What is West Nile virus?
How to Protect from West Nile virus
Health Effects of Pesticides Used to Combat Mosquitoes
Biology of Mosquitoes
Guidelines for Spraying
West Nile virus (WNV) is a mosquito-borne disease. The bite of a mosquito infected with the virus can cause illness or inflammation of the brain, known as encephalitis.
Who is at risk?
Anyone that lives in or visits an area with infected mosquitoes is at risk. People older than 50 years have the highest risk of severe encephalitis. However, according to CDC, "Less than 1% of those infected with West Nile virus will develop severe illness…Human illness from West Nile virus remains rare in areas where it has been reported, and the chance that any one person is going to become ill from a mosquito bite is low." Some animals are also at risk, including birds, horses, cats, and domestic rabbits. Current evidence shows that only mosquitoes can spread the disease, humans or other animals cannot.
What are the symptoms?
Symptoms of a mild infection include fever, head and body aches, skin rash, and swollen lymph glands. If you have high fever, experience confusion, muscle weakness, and severe headaches, call your health care provider immediately. It may take 3 to 15 days for any of these symptoms to show.
Where is WNV found?
WNV has spread throughout most of the United States. The disease is also found throughout the world, including Africa, West Asia, Eastern Europe, and the Middle East.
When is it most common?
Late summer and early fall is when mosquitoes infected with WN virus are most common in the United States and other temperate regions such as Europe. In warmer regions of the world, this disease can occur year-round. top
What can you do?
What can your community do?
The Centers of Disease Control and Prevention (CDC) state that spraying adulticides, pesticides intended to kill adult mosquitoes, is usually the least efficient mosquito control technique. Aside from adverse health effects posed to humans, adulticiding is not proven to reduce the risk of WNV in communities and may actually increase the number of mosquitoes by destroying their natural predators. Additionally, mosquitoes that survive the spraying may become resistant and have an increased prevalence of the virus within their bodies.
Synthetic Pyrethroids
Synthetic pyrethroids, which include resmethrin (Scourge) and sumithrin (Anvil), are adulticides patterned after pyrethrum, an extract from the chrysanthemum flower. While similar to pyrethrum, synthetic pyrethroids have been chemically engineered to have greater toxicity and longer breakdown times . Additionally, almost all synthetic pyrethroid mosquito products are combined with synergists, which increase potency and compromise the human body's ability to detoxify the pesticide. Symptoms of exposure include: dermatitis and asthma-like reactions, nasal stuffiness, headache, nausea, incoordination, tremors, convulsions, facial flushing and swelling, and burning and itching sensations . Synthetic pyrethroids are endocrine disruptors and have been linked to breast cancer . Deaths due to exposure have resulted from to respiratory failure. People with asthma and pollen allergies should be especially cautious. Breakdown times range from a few hours in direct sunlight, to several months in damp, dark environments.
Organophosphates
Organophosphates, which include malathion (Fyfanon), naled (Dibrom) and chlorpyrifos (Mosquitomist), are a highly toxic class of pesticides that affect the central nervous, cardiovascular and respiratory systems. Symptoms of exposure include: numbness, tingling sensations, headache, dizziness, tremors, nausea, abdominal cramps, sweating, incoordination, blurred vision, difficulty breathing, slow heartbeat, unconsciousness, incontinence, convulsions and fatality . Some organophosphates have been linked to birth defects and cancer. Breakdown times range from a few days in direct sunlight, to several months in damp, dark environments. top
In the United States, WNV is primarily associated with the Culex mosquitoes, also called the "backyard mosquito." Within this genus, three species, namely C. pipiens, C. restuans, and C. salinarius make up the majority of those mosquitoes found to be infected with WNV. Only female mosquitoes take blood meals; males do not bite humans or animals and usually die one or two days after emerging as adults. In contrast, adult females may live 2-4 weeks or more, depending on climate, species, predation, and a host of other factors.
All mosquitoes go through a four stage life cycle called "complete metamorphosis" from egg to larva to pupa and finally emerging as an adult. The length of time that each stage lasts depends on a number of variables with temperature having the greatest impact.
Eggs are laid in "rafts" on standing bodies of water. The eggs require one to two days in water before hatching into first instar larvae.
Larvae, or wigglers, develop as four instars. They molt three times during ten to twelve days before pupating.
Pupae, or tumblers, metamorphose over one to two days into adults.
Adults emerge from their pupal cases approximately twelve to sixteen days after being laid as eggs by their mother.
After mating, the female requires a blood meal in order to produce over 250 eggs. It takes her three to four days to digest the blood and produce the eggs. Females transmit diseases when they live long enough to spread infection from the first blood meal victim to the second blood meal victim. Only a very small percentage of females live this long. Culex mosquitoes are generally weak fliers and do not move far from their larval habitat, although they have been known to fly up to two miles. top
The risks of pesticide exposure to humans and the environment caused by spraying pesticides are great. Spraying also kills natural predators, including other insects, birds, and fish. It may also result in mosquito resistance, which in turn will lead to a larger problem in the future. Should the community insist on spraying, local decision makers and mosquito control should be pressed to protect the public and environment from unnecessary exposure using the following guidelines:
* Infants, children, pregnant women, the elderly, and individuals with compromised immune systems and chemical sensitivities are especially vulnerable and must take extra care to avoid pesticide exposure.
For a more detailed report by Beyond Pesticides see Public Health Mosquito Management Strategy- For Decision Makers and Communities (Revised August 2004). If you are concerned about improper mosquito management in your community, learn what you can do by visiting Tools For Activists.