Plasmodium falciparum-like Parasites Infecting Wild African Apes Do Not Represent a Recurrent Source of Human Malaria
Wild-living chimpanzees and gorillas harbor a multitude of Plasmodium spp., including six of the subgenus Laverania, one of which is the progenitor of P. falciparum. Despite the magnitude of this natural reservoir, it is unknown whether apes represent a recurrent source of human infections. Here, we used Plasmodium species-specific PCR, single genome amplification (SGA) and 454 sequencing to screen humans from remote areas of Cameroon for ape Laverania infections.  Among 1,403 blood samples, we found 1,000 to be positive for Plasmodium mitochondrial (mt)DNA, all of which contained human parasites as determined by sequencing and/or restriction enzyme digestion.  To exclude low abundance infections, we subjected 514 samples to 454 sequencing, targeting a region of the mtDNA genome that distinguishes ape from human Laverania species. Developing algorithms capable of differentiating rare Plasmodium variants from 454 sequencing error, we identified mono- and mixed-species infections with P. falciparum, P. malariae and/or P. ovale. However, none of the human samples contained ape Laverania parasites, including the gorilla precursor of P. falciparum. To characterize further the diversity of P. falciparum in Cameroon, we used SGA to amplify 3.4 kb mtDNA fragments from 229 infected humans. Phylogenetic analysis identified 62 new variants, all of which clustered with extant P. falciparum strains, providing further evidence that P. falciparum emerged following a single gorilla-to-human transmission. Thus, unlike P. knowlesi infected macaques in southeast Asia, African apes harboring Laverania parasites do not serve as a recurrent source of human malaria, a finding of import to ongoing control and eradication measures.