netting cages. The volunteers slept on mattresses on the floor and did not use bed nets.

Bottom Line: Outcomes were deterrence--reduction in house entry of mosquitoes; irritancy or excito-repellency--induced premature exit of mosquitoes; blood feeding inhibition and effect on mosquito fecundity.These effects are in addition to significant toxicity and reduced mosquito fecundity that affect mosquito densities and, therefore, provide community protection against diseases for both users and non-users.Airborne insecticides and freshly applied DDT had similar effects on deterrence, irritancy and feeding inhibition.

View Article: PubMed Central - HTML - PubMed

Affiliation: Ifakara Health Institute, Environmental Health and Ecological Sciences, P,O, Box 74, Bagamoyo, Tanzania. sogoma@ihi.or.tz.

ABSTRACT

Background: Current malaria vector control programmes rely on insecticides with rapid contact toxicity. However, spatial repellents can also be applied to reduce man-vector contact, which might ultimately impact malaria transmission. The aim of this study was to quantify effects of airborne pyrethroids from coils and DDT used an indoor residual spray (IRS) on entomological parameters that influence malaria transmission.

Methods: The effect of Transfluthrin and Metofluthrin coils compared to DDT on house entry, exit and indoor feeding behaviour of Anopheles gambiae sensu lato were measured in experimental huts in the field and in the semi-field. Outcomes were deterrence--reduction in house entry of mosquitoes; irritancy or excito-repellency--induced premature exit of mosquitoes; blood feeding inhibition and effect on mosquito fecundity.

Results: Transfluthrin coils, Metofluthrin coils and DDT reduced human vector contact through deterrence by 38%, 30% and 8%, respectively and induced half of the mosquitoes to leave huts before feeding (56%, 55% and 48%, respectively). Almost all mosquitoes inside huts with Metofluthrin and Transfluthrin coils and more than three quarters of mosquitoes in the DDT hut did not feed, almost none laid eggs and 67%, 72% and 70% of all mosquitoes collected from Transfluthrin, Metofluthrin and DDT huts, respectively had died after 24 hours.

Conclusion: This study highlights that airborne pyrethroids and DDT affect a range of anopheline mosquito behaviours that are important parameters in malaria transmission, namely deterrence, irritancy/excito-repellency and blood-feeding inhibition. These effects are in addition to significant toxicity and reduced mosquito fecundity that affect mosquito densities and, therefore, provide community protection against diseases for both users and non-users. Airborne insecticides and freshly applied DDT had similar effects on deterrence, irritancy and feeding inhibition. Therefore, it is suggested that airborne pyrethroids, if delivered in suitable formats, may complement existing mainstream vector control tools.

Show MeSH
Related in: MedlinePlus