Factors affecting the likelihood of monkeypox's emergence and spread in the post-smallpox era

Abstract

In 1980, the World Health Assembly announced that smallpox had been successfully eradicated as a disease of humans. The disease clinically and immunologically most similar to smallpox is monkeypox, a zoonosis endemic to moist forested regions in West and Central Africa. Smallpox vaccine provided protection against both infections. Monkeypox virus is a less efficient human pathogen than the agent of smallpox, but absent smallpox and the population-wide immunity engendered during eradication efforts, could monkeypox now gain a foothold in human communities? We discuss possible ecologic and epidemiologic limitations that could impede monkeypox's emergence as a significant pathogen of humans, and evaluate whether genetic constrains are sufficient to diminish monkeypox virus' capacity for enhanced specificity as a parasite of humans.

Figure 1

Map depicting the distribution of the smallpox in Africa 1954–1958, by country, before the inception of global eradication efforts (‘Smallpox 1958’, light green), and during the latter stages of eradication, at the time human monkeypox was discovered (‘Smallpox 1971’, dark green) [12]. Countries reporting at least one case of human monkeypox through 1990 are depicted with cross-hatching.

Figure 2

(a) Legs and feet of monkeypox patient (photo courtesy of J. Harvey). (b) Legs and feet of smallpox patient at similar stage of rash (pustular) (photo courtesy of J. Nobel, CDC).