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'''''Plasmodium knowlesi''''' is a [[primate]] [[malaria]] parasite commonly found in [[Southeast Asia]].<ref>{{cite journal | title = A molecular phylogeny of malarial parasites recovered from cytochrome ''b'' gene sequences | journal = Journal of Parasitology | year = 2002 | first = Susan L. | last = Perkins | coauthors = Jos. J. Schall | volume = 88 | issue = 2 | pages = 972–978| id = | accessdate = 2010-12-11}}</ref> It causes malaria in long-tailed macaques (''[[Macaca fascicularis]]''), but it may also infect humans, either naturally or artificially.
'''''Plasmodium knowlesi''''' is a [[primate]] [[malaria]] parasite commonly found in [[Southeast Asia]].<ref>{{cite journal | title = A molecular phylogeny of malarial parasites recovered from cytochrome ''b'' gene sequences | journal = Journal of Parasitology | year = 2002 | first = Susan L. | last = Perkins | coauthors = Jos. J. Schall | volume = 88 | issue = 2 | pages = 972–978| id = | accessdate = 2010-12-11}}</ref> It causes malaria in long-tailed macaques (''[[Macaca fascicularis]]''), but it may also infect humans, either naturally or artificially.


''Plasmodium knowlesi'' is the fifth major human malaria parasite. It may cause severe malaria as indicated by its asexual erythrocytic cycle of about 24 hours.<ref name=Chin>{{cite journal | author=Chin W, Contacos PG, Coatney RG, Kimbal HR. | journal=Science | year=1965 | title=A naturally acquired quotidian-type malaria in man transferable to monkeys | volume=149 | pages=865 | pmid=14332847 | doi=10.1126/science.149.3686.865 | issue=3686}}</ref><ref name=Jongwutiwes>{{cite journal | journal=Emerg. Infect. Dis | year=2004 | volume=10 | issue=12 | pages=2211–3 | title=Naturally acquired ''Plasmodium knowlesi'' malaria in human, Thailand | author=Jongwutiwes S, Putaporntip C, Iwasaki T, Sata T, Kanbara H. | pmid=15663864 }}</ref><ref name=Cox-Singh>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'''(2): 165-171, PMID 18171245, {{PMC|2533694}}, {{DOI10.1086/524888}}.</ref> The typical fever becomes quotidian.<ref name=Chin /> This is an emerging infection that was reported for the first time in humans in 1965.<ref name=Chin /> It accounts for up to 70%<ref name=McCutchan>McCutchan TF, Piper RC, Makler MT (2008). "Use of malaria rapid diagnostic test to identify plasmodium knowlesi infection." ''Emerg Infect Dis'' 14(11): 1750-1752, PMID 18976561, {{PMC|2630758}}.</ref> of malaria cases in South East Asia where it is mostly found. This parasite is transmitted by the bite of an ''[[Anopheles]]'' mosquito.<ref name=McCutchan/> ''Plasmodium knowlesi'' has health, social and economic consequences for the regions affected by it.
''Plasmodium knowlesi'' is the fifth major human malaria parasite. It may cause severe malaria as indicated by its asexual erythrocytic cycle of about 24 hours.<ref name=Chin>{{cite journal | author=Chin W, Contacos PG, Coatney RG, Kimbal HR. | journal=Science | year=1965 | title=A naturally acquired quotidian-type malaria in man transferable to monkeys | volume=149 | pages=865 | pmid=14332847 | doi=10.1126/science.149.3686.865 | issue=3686}}</ref><ref name=Jongwutiwes>{{cite journal | journal=Emerg. Infect. Dis | year=2004 | volume=10 | issue=12 | pages=2211–3 | title=Naturally acquired ''Plasmodium knowlesi'' malaria in human, Thailand | author=Jongwutiwes S, Putaporntip C, Iwasaki T, Sata T, Kanbara H. | pmid=15663864 }}</ref><ref name=Cox-Singh>{{cite journal | author = Cox-Singh J, Davis TM, Lee KS, Shamsul SS, Matusop A, Ratnam S, Rahman HA, Conway DJ, Singh B |year=2008 |title=Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening|journal=Clin. Infect. Dis.|volume=46|issue=2 |pages= 165-171 |pmid= 18171245 |doi=10.1086/524888}}</ref> The typical fever becomes quotidian.<ref name=Chin /> This is an emerging infection that was reported for the first time in humans in 1965.<ref name=Chin /> It accounts for up to 70%<ref name=McCutchan>{{cite journal | author = McCutchan TF, Piper RC, Makler MT |year=2008 |fitle=Use of malaria rapid diagnostic test to identify plasmodium knowlesi infection| journal = Emerg Infect Dis | volume= 14|issue=11|pages= 1750-1752 |pmid=18976561 }}</ref> of malaria cases in South East Asia where it is mostly found. This parasite is transmitted by the bite of an ''[[Anopheles]]'' mosquito.<ref name=McCutchan/> ''Plasmodium knowlesi'' has health, social and economic consequences for the regions affected by it.


