WASHINGTON, Aug. 1 (Xinhua) -- The U.S. Centers for Disease Control and Prevention (CDC) said Wednesday that 241 cases of West Nile virus disease, including four deaths, have been reported in 42 states so far this year.
This is the highest number of cases reported through the end of July since 2004. Almost 80 percent of the cases have been reported from three states - Texas, Mississippi and Oklahoma.
"It is not clear why we are seeing more activity than in recent years," said Marc Fischer, epidemiologist with CDC's Arboviral Diseases Branch. "Regardless of the reasons for the increase, people should be aware of the West Nile virus activity in their area and take action to protect themselves and their family."
West Nile virus is transmitted to people by infected mosquitoes. In the United States, most people are infected from June through September, and the number of these infections usually peaks in mid-August.
Approximately one in five people who are infected with West Nile virus will develop symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Less than 1 percent will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues).
About 10 percent of people who develop neurologic infection due to West Nile virus will die. There are no medications to treat, or vaccines to prevent, West Nile virus infection.
According to the CDC, the best way to prevent West Nile virus disease is to avoid mosquito bites: use insect repellents when you go outdoors; wear long sleeves and pants during dawn and dusk; install or repair screens on windows and doors; use air conditioning.