Plasmodium knowlesi was initially identified in 1931 in a Macaca fascicularis monkey originating in Singapore, and was shown to be capable of infecting humans one year later.1 The first naturally transmitted P. knowlesi infection in humans was reported in 1965 in a man after a visit to the Malaysian peninsula.2 No other reports were published on naturally acquired P. knowlesi infection in humans until 2004 when Sing and colleagues3 reported 100 human cases of P. knowlesi in Malaysian Borneo that were identified by polymerase chain reaction (PCR), having been first misdiagnosed as Plasmodium malariae on blood smears. Human P. knowlesi infection has since been observed in several Southeast Asian countries such as China,4 Thailand,5 Myanmar,6 Philippines,7 Singapore,8 and Indonesian Borneo.9 The geographical repartition of this zoonotic infection (the human-to-human cycle has not yet been documented) corresponds to the overlap of the distribution of the main natural hosts; the long-tailed (Macaca fascicularis) and the pig-tailed (Macaca nemestrina) macaques, and the competent vectors.10,11
Plasmodium knowlesi human infection has been also described in Western countries in travelers returning from Southeast Asia. In the six published cases, travelers had been infected in Malaysian Borneo (N = 3),9,12,13 in the Borneo peninsula (N = 1),14 in the Philippines (N = 1),15 and in Malaysia or in Vietnam (N = 1).16 We describe the first report of human P. knowlesi infection in a traveler returning from Thailand.
We gratefully acknowledge Valérie Bans, Elodie Duthu, Séverine Gisquet, and Catherine Paris for technical assistance and John Woodley for the English revision of the manuscript.
Chin W, Contacos PG, Coatney GR, Kimball HR, 1965. A naturally acquited quotidian-type malaria in man transferable to monkeys. Science 149: 865.
Singh B, Kim Sung L, Matusop A, Radhakrishnan A, Shamsul SS, Cox-Singh J, Thomas A, Conway DJ, 2004. A large focus of naturally acquired Plasmodium knowlesi infections in human beings. Lancet 363: 1017–1024.
Zhu HM, Li J, Zheng H, 2006. Human natural infection of Plasmodium knowlesi. Zhongguo Ji Sheng Chong Xue Yu Ji Sheng Chong Bing Za Zhi 24: 70–71.
Jongwutiwes S, Putaporntip C, Iwasaki T, Sata T, Kanbara H, 2004. Naturally acquired Plasmodium knowlesi malaria in humans, Thailand. Emerg Infect Dis 10: 2211–2213.
Jiang N, Chang Q, Sun X, Lu H, Yin J, Zhang Z, Wahlgren M, Chen Q, 2010. Co-infections with Plasmodium knowlesi and other malaria parasites, Myanmar. Emerg Infect Dis 16: 1476–1478.
Luchavez J, Espino F, Curameng P, Espina R, Bell D, Chiodini P, Nolder D, Sutherland C, Lee KS, Singh B, 2008. Human infections with Plasmodium knowlesi, the Philippines. Emerg Infect Dis 14: 811–813.
Ng OT, Ooi EE, Lee CC, Lee PJ, Ng LC, Pei SW, Tu TM, Loh JP, Leo YS, 2008. Naturally acquired human Plasmodium knowlesi infection, Singapore. Emerg Infect Dis 14: 814–816.
Figtree M, Lee R, Bain L, Kennedy T, Mackertich S, Urban M, Cheng Q, Hudson BJ, 2010. Plasmodium knowlesi in human, Indonesian Borneo. Emerg Infect Dis 16: 672–674.
Sallum MA, Peyton EL, Wilkerson RC, 2005. Six new species of the Anopheles leucosphyrus group, reinterpretation of An. elegans and vector implications. Med Vet Entomol 19: 158–199.
