More than a year after being diagnosed with a West Nile virus infection, half of the patients have ongoing health complaints including fatigue, memory problems, headaches, depression, and tremors, according to an article in the Sept. 15 issue of Clinical Infectious Diseases. The study reports that those patients who were diagnosed with the relatively benign manifestation of West Nile fever are just as likely to suffer later health problems as are those who were hospitalized with more severe West Nile virus-related illnesses such as encephalitis or meningitis.

People can become infected with West Nile virus when they are bitten by a mosquito that has previously bitten an infected bird. The virus was first found in the United States in 1999. In 2003, there were more than 9,000 human cases of West Nile virusrelated disease, including 264 deaths.

Most people infected with West Nile virus have no symptoms. However, approximately 20 percent of patients will develop a flu-like illness called West Nile fever. Up to 1 percent may develop more severe diseases such as meningitis or encephalitis.

Lead author Paul Carson, MD, of MeritCare Health System and the University of North Dakota School of Medicine and Health Science, said, "We were seeing patients coming back long after having had West Nile fever saying they had ongoing problems. People would say things like 'I'm not myself, I'm more fatigued, I have more trouble with my memory.'"

The authors of this study tested 49 patients approximately 13 months after they were diagnosed with either West Nile fever or one of the more severe diseases. The patients were given tests for neurological function, quality of life, fatigue, and depression.

"What we found," Dr. Carson said, "is that there is a substantial amount of ongoing symptoms both among those patients diagnosed with West Nile fever as well as those with the more severe diseases, encephalitis and meningitis."