Human Plasmodium knowlesi infection in Ranong province, southwestern border of Thailand

Natthawan Sermwittayawong,Nongyao Sawangjaroen,Mitsuaki Nishibuchi,Varaporn Vuddhakul,Balbir Singh

doi:10.1186/1475-2875-11-36

Natthawan Sermwittayawong, Nongyao Sawangjaroen + Show 3 more

Open Access

https://doi.org/10.1186/1475-2875-11-36

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Abstract

BackgroundPlasmodium knowlesi, a simian malaria parasite, has been reported in humans in many Southeast Asian countries. In Thailand, most of the limited numbers of cases reported so far were from areas near neighbouring countries, including Myanmar.MethodsBlood samples collected from 171 Thai and 248 Myanmese patients attending a malaria clinic in Ranong province, Thailand, located near the Myanmar border were investigated for P. knowlesi using nested PCR assays. Positive samples were also investigated by PCR for Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium ovale, and were confirmed by sequencing the gene encoding the circumsporozoite protein (csp).ResultsTwo samples, one obtained from a Thai and the other a Myanmese, were positive for P. knowlesi only. Nucleotide sequences of the csp gene derived from these two patients were identical and phylogenetically indistinguishable from other P. knowlesi sequences derived from monkeys and humans. Both patients worked in Koh Song, located in the Kawthoung district of Myanmar, which borders Thailand.ConclusionThis study indicates that transmission of P. knowlesi is occurring in the Ranong province of Thailand or the Kawthoung district of Myanmar. Further studies are required to assess the incidence of knowlesi malaria and whether macaques in these areas are the source of the infections.

Highlights

Plasmodium knowlesi, a simian malaria parasite, has been reported in humans in many Southeast Asian countries
Microscopy results By microscopy, 69 and 102 Thai blood samples were identified as P. falciparum and P. vivax, respectively whereas 121, 123 and four Myanmese blood samples were identified as P. falciparum, P. vivax and a mixed infection (P. falciparum and P. vivax), respectively
PCR analysis for Plasmodium knowlesi A total of 419 blood samples were investigated and a 153-bp SSU rRNA fragment specific for P. knowlesi was detected in only two samples (Figure 2)

Summary

Introduction

Plasmodium knowlesi, a simian malaria parasite, has been reported in humans in many Southeast Asian countries. Humans infected with Plasmodium knowlesi, a simian malaria parasite [1], have been described in a number of Southeast Asian countries including Malaysia [2,3], Singapore [4], Myanmar [5], Vietnam [6], Indonesia [7], the Philippines [8] and Thailand [9]. No other humans infected with this species of Plasmodium were reported in Thailand until 2009, when 10 cases from Tak, Prachuap Khiri Khan, Chantaburi, Yala and Narathiwat provinces were described [10]. These areas located near borders of Myanmar, Cambodia, and Malaysia (Figure 1). In order to assess whether there were additional cases of human knowlesi malaria, among the Myanmese, blood samples collected from malaria patients attending the malaria clinic at the Vector Borne Disease Control Center at Ranong were investigated

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