MADISON, WIS. ? Wisconsin officials said Friday it was unlikely that two health care workers who fell ill after treating patients with the monkeypox virus were infected with the disease.

The cases would have been the first known U.S. human-to-human transmissions of the virus. Monkeypox, a disease related to smallpox but less lethal, appeared in the country for the first time when at least a dozen people had contact in recent weeks with infected pet prairie dogs.

A nurse in Milwaukee and a medical assistant in Marshfield showed symptoms similar to those from monkeypox after treating patients with the disease. The boyfriend of the medical assistant also showed symptoms.

Jeff Davis, Wisconsin’s chief epidemiologist, said further examinations suggest the three did not have the disease, but the state was awaiting test results from the Centers for Disease Control and Prevention.

By Friday afternoon, health officials throughout the country had confirmed 12 human cases of monkeypox: four each in Wisconsin, Indiana and Illinois. Also, 71 possible cases had been reported — 22 in Indiana, 30 in Wisconsin, 15 in Illinois, two in Ohio and one each in Arizona and Kentucky.