Status of West Nile in the United States in 2013

Mosquito West Nile Virus Image

According to the U.S. Centers for Disease Control and Prevention (CDC), 48 states (all contiguous states) as well as the District of Columbia reported West Nile infections in mosquitoes, birds or people in 2013. Of the reported 2,469 cases of human West Nile virus (WNV) infection, 119 people died from the disease. In 2012, the rate of infection was the highest since 2003, and the number of deaths from WNV infection is the highest since the disease was first detected in the United States in 1999.

States with the highest WNV infection rates in 2013 included California, Colorado, Nebraska, Texas, South Dakota, North Dakota, and Illinois.

About West Nile Virus

The West Nile virus was first identified in 1937 in the eastern African country of Uganda. It was found for the first time in the United States during the summer of 1999 in New York. In North America, infection occurs seasonally beginning in the summer and continuing into the fall.

West Nile virus (WNV) usually is transmitted to mosquitoes from infected birds, and then spreads to people through the bite of an infected mosquito. In very rare cases, the virus can also be spread from mother to baby during pregnancy or breastfeeding, blood transfusions or organ transplants.

West Nile is a characterized as a flavivirus, one of group B arboviruses (arthropod-borne viruses) that are spread by ticks and mosquitoes and cause disease in animals and people. Infection with WNV can cause serious illness. Symptoms in people usually develop within 3 days to 2 weeks after being infected.

Symptoms of West Nile Virus Infection

In about 80 percent of cases, WNV infection does not cause symptoms. If symptoms do develop, they may last from a few days to several weeks and can include:

  • Body aches
  • Fever
  • Headache
  • Nausea and vomiting
  • Skin rash (usually on the torso)
  • Swollen lymph nodes

According to the CDC, about one out of every 150 people infected with WNV develops severe symptoms that last for several weeks, including neurological complications (e.g., brain damage, muscle weakness) that may be permanent. Serious symptoms include the following:

  • Convulsions
  • High fever
  • Muscle weakness
  • Numbness
  • Paralysis
  • Severe headache
  • Stiff neck
  • Stupor, disorientation
  • Tremors
  • Vision loss

People who spend a lot of time outdoors in warmer weather have a higher risk for WNV infection. People with a weakened immune system, including those with a chronic medical condition like HIV and those who have recently undergone chemotherapy, women who are pregnant, young children and people over the age of 50 are at increased risk for severe WNV infection.

If you develop severe symptoms of West Nile virus, contact your health care provider immediately. Treatment for WNV infection is supportive and includes rest, extra fluids, and in severe cases, hospitalization.

How to Prevent WNV Infection

West Nile virus prevention involves personal measures to reduce potential exposure to WNV, community mosquito control programs, and worldwide programs to identify patterns in risk, exposure and infection.

Preventing mosquito bites is the most effect way to reduce your risk for West Nile virus. Here are some tips:

  • Use insect repellent registered by the Environmental Protection Agency whenever you are outside where mosquitoes are present. Follow instructions for use on the label.
  • If possible, avoid being outside at dawn and dusk when many mosquitoes are most active. If you must be outside during this time, wear pants and a long-sleeved shirt and use insect repellent.
  • Make sure door and window screens are in good repair.
  • Get rid of standing water on your property (buckets, flower pots, gutters and drainage spouts, barrels)—mosquitoes breed in water. Change the water in bird baths, pet dishes and kiddie pools frequently.
  • Don't handle a dead bird with bare hands. Contact your local health department for further information.

Sources: Centers for Disease Control and Prevention (CDC), National Institutes of Health (NIH) and the U.S. National Library of Medicine

Publication Review By: the Editorial Staff at

Published: 23 Aug 2012

Last Modified: 22 Jan 2015