Federal health officials said yesterday they had confirmed that a shipment of infected rodents from Africa caused the first outbreak of monkeypox in the Western Hemisphere.

Tests have found that at least one Gambian giant pouched rat, three dormice and two rope squirrels imported from Ghana on April 9 by an exotic pet dealer in Texas were infected with the virus, the Centers for Disease Control and Prevention said.

"This shipment is believed to be the source of the current U.S. outbreak of monkeypox," the CDC said in a statement.

As a result, the CDC recommended that every animal in that shipment of 812 rodents, every prairie dog exposed to those animals and every prairie dog exposed to other potentially infected prairie dogs should be destroyed to prevent the virus from spreading further.

"The goal is to protect people, pets and wildlife in the United States by preventing the monkeypox virus from spreading or becoming established permanently," said Martin Cetron, director of the CDC's global migration and quarantine programs. The CDC had previously recommended that all animals that had been exposed be quarantined until officials could decide what to do with them.

Mammals of other species that have been kept in places where infected animals had been held should be quarantined for at least six weeks after exposure to a potentially infected animal and monitored for symptoms, the CDC said.

"These measures are essential in order to effectively address this public health issue," Cetron said. "This truly collaborative effect requires the support of public health officials, the pet industry and pet owners to successfully contain this outbreak."

The CDC also repeated warnings against releasing infected or sick prairie dogs or any other potentially infected animals into the wild, or disposing of their bodies in public landfills.

Pet owners should "contact state health departments or departments of agriculture for guidance on the disposition of animals," the CDC said.

Health officials are concerned that the virus could spread to local wildlife, allowing the disease to become permanently established in this country.

Federal, state and local health departments are still investigating 81 suspect or probable human cases of monkeypox in six states -- Illinois, Indiana, Kansas, Missouri, Ohio and Wisconsin. Thirty-two of the cases have been confirmed by laboratory tests so far. No one has died, although several people have become seriously ill. The virus causes flu-like symptoms and distinctive blisters.

The outbreak began in May when several people in Wisconsin developed symptoms. Officials determined the people had been infected by prairie dogs they had bought as pets. The prairie dogs were believed to have been infected by the African rodents, which were sold to various exotic pet dealers around the country, who then resold the rodents.

The monkeypox virus is closely related to the smallpox virus but is much less contagious and deadly. Previously, the disease had been reported only in Africa, where it has a mortality rate of about 10 percent and has been known to spread from person to person. No human-to-human transmissions have been reported in this country, and the disease appears to have been less severe than in Africa.

The arrival of the disease in the Western Hemisphere raised fears that it could spread widely among people and wildlife. Because the disease had never been seen in this part of the world, health officials were uncertain how serious a public health threat it might pose.

Federal officials have since banned the importation of rodents from Africa and have been intensively trying to trace all potentially infected animals and people so they can be isolated.

Jill Cox of Salt Lake City's Hogle Zoo displays a Gambian giant pouched rat. An infected rat is blamed for a U.S. monkeypox outbreak.