DENVER -- Colorado health officials have reported the first two human cases of West Nile virus in the state this summer -- in Boulder and Logan counties.

The state health department said Friday both patients are recovering. Their names haven't been released.

"Typically around the first week of July we start detecting our first positive mosquitoes, which the human cases show, already are out there," said John Pape, an epidemiologist who specializes in animal-related diseases at the Colorado Department of Public Health and Environment.

He said the numbers of Culex mosquitoes, which carry the virus, are still low but are increasing.

Pape said 2007 was the second most active season for West Nile virus cases following the 2003 epidemic. Last year, Colorado reported 576 cases with 7 deaths. Ninety-nine cases, or 17 percent, had meningitis or encephalitis, indicating the virus had entered the central nervous system.

"However, we know that even West Nile fever, the less severe form, can cause significant illness, last for weeks to months and can result in people being hospitalized. Prevention is the key," Pape said.

Data from 2003 to 2006 shows patterns, he said.

"Approximately 85 percent of people who became ill with West Nile virus were infected when bitten by an infected mosquito during a six-week period from July 1 through the second week of August. Therefore, we are entering the peak season of West Nile virus transmission," explained Pape.

Colorado had 576 cases of West Nile last year, including seven deaths.

The state's worst year was 2003, when it first appeared in Colorado. Sixty-three people died of West Nile and nearly 3,000 became ill.

Pape advised anyone who finds a dead bird to call the Colorado Health Emergency Line for the Public at 1-877-462-2911. Mosquitoes feed on infected birds and then pass on the virus to humans.