(CNN) Prairie dogs infected with the plague -- yes, the plague -- have shut down parts of a city and wildlife area near Denver this summer.

Sections of the Rocky Mountain Arsenal National Wildlife Refuge were closed in late July as a precautionary measure after the discovery of the disease, the US Fish and WIldlife Service said

Unaffected refuge areas reopened Saturday , but other locations in Commerce City, a suburb north of Denver, will remain closed until Labor Day weekend, the Tri-County Health Department said.

"The prairie dog colonies are being monitored and burrows are being treated with insecticide, but there is still evidence of fleas in the hiking and camping areas, which could put people and pets at risk, so those areas will remain closed," said John M. Douglas, Jr., the Executive Director of Tri-County Health Department.

No human infections have been reported, he said.

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