DENVER -- A case of West Nile virus has been found in the metro area, health officials said Tuesday.

According the Colorado Department of Public Health, a dead magpie found on Smith Road and Peoria on Monday tested positive for the mosquito-borne disease.

Another crow in Greeley also tested positive, making it the second crow in the area and the third bird that has come down with the virus.

The health department also said that a seventh Colorado horse has tested positive, making it five horses from Weld County and one each from Logan and Pueblo counties that are infected. Four of the horses had to be euthanized.

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"This is no longer a problem affecting other parts of Colorado. It has arrived in the metropolitan area. It needs to be taken seriously. Our ability to avoid human cases is dependent on our responsibility in taking protective measures," said Dr. Ned Calonge, the acting chief medical officer for the Department of Public Health.

No Human Cases In Colorado So Far

Tests have been performed on 18 residents in Colorado and five in Nebraska but so far no human cases have been diagnosed in either state.

Researchers say chances are low that any humans would be infected in Colorado.

Epidemiologist John Pape said the type of mosquitoes that carry the virus generally stop feeding on blood by early to mid September and Colorado's record drought has reduced mosquito populations.

However, even with the presence of the virus, the chances of any one person becoming seriously ill is remote, scientists say.

The elderly, the very young and those with weakened immune systems have the greatest risk of infection. Symptoms include a fever, headaches and body aches. Severe infections can result in encephalitis, an inflammation of the brain, or meningitis, an inflammation of the brain's lining and the spinal cord.

Virus Moving Westward

The virus has killed 12 people in Kentucky, Missouri, Illinois, Louisiana and Mississippi, with most of the deaths occurring in Louisiana. Health officials in Texas are waiting to find out whether a woman there is also a victim of the virus.

The CDC has confirmed more than 250 cases of the West Nile virus this year in the United States.

The virus has been on a steady westward march since first being found three years ago in New York. It has already been found in every state east of the Rocky Mountains.

The virus most likely was carried into Colorado by migratory birds moving along the Platte and Arkansas rivers, said Calonge.