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.
Highlights
It has been asked whether animal malaria could be considered as true zoonoses
Plasmodium cynomolgi, P. knowlesi, P. inui and P. eylesi are distributed in Asia, P. brasilianum and P. simium in the New World, while P. schwetzi is found in Africa [1]
P. cynomolgi is indistinguishable from P. vivax, and as shown in this report, one of the most used Polymerase chain reaction (PCR) for malaria infection can characterize those infections as P. vivax
Summary
It has been asked whether animal malaria could be considered as true zoonoses. It has been known for some time that malaria of some non-human primates may infect man [1]. The symptoms of the patient were non-specific, she experienced episodes of mild to moderate 24-hour cycles of morning fevers with chills and rigor, cough and cold which mimicked a flu-like syndrome These clinical symptoms were similar to those described in non-natural infection in humans and were usually present only during febrile episodes. Patient experienced fever at 24 hourly intervals, when it was expected every 48 hours, like asexual cycle period of P. cynomolgi, previous reports of infected volunteers with P. cynomolgi showed that fever had different presentations, from afebrile to daily or tertian fever [3,25] Despite she lives in a malaria-free area, physicians suspected malaria because the patient experienced the characteristic cyclic fever with chills. In these last volunteers no relapses were described which could indicate that hypnozoites of P. cynomolgi in humans are not activated to become hepatic schizonts, which suggests that a specific treatment with primaquine is not necessary to avoid relapses
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