Light micrograph of a section through a lesion in the skin of a monkey that had been infected with the monkeypox virus. This sample was obtained on day 13 of the rash. In monkeypox the rash appears in the recuperative stage of the disease. The monkeypox virus, which is found near rainforests in Central and West Africa, causes disease in humans and monkeys, although its natural hosts are rodents. It is capable of human-to-human transmission. In humans it causes fever, swollen glands and a rash of fluid-filled blisters. It is fatal in 10 percent of cases.