FORT COLLINS, Colo. — 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.

Scientists are baffled, because even though the number of infected mosquitoes is greater than usual this year, the total number of the insects is below average.

“I don’t know what to make of it,” said Dr. Chet Moore, faculty affiliate of the Arthropod-Borne and Infectious Disease Laboratory at Colorado State University’s College of Veterinary Medicine and Biomedical Sciences. “There’s a lot of virus activity relative to the mosquito numbers. This is an odd virus, and unusual things seem to happen with it every year.”

Studies show more mosquitoes become infected with West Nile during warmer periods, and Larimer County has had a hotter-than-usual summer and a lot of people are spending time outside, the Fort Collins Coloradoan reported (http://tinyurl.com/hg7hygy).

Larimer County and nearby Weld and Boulder counties also have lots of irrigated agricultural land.

September is usually the peak time for infections, which take about three weeks to confirm.

For people who get infected, 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.


Information from: Fort Collins Coloradoan, http://www.coloradoan.com