Monkeypox exposure? Offer smallpox vaccine. (Pregnancy not a Contraindication).

Persons who've had close or intimate contact with symptomatic individuals or animals confirmed to have monkeypox should receive the smallpox vaccine, ideally within 4 days of exposure.

That recommendation, issued by the Centers for Disease Control and Prevention in mid-June, extends to pregnant women, as the benefits of vaccination in these circumstances appear to outweigh the risks, the agency said.

Monkeypox has government officials on edge, even though the virus seems to be less contagious than other viral diseases such as measles and smallpox, and it appears that human populations alone cannot sustain transmission. The problem is that there's no telling what can happen when a virus enters a new environment.

"We're always very concerned with any new infection," said Dr. Stephen M. Ostroff, deputy director of the Centers for Disease Control and Prevention's National Center for Infectious Diseases. "Whenever you have a new virus being introduced into an ecosystem where it's not been present before, you have to be very concerned about the public health threat."

The monkeypox virus was apparently brought to this country by a Gambian giant pouched rat imported by a Chicago-area exotic pets dealer. But the human cases have come from contact with animals indigenous to North America: prairie dogs that were exposed to the rat and, in at least one case, a rabbit.

As of mid-June there were 81 cases of presumed monkeypox cases in humans in the United States.

Any physician who sees a febrile individual or an individual with a rash should ask about exposure to small mammals, particularly prairie dogs or Gambian rats, the CDC recommended. "The possibility of human-to-human transmission cannot be ruled out at this time," the CDC said at press time.