Facts about monkeypox, a virus that health officials say has infected at least four people in the Midwest and possibly dozens more. Officials suspect they caught the illness from exposure to pet prairie dogs.

• The disease has never before been reported in the Western Hemisphere. It is usually found in remote villages in Central and West Africa.

• Monkeypox is related to the virus that caused smallpox, and smallpox vaccinations also gave protection against it.

• The death rate among those with monkeypox ranges from 1 to 10 percent, with the highest rates among young children, but officials say the virus may be less lethal in the United States because of better nourishment and medical technology.

• The disease is usually transmitted to people from squirrels and primates through a bite or contact with the animal's blood; the Centers for Disease Control says a preliminary investigation showed the virus was transmitted to humans through "close contact" with the infected prairie dogs.

Source: World Health Organization