With over 250 million new cases occurring each year, malaria remains a major health problem in most tropical regions. In Africa 2 million people die every year from malaria. The malaria parasite is spread by the female anopheles mosquito. The parasite settles in the liver where it commences cycles of reproduction. During each cycle thousands of new parasites are produced, which can then be released into the circulation and enter red blood cells, where they can multiply further. The infected blood cells burst and the parasites flood the circulation and invade new red blood cells. This cycle is repeated every two to three days. The symptoms of malaria coincide with release of the parasites into the circulation. Symptoms can be variable and non-specific and can be difficult to distinguish from the flu or other tropical illnesses. The incubation period (the time between the mosquito bite and the symptoms appearing) is usually 1 - 3 weeks, but may be up to a year. Symptoms include:The five types of malaria parasite that infect humans are falciparum, vivax, ovale, malariae and knowlesi. Of these falciparum is the most serious and causes 95% of malaria deaths. It is essential to seek medical advice as soon as possible if any fever develops during or after travelling in an area where malaria occurs. Assume any fever is due to malaria until proven otherwise. Seek medical attention promptly, within 24-48 hours of onset of fever. Malaria is found in large parts of Central and South America, Sub-Saharan Africa, Indian Subcontinent, Southeast Asia, the Middle East and the Pacific Islands. Up to one in thirty long term travellers will catch malaria in high risk areas such as Papua New Guinea, Solomon Islands, and one in fifty in Sub-Saharan Africa. The risk is lower in India, Southeast Asia and Central and South America. A traveller's risk of malaria will vary greatly according to length of stay, accommodation, time of year and activities. Transmission is more common in rural areas and in the wet season. Malaria is not usually a risk at altitudes above 1800m.