Killer mosquitoes on mission to save mankind

Mad scientists load blood-sucking flying insects with toxic chemical bombs which are then dropped killing millions of their own kind. Science fiction? Think again. Not-so-mad researchers working in the Amazon city of Iquitos in Peru, have turned normal adult mosquitoes, the Dengue (and Yellow Fever) carrier Aedes aegypti, into infanticidal beasts by making them carry an insecticide to their breeding sites thus killing most of the eggs and larvae living there.

The insecticide, placed in resting areas of the mosquitoes, will stick to the insects’ bodies when they fly off to aquatic habitat to lay eggs. There, the insecticide will destroy immature mosquitoes at that site and wherever else they fly to deposit more eggs.

This is a huge breakthrough in mosquito control, say experts. It replaces costly and not very effective spraying of habitats, many of them hidden and cryptic, where mosquitoes lay their eggs and larvae develop. The method is also relevant to small island states where human settlements are clustered in coastal areas because it involves the control of mosquitoes that develop in small, protected aquatic habitats in urban areas

The senior author Gregor J. Devine and his colleagues from the UK, Peru, Tanzania and the US have published this work entitled “Using adult mosquitoes to transfer insecticides to Aedes aegypti larval habitats” in the Proceedings of the National Academy of Sciences (PNAS) of June 29 http://www.pnas.org/content/106/28/11530.full

The insecticide used is called pyriproxyfen which is an equivalent of an insect juvenile hormone. In the study it was placed at dissemination stations in a known resting area of mosquitoes in a cemetery in Iquitos. The pyriproxyfen was placed in only 3 to 5 percent of the total resting area, but it destroyed 42 to 98 percent of mosquitoes about to emerge at each breeding site.

Pyriproxyfen does not interfere with the fundamental behaviors of mosquitoes because it is neither lethal nor repellent to adults. “It is the act of oviposition (egg-laying) that contaminates the aquatic habitat, so the technique explicitly and precisely targets the mosquitoes’ preferred breeding sites.” the paper says.

Pyriproxyfen is also harmless to humans It is registered for public health use and the World Health Organization states that it is safe for drinking at 300 parts per billion, which is 1000 times the dose used by the researchers in the study.

Globally, 50 million dengue infections annually result in 500,000 cases of dengue hemorrhagic fever and 22,000 deaths. The most severe form of the disease, dengue haemorrhagic fever (DHF), strikes a half million people a year. Dengue is spread by Aedes aegypti as well as the Asian Tiger Mosquito Aedes albopictus, a widely occurring mosquito in Seychelles

The results of this study have now raised hopes that not just Dengue but other mosquito borne diseases can finally be controlled in our lifetime.

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Mosquitoes and Fevers

As the rainy season approaches I have noticed that the Asian Tiger Mosquito, that striped flying monster which is the carrier or vector for both chikungunya and dengue, is increasing in number and range. Research also suggests that climate change is assisting the spread of this mosquito in many parts of the world.

And the chikungunya virus keeps mutating. We already know that the last Indian Ocean outbreaks were caused by a different strain of the virus. This strain differs from those involved in earlier outbreaks and makes the virus more likely to enter the cells of the Asian Tiger Mosquito and replicate after the insect has fed on the blood of an infected person. In fact, the symptoms are also changing. At a meeting of WHO last month it was suggested revising the definition of chikungunya fever because researchers have noticed the symptoms have changed.

This points to the fact that there needs to be timely and better identification of fever cases. But for prevention there needs to be early warning systems set up in countries like Seychelles. In La Reunion, where the chikungunya outbreaks caused massive health, economic and social problems, a surveillance system is now in place. This collects information on the mosquito density in every area which is then used in scientific models to predict where the next outbreak might occur. The system gives citizens and government advance warning.

The mosquito density is only a possible indication of the presence of the chikungunya virus and not a certainty, but it does give an advance warning for early action. In some countries better early warning systems especially based on gis (geographical information system) are under development. gis -based modeling can predict chikungunya-prone areas using information on the distribution of the mosquito vectors, rainfall, temperature, altitude, vegetation cover and urbanization.

More sophisticated data such as on the mosquitoes’ ability to transmit the disease and the susceptibility of people in different parts of the country can also be used in GIS-based models to predict the spread of the disease and help pinpoint the time when an outbreak could become an epidemic.

In Seychelles such GIS based modeling would be very useful. Both Dengue and chikungunya cause huge hardships, loss of productivity and losses of millions of Rupees. The country does have a GIS unit with good GIS maps. Perhaps donors should be approached to assist with setting up with a GIS-based early warning system. Putting this in place is not as simple as it sounds but is greatly needed because early action based on early warning is critical in preventing an epidemic.