Malaria is an acute febrile illness. Symptoms appear seven days or more (usually 10–15 days) after the infective mosquito bite. The first symptoms – fever, headache, chills and vomiting – may be mild and difficult to recognize as malaria. If not treated within 24 hours, P. falciparum malaria can progress to severe illness often leading to death. Children in endemic areas with severe disease frequently develop one or more of the following syndromic presentations: severe anaemia, respiratory distress in relation to metabolic acidosis, or cerebral malaria. In adults, multi-organ involvement is also frequent.

For both P. vivax and P. ovale, clinical relapses may occur weeks to months after the first infection, even if the patient has left the malarious area. These new episodes arise from “dormant” liver forms (absent in P. Falciparum and P.malariae), and special treatment – targeted at these liver stages – is mandatory for a complete cure.