Viral infection with the smallpox virus, of which man is the only carrier; this fact has made it possible to eradicate the disease. The virus now exists only in laboratories, and so vaccination is no longer necessary. The pox virus is inhaled, and breeds in the air passages and lymph nodes, from which it moves to the skin and mucous membranes. Roughly 12 days after infection the patient feels sick, and has fever. Four days later a skin eruption appears on face, neck, arms and legs in particular; the trunk may be completely unaffected. The skin eruption follows a set sequence: lump, blister, crust, scar; all the spots all over the body are at the same stage simultaneously. There are two forms of smallpox: a severe form (variola major) which leaves scars and disfiguration of the face, and a mild form (variola minor), which causes less disfiguration and fewer deaths. Patients are infectious from the outbreak of the skin eruption, particularly during the first week. Good hygiene can prevent infection in those in close contact. There is no medication for the pox virus; vaccination is necessary immediately after contact to prevent the disease, and patients must be treated in isolation.