Monkeypox: How Globalization, Host Immunity, and Viral Evolution Create a New Pathogen

Monkeypox is an Orthopoxvirus, endemic to West Africa and the Congo Basin. It causes an illness characterized by fever, myalgias, lymphadenopathy, and a disseminated vesicular rash. Although similar to smallpox, monkeypox is typically milder, with a lower mortality rate. Endemicity in Africa was previously reduced owing to cross-protection from smallpox vaccine but has been increasing since cessation of universal vaccination. Sporadic cases have been imported to the United States (US), with a few secondary cases. A large global outbreak in 2022 has demonstrated changing epidemiology and increased person-to-person transmission. In May 2022, a returned traveler in Massachusetts pre-sented with monkeypox. As of October 7, 2022, 71,096 cases had been reported in 107 countries, and 26,577 of those were in the US. Most cases have been in younger people without previous smallpox vaccination and in men who have sex with men, a previously unrecognized mode of transmission.