Monkeypox, also known as mpox, is an infectious viral disease that can occur in humans and some other animals. Symptoms include fever, swollen lymph nodes, and a rash that forms blisters and then crusts over. The time from exposure to onset of symptoms ranges from five to twenty-one days. The duration of symptoms is typically two to four weeks. There may be mild symptoms, and it may occur without any symptoms being apparent. The classic presentation of fever and muscle pains, followed by swollen glands, with lesions all at the same stage, has not been found to be common to all outbreaks. Cases may be severe, especially in children, pregnant women or people with suppressed immune systems. The disease is caused by the monkeypox virus, a zoonotic virus in the genus Orthopoxvirus. The variola virus, the causative agent of smallpox, is also in this genus. Of the two types in humans, clade II causes a less severe disease than the Central African type.