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Monkeypox Home

Press Release

June 7, 2003
Contact: CDC Media Relations

Public Health Investigation Uncovers First Outbreak of Human Monkeypox Infection in Western Hemisphere

Public health officials from the Centers for Disease Control and Prevention (CDC) and the states of Wisconsin, Illinois and Indiana have reported the first outbreak of human infections with a monkeypox-like virus to be documented in the Western Hemisphere. Thus far, 19 cases have been reported: 17 in Wisconsin, one in Northern Illinois, and one in Northern Indiana. All patients who have become ill reported direct or close contact with ill prairie dogs.

CDC is advising physicians, veterinarians, and the public to report instances of rash illness associated with exposure to prairie dogs, Gambian rats and other animals to local and state public health authorities. CDC also has issued interim recommendations for infection control calling for health care personnel attending hospitalized patients to follow standard precautions for guarding against airborne or contact illness. Veterinarians examining or treating sick rodents, rabbits and such exotic pets as prairie dogs and Gambian rats are advised to use personal protective equipment, including gloves, surgical mask or N-95 respirator, and gowns.

The prairie dogs were sold by a Milwaukee animal distributor in May to two pet shops in the Milwaukee area and during a pet “swap meet” (pets for sale or exchange) in northern Wisconsin. The Milwaukee animal distributor obtained prairie dogs and a Gambian giant rat that was ill at the time from a northern Illinois animal distributor. Investigations are underway to trace the source of animals and the subsequent distribution of animals from the Illinois distributor. Preliminary information suggests that animals from this distributor may have been sold in several other states.

Human monkeypox is a rare, zoonotic, viral disease that occurs primarily in the rain forest countries of Central and West Africa. It is a member of the orthopox family of viruses. In humans, infection with monkeypox virus results in a rash illness similar to but less infectious than smallpox. Monkeypox in humans is not usually fatal. The incubation period is about 12 days. Animal species susceptible to monkeypox virus may include non-human primates, rabbits, and some rodents.

Scientists at the Marshfield Clinic in Marshfield, Wisconsin, recovered the first viral isolates from a patient and a prairie dog. Through examination with an electron microscope they demonstrated a poxvirus.

Physicians should consider monkeypox in persons with fever, cough, headache, myalgia, rash, or lymph node enlargement within 3 weeks after contact with prairie dogs or Gambian giant rats. Veterinarians examining sick exotic animal species, especially prairie dogs and Gambian giant rats, should consider the possibility of monkeypox. Veterinarians should also be alert to the development of illness in other animal species that may have been housed with ill prairie dogs or Gambian giant rats.

Local, state, and federal agencies and private institutions that have participated in this investigation to date have included the Marshfield Clinic and Marshfield Laboratories, Froedtert Hospital and Medical College of Wisconsin, the City of Milwaukee Health Department and at least 10 additional health departments in Wisconsin and Illinois, the Wisconsin Division of Public Health, Wisconsin Department of Agriculture Trade and Consumer Protection and Wisconsin State Laboratory of Hygiene, the Illinois Department of Public Health, the Illinois State Department of Agriculture, the Indiana State Department of Health, and the US Department of Agriculture.

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Note to Editors: For electron microscope images, please see

For additional information about monkeypox, see

CDC Monkeypox website

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