The vaccine can prevent the disease up to two weeks after exposure to the virus.
The recommendation from the Centers for Disease Control and Prevention came the same day that the federal investigation of the monkeypox outbreak was expanded to eight more states, bringing the total to 15.
This is the first outbreak of monkeypox in the Western Hemisphere, and CDC director Dr. Julie Gerberding said the serious illness must be controlled.
"We must do everything we can to protect persons who are exposed to monkeypox in the course of investigating or responding to the outbreak," she said.
The CDC said anyone who has cared for or had close contact with infected people or animals should get smallpox vaccinations. The agency also warned veterinarians and doctors to be on the lookout for the symptoms, especially in owners of prairie dogs or exotic rodents from Africa.
Monkeypox-infected prairie dogs distributed from Phil's Pocket Pets of Villa Park, Ill., may have been sold to numerous buyers in 15 states since April 15, according to a U.S. Department of Agriculture emergency warning issued Wednesday.
The states where possibly infected prairie dogs were being sought were Kentucky, Florida, Tennessee, Mississippi, Massachusetts, Michigan, New Jersey, New York, Illinois, Indiana, Wisconsin, Pennsylvania, Texas, Ohio and South Carolina.
As of Wednesday, health officials had confirmed a total of nine human cases of the disease - four in Wisconsin, four in Indiana and one in Illinois. Fifty possible cases had been reported - 23 in Indiana, 20 in Wisconsin, six in Illinois and one in New Jersey,
CDC spokesman Tom Skinner said.
No one has died of the disease.
Monkeypox, which produces pus-filled blisters, fever, rash, chills and aches, is a milder relative of smallpox. It has a mortality rate of 1 percent to 10 percent in Africa, but U.S. officials believe better nutrition and medical treatment here probably will prevent deaths.
Investigators are seeking people who have bought or swapped exotic pets distributed since April by Pocket Pets, where a shipment of prairie dogs is believed to have been infected by a Gambian giant rat imported from Africa.
CDC investigators found that Phil's Pocket Pets sold some of the animals at three swap meets. Sales were made at Lee Watson's Reptile Show in Schaumburg, Ill., on April 20, May 3 and May 18; the Midwest Reptile Show in Indianapolis on April 27 and an unspecified date in May; and the All-Ohio Reptile Show in Columbus on April 19.
A Wisconsin dealer also sold three prairie dogs from Pocket Pets at a swap meet in Wausau, Wis., in May, the USDA said.
By Daniel Yee