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[MANILA] A trap that uses an extract from black pepper to kill mosquito eggs and larvae has dramatically cut rates of dengue fever in areas of the Philippines where it has been tested, say its developers.

Scientists have known that extracts of black pepper (Piper nigrum) kill larvae, and chemicals similar to those found in black peppercorns have been suggested as mosquito repellents.

Now Nuna Almanzor, director of the Industrial Technology Development Institute, at the Philippine Department of Science and Technology (*), says researchers at this institute have developed a special formula with an additional ingredient that boosts peppercorn's anti-mosquito activity.

But she declined to give the exact details of the mechanism for intellectual property reasons, while the institute waits for a patent approval.

Female mosquitoes are attracted to the black colour of a trap container, where they lay eggs on a wooden stick submerged under the water solution containing peppercorn.

Only two per cent of these eggs hatch and mature into adults, and the solution also kills adult mosquitoes by interfering with their feeding ability, said Almanzor.

In two provinces south of Manila, where the trap was launched in February, dengue cases dropped sharply in the first six months of 2011 compared with the same period in 2010.

In Northern Samar, dengue cases dropped from 74 to zero, and in Leyte from 190 down to three. Dengue cases in areas without the traps have remained high.

Almanzor said they have agreements with two firms to produce commercially a pellet containing the pepper. The traps could be made at home or purchased for less than ten Philippine peso (around 20 US cents) and a pack of five-to-ten pellets will cost just two US cents. One pellet will be enough to trap mosquitoes for a week and an average household may need up to four traps.

The Department of Health will be promoting the traps in places of high dengue incidence.

Dengue fever, spread by the Aedes aegypti mosquito, is common in Asia and Latin America, but there is no cure or vaccine yet. Last year there were 120,000 dengue fever cases in the Philippines

Almanzor said that the traps could be useful in other countries and for curbing other diseases, such as malaria, since they work with any mosquito species.

Nelia Salazar, a consultant for the Research Institute for Tropical Medicine, at the Philippine Department of Science and Technology, said that the technology could be the best so far in the array of strategies against dengue. These include the traditional drive to remove water that mosquitoes lay their eggs in, insecticide spraying and the releasing of genetically modified insects, which could have unintended consequences.

*Updated to correct an error in the name of the department, on 26 July 2011

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