In the natural primate hosts (long and pig-tailed macaques), P. knowlesi causes asymptomatic low-grade parasitism. In contrast, hyperparasitaemia and death ensue in the well-used Rhesus experimental model [5] . Consequently, there is much information on experimental P. knowlesi malaria, including organ pathology in various animal models [6] [7] [8] . Natural P. knowlesi infections of humans were formerly missed because of morphological similarity with Plasmodium malariae [9, 10] . Now clinical descriptions of knowlesi malaria encompass a spectrum of disease ranging from uncomplicated to fatal malaria [3, 4] .