Tammy Kautzer's 3-year-old daughter had never been so sick. Her fever spiked above 103. Her glands were so swollen they looked like they were popping out of her neck. And then small, tender red welts began erupting all over her body.

"She kept getting worse. All she did was sleep. And when she wasn't sleeping, all she would do is cry," Kautzer said yesterday. "I don't know what the doctors were thinking, but I really didn't know if she was going to make it."

Kautzer's daughter, Schyan, did recover, but only after a harrowing week in the hospital, during which time Kautzer and her husband also got milder versions of the same sickness.

The illnesses of the family in Dorcester, Wis., were the start of the first outbreak reported in the Western Hemisphere of monkeypox, a sometimes life-threatening disease related to smallpox.

Health officials are investigating at least 29 suspected cases of people in three Midwestern states who may have been stricken in the outbreak so far, which state and federal health officials are urgently working to contain.

"We're doing everything possible to contain it," said Jeffrey P. Davis, Wisconsin's chief medical officer.

At least 18 of the suspected cases have been reported in Wisconsin, with at least one additional case in Illinois and 10 in Indiana. More potential cases, however, were being investigated, officials said.

State and federal authorities are tracing about 200 animals that were distributed in 15 states by an exotic pet dealer in Illinois. The dealer sold rodents known as prairie dogs, which are believed to be the source of the outbreak.

"There's the potential of transmission from animal to human, so certainly we are concerned," said Jeff Squibb of the Illinois Department of Agriculture.

In addition to trying to prevent more infections, officials are worried that the animals could spread the disease to wild rabbits and other indigenous creatures, allowing the virus to become entrenched in the United States. The last time a new disease became established in this country was in 1999, when the West Nile virus arrived. It has subsequently spread nationwide.

"That's probably the biggest concern we have other than the immediate concern of trying to get the message out as quickly as possible to try to identify people who might have been exposed," said Stephen Ostroff, deputy director of the National Center for Infectious Diseases in Atlanta.

The monkeypox outbreak came just as concerns were subsiding over severe acute respiratory syndrome (SARS), a deadly new lung infection believed to have jumped to humans in November from an exotic animal known as a civet, which is a delicacy in China.

"This situation is not just only people who come into contact with people. It's people who come into contact with animals. It's animals that come in contact with other animals," Squibb said. "It's more complex because of the combination and permutations of potential transmissions."

One of the Wisconsin cases involved a rabbit owner who was infected by his pet, which apparently became infected during a visit to the same veterinarian who treated a sick prairie dog, Davis said.

Although no cases of the disease apparently have spread directly from person to person in the United States, that has been known to occur with monkeypox in Africa.

At the same time, investigators are tracking the disease backward to try to determine how it first arrived in the Western Hemisphere.

Monkeypox is usually found only in central and western Africa. It is caused by a virus in the same family as the smallpox virus. It triggers similar symptoms -- fever, cough and a rash of small red blistering welts that eventually break open and scab over, sometimes leaving scars.

Monkeypox is believed to be much less deadly than smallpox, with a mortality rate of 1 percent to 10 percent compared with about 30 percent for smallpox, which has been eradicated from the wild. There is no known treatment for monkeypox, and it is unclear how the virus would behave in a new environment.

The outbreak was apparently started by a shipment of 38 prairie dogs that an exotic pet dealer, Phil's Pocket Pets of Villa Park, Ill., sold to another dealer, EK Exotics in Milwaukee. Phil's Pocket Pets purchased the animals from a dealer in Texas. It also purchased three Gambian giant rats from a dealer in Iowa, which in turn had bought them from another dealer in Texas. It is unclear whether the Gambian giant rats infected the prairie dogs or whether the prairie dogs acquired the virus another way.

Illinois and Wisconsin have temporarily banned the sale of prairie dogs and have quarantined the two animal dealers, as well as the Kautzers' home, a farm that houses an assortment of pets.

Officials are tracking down 115 customers who bought animals from Phil's Pocket Pets since April 15, when the first shipments arrived from Texas. All sick animals and people are being kept isolated to prevent further spread.

One of those buyers was EK Exotics, which sold prairie dogs to two pet stores in Milwaukee and at a "pet swap." That's where Kautzer said she and her husband acquired two prairie dogs on Mother's Day.

Two days later, one of them started to get sick. One eye began to swell shut and crust over, and a gland swelled up. A veterinarian gave the animal antibiotics, but it died several days later.

A few days after that, Kautzer's daughter, who had gotten a small bite on her hand from the animal, developed a high fever. At first doctors sent her home with antibiotics. But when she worsened, she was admitted to the Marshfield Clinic.

The wound on her finger continued to swell and developed a white ring around it. Then the red sores appeared on her body.

"The bite on her finger just kept getting bigger and bigger. All she did was sleep or cry. She couldn't eat anything. Her glands swelled up so much on her neck you could see them popping out," Kautzer said.

Doctors tried various medications, but nothing worked.

"I was worried she wasn't going to get better," Kautzer said.

Kautzer, 28, stayed with her daughter at the hospital and started to develop similar symptoms. Her glands swelled, making it hard to swallow. And the red welts broke out all over her body.

"I had the cold sweats for about three nights. I would wake up and I'd be totally drenched. My bedding was drenched. My clothes were drenched," she said.

Finally, after about three days, Schyan's condition started to improve, and so did Kautzer's. Her husband, Steve, 38, also developed similar symptoms in the interim, but never became as ill as his wife or daughter.

"It just started to go away on its own," Kautzer said.

Her doctors at Marshfield finally identified the virus that was making them sick, which the Centers for Disease Control and Prevention on Saturday confirmed as either the monkeypox virus or something very similar, prompting a nationwide alert.

Kautzer, whose farm houses dogs, goats, donkeys, horses and cats, said she will keep the remaining prairie dog, named Chuckles, if it does not get sick.

"He's very friendly. He runs over to you and rubs up against you. I've had prairie dogs before. I like them," she said. "But all I can say is that with exotic animals, I'm going to be a lot more careful from now on."

Prairie dogs are believed to be the source of an outbreak of the monkeypox virus in the Midwest, health officials said. There are at least 29 suspected cases in three states.