The number of West Nile virus cases in the U.S. has jumped dramatically in one week, increasing to 1,118, with 41 deaths, the Centers for Disease Control and Prevention said today.
The report marks a substantial increase from last week's report of 693 cases and 26 deaths.
Approximately 75 percent of the cases have been from five states: Texas, Mississippi, Louisiana, South Dakota and Oklahoma.
Texas has been hardest hit, accounting for almost half of all cases.
As of Tuesday there had been 21 deaths and 586 cases there, says Christine Mann with the Texas Department of State Health Services.
"The number of West Nile cases in people has risen dramatically in the last few weeks and indicates that we are in one of the biggest West Nile virus outbreaks we have ever seen in this country," says Lyle Petersen, director of the CDC's Division of Vector-borne Infectious Diseases.
So far this year, 47 states have reported West Nile virus in humans, birds or mosquitoes, the CDC says. Thirty-eight states have reported cases of human disease.
The 1,118 cases are the highest number of West Nile virus disease cases reported to CDC through the third week in August since West Nile virus was first detected in the United States in 1999, the CDC says.
Up to 20 percent of people who contract West Nile virus develop symptoms that include fever, headache, body ache, swollen lymph glands and occasionally a rash on the trunk of the body. They appear within three to 12 days and then disappear within a few days.
About 80 percent of people infected with the West Nile virus have no symptoms.
Of those who develop a fever, less than 1 percent develops West Nile neuroinvasive disease, which causes inflammation of the brain, spinal cord or the tissue surrounding the brain. About 10 percent of those will die. People over 50 and those with compromised immune systems are more likely to develop this form.
The West Nile virus first appeared in the United States in 1999, from Africa.