US health officials on Sunday were investigating the first outbreak in the Western hemisphere of the "monkeypox" virus, a smallpox-like disease spread by rodents and monkeys that rarely is fatal in humans and may have infected at least 28 people in three Midwest states.
Federal and state health officials were trying to find out why 17 people in Wisconsin, 10 in Indiana and one in Illinois became sick with symptoms such as fever and rashes following contact with sick Gambian rats and prairie dogs. No one in the US has died from the illness.
Prairie dogs are wild rodents that dig and live in holes on the western US plains, and are sometimes kept as pets or traded by North American animal dealers.
The Atlanta-based Centers for Disease Control said on Sunday that laboratory tests have virtually confirmed the US outbreak of monkeypox, a rare viral disease that is found mainly in central and West African rain forests where primates flourish. Animals susceptible to the disease also include rabbits and some rodents.
"We feel pretty certain now that it is monkeypox," Dr. Stephen Ostroff, the deputy director of the national center for infectious diseases, said in an interview.
He said monkeypox is virtually unknown outside of Africa and has never before been found in the Western hemisphere.
The symptoms in people are similar to smallpox although monkeypox is less infectious and is seldom fatal, the CDC said. Doctors should look for rashes, fever, enlarged lymph nodes and other symptoms in people who have been in contact with prairie dogs or Gambian giant rats in the last three weeks, it said.
Three people thought to be infected in Wisconsin and one in Indiana remained in hospitals, the Chicago Tribune said in its Sunday editions. The ill person in Illinois was not hospitalized, the Illinois Department of Public Health said.
* First observed in west Africa in early 1970s.
* Incubation period: 10-14 days.
* Smallpox vaccination also works for monkeypox.
* Highest mortality rate is among children, at 10 percent.
* Symptoms same as for smallpox: rash, fever, malaise, vomiting, headache, lesions.
Ostroff said the number of cases of the disease reported in the US could rise now that the public has been told about the virus and people are on alert for symptoms.
The Indiana Department of Health on Sunday said it was investigating 10 human cases and 31 people or businesses in the state that may have been exposed. That figure was up from only one human case in Indiana reported by the CDC on Saturday.
A pet dealership called Phil's Pocket Pets in a suburb of Chicago has been quarantined after the person in Illinois suspected of having the disease reported close contact with exotic animals at the facility, the Illinois agency said.
Health officials were investigating if the virus may have been spread when prairie dogs and an ill Gambian giant rat were obtained from the Illinois dealership by a Milwaukee, Wisconsin animal distributor. The distributor last month sold prairie dogs to two pet shops in the Milwaukee area and to others at an event in Wisconsin where dealers exchange exotic pets.
"Preliminary information suggests that animals from this distributor may have been sold in several other states," the CDC said.
In the past, most monkeypox cases in humans were in remote African villages close to tropical rain forests where there is frequent contact with infected monkeys and other animals.
Ostroff said little is known about the spread of the disease but it is conceivable that it could infect rodent-type pets such as gerbils or hamsters. The World Health Organization said monkeypox is usually transmitted to humans through contact with an animal's blood or by a bite.
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