1. Spraying is the Least Effective Measure
The US Center for Disease Control and other experts say that spraying or fogging is the least effective means for slowing the spread of WNV carrying mosquitoes. For fogging to have maximum effect, a mosquito has to be flying. Estimates are that fogging kills only about 10% of adult mosquitoes. The federal-provincial task force on WNV admits there is little evidence for the efficacy of insecticide spraying. Adult mosquitoes live only about two weeks, with new larvae hatching constantly. This means that spraying cannot be a one shot operation, but needs to be repeated frequently if chosen as a means of control .
2. Predators Harmed, Mosquitoes Thrive
Aerial spraying or fogging is more harmful to mosquito predators than to mosquitoes. Since predators are farther up the food chain, they will take in higher amounts of pesticide. By decreasing mosquito predator populations, aerial spraying actually leads to increases in mosquito populations. Data from a study in New York State published in the Journal for Mosquito Control found that after 11 years of insecticide spraying, the mosquito population had increased 15 times. Pesticide exposure also results in immune suppression in birds, which serve as the hosts for WNV. Birds exposed to organophosphate pesticides tend to suffer immune suppression (as do mammals, amphibians and other animals.) This makes them less able to fight off viral and bacterial infections, the very opposite of what is needed. Once infected with WNV, birds are more likely to develop symptoms and to remain ill longer than if they had not been exposed. Thus, pesticide spraying leads to more frequent and longer infections and higher viral loads in birds, making it more likely they will spread the disease to mosquitoes. This increases the possibility of mosquitoes transmitting the virus to humans and other mammals.
3. Super Mosquitoes, Sicker Mosquitoes
For some reason, as yet unknown, mosquitoes exposed to pesticides are more likely to have WNV in their salivary glands and develop a damaged gut lining which becomes more porous, allowing WNV to pass through. Over a decade of insecticide spraying to control encephalitis in Florida has not been effective, and mosquitoes are now 15 times more likely to pass on the disease. Mosquitoes, which have short life spans, go through many generations in a single year. The mosquitoes which are exposed to pesticides and survive are more likely to develop resistance to them. So spraying contributes to the development of “super mosquitoes” which can only be killed by using higher amounts or different types of pesticides.
4. Immediate Human Health Effects
Immediate health effects on humans from exposure to sprayed pesticides are considerable. A letter from 26 prominent physicians and scientists in Quebec released last summer states, “Indiscriminate spraying of pesticides, especially in heavily populated urban areas, is far more dangerous to human health and the natural environment than a relatively small risk of West Nile Virus…. Ironically, such spraying is especially dangerous to those with impaired immunity for whose ‘protection’ such spraying is mainly being done. ..Those individuals who are most vulnerable in this chemical action against mosquitoes include children, pregnant women, the elderly, chemically sensitive and immuno-suppressed individuals, such as patients with AIDS and cancer, and people suffering with asthma and other allergies.”
5. Long Term Health Effects
Pesticides used in mosquito control can contribute to immune suppression in humans. A report from the World Resources Institute notes, “Impairment of the immune system by chemical pesticides can lead to allergies, auto immune disorders such as lupus, and cancer. It may also lead to infections to which one may be normally resistant.” People with weakened immune systems are the most vulnerable to WNV. Thus, in the long term, aerial spraying may actually increase the number of people who become seriously ill from WNV. And immune system suppression has serious implications for other diseases as well, including SARS.
6. Long Term Environmental Effects
Most of the pesticides presently used for mosquito control do not selectively target mosquitoes. Insecticides kill all insects. This includes hundreds of beneficial insect species that pollinate crops and keep pests under control. Fish kills in the thousands have been reported following mosquito spraying. Since some species of fish feed on mosquito larvae, this is doubly counterproductive. Other organisms that feed on mosquito larva are also killed. Bird populations are also threatened. According to New York State wildlife pathologist Ward Stone, more of the birds sent to his unit for examination in 2000 died from pesticides than from WNV.
7. Keep Risk in Perspective
While the image of a new killer virus from the tropics is scary and makes for good media material, public health experts at all levels are attempting to help people put WNV in perspective. West Nile Virus is less dangerous than the flu. Only 1% of mosquitoes carry the WNV, even in places where WNV has been common for years. Because of our climate, the virus is not expected to overwinter, but would likely be reintroduced each year through bird migration. Less than 1% of people bitten by infected mosquitoes will have any symptoms, and most of those will be equivalent to a one day flu or headache. Studies in New York when WNV was most widespread found thousands of people who tested positive for WNV but had never experienced any symptoms of illness. People bitten by infected mosquitoes, even those who experience no symptoms, will develop a lifetime immunity to the disease. In Africa and Europe, the virus occurs in cycles, with typically three years of human infections in late summer, with the majority of infections in the first year of a cycle. Then the virus fades into the background, and may not reappear for many years. In Africa, WNV is a childhood disease; adults have developed immunity.
8. Taking a Long-term Approach
WNV may be one of a number of tropical diseases which will spread to our geo- graphic area with global warning. Instead of panic and sensationalism, we need a rational, long term problem-solving approach which is healthy for humans and the environment. Reducing mosquito breeding sites (standing water), known as source control, is the most effective mosquito control method. Since adult mosquitoes seldom travel more than 1 kilometer, source control in a neighborhood can be extremely effective and quite non-toxic. Experts stress the value of source controls such as mechanical flushing of sewer catch basins, and introduction of dragonfly larvae in nearby ponds and lakes. These methods have been practiced with great success in Wells, Maine for 26 years. Maintaining healthy mosquito predator populations is an important part of a mosquito control strategy. Eliminating mosquito larvae, through predators and biological means and if absolutely necessary via pesticides, is far more effective than trying to kill adult mosquitoes.