==History of discovery==
==History of discovery==
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In 1931, ''Plasmodium knowlesi'' was first isolated from a long-tailed macaque imported to [[India]] from [[Singapore]]. It caused a mild form of malaria when blood was passaged to other long-tailed macaques but caused lethal infections for rhesus [[macaque]]s. In 1932, using infected blood from macaques, it was demonstrated that these parasites could also infect humans.<ref name=Singh2004/> From early in the 1930s to 1955, ''P. knowlesi'' was used as a pyretic agent for the treatment of patients with [[neurosyphillis]].<ref name=Singh2004/>
In 1931, ''Plasmodium knowlesi'' was first isolated from a long-tailed macaque imported to [[India]] from [[Singapore]]. It caused a mild form of malaria when blood was passaged to other long-tailed macaques but caused lethal infections for rhesus [[macaque]]s. In 1932, using infected blood from macaques, it was demonstrated that these parasites could also infect humans.<ref name=Singh2004/> From early in the 1930s to 1955, ''P. knowlesi'' was used as a pyretic agent for the treatment of patients with [[neurosyphillis]].<ref name=Singh2004/>


In 1957 it was suggested by Garnham et al<ref name="Garnham1957">Garnham PCC, Lainson R, Cooper W (1957) The tissue stages and sporogony of ''Plasmodium knowlesi''. Trans Roy Soc Trop Med Hyg. 51 (5)384-396 </ref> that ''P. knowelsi'' could be the fifth species capable of causing endemic malaria in humans.
In 1957 it was suggested by Garnham et al<ref name="Garnham1957">Garnham PCC, Lainson R, Cooper W (1957) The tissue stages and sporogony of ''Plasmodium knowlesi''. ''Trans Roy Soc Trop Med Hyg.'' 51 (5)384-396 </ref> that ''P. knowelsi'' could be the fifth species capable of causing endemic malaria in humans.


In 1965, the first case of a naturally occurring infection of knowlesi malaria in humans was reported in an American man who had returned from visiting peninsular [[Malaysia]].<ref name=Haynes1988>Haynes JD, Dalton JP, Klotz FW, McGinniss MH, Hadley TJ, Hudson DE, Miller LH (1988). "Receptor-like specificity of a ''Plasmodium knowlesi'' malarial protein that binds to duffy antigen ligands on erythrocytes." ''J Exp Med'' '''167'''(6): 1873-1881, PMID 2838562, {{PMC|2189679}}.</ref> Although the infecting parasite was initially identified as ''P. falciparum'', one day later it was then identified as ''P. malariae'' and it was only confirmed to be ''P. knowlesi'' after infected blood was used to inoculate Rhesus monkeys.<ref name=Singh2004/> A second report emerged in 1971 about the natural infection of a man in Malaysia with ''Plasmodium knowlesi''<ref name=Singh2004/> However, since 2004, there have been an increasing number of reports of the incidence of ''P. knowlesi'' among humans in various countries in South East Asia, including [[Malaysia]], [[Thailand]], Singapore, the [[Philippines]], [[Vietnam]], [[Myanmar]] and [[Indonesia]].<ref name=Vythilingam2008>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'''(1): 26, PMID 18710577, {{PMC|2531168}}, {{DOI|10.1186/1756-3305-1-26}}.</ref>
In 1965, the first case of a naturally occurring infection of knowlesi malaria in humans was reported in an American man who had returned from visiting peninsular [[Malaysia]].<ref name=Haynes1988>{{cite journal | author = Haynes JD, Dalton JP, Klotz FW, McGinniss MH, Hadley TJ, Hudson DE, Miller LH |year=1988 |title=Receptor-like specificity of a ''Plasmodium knowlesi'' malarial protein that binds to duffy antigen ligands on erythrocytes | journal = J Exp Med | volume=167|issue=6 |pages= 1873-1881 |pmid=2838562 }}</ref> Although the infecting parasite was initially identified as ''P. falciparum'', one day later it was then identified as ''P. malariae'' and it was only confirmed to be ''P. knowlesi'' after infected blood was used to inoculate Rhesus monkeys.<ref name=Singh2004/> A second report emerged in 1971 about the natural infection of a man in Malaysia with ''Plasmodium knowlesi''<ref name=Singh2004/> However, since 2004, there have been an increasing number of reports of the incidence of ''P. knowlesi'' among humans in various countries in South East Asia, including [[Malaysia]], [[Thailand]], Singapore, the [[Philippines]], [[Vietnam]], [[Myanmar]] and [[Indonesia]].<ref name=Vythilingam2008>{{cite journal | author = Vythilingam I, Noorazian YM, Huat TC, Jiram AI, Yusri YM, Azahari AH, Norparina I, Noorrain A, Lokmanhakim S |year=2008|title=Plasmodium knowlesi in humans, macaques and mosquitoes in peninsular malaysia | journal=Parasit Vectors|volume=1|issue=1 |page= 26 | pmid= 18710577 |doi=10.1186/1756-3305-1-26}}</ref>


Work with archival samples have shown that infection with this parasite has occurred in Malaysia at least since the 1990s'<ref name=Lee>Lee K.S., Cox-Singh J., Brooke G., Matusop A., Singh B (2009). "''Plasmodium knowlesi'' from archival blood films: Further evidence that human infections are widely distributed and not newly emergent in Malaysian Borneo." ''Int J Parasitol,'' {{DOI|10.1016/j.ijpara.2009.03.003}}</ref> and it is now known to cause 70% of the malaria cases in certain areas of [[Sarawak]].<ref name=Daneshvar2009>Daneshvar C., Davis T.M.E., Cox‐Singh J., ''et al.different from P inui and P. cynmoglgi'' (2009). "Clinical and Laboratory Features of Human ''Plasmodium knowlesi'' Infection." ''Clin Infect Dis'' '''49'''(6): 852&ndash;860, {{DOI|10.1086/605439}}</ref>
Work with archival samples have shown that infection with this parasite has occurred in Malaysia at least since the 1990s'<ref name=Lee>Lee K.S., Cox-Singh J., Brooke G., Matusop A., Singh B (2009). "''Plasmodium knowlesi'' from archival blood films: Further evidence that human infections are widely distributed and not newly emergent in Malaysian Borneo." ''Int J Parasitol'' {{DOI|10.1016/j.ijpara.2009.03.003}}</ref> and it is now known to cause 70% of the malaria cases in certain areas of [[Sarawak]].<ref name=Daneshvar2009>Daneshvar C., Davis T.M.E., Cox‐Singh J., ''et al. different from P inui and P. cynmoglgi'' (2009). "Clinical and Laboratory Features of Human ''Plasmodium knowlesi'' Infection." ''Clin Infect Dis'' '''49'''(6): 852&ndash;860, {{DOI|10.1086/605439}}</ref>


