Displaying publications 1 - 20 of 88 in total

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  1. Hu TH, Rosli N, Mohamad DSA, Kadir KA, Ching ZH, Chai YH, et al.
    Sci Rep, 2021 10 11;11(1):20117.
    PMID: 34635723 DOI: 10.1038/s41598-021-99644-8
    Plasmodium knowlesi, a simian malaria parasite responsible for all recent indigenous cases of malaria in Malaysia, infects humans throughout Southeast Asia. There are two genetically distinct subpopulations of Plasmodium knowlesi in Malaysian Borneo, one associated with long-tailed macaques (termed cluster 1) and the other with pig-tailed macaques (cluster 2). A prospective study was conducted to determine whether there were any between-subpopulation differences in clinical and laboratory features, as well as in epidemiological characteristics. Over 2 years, 420 adults admitted to Kapit Hospital, Malaysian Borneo with knowlesi malaria were studied. Infections with each subpopulation resulted in mostly uncomplicated malaria. Severe disease was observed in 35/298 (11.7%) of single cluster 1 and 8/115 (7.0%) of single cluster 2 infections (p = 0.208). There was no clinically significant difference in outcome between the two subpopulations. Cluster 1 infections were more likely to be associated with peri-domestic activities while cluster 2 were associated with interior forest activities consistent with the preferred habitats of the respective macaque hosts. Infections with both P. knowlesi subpopulations cause a wide spectrum of disease including potentially life-threatening complications, with no implications for differential patient management.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  2. Malijan RPB, Mechan F, Braganza JC, Valle KMR, Salazar FV, Torno MM, et al.
    Parasit Vectors, 2021 Jul 07;14(1):357.
    PMID: 34233742 DOI: 10.1186/s13071-021-04853-9
    BACKGROUND: A small number of human cases of the zoonotic malaria Plasmodium knowlesi have been reported in Palawan Island, the Philippines. Identification of potential vector species and their bionomics is crucial for understanding human exposure risk in this setting. Here, we combined longitudinal surveillance with a trap-evaluation study to address knowledge gaps about the ecology and potential for zoonotic spillover of this macaque malaria in Palawan Island.

    METHODS: The abundance, diversity and biting behavior of human-biting Anopheles mosquitoes were assessed through monthly outdoor human landing catches (HLC) in three ecotypes representing different land use (forest edge, forest and agricultural area) across 8 months. Additionally, the host preference and biting activity of potential Anopheles vectors were assessed through comparison of their abundance and capture time in traps baited with humans (HLC, human-baited electrocuting net-HEN) or macaques (monkey-baited trap-MBT, monkey-baited electrocuting net-MEN). All female Anopheles mosquitoes were tested for the presence of Plasmodium parasites by PCR.

    RESULTS: Previously incriminated vectors Anopheles balabacensis and An. flavirostris accounted for > 95% of anophelines caught in longitudinal surveillance. However, human biting densities were relatively low (An. balabacensis: 0.34-1.20 per night, An. flavirostris: 0-2 bites per night). Biting densities of An. balabacensis were highest in the forest edge, while An. flavirostris was most abundant in the agricultural area. The abundance of An. balabacensis and An. flavirostris was significantly higher in HLC than in MBT. None of the 357 female Anopheles mosquitoes tested for Plasmodium infection were positive.

    CONCLUSIONS: The relatively low density and lack of malaria infection in Anopheles mosquitoes sampled here indicates that exposure to P. knowlesi in this setting is considerably lower than in neighboring countries (i.e. Malaysia), where it is now the primary cause of malaria in humans. Although anophelines had lower abundance in MBTs than in HLCs, An. balabacensis and An. flavirostris were caught by both methods, suggesting they could act as bridge vectors between humans and macaques. These species bite primarily outdoors during the early evening, confirming that insecticide-treated nets are unlikely to provide protection against P. knowlesi vectors.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  3. Mahittikorn A, Masangkay FR, Kotepui KU, Milanez GJ, Kotepui M
    Malar J, 2021 Apr 09;20(1):179.
    PMID: 33836773 DOI: 10.1186/s12936-021-03714-1
    BACKGROUND: Plasmodium knowlesi is recognized as the fifth Plasmodium species causing malaria in humans. It is morphologically similar to the human malaria parasite Plasmodium malariae, so molecular detection should be used to clearly discriminate between these Plasmodium species. This study aimed to quantify the rate at which P. knowlesi is misidentified as P. malariae by microscopy in endemic and non-endemic areas.

    METHODS: The protocol of this systematic review was registered in the PROSPERO International Prospective Register of Systematic Reviews (ID = CRD42020204770). Studies reporting the misidentification of P. knowlesi as P. malariae by microscopy and confirmation of this by molecular methods in MEDLINE, Web of Science and Scopus were reviewed. The risk of bias in the included studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS). The pooled prevalence and 95% confidence interval (CI) of the misidentification of P. knowlesi as P. malariae by microscopy were estimated using a random effects model. Subgroup analysis of the study sites was performed to demonstrate any differences in the misidentification rates in different areas. Heterogeneity across the included studies was assessed and quantified using Cochran's Q and I2 statistics, respectively. Publication bias in the included studies was assessed using the funnel plot, Egger's test and contour-enhanced funnel plot.

