Natural infection of Plasmodium brasilianum in humans: Man and monkey share quartan malaria parasites in the Venezuelan Amazon

• We found human infections with ‘Plasmodium brasilianum’, a quartan malaria parasite of New World monkeys in South America
• We show that in areas of close contact humans and non-human primates are concurrently infected with quartan malaria parasites
• We conclude that quartan malaria parasites can transcend host species boundaries with impunityWe found naturally acquired infections in humans with Plasmodium brasilianum parasites, a quartan malaria parasite which usually infects more than 35 monkey species in South America. This confirms that malaria parasites, which cause the quartan type of fever (two days without fever between fever peaks), are easily exchanged between humans and monkeys in Latin America. The wide host reservoir of quartan malaria parasites requires particular malaria research efforts.

BackgroundThe quartan malaria parasite Plasmodium malariae is the widest spread and best adapted human malaria parasite. The simian Plasmodium brasilianum causes quartan fever in New World monkeys and resembles P. malariae morphologically. Since the genetics of the two parasites are nearly identical, differing only in a range of mutations expected within a species, it has long been speculated that the two are the same. However, no naturally acquired infection with parasites termed as P. brasilianum has been found in humans until now.MethodsWe investigated malaria cases from remote Yanomami indigenous communities of the Venezuelan Amazon and analyzed the genes coding for the circumsporozoite protein (CSP) and the small subunit of ribosomes (18S) by species-specific PCR and capillary based-DNA sequencing.FindingsBased on 18S rRNA gene sequencing, we identified 12 patients harboring malaria parasites which were 100% identical with P. brasilianum isolated from the monkey, Alouatta seniculus. Translated amino acid sequences of the CS protein gene showed identical immunodominant repeat units between quartan malaria parasites isolated from both humans and monkeys.InterpretationThis study reports, for the first time, naturally acquired infections in humans with parasites termed as P. brasilianum. We conclude that quartan malaria parasites are easily exchanged between humans and monkeys in Latin America. We hypothesize a lack of host specificity in mammalian hosts and consider quartan malaria to be a true anthropozoonosis. Since the name P. brasilianum suggests a malaria species distinct from P. malariae, we propose that P. brasilianum should have a nomenclatorial revision in case further research confirms our findings. The expansive reservoir of mammalian hosts discriminates quartan malaria from other Plasmodium spp. and requires particular research efforts.