Is the rise of simian zoonotic malarias a public health problem caused by humans? A review of simian malaria in humans

Infections caused by Plasmodium falciparum, P. vivax, and P. malariae have decreased globally following the successful roll-out of malaria elimination strategies. However, there have been increasing reports of human P. knowlesi infections across Southeast Asia; in some areas, it is now the only malaria species reported in humans. This is driven by land use change, forcing the simian macaque hosts and the Anopheles mosquito vectors into closer contact with humans, coupled with the potential loss of cross-protective immunity in countries approaching the elimination of human malaria species. P. knowlesi usually causes asymptomatic or mild disease in children, but adults may experience disease resembling severe falciparum malaria. It remains a public health burden on the local health systems, especially the need for rapid diagnosis and treatment to prevent severe disease. Following the introduction of polymerase chain reaction-based diagnostic technologies, other simian malarias such as P. coatneyi, P. cynomolgi, P. inui, P. inui-like and P. simiovale have also been found to cause natural human disease that had not previously been recognised. Furthermore, the discovery of P. brasilianum and P. simium as causes of naturally acquired malaria in South America has highlighted the need to incorporate a One Health approach to malaria control. This article reviews the clinical and epidemiological features of these malarias.