The first signs of malaria can be a non-specific flu-like illness such as fever, rigors, sweating, headache, cough, muscle aches, and gastrointestinal upset. 

If severe, symptoms include impaired consciousness, seizures, renal impairment, acidosis, hypoglycaemia, pulmonary oedema, shock, spontaneous bleeding, and haemoglobinuria.

Malaria is a medical emergency and should be considered in every unwell patient who has returned from the tropics in the previous year, particularly in the previous three months. Any fever present should be considered as malaria until proven otherwise. Travellers should seek advice without delay if they experience any flu-like symptoms while abroad, or on return, and should mention they have been in a malaria endemic area.