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Ohio State University Extension


What Outdoor Enthusiasts Should Know About West Nile Virus

William J. A. Saville, DVM, PhD, Dipl ACVIM, Chair, Veterinary Preventive Medicine
Jeffrey D. Workman, PhD, Extension Program Coordinator, Veterinary Preventive Medicine

West Nile virus (WNV) is a viral disease that can cause encephalitis or meningitis, infection of the brain and the spinal cord or their protective covering. Prior to 1999, the disease was found only in Africa, Asia and southern Europe. Since 1999, WNV has spread throughout North America and has continued to cause disease in the United States. The yearly number of cases and fatalities has fluctuated depending on the weather conditions throughout the nation.

WNV—Human Cases/Deaths
Year United States Ohio
Cases Deaths Cases Deaths
1999 62 7 0 0
2000 21 2 0 0
2001 66 10 0 0
2002 4,156 284 441 31
2003 9,862 264 108 8
2004 2,539 100 12 2
2005 3,000 119 61 2
2006 4,269 177 48 4
2007 3,630 124 23 3
2008 1,356 44 15 1
2009 720 32 2 0
2010 1,021 57 5 0
2011 712 43 21 1
2012 5,674 286 122 7
2013 2,469 119 24 4
2014 2,122 85 11 1

WNV is spread to people by the bite of an infected mosquito. The principal transmitter of WNV is the Northern House Mosquito (Culex pipiens). Mosquitoes first become exposed to the virus when they feed on birds that are infected with WNV. Once the mosquito is infected, it may transmit the virus to people or other animals when it bites them. Many birds can be infected with WNV, but crows and blue jays are most likely to die from the infection. Horses, too, are prone to severe WNV infection. People cannot get WNV from another person or from a horse that has the disease.

There is no vaccine currently available for WNV for people or most animals. However, there are vaccines available for horses, which represent 96.9 percent of all reported nonhuman mammalian cases.

WNV has become endemic in the United States and remains a serious disease threat; however, the number of cases and deaths vary significantly as climatic conditions vary by region from year to year. Sporadic seasonal epidemics will continue to occur in various regions of the country when weather and environmental conditions are most suitable. State, federal and local agencies continue to work together to address the health risks of WNV to Ohio families and their animals. Mosquito control efforts are often increased in urban areas during the summer to protect people from potential exposure to the disease.

Q. Does WNV pose a special risk to outdoor enthusiasts?

A. Any person bitten by a mosquito infected with WNV is at risk. The mosquito most closely associated with the disease (northern house mosquito) breeds in the stagnant water of mud puddles, ditches, flower pots, discarded tires, clogged gutters and similar reservoirs of water. It is important to apply mosquito repellant when participating in any outdoor activity—especially when fishing, camping or boating at night. Wearing light-colored clothing with long sleeves and long pants helps prevent mosquito bites. Window screens on campers and boats should be kept "bug-tight," as should netting on tents and similar outdoor gear. Keeping a campsite neat and orderly and eliminating any potential mosquito breeding sites is always recommended. Electric "bug zappers" do not help since these devices attract more mosquitoes than they kill.

Q. Are hunters who field-dress wild game birds at risk for WNV?

A. There is no evidence that WNV can be transmitted directly from birds or mammals to humans through direct blood contact. However, hunters are always urged to take proper precautions and wear rubber gloves when field-dressing game.

Q. Can a person contract WNV by eating infected game birds?

A. Proper cooking kills WNV. Consequently, there is no danger associated with eating well-cooked wild game that might be infected.

Q. Is feeding wild birds a health risk for humans?

A. It is completely safe to feed and provide habitat for wild birds in Ohio. Residents are urged to clean birdbaths regularly (at least weekly); aerate backyard ponds or stock them with mosquito-eating species such as goldfish; and eliminate containers of stagnant water.

Q. What should outdoor enthusiasts do if they encounter dead birds?

A. During summer 2002, WNV was responsible for widespread illness and death among Ohio's birds-of-prey, especially hawks and owls. Anyone who encounters an ill raptor in the wild should take special care to avoid direct contact with the bird. A list of raptor rehab centers is available on the ODNR website. While WNV cannot be contracted through touch, the sharp beaks and claws of raptors pose a different kind of danger. Anyone handling dead wildlife, including raptors, should always wear rubber gloves. Dead birds should be double-bagged in trash bags and disposed of. Responsible public action coupled with responsible individual behavior is the best way to prevent the spread of WNV and keep Ohioans safe from this disease.

The Status of WNV in Ohio

WNV has been confirmed in Ohio every year since 2001. Infected mosquitoes, birds, horses and humans have been found in all Ohio counties. Therefore, the virus can be present throughout the state.


For the current status of WNV in Ohio and for more information, you can visit the following websites or contact your local health department.

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Originally posted May 8, 2015.