Bronner U, Divis PC, Farnert A, Singh B, 2009. Swedish traveller with Plasmodium knowlesi malaria after visiting Malaysian Borneo. Malar J 8: 15.
van Hellemond JJ, Rutten M, Koelewijn R, Zeeman AM, Verweij JJ, Wismans PJ, Kocken CH, van Genderen PJ, 2009. Human Plasmodium knowlesi infection detected by rapid diagnostic tests for malaria. Emerg Infect Dis 15: 1478–1480.
Kantele A, Marti H, Felger I, Muller D, Jokiranta TS, 2008. Monkey malaria in a European traveler returning from Malaysia. Emerg Infect Dis 14: 1434–1436.
Centers for Disease Control and Prevention (CDC). Simian malaria in a U.S. traveler–New York, 2008. MMWR Morb Mortal Wkly Rep 58: 229–232.
Ta TT, Salas A, Ali-Tammam M, Martinez Mdel C, Lanza M, Arroyo E, Rubio JM, 2010. First case of detection of Plasmodium knowlesi in Spain by real-time PCR in a traveller from Southeast Asia. Malar J 9: 219.
Fabre R, Berry A, Morassin B, Magnaval JF, 2004. Comparative assessment of conventional PCR with multiplex real-time PCR using SYBR Green I detection for the molecular diagnosis of imported malaria. Parasitology 128: 15–21.
Tan TM, Nelson JS, Ng HC, Ting RC, Kara UA, 1997. Direct PCR amplification and sequence analysis of extrachromosomal Plasmodium DNA from dried blood spots. Acta Trop 14: 105–114.
Tham JM, Lee SH, Tan TM, Ting RC, Kara UA, 1999. Detection and species determination of malaria parasites by PCR: comparison with microscopy and with ParaSight-F and ICT malaria Pf tests in a clinical environment. J Clin Microbiol 37: 1269–1273.
Rubio JM, Benito A, Berzosa PJ, Roche J, Puente S, Subirats M, Lopez-Velez R, Garcia L, Alvar J, 1999. Usefulness of seminested multiplex PCR in surveillance of imported malaria in Spain. J Clin Microbiol 37: 3260–3264.
Tan CH, Vythilingam I, Matusop A, Chan ST, Singh B, 2008. Bionomics of Anopheles latens in Kapit, Sarawak, Malaysian Borneo in relation to the transmission of zoonotic simian malaria parasite Plasmodium knowlesi. Malar J 7: 52.
Vythilingam I, Noorazian YM, Huat TC, Jiram AI, Yusri YM, Azahari AH, Norparina I, Noorrain A, Lokmanhakim S, 2008. Plasmodium knowlesi in humans, macaques and mosquitoes in peninsular Malaysia. Parasit Vectors 1: 26.
Cox-Singh J, Davis TM, Lee KS, Shamsul SS, Matusop A, Ratnam S, Rahman HA, Conway DJ, Singh B, 2008. Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening. Clin Infect Dis 46: 165–171.
Cox-Singh J, Hiu J, Lucas SB, Divis PC, Zulkarnaen M, Chandran P, Wong KT, Adem P, Zaki SR, Singh B, Krishna S, 2010. Severe malaria—a case of fatal Plasmodium knowlesi infection with post-mortem findings: a case report. Malar J 9: 10.
McCutchan TF, Piper RC, Makler MT, 2008. Use of malaria rapid diagnostic test to identify Plasmodium knowlesi infection. Emerg Infect Dis 14: 1750–1752.
Kawai S, Hirai M, Haruki K, Tanabe K, Chigusa Y, 2009. Cross-reactivity in rapid diagnostic tests between human malaria and zoonotic simian malaria parasite Plasmodium knowlesi infections. Parasitol Int 58: 300–302.
Imwong M, Tanomsing N, Pukrittayakamee S, Day NP, White NJ, Snounou G, 2009. Spurious amplification of a Plasmodium vivax small-subunit RNA gene by use of primers currently used to detect P. knowlesi. J Clin Microbiol 47: 4173–4175.