As of August 14, 2012, 43 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 693 cases of West Nile virus disease in people, including 26 deaths, have been reported to CDC. Of these, 406 (59%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 287 (41%) were classified as non-neuroinvasive disease.
This is the highest number of cases reported through the end of July since 2004. Over 80 percent of the cases have been reported from six states (Texas, Mississippi, Louisiana, Oklahoma, South Dakota, and California) and almost half of all cases have been reported from Texas.
Non-human West Nile virus infections have been reported to CDC ArboNET from the following states: Alabama, Arizona, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Washington, West Virginia, Wisconsin and Wyoming.
Eight hundred sixty-one human West Nile virus infections have been reported to CDC ArboNET from Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Jersey, New Mexico, New York, North Dakota, Ohio, Oklahoma, Pennsylvania, South Carolina, South Dakota, Tennessee and Texas.
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. Seasonal outbreaks often occur in local areas that can vary from year to year. Many factors impact when and where outbreaks occur, such as weather, numbers of mosquitoes that spread the virus, and human behavior.
“It is not clear why we are seeing more activity than in recent years,” said Marc Fischer, M.D., M.P.H., medical 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.”
Approximately 1 in 5 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. People over 50 years of age and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and organ transplants, are at greater risk for serious illness.