West Nile VirusTire & Container

West Nile virus (WNV) is an arthropod-borne virus (arbovirus) spread by the bite of infected mosquitoes.

Most people are infected in Ohio by the northern house mosquito, Culex pipiens.  Mosquitoes become infected when they feed on infected birds.  Infected mosquitoes can then spread the virus to humans and other animals when they bite.

West Nile virus was first detected in the United States in New York City in 1999 and quickly spread across the country within a few years.  In Ohio, West Nile virus was first identified in birds and mosquitoes in 2001.  The following year, the first human cases and deaths were reported.  By the end of 2002, all but one of the state’s 88 counties reported positive humans (441 total human cases), mosquitoes, birds or horses.  West Nile virus is now established in Ohio where cases occur each year and seasonal epidemics can flare up under certain conditions in the summer and continue into the fall.

The best way to prevent West Nile virus disease is to prevent mosquito bites.

What are the signs and symptoms of West Nile virus disease?

Approximately 80 percent of people who are infected with West Nile virus will not show any symptoms at all, but there is no way to know in advance if you will develop an illness or not.  Those who do develop symptoms usually do so between two to 14 days after they are bitten by the infected mosquito.

Up to 20 percent of people who become infected will have symptoms that can last for a few days to as long as several weeks and include:

  • Fever
  • Headache
  • Body aches
  • Nausea
  • Vomiting
  • Swollen lymph glands
  • Rash on chest, stomach or back

About one in 150 people infected with West Nile virus will develop severe illness.  The severe symptoms may last several weeks, and neurologic effects may be permanent.  Symptoms of severe illness can include:

  • High fever
  • Headache
  • Neck stiffness
  • Stupor
  • Disorientation
  • Coma
  • Tremors
  • Convulsions
  • Muscle weakness
  • Vision loss
  • Numbness
  • Paralysis

Death from infection with West Nile virus is 10 percent for those diagnosed with severe illness, but is much higher for patients diagnosed with West Nile virus encephalitis and acute flaccid paralysis.

For more information, see the Centers for Disease Control and Prevention (CDC)'s website for West Nile virus disease symptoms.

How is West Nile virus disease diagnosed?

West Nile virus infection can only be diagnosed by a healthcare provider.  A blood or cerebrospinal fluid sample may be collected for laboratory testing.  Please visit the CDC's website for information on diagnosis and testing.

What is the treatment for West Nile virus disease?

There is no specific treatment for West Nile virus infection, and care is based on symptoms.

Who is at risk in Ohio?

Anyone who spends time outdoors can be at risk for West Nile virus infection.  The mosquito that transmits West Nile virus, the northern house mosquito, is found in catch basins, stagnant water in ditches and containers of water with high organic matter (e.g., flowerpot saucers, clogged rain gutters) so people who live or recreate near these habitats are at increased risk.

Ohioans of all ages can get sick with West Nile virus, but adults greater than 50 years of age are more at risk for severe disease.  Most cases of West Nile virus reported in Ohio are in adults aged 70-79 years, particularly men.

Graph: West Nile virus disease in Ohio by age and sex

What time of year are Ohioans at risk for contracting West Nile virus disease?

In Ohio, West Nile virus infection can occur anytime during mosquito season, which typically runs from May through October.  Most human cases are reported in July through October.

It can take anywhere from two to 14 days from when the mosquito bite occurs to when symptoms of West Nile virus disease appear.  Since most human cases become ill in late July through October, that means most are bitten by an infected northern house mosquito between early July and mid-September.  Therefore, summer through early fall is the time of year when Ohioans are most at risk for contracting West Nile virus disease.

Graph: West Nile virus in Ohio by week of illness onset

Where in Ohio are people at risk?

Northern house mosquitoes that can carry West Nile virus are found throughout Ohio wherever suitable habitats for breeding are found.  However, the majority of West Nile virus disease human cases reported in Ohio are in the northern and western parts of the state.

Map: West Nile virus in Ohio

What are the trends over time?

Ohio has tracked human, mosquito and veterinary cases of West Nile virus infection since 2001 when it was first detected here.  An average of 58 human cases are reported each year in Ohio.  However, epidemics can flare up under certain environmental conditions in the summer and continue into the fall as was seen in Ohio during 2002 and again in 2012.

Ohio West Nile virus human case statistics

Ohio West Nile virus mosquito, bird and veterinary case statistics

How can I reduce my risk of West Nile virus infection?

Steps to prevent West Nile virus infection include avoiding mosquitoes and mosquito bites, planning ahead when traveling to areas at risk for West Nile virus infection and stopping mosquitoes from breeding in and around your home.

Additional resources



Educational material:

Contact information

Ohio Department of Health
Bureau of Infectious Diseases
Zoonotic Disease Program
246 N. High St.
Columbus, OH  43215
Phone: (614) 752-1029
Fax: (614) 564-2437


Page Updated:  06/28/2018

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