==Evolution==
==Evolution==
Line 51: Line 51:


==Epidemiology==
==Epidemiology==
''P. knowlesi'' infection is normally considered a parasite of long-tailed (''[[Macaca fascicularis]]'') and pig-tailed (''[[Macaca nemestrina]]'') macaques <ref name=Vythilingam2008/><ref name=Ng>Ng O.T., Ooi E.E., Lee C.C., Lee P.J., Ng L.C., Pei S.W., Tu T.M., Loh J.P., Leo Y.S. (2008) Naturally acquired human ''Plasmodium knowlesi'' infection, Singapore. Emerg. Infect. Dis. 14(5): 814-816, PMID 18439370, {{PMC|2600232}}</ref> but humans who work at the forest fringe or enter the rainforest to work are at risk of infection. With the increasing popularity of deforestation and development efforts in South East Asia, many macaques are now coming in close and direct contact with humans.<ref name=Vythilingam2008/> Hence more and more people who live in the semi-urban areas are being found to be infected with knowlesi malaria.
''P. knowlesi'' infection is normally considered a parasite of long-tailed (''[[Macaca fascicularis]]'') and pig-tailed (''[[Macaca nemestrina]]'') macaques <ref name=Vythilingam2008/><ref name=Ng>Ng O.T., Ooi E.E., Lee C.C., Lee P.J., Ng L.C., Pei S.W., Tu T.M., Loh J.P., Leo Y.S. (2008) Naturally acquired human ''Plasmodium knowlesi'' infection, Singapore. ''Emerg. Infect. Dis.'' 14(5): 814-816, PMID 18439370</ref> but humans who work at the forest fringe or enter the rainforest to work are at risk of infection. With the increasing popularity of deforestation and development efforts in South East Asia, many macaques are now coming in close and direct contact with humans.<ref name=Vythilingam2008/> Hence more and more people who live in the semi-urban areas are being found to be infected with knowlesi malaria.


This parasite is mostly found in South East Asian countries particularly in [[Borneo]], [[Malaysia]], [[Myanmar]], [[Philippines]], [[Singapore]],<ref name="Jeslyn201">Jeslyn WP, Huat TC, Vernon L, Irene LM, Sung LK, Jarrod LP, Singh B, Ching NL (2010) Molecular epidemiological investigation of ''Plasmodium knowlesi'' in humans and macaques in Singapore. Vector Borne Zoonotic Dis.</ref> [[Thailand]] and neighboring countries and it appears to occur in regions that are reportedly free of the other four types of human malaria. It has also been reported in [[Bangladesh]]. Infective mosquitoes are restricted to the forest areas. Non-infective mosquitoes are typically found in the urban areas but transmission may occur due to the abundance of mosquitoes in this region.<ref name=Chin /><ref name=Yap>{{cite journal | journal=Trans R Soc Trop Med Hyg | year=1971 | volume=65 | issue=6 | pages=839–40 | title=A presumptive case of naturally occurring ''Plasmodium knowlesi'' malaria in man in Malaysia | author=Yap FL, Cadigan FC, Coatney GR. | pmid=5003320 | doi=10.1016/0035-9203(71)90103-9 }}</ref> particularly [[Malaysia]],<ref name=Singh2004>{{cite journal | journal=Lancet | year=2004 | volume=363 | issue=9414 | pages=1017–24 | title=A large focus of naturally acquired ''Plasmodium knowlesi'' infections in human beings | author=Singh B, Lee KS, Matusop A, Radhakrishnan A, Shamsul SSG, Cox-Singh J, Thomas A, Conway DJ | doi=10.1016/S0140-6736(04)15836-4 | pmid=15051281 }}</ref> but there are also reports on the Thai-Burmese border.<ref name=Jongwutiwes/> One fifth of the cases of malaria diagnosed in [[Sarawak]], [[Malaysian Borneo]] are due to ''P. knowlesi''.<ref name=Singh2004/>
This parasite is mostly found in South East Asian countries particularly in [[Borneo]], [[Malaysia]], [[Myanmar]], [[Philippines]], [[Singapore]],<ref name="Jeslyn201">Jeslyn WP, Huat TC, Vernon L, Irene LM, Sung LK, Jarrod LP, Singh B, Ching NL (2010) Molecular epidemiological investigation of ''Plasmodium knowlesi'' in humans and macaques in Singapore. ''Vector Borne Zoonotic Dis.''</ref> [[Thailand]] and neighboring countries and it appears to occur in regions that are reportedly free of the other four types of human malaria. It has also been reported in [[Bangladesh]]. Infective mosquitoes are restricted to the forest areas. Non-infective mosquitoes are typically found in the urban areas but transmission may occur due to the abundance of mosquitoes in this region.<ref name=Chin /><ref name=Yap>{{cite journal | journal=Trans R Soc Trop Med Hyg | year=1971 | volume=65 | issue=6 | pages=839–40 | title=A presumptive case of naturally occurring ''Plasmodium knowlesi'' malaria in man in Malaysia | author=Yap FL, Cadigan FC, Coatney GR. | pmid=5003320 | doi=10.1016/0035-9203(71)90103-9 }}</ref> particularly [[Malaysia]],<ref name=Singh2004>{{cite journal | journal=Lancet | year=2004 | volume=363 | issue=9414 | pages=1017–24 | title=A large focus of naturally acquired ''Plasmodium knowlesi'' infections in human beings | author=Singh B, Lee KS, Matusop A, Radhakrishnan A, Shamsul SSG, Cox-Singh J, Thomas A, Conway DJ | doi=10.1016/S0140-6736(04)15836-4 | pmid=15051281 }}</ref> but there are also reports on the Thai-Burmese border.<ref name=Jongwutiwes/> One fifth of the cases of malaria diagnosed in [[Sarawak]], [[Malaysian Borneo]] are due to ''P. knowlesi''.<ref name=Singh2004/>


