01 April 2014

Towards effective spatial mosquito repellent

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Repellents derived from Greek herb extracts show potent effects against malaria carrying mosquitoes. They constitute a more sustainable solution that traditional repellent.

Global warming is leading to an increase in mosquito-borne diseases such as malaria. It is considered the plague of developing countries. According to the World Health Organisation, it is responsible for one child death every minute. A major challenge in combatting malaria is thus to develop effective, yet sustainable, mosquito repellents. Now, the ENAROMaTIC project, completed in 2012, may have done just that. “We have developed natural nontoxic products that alone and in combination are as good as or even better than DEET as spatial repellents,” says Kostas Iatrou, research director of the Institute of Biosciences and Applications of the National Centre for Scientific Research Demokritos, in Athens, Greece, who is also the project coordinator. Their efficacy as spatial repellents was demonstrated in field trials in Nigeria.

The project findings are thought by experts to be extremely significant. “Efforts to develop repellents that provide protection from bites by malaria mosquitoes are expected to have a major impact in disease control strategies,” comments Antony James, distinguished professor of microbiology, molecular genetics, molecular biology and biochemistry at the University of California-Irvine, USA. “The recent development of these tools is a major step forward in personal protection tools,” he tells youris.com.

Malaria is transmitted by female mosquitoes sucking blood from their human hosts. The main goal of the project was to reduce the spread of malaria. Specifically, it aimed to reduce malaria transmission rates by interfering with the way Anopheles gambiae detects the presence of odours of human origin in its environment, when searching for a blood meal. “We discovered … that extracts from the same herb can either repel or attract mosquitoes,” Iatrou tells youris.com, adding: “Moreover, frequently the same substance in different concentrations can either repel or attract mosquitoes.”

Specific blends of these compounds appear to be even more powerful than the repellents in current use. “These products could be considered as components of an integrated approach to reducing mosquito bites within households, whereas DEET might not because of misgivings about its safety,” notes Iatrou. Instead, he claims the project’s repellents are environmentally responsible compounds derived from natural products and sustainable sources. The repellents developed under the project are now ready for large-scale commercial development and the consortium announced the availability of production licenses in August 2012.

This approach appears to tackle the main limitation with existing repellents, which is that they are short-lived. “The best on the market, DEET, is effective for only 4 hours so does not last through the night, leaving the person vulnerable to mosquito bites once the repellent has worn off,” says Maureen Coetzee, Director at the Wits Research Institute for Malaria, University of the Witwatersrand, in Johannesburg, South Africa. “If [these] product has overcome this limitation, then that is a real advance”, Coetzee tells youris.com.

But research on mosquitoes and malaria does not stop here, Iatrou believes. “Mosquitoes develop impressive resistance mechanisms, mainly against insecticides and, possibly, against repellents too. We want to be ready for mosquitoes' potential resistance development so we are already expanding our arsenal. We still have a variety of herbs and plants that have not been analysed” explains Iatrou. “We have a lot of work ahead of us.”

“It has been demonstrated in the laboratory that mosquitoes can also become ‘insensitive’ to repellents such as DEET, no longer being repelled by them,” says Nina Stanczyk, research fellow at the department of disease control of the London School of Hygiene & Tropical Medicine, UK, tells youris.com. “One of the best ways to prepare for the possibility of repellent insensitivity in the future is to fully understand the pathways and mechanisms by which repellents work, which is a large part of the project. Repellents are best used in conjunction with other methods of control, but are an excellent way of providing personal protection.” says Stanczyk.

The findings go one step further. “The [project] group seized the opportunity to tackle important questions about mosquito biology, particularly how they sense the environment,” notes Walter Leal, professor of entomology at the University of California-Davis, USA. “Clearly, the best way to prevent and, or reduce vector-borne diseases is to reduce populations of the vector, but this can be done only with an in-depth knowledge of the biology of the animal,” he tells youris.com. He then concludes that it is exactly what the project is doing.

Project scientists made an unexpected discovery. “Although our compounds were designed using proteins from the Anopheles mosquito, which is the carrier of malaria, the same compounds had significant repellent action against a wide variety of blood feeding and biting insects, like the Culex mosquitoes, which is the carrier of other diseases, such as West Nile Virus,” says Iatrou. The project’s discovery could thus pave the way for a broad-spectrum repellent in the near future.

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