Featured Research

from universities, journals, and other organizations

Malaria: Effective Insecticide-repellent Synergy Against Mosquito Vectors

Date:
July 24, 2007
Source:
Institut De Recherche Pour Le Développement
Summary:
The mosquitoes responsible for malaria transmission to humans belong to the Anopheles genus. One of the best known and most extensively studied is Anopheles gambiae, Africa's principal malaria vector. The protection recommended by the World Health Organization for people at risk from this devastating disease is the use of mosquito nets impregnated with pyrethroids, of low toxicity for mammals and highly active against mosquitoes.

The mosquitoes responsible for malaria transmission to humans belong to the Anopheles genus. One of the best known and most extensively studied is Anopheles gambiae, Africa’s principal malaria vector. The protection recommended by the World Health Organization for people at risk from this devastating disease is the use of mosquito nets impregnated with pyrethroids, of low toxicity for mammals and highly active against mosquitoes.

Unfortunately, excessive and inappropriate use of this family of insecticide, particularly by spraying, has induced a disturbing rise in the number of resistant individuals in the Anopheles populations. The mosquito nets treated with pyrethroids can therefore lose their effectiveness. It is therefore essential to devise new control strategies against these malaria vectors that are resistant to these insecticides.

IRD researchers and their partners (1) obtained encouraging results by combining a non-pyrethroid insecticide, propoxur, and a repellent, N,N-diethyl toluamide (DEET). They based their investigations on previous work which had revealed a strong synergy between the two components.

A combination of the two had proved to be much more effective than the straightforward addition of their respective properties. Mosquito nets soaked with this mixture had a lethal power and irritant effect that inhibited the mosquitoes from biting. Moreover, the mosquitoes are hit by a powerful paralysing action, known as the “knockdown” effect (3), on contact with the mixture.

The mortality rates determined were satisfactory, in that they equalled those obtained by using deltamethrin, a commonly-used synthetic pyrethroid, highly effective against mosquitoes. The researchers tested two mixtures composed of a non-pyrethroid insecticide of the organophosphate family, combined with either a standard repellent, DEET, or with a new-generation synthetic repellent. Both of these mixtures show a strong synergy in the resulting lethal and paralysing effects on the mosquitoes.

However, only the association between the insecticide and the standard repellent produced a synergistic effect that inhibited the mosquito from taking its blood feed. A synergistic effect was also observed with regard to the treatment’s residual efficacy which is several months longer than that of either agent applied alone.

The advantage of the synergistic property of these combinations is enhanced by the fact that it significantly reduced the necessary effective doses against the mosquitoes (about 6 times that of the insecticide applied alone), to attain an efficacy equivalent to that of deltamethrin.

The nets treated with the two mixtures in the laboratory were subsequently tested in field trials, in the rice-growing area 40 km North of Bobo-Dioulasso, in Burkina Faso. This area has the specificity of harbouring two different forms of Anopheles gambiae. The first appears in May and June in the rice-fields. It shows no resistance to pyrethroids.

The second emerges in September and October in puddles left by monsoon rains. These do show resistance to these insecticides. As expected, the usual pyrethroid-treated nets turned out to be effective only against non-resistant mosquitoes of the first population. Conversely, the nets pre-soaked with non-pyrethroid–repellent combinations proved excellent protection for the people of the local villages, whatever the population of mosquitoes present.

Nevertheless, their residual efficacy (about 15 days) in real conditions did not match the researchers’ expectations. The team consequently envisage working in conjunction with a company able to devise a system for encapsulating the mixture to prolong the residual life of treated mosquito nets.

The efficacy of these mixtures between organophosphates and repellents therefore opens up a new pathway towards controlling pyrethroid-resistant malaria vectors. In the long term, the researchers plan to test their method on mosquitoes resistant to two other types of insecticide utilized against malaria transmission: organophosphates and carbamates.

Notes

(1)This research work was conducted at the IRD laboratory of Cotonou, Benin, with the participation of the Centre de Recherches Entomologiques de Cotonou (CREC), IRD’s Laboratoire de Lutte contre les Insectes Nuisibles (LIN) in Montpellier, and the Institut de recherche en science de la santé, Bobo-Dioulasso, Burkina Faso.

(2)”Combination of a non-pyrethroid insecticide and a repellent: a new approach for controlling knockdown-resistant mosquitoes”. Am. J. Trop. Med. Hyg. 72(6), 2005, pp. 739-744

(3)“Knockdown” effect: action inducing paralysis of the muscles and nervous system, then death, of the insects. It is a characteristic effect of pyrethroid insecticides.

References

Pennetier C, Corbel V and Hougard JM. – “Combining a non-pyrethroid insecticide and a repellent: a new approach for controlling knockdown resistant mosquitoes”, Am.J. Trop. Med Hyg. 2005, 72 (6), 739-744.

Pennetier C, Corbel V, Boko P, Odjo A, N’Guessan R, Lapied B, Hougard JM. –“Synergy between repellents and non-pyrethroid insecticides strongly extends the efficacy of treated nets against Anopheles gambiae.” Malaria Journal , 2007, 6 (1) 38 doi: 10.1186 /1475-2875-6-38


Story Source:

The above story is based on materials provided by Institut De Recherche Pour Le Développement. Note: Materials may be edited for content and length.


Cite This Page:

Institut De Recherche Pour Le Développement. "Malaria: Effective Insecticide-repellent Synergy Against Mosquito Vectors." ScienceDaily. ScienceDaily, 24 July 2007. <www.sciencedaily.com/releases/2007/07/070722222013.htm>.
Institut De Recherche Pour Le Développement. (2007, July 24). Malaria: Effective Insecticide-repellent Synergy Against Mosquito Vectors. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2007/07/070722222013.htm
Institut De Recherche Pour Le Développement. "Malaria: Effective Insecticide-repellent Synergy Against Mosquito Vectors." ScienceDaily. www.sciencedaily.com/releases/2007/07/070722222013.htm (accessed July 23, 2014).

Share This




More Plants & Animals News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Michigan Plant's Goal: Flower and Die

Michigan Plant's Goal: Flower and Die

AP (July 22, 2014) — An 80-year-old agave plant, which is blooming for the first and only time at a University of Michigan conservatory, will die when it's done (July 22) Video provided by AP
Powered by NewsLook.com
San Diego Zoo Welcomes New, Rare Rhino Calf

San Diego Zoo Welcomes New, Rare Rhino Calf

Reuters - US Online Video (July 21, 2014) — An endangered black rhino baby is the newest resident at the San Diego Zoo. Sasha Salama reports. Video provided by Reuters
Powered by NewsLook.com
Shark Sightings a Big Catch for Cape Tourism

Shark Sightings a Big Catch for Cape Tourism

AP (July 21, 2014) — A rise in shark sightings along the shores of Chatham, Massachusetts is driving a surge of eager vacationers to the beach town looking to catch a glimpse of a great white. (July 21) Video provided by AP
Powered by NewsLook.com
$23.6 Billion Awarded To Widow In Smoking Lawsuit

$23.6 Billion Awarded To Widow In Smoking Lawsuit

Newsy (July 20, 2014) — Cynthia Robinson claims R.J. Reynolds Tobacco Company hid the health and addiction risks of its products, leading to the death of her husband in 1996. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins