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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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Impact of insecticides on mosquito behaviour around and insides houses. The graph illustrates the effect of DDT, Transfluthrin and Metofluthrin coils on the house entry and behaviour of 100 female An. arabiensis and An. gambiae s.s. mosquitoes are approaching the house. Assumptions made included the fact that deterrence was the first mode of action followed by irritancy, feeding inhibition, toxicity and fecundity. The data used was derived from field experiments for deterrence and semi-field system experiments for irritancy, feeding inhibition, toxicity and fecundity.
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Figure 8: Impact of insecticides on mosquito behaviour around and insides houses. The graph illustrates the effect of DDT, Transfluthrin and Metofluthrin coils on the house entry and behaviour of 100 female An. arabiensis and An. gambiae s.s. mosquitoes are approaching the house. Assumptions made included the fact that deterrence was the first mode of action followed by irritancy, feeding inhibition, toxicity and fecundity. The data used was derived from field experiments for deterrence and semi-field system experiments for irritancy, feeding inhibition, toxicity and fecundity.

Mentions: Using figures collected from the field (deterrence) and the semi field experiments (irritancy, feeding inhibition, mortality and fecundity) it can be seen that in a scenario where 100 mosquitoes approach a house, deterrence comes into play in the first instance and only approximately 62, 70 and 92 mosquitoes enter the house with Transfluthrin, Metofluthrin coils and DDT respectively. The next behavioural effect of the insecticides is then likely to be irritancy or excito–repellency. After mosquitoes are repelled and exit a house, 35, 39 and 44 would remain inside the house with Transfluthrin, Metofluthrin coils and DDT respectively. Of those, approximately 1, 3 and 10 mosquitoes would manage to acquire a blood meal, which in turn directly influences the proportion of eggs laid, i.e. female mosquito fecundity. Lastly, the survival rate of mosquitoes in Transfluthrin and Metofluthrin huts would be close to 0 and approximately 10 in DDT huts (Figure 8). This implies that through deterrence, irritancy and feeding inhibition of pyrethroid coils and DDT, more than 90% of the mosquitoes would be prevented from contacting humans inside houses before mortality is even considered. By reducing human-vector contact, coils and DDT directly influence the biting rate of mosquitoes (ma): an important parameter of malaria transmission Vectorial capacity equation, subsection). The data collected on DDT, agrees with field observations [9] of feeding inhibition and population level data that consistently demonstrate a reduction in the Human Blood Index (HBI) after DDT is applied to dwellings [32,33]. However, the experimental design does have the limitation of combining data from two species: An. arabiensis and An. gambiae s.s.


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)

Impact of insecticides on mosquito behaviour around and insides houses. The graph illustrates the effect of DDT, Transfluthrin and Metofluthrin coils on the house entry and behaviour of 100 female An. arabiensis and An. gambiae s.s. mosquitoes are approaching the house. Assumptions made included the fact that deterrence was the first mode of action followed by irritancy, feeding inhibition, toxicity and fecundity. The data used was derived from field experiments for deterrence and semi-field system experiments for irritancy, feeding inhibition, toxicity and fecundity.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 8: Impact of insecticides on mosquito behaviour around and insides houses. The graph illustrates the effect of DDT, Transfluthrin and Metofluthrin coils on the house entry and behaviour of 100 female An. arabiensis and An. gambiae s.s. mosquitoes are approaching the house. Assumptions made included the fact that deterrence was the first mode of action followed by irritancy, feeding inhibition, toxicity and fecundity. The data used was derived from field experiments for deterrence and semi-field system experiments for irritancy, feeding inhibition, toxicity and fecundity.
Mentions: Using figures collected from the field (deterrence) and the semi field experiments (irritancy, feeding inhibition, mortality and fecundity) it can be seen that in a scenario where 100 mosquitoes approach a house, deterrence comes into play in the first instance and only approximately 62, 70 and 92 mosquitoes enter the house with Transfluthrin, Metofluthrin coils and DDT respectively. The next behavioural effect of the insecticides is then likely to be irritancy or excito–repellency. After mosquitoes are repelled and exit a house, 35, 39 and 44 would remain inside the house with Transfluthrin, Metofluthrin coils and DDT respectively. Of those, approximately 1, 3 and 10 mosquitoes would manage to acquire a blood meal, which in turn directly influences the proportion of eggs laid, i.e. female mosquito fecundity. Lastly, the survival rate of mosquitoes in Transfluthrin and Metofluthrin huts would be close to 0 and approximately 10 in DDT huts (Figure 8). This implies that through deterrence, irritancy and feeding inhibition of pyrethroid coils and DDT, more than 90% of the mosquitoes would be prevented from contacting humans inside houses before mortality is even considered. By reducing human-vector contact, coils and DDT directly influence the biting rate of mosquitoes (ma): an important parameter of malaria transmission Vectorial capacity equation, subsection). The data collected on DDT, agrees with field observations [9] of feeding inhibition and population level data that consistently demonstrate a reduction in the Human Blood Index (HBI) after DDT is applied to dwellings [32,33]. However, the experimental design does have the limitation of combining data from two species: An. arabiensis and An. gambiae s.s.

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