Monkeypox is caused by an orthopoxvirus that is related to smallpox. It was first discovered in monkeys in 1958 but can infect humans through direct contact with infected animals or humans. Transmission between humans occurs through contact with infectious skin lesions, body fluids, or contaminated materials. While smallpox was officially eradicated in 1980 after a global vaccination program, monkeypox still occurs sporadically in parts of Central and West Africa.