''Plasmodium knowlesi'' is absent in [[Africa]]. This may be because there are no long-tailed and pig-tailed macaques (the reservoir hosts of ''P. knowlesi'') in Africa and many West Africans lack the [[Duffy antigen]] - a protein on the surface of the red blood cell that the parasite to uses to invade.
''Plasmodium knowlesi'' is absent in [[Africa]]. This may be because there are no long-tailed and pig-tailed macaques (the reservoir hosts of ''P. knowlesi'') in Africa and many West Africans lack the [[Duffy antigen]] - a protein on the surface of the red blood cell that the parasite to uses to invade.
Line 79: Line 79:
Symptoms of ''P. knowlesi'' in humans include headache, fever, chills and cold sweats.<ref name="Bronner2009"/> Singh ''et al.'' (2004)<ref name=Singh2004/> showed clinical symptoms in 94 patients with single species ''P. knowlesi'' infection at Kapit Hospital, Sarawak, Malaysian Borneo. Symptoms included fever, chills, and rigor in 100% of patients, headache in 32%, cough in 18%, vomiting in 16%, nausea in 6%, and diarrhea in 4%. Asexual cycle of the parasite in humans and its natural host macaque is about 24 hours.<ref name=Chin/><ref name=Jongwutiwes/><ref name=Cox-Singh/> Hence the disease may be called quotidian malaria,<ref name=Chin/> in concert with designation of tertian malaria and quartan malaria.<ref name=Manson>Manson-Bahr PEC, Bell DR, eds. (1987). ''Manson's Tropical Diseases.'' London: Bailliere Tindall, ISBN 0-7020-1187-8.</ref> In addition to a lab diagnosis using PCR assay, knowlesi malaria may also present itself with elevated levels of C-reactive protein and thrombocytopenia.
Symptoms of ''P. knowlesi'' in humans include headache, fever, chills and cold sweats.<ref name="Bronner2009"/> Singh ''et al.'' (2004)<ref name=Singh2004/> showed clinical symptoms in 94 patients with single species ''P. knowlesi'' infection at Kapit Hospital, Sarawak, Malaysian Borneo. Symptoms included fever, chills, and rigor in 100% of patients, headache in 32%, cough in 18%, vomiting in 16%, nausea in 6%, and diarrhea in 4%. Asexual cycle of the parasite in humans and its natural host macaque is about 24 hours.<ref name=Chin/><ref name=Jongwutiwes/><ref name=Cox-Singh/> Hence the disease may be called quotidian malaria,<ref name=Chin/> in concert with designation of tertian malaria and quartan malaria.<ref name=Manson>Manson-Bahr PEC, Bell DR, eds. (1987). ''Manson's Tropical Diseases.'' London: Bailliere Tindall, ISBN 0-7020-1187-8.</ref> In addition to a lab diagnosis using PCR assay, knowlesi malaria may also present itself with elevated levels of C-reactive protein and thrombocytopenia.


This parasite causes non-relapsing [[malaria]]<ref name=Cogswell1992>Cogswell F.B. (1992). The hypnozoite and relapse in primate malaria. ''Clin. Microbiol. Rev'' 5(1): 26-35, PMID 1735093, {{PMC|358221}}.</ref> due to lack of hypnozoites in its exoerythrocytic stage.<ref name=Krotoski1982>Krotoski W.A., Collins W.E. (1982). Failure to detect hypnozoites in hepatic tissue containing exoerythrocytic schizonts of ''Plasmodium knowlesi''. ''Am. J. Trop. Med. Hyg.'' 31(4): 854-856, PMID 7048949.</ref>
This parasite causes non-relapsing [[malaria]]<ref name=Cogswell1992>Cogswell F.B. (1992). The hypnozoite and relapse in primate malaria. ''Clin. Microbiol. Rev'' 5(1): 26-35, PMID 1735093, {{PMC|358221}}.</ref> due to lack of hypnozoites in its exoerythrocytic stage.<ref name=Krotoski1982>Krotoski W.A., Collins W.E. (1982). Failure to detect hypnozoites in hepatic tissue containing exoerythrocytic schizonts of ''Plasmodium knowlesi''. ''Am. J. Trop. Med. Hyg.'' 31(4): 854-856, PMID 7048949</ref>


