DENVER -- An eagle from the Pueblo Zoo was one of the latest animals infected with West Nile Virus.

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In addition, more horses and birds infected with West Nile Virus were found in counties along Colorado's two major east-flowing rivers and their tributaries.

Twenty-three new cases in horses and a sentinel chicken were confirmed Thursday by the state health and agriculture departments -- raising the statewide total to 83 infected horses and 13 birds, including the sentinel chicken.

Nineteen horses have died as the virus has spread to 15 counties.

But, Cindy Parmenter of the state Department of Public Health and Environment said no human cases have been reported.

"I'm not sure what it's going to take to stop the progression of this disease," said Linh Truong, an agriculture department spokeswoman. "Everybody is thinking it's going to spread westward. We haven't seen it in our Western Slope and hopefully that won't happen this year, but you never know."

Most of the cases have been found in counties along the South Platte and Arkansas rivers. The drought, which has left many rivers running at historic lows, has created stagnant pools where mosquitoes breed.

The virus is carried by mosquitoes that have fed on infected animals. Weld County, on the South Platte, has 30 confirmed equine cases.

The virus has infected more than 480 people nationwide this year and killed at least 29. It first appeared in New York in 1999 and has been traveling west.