FORT COLLINS, Colo. (AP) -- Experts are trying to determine why a county in northern Colorado has a high number of West Nile virus cases, compared with Los Angeles, Dallas and Phoenix, which also have a high number of cases.
Larimer County had 28 human cases this year as of Tuesday, the most in the state.
Researchers say weather, a large number of infected birds and problems caused by humans are common factors.
The Fort Collins Coloradoan reports (http://tinyurl.com/hg7hygy ) studies show more mosquitoes become infected with West Nile during warmer periods, and Larimer County has had a hotter-than-usual summer.
Initial human symptoms of West Nile virus can include fever, headache, nausea, vomiting, muscle aches, weakness and rash. More severe symptoms can include stupor, disorientation, coma, tremors, vision loss and paralysis.