The parasites develop and are all released from the red blood corpuscles at the same time. This simultaneous release of parasites and their waste products produces periodic high fever, preceded by cold shivers. Sometimes the parasites remain in the liver for years, which can result in recurrent attacks of the disease. There are various kinds of malaria. In malaria caused by Plasmodium vivax and P. ovale, the patient has fever, with peaks every 48 hours. Malaria caused by Plasmodium malariae is characterized by peaks of fever every 72 hours. This clinical picture is rare in Western Europe. Malaria caused by is the most serious form. Fever is irregular. The red corpuscles containing parasites can block the blood supply to various organs, causing death. This form of malaria is sometimes introduced from tropical Africa. An attack of malaria begins usually with headache, muscular pain, loss of appetite, and sometimes vomiting and diarrhoea. Anaemia can occur because the parasites destroy red blood cells. Not all infected patients become ill; those who do not are carriers of the disease. The number of parasites, their size and the patient’s resistance are among factors influencing whether the patient becomes ill or not. Infection can be identified by the presence of larvae or eggs in the faeces. Clinical pictures vary considerably and depend on the parasite concerned. Drug treatment is the usual therapy.