While infection with this organism is normally not serious, life threatening complications or even death may occur in a minority of cases. The most common complications are respiratory distress, abnormal liver function including jaundice and renal failure. Mortality in one series of cases was about 2%.<ref name="Daneshvar2009">Daneshvar C., Davis T.M., Cox-Singh J., Rafa'ee M.Z., Zakaria S.K., Divis P.C., Singh B. (2009) Clinical and laboratory features of human ''Plasmodium knowlesi'' infection. Clin. Infect. Dis.</ref>
While infection with this organism is normally not serious, life threatening complications or even death may occur in a minority of cases. The most common complications are respiratory distress, abnormal liver function including jaundice and renal failure. Mortality in one series of cases was about 2%.<ref name="Daneshvar2009">Daneshvar C., Davis T.M., Cox-Singh J., Rafa'ee M.Z., Zakaria S.K., Divis P.C., Singh B. (2009) Clinical and laboratory features of human ''Plasmodium knowlesi'' infection. ''Clin. Infect. Dis.''</ref>


==Diagnosis==
==Diagnosis==
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Because ''P. knowlesi'' takes only 24 hours to complete its erythrocytic cycle, it can result in very high parasite density quickly and may be fatal in humans. For this reason early treatment is advised. It responds well to treatment with [[chloroquine]] and [[primaquine]].<ref name=Singh2004/> It has been advised that those who reside in or have traveled to the [[South East Asia]] should be treated as intensively when found to be suffering from malaria.<ref name=Cox-Singh/>
Because ''P. knowlesi'' takes only 24 hours to complete its erythrocytic cycle, it can result in very high parasite density quickly and may be fatal in humans. For this reason early treatment is advised. It responds well to treatment with [[chloroquine]] and [[primaquine]].<ref name=Singh2004/> It has been advised that those who reside in or have traveled to the [[South East Asia]] should be treated as intensively when found to be suffering from malaria.<ref name=Cox-Singh/>


In a clinical study of treatment involving oral chloroquine for three days and at 24 hours oral primaquine was administered for two consecutive days.<ref name="Daneshvar2010">Daneshvar C, Davis TM, Cox-Singh J, Rafa'ee MZ, Zakaria SK, Divis PC, Singh B (2010) Clinical and parasitological response to oral chloroquine and primaquine in uncomplicated human ''Plasmodium knowlesi'' infections. ''Malar. J.'' 19;9:238</ref> This regime gave a rapid response with a median time to parasite clearance of three hours. This was more rapid that is found in ''[[Plasmodium vivax]]'' malaria where the median time to clearance is between six and seven hours.
In a clinical study of treatment involving oral chloroquine for three days and at 24 hours oral primaquine was administered for two consecutive days.<ref name="Daneshvar2010">Daneshvar C, Davis TM, Cox-Singh J, Rafa'ee MZ, Zakaria SK, Divis PC, Singh B (2010) "Clinical and parasitological response to oral chloroquine and primaquine in uncomplicated human ''Plasmodium knowlesi'' infections." ''Malar. J.'' 19;9:238</ref> This regime gave a rapid response with a median time to parasite clearance of three hours. This was more rapid that is found in ''[[Plasmodium vivax]]'' malaria where the median time to clearance is between six and seven hours.


==Public health, Prevention strategies and Vaccines==
==Public health, Prevention strategies and Vaccines==

Revision as of 22:38, 9 May 2011

Plasmodium knowlesi
Scientific classification
Kingdom:
Protista
Phylum:
Apicomplexa
Class:
Aconoidasida
Order:
Haemosporida
Family:
Plasmodiidae
Genus:
Plasmodium
Species:
knowlesi
Binomial name
Plasmodium knowlesi

Plasmodium knowlesi is a primate malaria parasite commonly found in Southeast Asia.[1] It causes malaria in long-tailed macaques (Macaca fascicularis), but it may also infect humans, either naturally or artificially.

Plasmodium knowlesi is the fifth major human malaria parasite. It may cause severe malaria as indicated by its asexual erythrocytic cycle of about 24 hours.[2][3][4] The typical fever becomes quotidian.[2] This is an emerging infection that was reported for the first time in humans in 1965.[2] It accounts for up to 70%[5] of malaria cases in South East Asia where it is mostly found. This parasite is transmitted by the bite of an Anopheles mosquito.[5] Plasmodium knowlesi has health, social and economic consequences for the regions affected by it.

History of discovery

The first person to see P. knowlesi was Franchiti in 1927 when he was examining the blood of Macaca fasicularis and he noted that it differed from Plasmodium cynomogli and Plasmodium inui. It was later seen by Campbell in 1931 who was interested in kala azar and passed the isolate onto his collegue Napier. Napier innoculated the strain into three monkeys one of which developed a fulminating infection. Das Gupta with whom Napier also worked maintained the species by seial passage. In 1932 Napier and Das Gupta described the species for the first time and showed that it could be transmitted to man but failed to name it. It was named by Sinton and Mulligan in 1932 after Dr R Knowles.

In 1931, Plasmodium knowlesi was first isolated from a long-tailed macaque imported to India from Singapore. It caused a mild form of malaria when blood was passaged to other long-tailed macaques but caused lethal infections for rhesus macaques. In 1932, using infected blood from macaques, it was demonstrated that these parasites could also infect humans.[6] From early in the 1930s to 1955, P. knowlesi was used as a pyretic agent for the treatment of patients with neurosyphillis.[6]

In 1957 it was suggested by Garnham et al[7] that P. knowelsi could be the fifth species capable of causing endemic malaria in humans.

