Wiping out mosquito-borne diseases - with mosquitoes

Scientists fighting mosquito-borne diseases are racing to obtain approval to release genetically modified insects designed to stop the spread of dengue, a potentially fatal virus.



However, such moves have made environmentalists nervous as a science long used in agriculture is applied to public health.



These mosquitoes are engineered with an extra gene or inserted bacterium or have had a gene altered so that either their offspring are sterile and unable to spread dengue, or simply die.



"People generally do not like the unknown and are alarmist. Because there has never been a [field] release of GM [genetically modified] mosquitoes, critics are free to imagine what can possibly go wrong," said UK-based entomologist and professor at Imperial College London, John Mumford.



He is also the principal investigator for the World Health Organization (WHO)-funded regulatory group, Mosqguide, founded to develop best practices for deploying genetically modified mosquitoes to fight mosquito-borne diseases, primarily dengue and malaria.



For half a century, scientists have released billions of engineered insects - for example, fruit flies - to save plants, but to date there has not been a field release of insects engineered to save humans.



The Malaysia-headquartered NGO Pesticide Action Network-Asia and the Pacific opposed a since-granted request to release modified mosquitoes on the grounds that "it may have environmental or health consequences as well as carry risks arising from horizontal gene transfer", wrote executive director, Sarojeni V. Rengam, who stressed the "possibility of new health risks to humans and animals....the insect may become more virulent, aggressive, or its bite might have different effects on the host."



According to the Malaysian Health Ministry, 37,419 dengue cases were reported from January to 2 October, an increase of 17 percent on the same period last year.



Balancing act



If fish eat the larvae of modified mosquitoes and people eat the fish, one fear is how this diet may affect people, Mumford explained. "But we are forgetting that people eat modified corn and soybeans," he said.



"We have to look at the balance of risks. The risk of not controlling dengue is well-known. People die without better vector control... We need to move from worrying about risks to looking at public health benefits and addressing these risks," Mumford added.



The WHO estimates at least 50 million people worldwide are infected with dengue annually, with the number of cases doubling in the past decade and 70 percent of them recorded in Asia.



Australian researchers from the University of Queensland, funded by the Bill & Melinda Gates Foundation, have received regulatory approval to begin in December to release mosquitoes infected with a bacterium that prevents the dengue virus from multiplying, as has the Malaysian Ministry of Health.



In addition, Brazil, Panama, the US, Italy and Sudan are at varying stages in fighting mosquito-borne diseases with mosquitoes. "There are a lot of competing strategies, which is a good thing," said Mumford.



Mosqguide is cataloguing these different approaches and expects to publish case studies over the next year.



pt/ds/mw