West Nile virus showing earlier, greater activity in the United States this year

West Nile virus infections among people, birds and mosquitoes have been reported in 42 states so far this year, according to a CDC press release.

There have been a total of 241 cases of West Nile virus reported to the CDC. Four of these cases have resulted in death. This is the highest number of cases reported through the end of July since 2004. Three states, Texas, Mississippi and Oklahoma, reported 80% of the cases.

“It is not clear why we are seeing more activity than in recent years,” Marc Fisher, MD, MPH, medical epidemiologist with the CDC’s Arboviral Disease Branch, said in the press release. “Regardless of the reasons for the increase, people should be aware of West Nile virus activity in their area and take action to protect themselves and their family.”

Although West Nile virus outbreaks occur in the United States each summer, this year, certain areas are experiencing earlier and greater activity. Most people in the United States are infected from June to September, with mid-August seeing a peak in the number of infections. Weather, number of mosquitoes that spread the virus and human behavior all affect when and where outbreaks occur.

Symptoms of West Nile virus, including fever, headache, body aches, joint pains, vomiting, diarrhea and rash, occur in approximately 1 in 5 people infected. Less than 1% of people infected will develop serious neurologic illnesses such as encephalitis or meningitis and approximately 10% of those who develop a neurologic infection due to West Nile virus will die.