Plasmodium knowlesi is primarily a chronic infection of the long-tailed and pig-tailed macaques, but can infect humans. P. knowlesi’s early stages can be confused with P. falciparum while the later stages can mimic P. malariae. Erythrocytic invasion occurs in red blood cells of all ages which can result in high parasitemia. P. knowlesi has a unique 24-hour erythrocytic cycle.
P. knowlesi is closely related to P. vivax and shares some of the same common features such as occasional severity and marked thrombocytopenia. Patients present with febrile illness with daily fever and chills, headache, rigors, malaise, myalgia, and productive cough.
