Surprise weapon

Oil from summer cypress can combat West Nile virus

Published: Wednesday 15 December 1999

it is easily available and a cheaper alternative to combat the deadly West Nile virus that struck New York city sometime ago: oil from summer cypress, an ornamental prized bush, can possibly save the day for all those trying to fight the virus.

The bush might also provide a cheap treatment for the world's poorest countries to fight filariasis -- a disfiguring parasitic disease that affects 15 million people in Africa alone. The virus attacks the central nervous system. In New York, it killed three people and doctors checked another 102 for symptoms of viral attack.

Summer cypress is also called the Burning Bush because it becomes deep red in the autumn. This is because it contains a substance, which when converted into a pheromone (a chemical secreted and released by an organism which causes a specific response when detected by another organism of the same species) can lure mosquitoes and lead them to their death. When the outbreak of the viral was reported in New York, health officials tried fighting the menace with insecticides like malathion and pyrethroid.

Researchers from Britain and Nigeria have turned oil from the plant seeds into a pheromone. This biological messenger, odourless to humans, could lure female mosquitoes away from places where people live ( Journal of Agricultural Food Chemistry , Vol 47, p3411).

This revelation was a chance happening. The importance of the oil became evident when a team from the Institute of Arable Crops Research at Harpenden in Hertfordshire discovered that the bush releases a fatty acid strikingly similar to the pheromone that attracts the filariasis-carrying mosquitoes. "It is a cue for female mosquitoes, telling them that there's a safe place where they can lay their eggs," says Mike Birkett, a member of the Rothamsted team.

Health officials can use pheromone from the bush to lure mosquitoes to death by leading them to drums of water laced with pesticide, says Birkett. Pickett is confident that the pheromone attracts females of all Culex species.

The team has also tested a synthetic version of the same pheromone but this has proved expensive. The are now screening plants for substances that can be turned into pheromone cheaply.

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