Maryland health officials said Friday that an adult in the central region has a confirmed West Nile virus infection, the first case in the region this season. The virus has already been found in pools of mosquitoes in the District, Virginia and Maryland.

Most people infected with the virus will not have symptoms. People who do develop illness usually have any combination of fever, headache, body aches, skin rash and swollen lymph glands. The symptoms generally appear three to 15 days after the bite of an infected mosquito. In rare instances, West Nile virus can be fatal.

More serious illnesses from West Nile virus have been reported so far this year than any since 2004, according to the federal Centers for Disease Control and Prevention. Maryland is not among those states reporting increased West Nile activity.

The number of human cases in Maryland has varied over the past several years. In 2011, there were 19 human cases. In 2010, there were 23 cases. In the peak year of 2003, there were 73 human cases.