br Declaration of Interests br Acknowledgments This study wa
Declaration of Interests
Acknowledgments This study was funded by the French Centre National de la Recherche Scientifique, the Université Grenoble Alpes, and the Direction de la Recherche Clinique et de l\'Innovation (DRCI) Centre Hospitalier Universitaire de Grenoble. LS thanks to Damascus University (Damascus, Syria) for a Ph.D fellowship. IA thanks Tishreen University (Latakia, Syria) for a Ph.D fellowship. We thank Katia Fusiller and Jeanne-Noëlle Del Bano for technical assistance, and Linda Northrup for English editing. We also thank Roche Diagnostics (Meylan, France) for providing the GS Junior 454 apparatus for next generation deep sequencing experiments.
Introduction Since malaria eradication is on the global health agenda again, non-human primates as source for Plasmodium infections in humans have received increased attention (Ramasamy, 2014). In this context, the simian Plasmodium brasilianum is particularly interesting. In 1908, a quartan malaria parasite was identified by Gonder and von Berenberg-Gossler in an imported ‘bald-headed uakari’ (Cacajao calvus) and named P. brasilianum, the quartan malaria parasite of New World monkeys in Latin America (Gonder and Von Berenberg-Gossler, 1908). P. brasilianum resembles the human quartan parasite Plasmodium malariae under the microscope, but early cross-species experimental infections by subcutaneous transfer of parasitized blood from black spider monkeys in the 1930s were unsuccessful. Hence, the names of two distinct parasites were maintained (Coatney et al., 2003). Later investigations in the 1960s demonstrated that humans could very well be experimentally infected with P. brasilianum from monkeys, and, vice versa, New World monkeys could be experimentally infected with P. malariae from humans (Coatney et al., 2003; Geiman and Siddiqui, 1969). Moreover, studies in the 1980s showed that monoclonal mitotic inhibitors against the circumsporozoite protein (CSP) of P. malariae cross-reacted and even neutralized the infectivity of P. brasilianum sporozoites to monkeys and vice versa (Cochrane et al., 1985). Sequencing of the gene coding for CSP confirmed the identity of this otherwise species-specific epitope in the two parasites (Lal et al., 1988). Another common tool for the molecular species identification of malaria parasites is the gene for the small subunit (18S) of ribosomes (Snounou et al., 1993). In 1999, Fandeur et al. analyzed the 18S gene sequences from quartan malaria parasites (P. brasilianum) found in four monkey species from French Guiana with the highest prevalence in Alouatta monkeys (Fandeur et al., 2000). The similarity between 18S sequences from P. brasilianum and P. malariae is more than 99% differing only in single nucleotide polymorphisms (SNPs). SNPs are distributed at random like in the genetic pool of one single species, and no distinctive marker has been identified so far. Unlike other human Plasmodium species, no whole genome sequence is available for quartan malaria parasites. We reviewed other published gene targets (msp-1, dhfr, cytochrome b, microsatellite DNA markers) and found striking homologies in all the markers without any specific identifying SNPs between the two parasite types (Fandeur et al., 2000; Guimarães et al., 2012; Tanomsing et al., 2007). The two parasites are nowadays perceived as variants of the same species, which had specialized on different hosts. Or, in practical terms, when quartan malaria parasites were identified in monkeys, they were designated as P. brasilianum. Conversely, when quartan malaria parasites were detected in humans, they were classified as P. malariae. Thus, the infected host determined the Plasmodium designation. At the time of writing, altogether thirteen 18S sequences of P. brasilianum and thirty-four 18S sequences of P. malariae were registered in the NCBI GenBank nucleotide database. Sero-epidemiological studies in Brazil and French Guyana already suggested that non-human primates might constitute a natural reservoir for human malaria, and may contribute to the maintenance of foci for P. malariae (Volney et al., 2002). However, as naturally-acquired infections with parasites termed as P. brasilianum were never described in humans (Baird, 2009), the idea of host specificity was upheld and the classification of P. brasilianum as an independent Plasmodium species was retained.