In four short years, a deadly virus has jumped an ocean and established a permanent place in North America. Experts don't know how this imported virus found its way into the common mosquito (Culex pipiens) and five other mosquito species. Since the virus is identical to a more potent strain that killed geese and humans in Israel, scientists now believe it originated from the Middle East.

Did an infected bird or human introduce it? Was it transported with mosquitoes in an airplane cargo hold? Was it intentionally imported? Is its rapid spread across this country the result of favorable habitat changes or warmer climatic conditions? At this point, there are more questions than answers.

Although the culprits include the common mosquitoes, scientists are learning more about the role of introduced mosquitoes from other parts of the world. An alarming trend is the spread of new species like the Aedes japonicus, an Asian mosquito, and Aedes albopictus, the Asian tiger mosquito, that have a greater capacity for spreading viral diseases. The tiger mosquito arrived in 1985 and is now in more than thirty states. This winter-hardy species is responsible for a number of documented cases of dengue fever and has been linked to the transmission of LaCrosse Encephalitis, an often-fatal disease. In laboratory experiments, Aedes japonicus has been four to five times more effective than Culex pipiens in transmitting West Nile among chickens. Its spread in the US coincides with the spread of the virus.

There are some important lessons to learn from this virus as it moves through new ecosystems. It's now clear that the disease paradigm that has protected us through the ages has shifted and many of the old ecological safeguards are gone. We need to understand the following 21st Century changes and develop better strategies to cope with them.

1. Human activity is rapidly and profoundly changing the world's ecological systems in ways we don't yet understand and these changes will affect the spread of diseases in ways we cannot yet fully imagine. Scientists studying global climate change for example have been warning us for more than a decade that mosquito-borne disorders are projected to become more prevalent because mosquitoes respond to favorable meteorological conditions in a warming world. Winter freezing generally kills many eggs, larvae and adults. As winters become milder, mosquitoes in their various forms are more likely to survive the colder months in protected urban areas, which don't experience temperatures below 50 degrees.
   
   
2. Diseases that were isolated to a particular geography are no longer constrained by traditional boundaries. Today, insect vectors and pathogens are opportunistic hitchhikers of modern global travel and trade. International commerce and travel hubs such as New York City are likely places for initial outbreaks of exotic diseases like the West Nile virus. In this highly mobile world, an infectious disease that historically resided in one part of the world can quickly jump continents and become a serious threat if the pathogens or their vectors find the right conditions. We must study the cycles of transmission to identify rational control strategies and to prevent future viruses from being imported and spread in similar fashion.
   
   
3. Introducing pathogens into a new ecosystem can lead to heightened virulence, can create new relationships between more efficient vectors and pathogens and can result in increased vulnerability to victims because they have little inherited or developed resistances. What was true of West Nile Virus when it was first isolated from a woman in the West Nile District of Uganda in 1937 may no longer be true today in North America.
   
   
4. If we have learned anything from our past, the widespread spraying of chemicals to kill mosquitoes is not a solution. For example, a class of pesticides known as "pyrethroids" being used on West Nile carrying mosquitoes is known to be a toxic chemical that may damage the thyroid, liver, affect the immune systems and alter the activity of the endocrine glands. Studies show that pyrethroids are environmental estrogens-chemicals that emulate estrogen. Through hormonal pathways, exposure to certain pyrethroids may contribute to reproductive dysfunction, developmental impairment, and promote cancer. Insecticides also have the unintended consequence of harming beneficial aquatic organisms, insects and wildlife including those that feed on mosquitoes and their larva. Once insecticides eliminate predators that were helping to keep pests in check, the pest populations skyrocket. In short, the use of chemical sprays may be a quick political fix but they tend to exchange one human health threat with another while damaging the ecosystem and suppressing natural controls.
   
   
5. Nature can be our best friend if we better understand it and use it to reduce the viral threats. Mosquitoes are more likely to be prevalent in disturbed (including somewhat polluted) ecosystems. By maintaining healthy ecosystems we are more likely to have a balance that presents fewer mosquitoes. We need to learn more about the virus, its vectors and the myriad of interactions with its new ecological home to better understand how to create an ecologically sound approach to deal with it. For example, it has been estimated that one bat can consume roughly 600-1,000 insects each hour. We should take steps to encourage more bats, swallows and purple martins to our backyards. It makes sense to erect bat and martin houses in our back yards, parks and community spaces. (Western Pennsylvania Conservancy and several partners recently purchased a property in Huntingdon County to protect a colony of 22,000 bats and we are installing a bat hotel at our Bear Run facilities.) Many fish species feed on the larval stages of mosquitoes. We need to take steps to promote habitat for larval eating fish, dragonfly and damselfly larvae, copepods (crustaceans) and other important larval predators. The more we understand about these interactions, the more knowledge we will have to act.
6. 
   The threat of West Nile must be kept in perspective by understanding the real risks and consequences. In areas where the virus has shown up, only about one percent of mosquitoes carry the disease. In the event a carrier insect bites a person, the chance of developing severe human meningoencephalitis is generally less than one percent. However, simply tracking the deaths understates the problem as many patients who developed the full-blown disease have chronic fatigue, lingering memory loss, muscle weakness and depression.

Until a vaccine is developed, licensed and released, we can eliminate human-created mosquito breeding sites, foster habitat for bats and other wildlife friends and use personal protection. The best way to prevent infection is to avoid getting bites during the time of year that mosquitoes are most active. Take precautions when in areas where mosquitoes are common. Consider using insect repellant and wear protective clothing such as long pants, long-sleeved shirts and socks.

There are other simple things that we each can do. Because mosquitoes like to breed in stagnant pools of water in the absence of predators, we should check our property to remove objects such as empty buckets, cans, old tires, other containers or water-bearing trash where mosquitoes may breed. If these water-collecting objects cannot be removed, they should be emptied, turned over or covered. Drill holes in the bottom of a container so that water cannot collect. At home, make sure door and window screens are free from holes and fit tightly in your windows. Fix your sagging and clogged rain gutters, as they are a ready source of mosquitoes. Drain water from flat roof surfaces. Change the water in birdbaths every other day. Keep swimming pools clean and chlorinated, or drain and cover them if they are not being used. Organize community trash pick-up days to eliminate water-collecting objects along roadsides and in other public places.

Many local, state and Federal agencies are tracking the spread of the West Nile virus but they are helpless in stopping it. Containing a disease that hitchhikes on the wings of migrating birds is next to impossible. Barring a miracle, the virus is now established in North America forever. While we cannot stop this virus from spreading, we must learn some ecological lessons to reduce its impact and to avoid future imported diseases.