On the prowl

Insecticides are being used to control a virus in the US

 
Published: Friday 15 September 2000

the west Nile virus has been making headlines in the us for quite some time now. Till now, three people, 213 birds and 114 mosquito pools have been reported infected with the virus in different parts of the country. It is believed that the virus, which killed seven people last year, was brought into the country by migratory birds.

Though birds cannot transmit the disease, mosquitoes feeding on them can carry the virus and infect humans. Those with a weak immune system, such as children and the elderly, are at increased risk. The symptoms include severe headaches, fever and muscular disability. In acute cases, it causes encephalitis (swelling of the brain) and there is no cure, except to give the patient an intensive support therapy such as intravenous fluids, ventilators and antibiotics.

When the us Center for Disease Control and Prevention found that the virus had survived through the winters in birds and mosquitoes, they undertook a massive spraying of insecticides to kill mosquitoes. They are also using larvicides and biological control agents like bacteria to control the mosquitoes that might hatch in stagnant water bodies and storm drains.

Environmentalists, however, have protested against the massive spraying of the insecticides. "The city is taking an irresponsible course of action," said Kimberly Flynn, a researcher at the New York Environmental Law and Justice Project. This year, the authorities are using synthetic pyrethroids -- chemicals which resemble natural pesticides extracted from chrysanthemum flowers. The insecticides disintegrate when they come in contact with sunlight, air or water and thus, pose less of an environmental hazard.

Experts, however, warn that the synthetic pyrethroids could affect human hormones, the liver and thyroid gland besides increasing the risk of breast cancer. A case was filed by environmentalists in us courts to stop the spraying of the insecticides. But the court rejected their claim saying that there was not enough data to prove the insecticides were harmful.

Robert McLean, director of the National Wildlife Center, says that the insecticides may also kill beneficial insects and "may temporarily modify the predator/prey foodchain". Experts warn that these chemicals are also dangerous to aquatic life and the spraying is unnecessary. The department of wildlife in Massachusetts has said that the spraying could harm the freshwater three-spine stickleback, one of the nine endangered species of fish in the state.

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