Rash on the genitals of a male patient infected with mpox (monkeypox). Mpox is a zoonotic virus found near rainforests in Central and West Africa. It causes disease in humans and monkeys, although its natural hosts are rodents. It is capable of human to human transmission and can be sexually transmitted. In humans it causes fever, swollen glands and a rash of fluid-filled blisters. Symptoms usually start within 3 weeks of exposure to the virus.