A Pox on Monkeypox

Medical Author: Frederick Hecht, M.D.
Medical Editor: Barbara K. Hecht, Ph.D. and Leslie J. Schoenfield, M.D., Ph.D.

June 18, 2003 -- Whoever had heard of monkeypox until this month? Monkeypox became news in the American media because of an outbreak of the disease in the Upper Midwest.

The outbreak is thought to have begun because of a Gambian giant rat. This exotic animal, although ill with monkeypox, was imported to Wisconsin. There, in a pet store, the Gambian rat transmitted the monkeypox virus to a prairie dog. The prairie dog, unfortunately, proved to be a super-transmitter of this virus and infected at least 18 people. And so the disease spread.

Monkeypox seems new but it is really not. It has been known for over 40 years. Monkeypox was identified in monkeys in 1959. Its ability to infect people, however, was not recognized until 1970. Scientists subsequently realized that the usual hosts of the virus are rodents. In fact, the main hosts are African squirrels. Thus, infections in monkeys and people are accidental. People are infected from handling sick squirrels. (Squirrels are eaten in some parts of Africa.)

Monkeypox is usually said to be "milder" than smallpox. Still, monkeypox is not all that mild. The death rate with smallpox in Africa was 30% (before smallpox was eradicated). By comparison, the death rate with monkeypox in Africa is as high as 10%.