Spraying for West Nile could do more harm than good
By Erika McDonald

While the spread of West Nile virus saturates local media coverage, little mention is made of the environmental and health impacts of the pesticides sprayed to combat infected mosquitoes. Around the country and here in Houston however, environmentalists objected to massive spraying campaigns like the ones in effect in Harris County.

Photo by Ed Betz, associated Press

Activists like Martin Reiner, executive director of Texans for Alternatives to Pesticides, contend that the media has inflated the seriousness of West Nile virus, which in reality, poses less of a health threat than the use of toxic pesticides. At press time, the Centers for Disease Control reported 68 confirmed cases of West Nile in Texas with two cases resulting in death. Health officials confirmed that the chance of dying from West Nile virus, once infected, is about one in 1,000.

According to Dr. Ray Parsons, director of Harris County Mosquito Control, pesticide spraying is a necessary response to a dangerous disease. The county uses resmethrin for ground spraying and dibrom for aerial spraying. Both pesticides were approved by the Environmental Protection Agency. They were sprayed at levels below the maximum allowable rate and only at night, Parson said.

Despite EPA approval, independent scientific studies, including one at Mt. Sinai Hospital, found that pyrethroids like resmethrin act as an endocrine disrupter by mimicking the effects of the female hormone estrogen. This can lead to reproductive dysfunction, developmental impairment, breast cancer in women and lowered sperm counts in men. Other studies linked pyrethroids to long-term neurological damage, thyroid damage, and childhood cancer. In a report published in Environmental Health Perspectives, Toshio Narahashi, an international toxicology expert, said nervous system damage caused by pyrethroids is comparable to the effects of DDT.

Dibrom, used by Harris County for ground spraying, contains dichlorvos, an organophosphate that numerous studies have linked to brain and liver damage, breast cancer and childhood leukemia. The EPA considers organophosphates more acutely toxic than pyrethroids and is currently studying their effects. A comprehensive study on pyrethroids is scheduled for 2004. Meanwhile, dibrom and resmethrin maintain approval status and widespread use.

Evidence from New York suggests that pesticides also pose a serious threat to wildlife. State wildlife pathologist Dr. Ward Stone reported that more birds were dying from pesticide poisoning than from West Nile virus. Based on a sample of 4,000 birds brought in for testing out of concern over the spreading virus, Ward found that 31 percent tested positive for West Nile while 48 percent died of pesticide poisoning. For many of the remaining birds, pesticide poisoning was a major contributing factor in their deaths, though not the immediate cause. Birds that were disoriented or sickened by pesticide died from crashing into buildings, being hit by cars or other similar trauma. Not all birds that tested positive for the virus actually died from it.

Environmentalists contend that, in addition to being toxic, pesticides are also ineffective. There is evidence that long-term spraying may actually increase the number of mosquitoes by destroying predators that feed on them. Mosquitoes that are sprayed but not killed by the poisons may become resistant and become more aggressive biters. Pesticides also kill beneficial insects that play an important role in maintaining ecological balance. In its 2001 report on West Nile, the CDC identified adulticide (spraying for adult mosquitoes) as the least efficient mosquito control technique.

According to Reiner, there are eco-friendly alternatives that are more effective than pesticide spraying. Alternatives include bat houses (bats are natural mosquito predators) and traps that attract mosquitoes by emitting carbon dioxide – the same thing that attracts them to people. Some environmentalists also consider biopesticides a good alternative because they generally affect only the target pest sparing the birds, mammals and beneficial insects harmed by broad-spectrum pesticides. They are also less toxic and decompose quickly, which results in less pollution than conventional pesticides.

Reiner said the best weapon against West Nile virus is personal responsibility. “If everyone would get rid of standing water around their own homes, that would accomplish so much more than spraying ever could,” he said.

While the EPA maintains that pesticides like the ones used in Harris County are relatively safe, it does not recommend they be used as the sole weapon against mosquitoes. An Integrated Pest Management Program, touted by the EPA as the best way to protect communities from the West Nile virus, is an ecologically based, multi-faceted approach that includes use of pesticides only after systematic monitoring of pest populations indicates a need. IPM strategy relies heavily upon prevention tactics like eliminating standing water and using larvacides, which kill mosquito larvae.

Parsons said that Harris County does employ methods other than adulticide to combat mosquitoes. The county maintains a program of source reduction (eliminating mosquito breeding grounds), larvacides and neighborhood clean-ups. The county’s public education program includes an elementary school project called CATCH and presentations to community organizations. The county is currently working to develop a mosquito trap to be used for future campaigns. Parsons said the county uses pesticides responsibly and that a press conference is held before each spraying to ensure people know when and where pesticides will be used. He insisted that his office had not received any complaints about people becoming ill from pesticide exposure.

“The only (complaint) calls we’ve gotten are from anti-pesticide activists who don’t want us to use any pesticides at all,” he said.