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Ohio State University Extension


Wetlands and 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. If I'm hiking or walking in an area with wetlands, how can I protect myself from WNV infection?

A. WNV infections usually peak in late summer and early autumn, before mosquito numbers are reduced by hard freezes. If you hike or walk outdoors during this period, you should wear a long-sleeved shirt and long pants, and your should apply insect repellants to clothing and skin, following the label directions, to prevent mosquito bites.

Q. What is the value of a wetland?

A. Wetlands are among the most biologically productive habitats in the world. Before European settlement, Ohio's wetlands covered 18.9 percent (5 million acres) of the state. As settlers moved west, they drained the wetlands for timber and farming, thus eliminating 87 percent of the state's original wetlands. Wetland-dependent wildlife species have been severely impacted by this significant reduction in the amount and quality of wetland habitat. Wetlands are highly productive. They warm quickly in spring and produce abundant quantities of food for amphibians, reptiles, shorebirds, migrating birds and waterfowl. Even small sites, much less than an acre, can produce hundreds of frogs, toads and salamanders. Wetlands also provide critical links to other habitat types and wildlife populations.

Q. Should wetlands be drained to control mosquitoes?

A. Because the Culex mosquito can breed in very small amounts of water, eliminating temporary standing water in plastic containers, discarded tires or other water-holding containers around one's property can greatly reduce breeding areas. Any stagnant water in rain barrels, irrigation ditches, clogged gutters, backyard home septic systems and road-side ditches can serve as breeding sites. The difference between these water-holding places and wetlands is the presence of mosquito-eating predators. Wetlands are home to a host of mosquito-eating beetles, backswimmers, water striders, dragonfly larvae, etc., making them significantly less ideal breeding sites for Culex mosquitos.

Q. Can wetlands be drained or are there regulations that protect them?

A. Wetlands are afforded protection from draining under the authority of the Ohio Environmental Protection Agency in several sections of Ohio Administrative Code 3745. Under this authority, the hydrology necessary to support the biological and physical characteristics naturally present in wetlands shall be protected to prevent significant adverse impacts on the wetlands. A person cannot alter the wetland's water levels, which also includes groundwater recharge and discharge.

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.