In 1965, the first case of a naturally occurring infection of knowlesi malaria in humans was reported in an American man who had returned from visiting peninsular Malaysia.[8] Although the infecting parasite was initially identified as P. falciparum, one day later it was then identified as P. malariae and it was only confirmed to be P. knowlesi after infected blood was used to inoculate Rhesus monkeys.[6] A second report emerged in 1971 about the natural infection of a man in Malaysia with Plasmodium knowlesi[6] However, since 2004, there have been an increasing number of reports of the incidence of P. knowlesi among humans in various countries in South East Asia, including Malaysia, Thailand, Singapore, the Philippines, Vietnam, Myanmar and Indonesia.[9]

Work with archival samples have shown that infection with this parasite has occurred in Malaysia at least since the 1990s'[10] and it is now known to cause 70% of the malaria cases in certain areas of Sarawak.[11]

Evolution

Based on a Bayesian coalescent approach the most probable time of evolution of P. knowelsi is 257,000 years ago (95% ranged 98,000–478,000).[12]

Life cycle

Plasmodium knowlesi parasite replicates and completes its blood stage cycle in 24 hour cycles[4] resulting in fairly high loads of parasite densities in a very short period of time. This makes it a potentially very severe disease if it remains untreated. Life cycle: merozoite → schizont → trophozoites. These stages are microscopically indistinguishable from Plasmodium malariae.

Mosquito stages:[13] A mosquito ingests gametocytes, which have been formed in the mammalian host. These are either microgametocytes (which give rise to male gametocytes) or macrogametocytes (which give rise to female gametocytes). These gametocytes mature into microgametes and macrogametes respectively, and then form zygotes within the midgut of the mosquito by fertilization. The zygotes mature into ookinetes, then into oocysts. Finally, the oocysts mature into sporozoites which move to salivary gland of the mosquito.

Summary: gametocyte → (microgamete or macrogamete) → zygote → ookinete → oocyst → sporozoites.

In man: exoerythrocytic stage (in the liver):[13] The sporozoites are injected into humans when the mosquito bites and they travel to the liver through blood stream and undergo asexual reproduction to become merozoites through schizonts in the liver cell. Hypnozoites in the liver has not yet been found.

Summary: sporozoites → schizonts → merozoites.

In man: erythrocytic stage (in the blood):[13] Merozoites are unleashed into the blood stream to infect into the erythrocytes constituting one asexual cycle of infection of the erythrocytes. Some merozoites become microgametocytes or macrogametocytes after infection of the erythrocytes. These remain in the blood to be ingested by mosquitoes.

Summary: Merozoite → trophozoite → schizont → merozoites.

Epidemiology

P. knowlesi infection is normally considered a parasite of long-tailed (Macaca fascicularis) and pig-tailed (Macaca nemestrina) macaques [9][14] but humans who work at the forest fringe or enter the rainforest to work are at risk of infection. With the increasing popularity of deforestation and development efforts in South East Asia, many macaques are now coming in close and direct contact with humans.[9] Hence more and more people who live in the semi-urban areas are being found to be infected with knowlesi malaria.

This parasite is mostly found in South East Asian countries particularly in Borneo, Malaysia, Myanmar, Philippines, Singapore,[15] Thailand and neighboring countries and it appears to occur in regions that are reportedly free of the other four types of human malaria. It has also been reported in Bangladesh. Infective mosquitoes are restricted to the forest areas. Non-infective mosquitoes are typically found in the urban areas but transmission may occur due to the abundance of mosquitoes in this region.[2][16] particularly Malaysia,[6] but there are also reports on the Thai-Burmese border.[3] One fifth of the cases of malaria diagnosed in Sarawak, Malaysian Borneo are due to P. knowlesi.[6]

Plasmodium knowlesi is absent in Africa. This may be because there are no long-tailed and pig-tailed macaques (the reservoir hosts of P. knowlesi) in Africa and many West Africans lack the Duffy antigen - a protein on the surface of the red blood cell that the parasite to uses to invade.

P. knowlesi is the most common cause of malaria in chldhood in Sabah, Malaysia.[17]

Vectors

Theoretically there are four modes of transmission: from an infected monkey to another monkey, from an infected monkey to a human, from an infected human to another human and from an infected human back to a monkey.[9] In practice human malaria appears to be almost entirely due to monkey to human transmission.

The known vectors belong to the genus Anopheles, subgenus Cellia, series Neomyzomyia and group Leucosphyrus.[4] Mosquitoes of this group are typically found in forest areas in South East Asia but with a greater clearing of forest areas for farmland, humans are increasingly becoming exposed to these vectors.

Within the monkey population in Peninsular Malaysia, Anopheles hackeri is believed to be the main vector of P. knowlesi: although A. hackeri is capable of transmitting malaria to humans,[18] it is not normally attracted to humans and seems unlikely to be an important vector for transmission to humans.[19]

Anopheles latens is attracted to both macaques and humans and has been shown to be the main vector transmitting P. knowlesi to humans in the Kapit Division of Sarawak, Malaysian Borneo.[20]

Anopheles crucens has also been reported as a vector of P. knowlesi. Both species of mosquitoes have been shown to contain as many as 1,000 sporozoites suggesting that they may be efficient vectors.[9]

Clinical

Two possible modes of transmission to humans have been proposed: either from an infected monkey to a human or from an infected human to another human.

Symptoms typically begin approximately 11 days after an infected mosquito has bitten a person and the parasites can be seen in the blood between 10 – 12 days after infection.[21] The parasite may multiply rapidly resulting in very high parasite densities that may be fatal.[21]

Although the current infection rate with Plasmodium knowlesi is relatively low, one risk it presents is misdiagnosis with other forms of malarial parasites such as P. malariae especially when microscopy is used. P. knowlesi is more accurately distinguished from P. malariae using PCR assay and molecular characterization.

