For the first time in the United States, monkeypox may have spread from person-to-person.

A southeastern Wisconsin health care worker may have contracted monkeypox from a human patient, state epidemiologist Jeff Davis said.

MONKEYPOX Fact Sheet Q&A CDC Info. WHO Info. Guidelines For Vets, Pet Owners

Previously, U.S. patients with monkeypox contracted the disease from infected animals.

Davis declined to identify the health care worker or where the worker was located.

He said health officials and scientists haven't confirmed the presence of the monkeypox virus in the worker, but they suspect it and are still testing tissue specimens.

The virus has been shown to spread among humans in Africa. Davis said a monkeypox outbreak in the Congo in 1996 and 1997, for example, grew primarily through person-to-person transmission.

But experts say human transmission isn't the primary way the virus is spread. Usually the virus passes among infected animals, and then from the animals to humans who have contact with them.

Davis said in this case, there was no animal exposure -- the only contact was with a human.

As of Wednesday afternoon, the Centers for Disease Control and Prevention reported 54 suspected cases of the disease in four states -- nine of them confirmed. About 10 people have been hospitalized.

With more cases of monkeypox being suspected, federal health officials are moving more aggressively to prevent it from spreading further.

The government has issued a ban on selling rodents from Africa as pets in the United States. The rodents are apparently the source of the virus.

Gambian rats and five other types of large African rodents are included in the ban because a Gambian rat is believed to have spread the virus to prairie dogs, which are actually rodents and are native to the American Plains. Some people keep prairie dogs as pets.

The government also issued a ban on the sale or movement of prairie dogs between states and within state boundaries.

The CDC recommends smallpox vaccinations for people who have come in contact with infected persons or animals. The smallpox vaccine can prevent monkeypox up to two weeks after exposure, but it's most effective in the first four days.

The CDC said studies have shown that smallpox vaccination is about 85 percent effective in preventing monkeypox. But the agency expects the number of people who will need the vaccine to be modest.

Monkeypox is a virus related to smallpox, but its symptoms are milder. In Africa, the mortality rate has shown to be between 1 and 10 percent.

"Monkeypox can be a serious illness, and it has not been previously seen in humans in this hemisphere. CDC and a team of expert advisors carefully weighed the risk of smallpox vaccination against the risks posed by exposure to monkeypox infection in arriving at this important decision," said Dr. Julie Gerberding, CDC director.

The agency also issued guidelines for people who own prairie dogs or other exotic pets. Under no circumstances should they release their pets into the wild. If the pets are ill, owners should contact their state health departments for guidance.

"The biggest risk here, what we're trying to avoid is inadvertently introducing monkeypox into the natural wildlife system in this country. So do not, do not release sick animals out into the wild," said Dr. David Fleming, deputy director for CDC, at a press conference Wednesday.

In general, the CDC is recommending euthanasia for animals diagnosed with monkeypox.