The 2003 Midwest monkeypox outbreak marked the first time monkeypox infection has appeared in the United States, and the first time in the Western Hemisphere. Beginning in May, 2003, by July a total of 71 cases of human monkeypox were found in five Midwestern states including Wisconsin, Indiana, Illinois, Kansas, Missouri, and Ohio. The cause of the outbreak was traced to Gambian pouched rats imported into the United States by an exotic animal importer in Texas. The rats were shipped from Texas to an Illinois distributor, who housed them with prairie dogs. No deaths were reported. No human-to-human transmission was found. All cases involved direct contact with infected prairie dogs. Electron microscopy and testing by polymerase chain reaction and immunohistochemistry were used to confirm the causative agent was human monkeypox.
Background
In May, 2003, a three-year-old Wisconsin resident was bitten by a prairie dog purchased from a local pet store. The child was hospitalized after developing fever of unknown origin, swollen eyes, and a red vesicular skin rash. The child's parents also developed a rash, but no other symptoms. Physicians immediately associated the symptoms with the animal bite and reported the case to the Milwaukee Health Department. Testing of both the child and the prairie dog confirmed the monkeypox virus as the causative agent. Between May 15, 2003, when the three-year-old index patient was first diagnosed through June 20, the date of the last patient with a laboratory-confirmed case of monkeypox, a total of 71 people ranging in age from 1 to 51 were infected.
Epidemiology
On April 9, 2003, a Texas importer received a shipment of 762 African rodents from Accra, Ghana. The shipment included Gambian pouched rats, rope squirrels, tree squirrels, African brush-tailed porcupines, dormice, and striped mice. Of the 762 rodents received, 584 were shipped to distributors in six states and Japan. The remaining 178 rodents could not be traced beyond the Texas importer due to lack of documentation. From April 9, 2003, through June 5, 2003, 584 animals were shipped from the Texas distributor to distributors in Texas, New Jersey, Iowa, Japan, Illinois, Minnesota, and Wisconsin. Illinois distributor number one received Gambian rats and dormice. This distributor housed the rodents with 200 prairie dogs. This distributor shipped prairie dogs to pet stores in Wisconsin, Illinois, Indiana, Missouri, Kansas, South Carolina, and Michigan. No human cases of monkeypox were reported in Japan, Michigan, and South Carolina. Laboratory-confirmed cases occurred in Kansas, Missouri, Indiana, Illinois, and Wisconsin. Of the 200 prairie dogs housed with the Gambian rats and dormice, 94 tested positive for monkeypox virus, including prairie dogs in pet stores in Wisconsin, Indiana, Illinois, Ohio, Kansas, Missouri, and one case in the eastern seaboard state of New Jersey. The Gambian rats and dormice housed with the prairie dogs at Illinois distributor number one tested positive for monkeypox virus. The most recent incidence of monkeypox prior to the Midwest outbreak occurred in the Democratic Republic of the Congo in 1996-1997, with a reported 88 cases. No deaths occurred in the Midwest outbreak. This was attributed to the prompt medical care received and the standard of living in the United States, which includes soap, running water, washing machines, sterile dressing materials, and hospital use of universal precautions, including isolation, gown, mask, gloves, and handwashing.
Transmission
No human-to-human transmission was found during this outbreak. All cases were found to be the direct result of contact with infected prairie dogs. Human-to-human transmission has been reported in Central and West Africa.
Signs and symptoms
The onset of the illness among the patients in the United States began in early May 2003. Patients typically experienced fever, headaches, muscle aches, chills, and nonproductive coughs. This was followed 1–10 days later by the development of a generalized papular rash that developed first on the trunk, then limbs and head. The papules evolved through phases of vesiculation, pustulation, umbilication, and crusting. All patients reported direct or close contact with recently acquired prairie dogs.
Treatment
No direct antiviral treatment for monkeypox is known, only supportive care and prevention of secondary infection. Use of universal precautions in the care of those with the disease has been shown to prevent human-to-human transmission. However, inoculation with the smallpox vaccine has shown to be effective in abating the progression of the disease in those with active infection, and in the prevention of the disease in the general population.
Use of smallpox vaccine
In the Midwest outbreak, the CDC issued guidance on the use of smallpox vaccine, Cidofovir, and Vaccinia immune globulin. Twenty-six residents in five states received the smallpox vaccination. This included 24 adults and two children. Among the adults vaccinated were two laboratory workers, before exposure and to 24 persons after exposure. One adult who was vaccinated as a child did not have a major vaccine reaction or "take" 7 days after vaccination and required revaccination. No adverse reactions to the smallpox vaccine were reported to the Vaccine Adverse Event Reporting System.
Prevention
To prevent the monkeypox virus from entering into the United States again, the Centers for Disease Control banned the importation of all African rodents. The U.S. Food and Drug Administration also issued orders banning the interstate shipment of prairie dogs and all African rodents.