Symptoms of P. knowlesi in humans include headache, fever, chills and cold sweats.[21] Singh et al. (2004)[6] showed clinical symptoms in 94 patients with single species P. knowlesi infection at Kapit Hospital, Sarawak, Malaysian Borneo. Symptoms included fever, chills, and rigor in 100% of patients, headache in 32%, cough in 18%, vomiting in 16%, nausea in 6%, and diarrhea in 4%. Asexual cycle of the parasite in humans and its natural host macaque is about 24 hours.[2][3][4] Hence the disease may be called quotidian malaria,[2] in concert with designation of tertian malaria and quartan malaria.[13] In addition to a lab diagnosis using PCR assay, knowlesi malaria may also present itself with elevated levels of C-reactive protein and thrombocytopenia.

This parasite causes non-relapsing malaria[22] due to lack of hypnozoites in its exoerythrocytic stage.[23]

While infection with this organism is normally not serious, life threatening complications or even death may occur in a minority of cases. The most common complications are respiratory distress, abnormal liver function including jaundice and renal failure. Mortality in one series of cases was about 2%.[11]

Diagnosis

P. knowlesi infection is diagnosed by examining thick and thin blood films in the same way as other malarias. The appearance of P. knowlesi is similar to that of P. malariae and is unlikely to be correctly diagnosed except by using molecular detection assays[6] in a malaria reference laboratory.

The morphology of Plasmodium knowlesi is similar to that of Plasmodium malariae. P. malariae is characterized by a compact parasite (all stages) and does not alter the host erythrocyte's shape or size or cause enlargement. Elongated trophozoites stretching across the erythrocyte, called band forms, are sometimes observed. Schizonts will typically have 8-10 merozoites that are often arranged in a rosette pattern with a clump of pigment in the center.[24]

Rapid diagnostic tests kits may or may not recognize P. knowlesi because of their specificity.

Currently PCR assay and molecular characterization are the most reliable methods for detecting and diagnosing P. knowlesi infection. PCR identifies the parasite DNA but this technique is not rapid and cannot be used for routine identification. PCR is also expensive and requires very specialized equipment.[6]

Treatment

Because P. knowlesi takes only 24 hours to complete its erythrocytic cycle, it can result in very high parasite density quickly and may be fatal in humans. For this reason early treatment is advised. It responds well to treatment with chloroquine and primaquine.[6] It has been advised that those who reside in or have traveled to the South East Asia should be treated as intensively when found to be suffering from malaria.[4]

In a clinical study of treatment involving oral chloroquine for three days and at 24 hours oral primaquine was administered for two consecutive days.[25] This regime gave a rapid response with a median time to parasite clearance of three hours. This was more rapid that is found in Plasmodium vivax malaria where the median time to clearance is between six and seven hours.

Public health, Prevention strategies and Vaccines

  1. Mosquito bed nets
  2. Medication – Mefloquine, Chloroquine
  3. Vector control
is not effective in forest area
  1. Residual spraying using insecticides
is not effective in forest area
  1. Meteo-Biological Prediction of Vector population

Pathology

A single post mortum case has been described to date[26] The patient was a male who became unwell 10 days after exposure. After four days he presented acutely unwell to a hospital. He was found to have a raised eosinophil count, to be thrombocytopaenic, hyponatraemic with an elevated blood urea, potassium, lactate dehydrogenase and amino transferase values. Dengue fever was suspected but ruled out on investigation. Malarial parasites were seen on the blood film and later identified as Plasmodium knowlesi by PCR. At post mortum the liver and spleen were enlarged. The brain and endocardium showed multiple petechial haemorrhages. The lungs had features consistent with acute respiratory distress syndrome. Histological examination showed sequestration of pigmented parasitized red blood cells in the vessels of the cerebrum, cerebellum, heart and kidney without evidence of chronic inflammatory reaction in the brain or any other organ examined. The spleen and liver had abundant pigment containing macrophages and parasitized red blood cells. The kidney had evidence of acute tubular necrosis. Endothelial cells in heart sections were prominent. Brain sections were negative for intracellular adhesion molecule-1.

The overall post mortem picture was very similar to that found in cases of Plasmodium falciparum. There were important differences including the absence of coma despite petechial haemorrhages and parasite sequestration in the brain.

Notes

There are at least two subspecies of P. knowlesi known - P. knowlesi edesoni and P. knowlesi knowlesi. It is not known if there are any clinical differences between these two subspecies.

