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 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. Are duck and other wild game hunters at risk for WNV infections?
A. Because they are outdoors, hunters who go into the field while mosquitoes are still active may be at risk if they are bitten by mosquitoes in areas with WNV activity. The extent to which WNV may be present in wild game is unknown at this time.
Q. What should wild game hunters do to protect themselves from WNV infection?
A. WNV infections usually peak in late summer and early autumn, before mosquito numbers are reduced by hard freezes. If hunting during this time, wear a long-sleeved shirt and long pants, and apply insect repellants to clothing and skin, following the label directions, to prevent mosquito bites.
Q. Will the wetland where I hunt ducks be drained to control mosquitoes?
A. Although mosquitoes are found in wetlands, natural predators help reduce their numbers in typical years. In order to successfully transmit WNV to people, a mosquito must first bite an infected bird and then bite a person. Few mosquitoes feed on both birds and people. The virus-carrying northern house mosquito has been identified as an important threat, and it breeds in stagnant pools around homes. You can reduce their numbers by removing all discarded tires from your property; disposing of tin cans, plastic containers, ceramic pots and similar water-holding containers; making certain that your roof gutters drain properly; draining water from pool covers; turning over wheelbarrows and plastic wading pools when not in use; and eliminating standing water around your property.
Q. Can I get WNV by eating wild meat?
A. As far as we know, proper cooking kills WNV, so there is no danger in eating wild game. The Centers for Disease Control and Prevention (CDC) does recommend that hunters wear gloves when handling and cleaning all game, to prevent blood exposure to the bare hands.
Q. Who should hunters contact for information about the risk of WNV infection in a specific geographic area?
A. Local health departments will know where WNV has been found in Ohio.
Q. I Enjoy watching birds. If I see a lot of crows roosting in an area, should I be concerned about WNV?
A. No. Seeing crows alive and well is a good indication that the virus is not in your area. Dead crows, however, may indicate the presence of the virus and should be reported to your local health department.
Q. Are crows the only birds affected by WNV?
A. No, but crows and their relatives (especially blue jays) are most seriously affected by the virus. Large numbers of North American crows and other birds have died from WNV infection. Some exotic birds in zoos have died. WNV has been identified in at least 200 species of free-ranging and captive birds found dead in the United States. The public reported most of these birds. Wildlife biologists have also found evidence that some healthy birds have been exposed to WNV and have survived.
Q. Will WNV cause songbird populations to become endangered?
A. While we are still learning about the impact of WNV on our native birds, it seems unlikely that healthy native songbirds will be greatly threatened. Studies show that many species and individuals survive WNV infections. Wildlife disease scientists are monitoring the impact of WNV as it moves west across the country.
Q. Are any other wild animals at risk of WNV?
A. We are still learning about the susceptibility of other species to WNV. While it does appear that some mammals are affected, at this time, it appears that crows and members of the crow family are the most susceptible bird species impacted by WNV.
Q. Can infected mammals be carriers/reservoirs of WNV and transmit the virus to humans?
A. WNV is transmitted by infected mosquitoes. At this time, there is no documented evidence of animal-to-animal or animal-to-person transmission of WNV. Bird-to-bird transmission has been reported in laboratory studies; however, the significance of this under natural conditions is unknown at this time.
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.
- The Ohio State University: extension.vet.osu.edu/epidimiology-and-public-health-resources/west-nile-virus-resources
- Ohio Department of Health: www.odh.ohio.gov/wnv