EAST TEXAS — Four East Texas counties now have cases of West Nile virus: Gregg, Van Zandt, Henderson, and Angelina County.

According to KETK news partner, The Longview News-Journal, health workers at Good Shepherd Medical Center in Longview have confirmed treating several patients with symptoms that match West Nile, but are waiting for results from a Texas State Health Department lab in Tyler.

Federal health officials are calling it "one of the worst outbreaks of West Nile virus in our nation's history".

The outbreak is being blamed on the unusually warm winter, followed by a historic drought.

So far, nearly 700 people have been infected this summer alone. At least 20 have died.

The City of Longview is urging residents to take precaution to prevent mosquito activity and bites.

The Environmental Health Department is working to restrict larve growth at stagnant water sites, and is spraying in neighborhoods where there is a specific concern.

According to Environmental Health Supervisor Buck Farrar, "The chance of a normally healthy individual being bitten by an infected mosquito and developing the disease is still extremely small, but the virus is still a serious concern. So we encourage everyone to take some simple steps to help prevent mosquitos around your home.”

Here are some effective ways experts say you can avoid mosquito bites:

• Get rid of any standing water near residence
• Remain indoors during the dusk and dawn hours
• Wear long pants and long sleeves when outside
• Use an effective mosquito repellant according to label directions