Since being detected in the Western Hemisphere in 1999, West Nile virus (WNV) has rapidly spread throughout most of North America. According to estimates, more than 15,000 people in the U.S. have tested positive for WNV infection, resulting in more than 500 deaths. Less than one percent of those infected develop serious illness from the virus. Most often, WNV is spread by a vector, or carrier. For WNV, the vector is an infected mosquito that transmits the disease to a new host. Mosquitoes become infected when they feed on infected birds. The virus is located in the mosquito's salivary glands, and infected mosquitoes can spread WNV to humans and other animals when they bite.

Most diseases affect a narrow range of species. But with climate change and ecological disruption, scientists are warning of a rise in zoonotic diseases, or diseases that can be passed from animals to humans. More than 200 zoonoses have been described, caused by bacteria, parasites, fungi, viruses, and other agents. These diseases may be spread more readily today than in the past, due in large part to an increase in air travel. But Earth's warmer temperatures are allowing insects and microbes to spread to areas that were once too cold. And because of population growth and development, humans are coming in more frequent contact with migratory birds, some of which carry flu viruses capable of mutating into pathogenic forms. AIDS is probably the best-known example of a disease passed from animals to humans. The HIV virus is thought to have crossed from chimpanzees to humans in West Africa. The swine (H1N1) flu pandemic that emerged in Mexico in 2009 is another example. The potential rapid spread of diseases like H1N1 is accelerating research on zoonoses.

Information sharing is key to preventing and controlling the spread of zoonotic diseases. Traditionally, however, human medicine and veterinary medicine are viewed separately. This makes some sense, as doctors treat people and veterinarians care for animals. The physiologies of people and animals differ, as do the treatments for illness. Yet the two professions are now working together more and more. Knowing such information as whether human and animal outbreaks are simultaneous in a community or whether they are occurring across borders may help identify what kind of agent is responsible for a disease. This, in turn, would help authorities develop appropriate control strategies. At the individual level, input from both veterinarians and physicians would help assess a patient's potential zoonotic disease risk from animal exposure.

As the video indicates, physicians treating human WNV patients in New York City in 1999 might have benefited had they known right away that veterinarians in the surrounding area were examining dead or dying crows with neurologic symptoms similar to those of the affected humans. However, because at the time no local or state agency assumed responsibility for the animal investigation, communications between the veterinarians, physicians, and public health officials were infrequent at best.

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