In June 2003, the first outbreak in the Western hemisphere of human monkeypox infection occurred in the midwestern United States. Close contact with infected wild or exotic pets, mainly prairie dogs, was discovered to be the cause of the outbreak.

U.S. health officials now warn that people exposed to monkeypox virus can develop a spectrum of clinical illnesses, including severe neurologic illness.

In the Journal of Infectious Diseases, Dr. James J. Sejvar from the Centers for Disease Control and Prevention in Atlanta and colleagues describe a cluster of monkeypox cases in one family exposed to a common source of the virus.

The family bought two prairie dogs at a trade show. The animals became ill and died within a week, and three days later all three family members came down with a flu-like illness.

The mother and father displayed only a rash, but the daughter - a previously healthy 6-year-old - had severe brain inflammation requiring hospital admission.

The individual with the “mildest clinical course” had had a smallpox vaccination as a child. The vaccinia virus used in smallpox vaccinations is similar to monkeypox virus.

“These three patients illustrate a spectrum of clinical illness with monkeypox despite a common source of exposure,” Sejvar and colleagues write, noting also that age and prior smallpox vaccination may affect the severity of monkeypox illness.

While there is currently no FDA-approved treatment for monkeypox, the antiviral drug cidofovir may be of potential benefit, they suggest.

SOURCE: Journal of Infectious Diseases, November 15, 2004.