First case of a naturally acquired human infection with Plasmodium cynomolgi

Abstract

Since 1960, a total of seven species of monkey malaria have been reported as transmissible to man by mosquito bite: Plasmodium cynomolgi, Plasmodium brasilianum, Plasmodium eylesi, Plasmodium knowlesi, Plasmodium inui, Plasmodium schwetzi and Plasmodium simium. With the exception of P. knowlesi, none of the other species has been found to infect humans in nature. In this report, it is described the first known case of a naturally acquired P. cynomolgi malaria in humans.The patient was a 39-year-old woman from a malaria-free area with no previous history of malaria or travel to endemic areas. Initially, malaria was diagnosed and identified as Plasmodium malariae/P. knowlesi by microscopy in the Terengganu State Health Department. Thick and thin blood films stained with 10% Giemsa were performed for microscopy examination. Molecular species identification was performed at the Institute for Medical Research (IMR, Malaysia) and in the Malaria & Emerging Parasitic Diseases Laboratory (MAPELAB, Spain) using different nested PCR methods.Microscopic re-examination in the IMR showed characteristics of Plasmodium vivax and was confirmed by a nested PCR assay developed by Snounou et al. Instead, a different PCR assay plus sequencing performed at the MAPELAB confirmed that the patient was infected with P. cynomolgi and not with P. vivax.This is the first report of human P. cynomolgi infection acquired in a natural way, but there might be more undiagnosed or misdiagnosed cases, since P. cynomolgi is morphologically indistinguishable from P. vivax, and one of the most used PCR methods for malaria infection detection may identify a P. cynomolgi infection as P. vivax.Simian Plasmodium species may routinely infect humans in Southeast Asia. New diagnostic methods are necessary to distinguish between the human and monkey malaria species. Further epidemiological studies, incriminating also the mosquito vector(s), must be performed to know the relevance of cynomolgi malaria and its implication on human public health and in the control of human malaria.The zoonotic malaria cannot be ignored in view of increasing interactions between man and wild animals in the process of urbanization.

Figure 1

Neighbour joining phylogenetic tree. Phylogenetic tree comparing the A-type SSU rRNA gene sequence obtained (GenBank accession number JQ794445) with other Plasmodium species identified in our laboratory as well, but not submitted to the GenBank (identified as “ML plus an internal number” given in our Malaria Laboratory followed of the country name in the cases where this is known) and with known Plasmodium A-type SSU rRNA sequences from GenBank (accession numbers are indicated in parenthesis). The sequence of our patient clusters with all other P. cynomolgi strains. Sequence Theileria (AF162432) was used as outgroup. Significative bootstrap values are indicated.

Figure 2

Partial A-type SSU rRNA gene alignment from Plasmodium vivax and Plasmodium cynomolgi in vivax-primers regions. Alignment of partial sequences from Plasmodium vivax and Plasmodium cynomolgi with the Malay case (in blue color and with the GenBank accession number JQ794445) taking as reference the primers VIRsh and rVIV1-rVIV2. Note: The alignment is in forward sense 5’-3’ and the VIVsh and rVIV2 primers sequences are in reverse and complementary form (R&C) to allow the correct alignment. (.) Represents an identical nucleotide. (-) Represents an alignment gap.