Three more people in Colorado have been diagnosed with the plague after coming in contact with an infected dog whose owner contracted a life-threatening form of the disease, state health officials said on Friday.

In all, four people were infected with the disease from the same source, the Colorado Department of Public Health and Environment said in a statement.

Last week the department said a man in an eastern Colorado county whose dog died of the plague had been diagnosed with pneumonic plague, a rare and serious form of the disease.

The man remains hospitalized, but authorities have not released his condition.

The three people in the latest reported cases had "mild symptoms" and have fully recovered after being treated with antibiotics, the department said, adding that they are no longer contagious.

Two of the patients in the new cases contracted pneumonic plague, the department said