Plasmodium malariae and P. ovale genomes provide insights into malaria parasite evolution
The genome sequences of the neglected human-infective malaria species Plasmodium malariae and P. ovale provide new insights into their biology that are pertinent to understanding their epidemiology and to the broader agenda of malaria elimination. Thomas Otto, Matthew Berriman and colleagues report the genome sequences of Plasmodium malariae and P. ovale, two of the malaria parasites that infect humans. These species have been more difficult to study than most because of lower parasitaemia levels in the blood in human infections, as well as frequent co-infection. Carriers may have less severe symptoms, and these parasites are estimated to be present in up to 5% of clinical malaria cases, often found in co-infections with P. falciparum and P. vivax. The new genome sequences provide a resource for studies of the human infectivity of Plasmodium and malaria epidemiology. Elucidation of the evolutionary history and interrelatedness of Plasmodium species that infect humans has been hampered by a lack of genetic information for three human-infective species: P. malariae and two P. ovale species (P. o. curtisi and P. o. wallikeri)1. These species are prevalent across most regions in which malaria is endemic2,3 and are often undetectable by light microscopy4, rendering their study in human populations difficult5. The exact evolutionary relationship of these species to the other human-infective species has been contested6,7. Using a new reference genome for P. malariae and a manually curated draft P. o. curtisi genome, we are now able to accurately place these species within the Plasmodium phylogeny. Sequencing of a P. malariae relative that infects chimpanzees reveals similar signatures of selection in the P. malariae lineage to another Plasmodium lineage shown to be capable of colonization of both human and chimpanzee hosts. Molecular dating suggests that these host adaptations occurred over similar evolutionary timescales. In addition to the core genome that is conserved between species, differences in gene content can be linked to their specific biology. The genome suggests that P. malariae expresses a family of heterodimeric proteins on its surface that have structural similarities to a protein crucial for invasion of red blood cells. The data presented here provide insight into the evolution of the Plasmodium genus as a whole.