West Nile virus infections in Colorado are down about 65 percent from this time last year, thanks to less rain and cooler weather earlier this season.
“Environmental factors play a role,” said John Pape, an epidemiologist with the Colorado Department of Public Health and Environment. “There has to be the right amount of heat and water.”
The weather pattern provided less than desirable breeding conditions for Culex mosquitoes, the type that can carry the virus, he said.
Pape says that both mosquito populations and the number of insects infected with the virus are down across the state.
“At this point, given what we are seeing, we are not going to have a surge in cases,” he said.
So far this year, nine cases of West Nile virus in humans have been confirmed by county health departments: four in Boulder County, three in Larimer County; one in Weld County and one in Logan County. No deaths have occurred.
The Colorado Department of Public Health and Environment has confirmed three of those infections.
By the end of July 2007, 22 cases had been reported to the state health department. There were 576 cases by season’s end and seven deaths.
West Nile virus can cause encephalitis, or swelling of the brain, and/or meningitis. In most cases, fever ensues. Serious infections can lead to death.
People should remain wary of mosquitoes because the state is still in peak season for infections, Pape said.
About 85 percent of people who became infected with West Nile virus from 2003 to 2006 contracted the disease between July 1 and the second week of August, according to the state health department.
Last week in Larimer County, two residents from Fort Collins and one from Loveland tested positive for the virus. Two of the three people became infected outside the county, health officials reported. All are recovering at home.
Significant numbers of mosquitoes have been identified in traps in Boulder County this season, but none have tested positive for the virus.
The first reported infection was in late June, when a 51-year-old Logan County resident tested positive.
Mosquito pools in Otero and Prowers counties tested positive for the virus last week. There were no reported cases of infection.
In 2003, by far the state’s worst year, 63 people died of West Nile and almost 3,000 became infected.
Steve Graff: 303-954-1661 or sgraff@denverpost.com
