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Ohio State University Extension


Farmers 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. Who is most at risk?

A. People over 50 years of age have the highest risk of developing severe illness because, as we age, our bodies have a harder time fighting off disease. People with compromised immune systems are also at risk. However, anyone can get the virus.

Q. What are the symptoms?

A. People with mild infections may experience fever, headache, body aches, skin rash and swollen lymph glands. People with more severe infections may experience high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions, paralysis and, rarely, death. If you have any of these symptoms, contact your doctor.

Q. Is there a treatment?

A. There is no specific treatment for WNV infection. While most people fully recover from the virus, in some severe cases, hospitalization may be needed.

Q. Is my farm a mosquito-breeding site?

A. Several habitats found on farms can support the production of mosquitoes. Larvae can develop in watering troughs, small ponds, irrigation ditches, rain barrels, manure lagoons, ruts where farm equipment frequently travels, and other areas where water is allowed to accumulate. Even hoof prints can accumulate water and provide a breeding habitat. The close proximity of livestock, nuisance animals (such as birds) and other animals to mosquito breeding habitats increases the risk for the transmission of animal and human disease.

Q. What should I do about birds (both alive and dead) on my farm?

A. Remove all bird nests from farm buildings. Periodically look around the property for dead birds, such as crows. Use rubber gloves or an implement, such as a shovel, to dispose of dead birds.

Q. How can I prevent mosquitoes from breeding?

A. There are many ways to eliminate mosquito-breeding areas on farms. This might include improving drainage in areas that are irrigated or using stone to fill in ruts where farming equipment frequently travels. Make sure you thoroughly clean watering troughs regularly.

Remove or frequently empty any containers that accumulate water, including discarded tires and old equipment. When a farm uses scrap tires for additional purposes such as to maintain the plastic on bunker silos, the tires should be split to avoid water collection or treated with larvicides. Aerate small ponds and stock them with fish.

In situations where eliminating mosquito breeding areas is not a practical alternative, larviciding is the most effective control technique. Several larvicides are well suited for wastewater treatment facilities, including Bacillus sphaericus, B. thuringiensis israelensis (Bti), Temephos, growth regulators, oils and monomolecular films. A local pest control company can help you to determine which product would best suit your situation, and what type of control activities should be conducted.

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.