several reasons for this: deforestation, "bush meat" trade (i.e. eating monkey meat), and because smallpox vaccination gave people protection, but now that Smallpox has been eliminated and the vaccination stopped, people no longer have this immunity.
the mortality is ten percent, but many cases occur in areas with suboptimal health care, so the real extent is not known.
WHO REPORT on December's outbreak in Nigeria.
Monkeypox, a rare zoonosis that occurs sporadically in forested areas of Central and West Africa, is an orthopoxvirus that can cause fatal illness. The disease manifestations are similar to human smallpox (eradicated since 1980), however human monkeypox is less severe. The disease is self-limiting with symptoms usually resolving within 14–21 days. Treatment is supportive. This is the first outbreak in Nigeria since 1978. The virus is transmitted through direct contact with blood, bodily fluids and cutaneous/mucosal lesions of an infected animals (rats, squirrels, monkeys, dormice, striped mice, chimpanzees amongst others rodents) Secondary human-to-human transmission is limited but can occur via exposure to respiratory droplets, contact with infected persons or contaminated materials.the question is why the outbreaks didn't spread to more people. This is probably good news, meaning an epidemic is less likely.