West Nile Virus Underlines Threat From Mosquito-Borne Diseases

West Nile virus is spreading rapidly across the United States and poses a significant threat to human health, according to the Centers for Disease Control and Prevention (CDC).

West Nile virus now has been identified in every state east of the Mississippi River except South Carolina and West Virginia. Scientists expect it to reach the Rocky Mountains this year and perhaps even the West Coast.

"West Nile virus is moving across the country, probably much more rapidly than people had originally thought," said Jim Stark, public affairs coordinator for the Metropolitan Mosquito Control District in St. Paul, Minn. "We fully expect that it will show up in Minnesota this year."

West Nile virus burst on the scene in 1999, when West Nile encephalitis killed seven people in the New York area. CDC statistics show that, as of the end of 2001, there have been 149 human cases of West Nile virus illness reported and confirmed, including 18 fatalities.

Humans can contract the disease when bitten by mosquitoes infected with West Nile virus. Mosquitoes contract the virus when they feed on infected birds, which may circulate the virus in their blood for several days.

Migratory birds appear to be the most common factor in the spread of West Nile virus. Nonmigratory birds, like crows and blue jays, are often killed by the infection, but infected migratory species often survive. Birds that carry the virus are called "sentinel" birds.

West Nile virus has been identified in more than 70 species of birds found dead in the United States. Many of these were found through the public reporting dead birds. People who notice unusual cases of dead birds should report them to their local or state health department.

Horses also are highly susceptible to West Nile virus, and horse owners are encouraged to vaccinate for several types of equine encephalitis. Other animals that may become infected include cats, dogs, bats and rabbits.

Larvicides Provide Effective Control

West Nile virus was first identified in Uganda in 1937. Exactly how it reached North America is unknown. Among diseases transmitted by mosquitoes in the United States, West Nile joins St. Louis encephalitis and Eastern equine encephalitis.

To tackle the annoying pests and control West Nile virus at the source, some communities spray for adult mosquitoes. Many critics, however, say that's too late. They suggest using larvicides, which kill mosquitoes in the larval stage.

"It's really difficult to control very mobile populations of adult mosquitoes," said Stark. "The best time to control mosquitoes is when you've got them confined in small wetlands, where you can apply biorational control materials that are very effective at keeping mosquito larvae from hatching into adults."

Larviciding can lower overall pesticide usage in a control program by reducing or eliminating the need for ground or aerial applications to kill adult mosquitoes.

Tips to Protect Yourself

Mosquitoes often breed in stagnant water. The public should take the following steps to eliminate these sites:

• Remove any sources of standing water around your house, including flowerpots, toys, tires and other containers.

• Clean roof gutters regularly.

• Drain and seal tree holes so they don't collect water.

• Dump out or change the water in birdbaths and children's wading pools at least weekly.

• Treat ponds and other permanent bodies of water with larvicides, and stock them with mosquito-eating fish.

• Fill in low areas that hold water for more than seven days.

To protect yourself from being bitten by mosquitoes, follow these precautions:

• Avoid being outdoors during peak mosquito activity, typically dusk to dawn.

• Avoid mosquito breeding and resting sites.

• Wear pants and long-sleeved shirts when outdoors.

• Use repellents containing DEET.

To learn more about West Nile virus, contact your state or local health department or visit www.cdc.gov. For more information about Altosid or other Zoëcon products for pest control, visit www.altosid.com.

Zoëcon is a leading producer of chemical and biological products for professional pest control. Located in Schaumburg, Ill., Zoëcon is a division of Wellmark International.

Always read and follow label directions. Altosid and Zoëcon are registered trademarks of Wellmark International, Schaumburg, Ill. ©2002 Wellmark International.