Useful Web Links

Plasmodium knowlesi genome data

References

  1. ^ Perkins, Susan L. (2002). "A molecular phylogeny of malarial parasites recovered from cytochrome b gene sequences". Journal of Parasitology. 88 (2): 972–978. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ a b c d e f Chin W, Contacos PG, Coatney RG, Kimbal HR. (1965). "A naturally acquired quotidian-type malaria in man transferable to monkeys". Science. 149 (3686): 865. doi:10.1126/science.149.3686.865. PMID 14332847.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ a b c Jongwutiwes S, Putaporntip C, Iwasaki T, Sata T, Kanbara H. (2004). "Naturally acquired Plasmodium knowlesi malaria in human, Thailand". Emerg. Infect. Dis. 10 (12): 2211–3. PMID 15663864.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ a b c d e 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 (2): 165–171. doi:10.1086/524888. PMID 18171245.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ a b McCutchan TF, Piper RC, Makler MT (2008). Emerg Infect Dis. 14 (11): 1750–1752. PMID 18976561. {{cite journal}}: Missing or empty |title= (help); Unknown parameter |fitle= ignored (help)CS1 maint: multiple names: authors list (link)
  6. ^ a b c d e f g h i j Singh B, Lee KS, Matusop A, Radhakrishnan A, Shamsul SSG, Cox-Singh J, Thomas A, Conway DJ (2004). "A large focus of naturally acquired Plasmodium knowlesi infections in human beings". Lancet. 363 (9414): 1017–24. doi:10.1016/S0140-6736(04)15836-4. PMID 15051281.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Garnham PCC, Lainson R, Cooper W (1957) The tissue stages and sporogony of Plasmodium knowlesi. Trans Roy Soc Trop Med Hyg. 51 (5)384-396
  8. ^ Haynes JD, Dalton JP, Klotz FW, McGinniss MH, Hadley TJ, Hudson DE, Miller LH (1988). "Receptor-like specificity of a Plasmodium knowlesi malarial protein that binds to duffy antigen ligands on erythrocytes". J Exp Med. 167 (6): 1873–1881. PMID 2838562.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ a b c d e 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 (1): 26. doi:10.1186/1756-3305-1-26. PMID 18710577.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
  10. ^ Lee K.S., Cox-Singh J., Brooke G., Matusop A., Singh B (2009). "Plasmodium knowlesi from archival blood films: Further evidence that human infections are widely distributed and not newly emergent in Malaysian Borneo." Int J Parasitol doi:10.1016/j.ijpara.2009.03.003
  11. ^ a b Daneshvar C., Davis T.M.E., Cox‐Singh J., et al. different from P inui and P. cynmoglgi (2009). "Clinical and Laboratory Features of Human Plasmodium knowlesi Infection." Clin Infect Dis 49(6): 852–860, doi:10.1086/605439 Cite error: The named reference "Daneshvar2009" was defined multiple times with different content (see the help page).
  12. ^ Lee KS, Divis PC, Zakaria SK, Matusop A, Julin RA, Conway DJ, Cox-Singh J, Singh B (2011). "Plasmodium knowlesi: Reservoir Hosts and tracking the emergence in humans and macaques". PLoS Pathog. 7 (4): e1002015.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ a b c d Manson-Bahr PEC, Bell DR, eds. (1987). Manson's Tropical Diseases. London: Bailliere Tindall, ISBN 0-7020-1187-8.
  14. ^ Ng O.T., Ooi E.E., Lee C.C., Lee P.J., Ng L.C., Pei S.W., Tu T.M., Loh J.P., Leo Y.S. (2008) Naturally acquired human Plasmodium knowlesi infection, Singapore. Emerg. Infect. Dis. 14(5): 814-816, PMID 18439370
  15. ^ Jeslyn WP, Huat TC, Vernon L, Irene LM, Sung LK, Jarrod LP, Singh B, Ching NL (2010) Molecular epidemiological investigation of Plasmodium knowlesi in humans and macaques in Singapore. Vector Borne Zoonotic Dis.
  16. ^ Yap FL, Cadigan FC, Coatney GR. (1971). "A presumptive case of naturally occurring Plasmodium knowlesi malaria in man in Malaysia". Trans R Soc Trop Med Hyg. 65 (6): 839–40. doi:10.1016/0035-9203(71)90103-9. PMID 5003320.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ Barber BE, William T, Jikal M, Jilip J, Dhararaj P, Menon J, Yeo TW, Anstey NM (2011). "Plasmodium knowlesi malaria in children". Emerg Infect Dis. 17 (5): 814–820. PMID 21529389.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ^ Wharton RH, Eyles DE. (1961). "Anopheles hackeri, a vector of Plasmodium knowlesi in Malaya". Science. 134 (3474): 279–80. doi:10.1126/science.134.3474.279. PMID 13784726.
  19. ^ Reid JA, Weitz B. (1961). "Anopheline mosquitoes as vectors of animal malaria in Malaya". Ann Trop Med Parasitol. 55: 180–6. PMID 13740488.
  20. ^ Vythilingam I, Tan CH, Asmad M, Chan ST, Lee KS, Singh B. (2006). "Natural transmission of Plasmodium knowlesi to humans by Anopheles latens in Sarawak, Malaysia". Trans R Soc Trop Med Hyg. 100 (11): 1087–88. doi:10.1016/j.trstmh.2006.02.006. PMID 16725166.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  21. ^ a b c Bronner U., Divis P.C., Farnert A., Singh B. (2009). Swedish traveller with Plasmodium knowlesi malaria after visiting Malaysian Borneo. Malar J. 8: 15, PMID 19146706, PMC 2634766, doi:10.1186/1475-2875-8-15.
  22. ^ Cogswell F.B. (1992). The hypnozoite and relapse in primate malaria. Clin. Microbiol. Rev 5(1): 26-35, PMID 1735093, PMC 358221.
  23. ^ Krotoski W.A., Collins W.E. (1982). Failure to detect hypnozoites in hepatic tissue containing exoerythrocytic schizonts of Plasmodium knowlesi. Am. J. Trop. Med. Hyg. 31(4): 854-856, PMID 7048949
  24. ^ http://www.tulane.edu/~wiser/protozoology/notes/pl_sp.html#morph
  25. ^ Daneshvar C, Davis TM, Cox-Singh J, Rafa'ee MZ, Zakaria SK, Divis PC, Singh B (2010) "Clinical and parasitological response to oral chloroquine and primaquine in uncomplicated human Plasmodium knowlesi infections." Malar. J. 19;9:238
  26. ^ Cox-Singh J, Hiu J, Lucas SB, Divis PC, Zulkarnaen M, Chandran P, Wong KT, Adem P, Zaki SR; et al. (2010). "Severe malaria - a case of fatal Plasmodium knowlesi infection with post-mortem findings: a case report". Malar J. 9 (1): 10. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
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