    RESULTS: Among 375 reviewed studies, 11 studies with a total of 1569 confirmed P. knowlesi cases in humans were included. Overall, the pooled prevalence of the misidentification of P. knowlesi as P. malariae by microscopy was estimated at 57% (95% CI 37-77%, I2: 99.3%). Subgroup analysis demonstrated the highest rate of misidentification in Sawarak, Malaysia (87%, 95% CI 83-90%, I2: 95%), followed by Sabah, Malaysia (85%, 95% CI 79-92%, I2: 85.1%), Indonesia (16%, 95% CI 6-38%), and then Thailand (4%, 95% CI 2-9%, I2: 95%).

    CONCLUSION: Although the World Health Organization (WHO) recommends that all P. malariae-positive diagnoses made by microscopy in P. knowlesi endemic areas be reported as P. malariae/P. knowlesi malaria, the possibility of microscopists misidentifying P. knowlesi as P. malariae is a diagnostic challenge. The use of molecular techniques in cases with malariae-like Plasmodium with high parasite density as determined by microscopy could help identify human P. knowlesi cases in non-endemic countries.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  4. Lai MY, Ooi CH, Lau YL
    Malar J, 2021 Mar 25;20(1):166.
    PMID: 33766038 DOI: 10.1186/s12936-021-03707-0
    BACKGROUND: As an alternative to PCR methods, LAMP is increasingly being used in the field of molecular diagnostics. Under isothermal conditions at 65 °C, the entire procedure takes approximately 30 min to complete. In this study, we establish a sensitive and visualized LAMP method in a closed-tube system for the detection of Plasmodium knowlesi.

    METHODS: A total of 71 malaria microscopy positive blood samples collected in blood spots were obtained from the Sarawak State Health Department. Using 18s rRNA as the target gene, nested PCR and SYBR green I LAMP assay were performed following the DNA extraction. The colour changes of LAMP end products were observed by naked eyes.

    RESULTS: LAMP assay demonstrated a detection limit of 10 copies/µL in comparison with 100 copies/µL nested PCR. Of 71 P. knowlesi blood samples collected, LAMP detected 69 microscopy-positive samples. LAMP exhibited higher sensitivity than nested PCR assay. The SYBR green I LAMP assay was 97.1% sensitive (95% CI 90.2-99.7%) and 100% specific (95% CI 83.2-100%). Without opening the cap, incorporation of SYBR green I into the inner cap of the tube enabled the direct visualization of results upon completion of amplification. The positives instantaneously turned green while the negatives remained orange.

    CONCLUSIONS: These results indicate that SYBR green I LAMP assay is a convenient diagnosis tool for the detection of P. knowlesi in remote settings.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  5. Fungfuang W, Udom C, Tongthainan D, Kadir KA, Singh B
    Malar J, 2020 Oct 01;19(1):350.
    PMID: 33004070 DOI: 10.1186/s12936-020-03424-0
    BACKGROUND: Certain species of macaques are natural hosts of Plasmodium knowlesi and Plasmodium cynomolgi, which can both cause malaria in humans, and Plasmodium inui, which can be experimentally transmitted to humans. A significant number of zoonotic malaria cases have been reported in humans throughout Southeast Asia, including Thailand. There have been only two studies undertaken in Thailand to identify malaria parasites in non-human primates in 6 provinces. The objective of this study was to determine the prevalence of P. knowlesi, P. cynomolgi, P. inui, Plasmodium coatneyi and Plasmodium fieldi in non-human primates from 4 new locations in Thailand.

    METHODS: A total of 93 blood samples from Macaca fascicularis, Macaca leonina and Macaca arctoides were collected from four locations in Thailand: 32 were captive M. fascicularis from Chachoengsao Province (CHA), 4 were wild M. fascicularis from Ranong Province (RAN), 32 were wild M. arctoides from Prachuap Kiri Khan Province (PRA), and 25 were wild M. leonina from Nakornratchasima Province (NAK). DNA was extracted from these samples and analysed by nested PCR assays to detect Plasmodium, and subsequently to detect P. knowlesi, P. coatneyi, P. cynomolgi, P. inui and P. fieldi.

    RESULTS: Twenty-seven of the 93 (29%) samples were Plasmodium-positive by nested PCR assays. Among wild macaques, all 4 M. fascicularis at RAN were infected with malaria parasites followed by 50% of 32 M. arctoides at PRA and 20% of 25 M. leonina at NAK. Only 2 (6.3%) of the 32 captive M. fascicularis at CHA were malaria-positive. All 5 species of Plasmodium were detected and 16 (59.3%) of the 27 macaques had single infections, 9 had double and 2 had triple infections. The composition of Plasmodium species in macaques at each sampling site was different. Macaca arctoides from PRA were infected with P. knowlesi, P. coatneyi, P. cynomolgi, P. inui and P. fieldi.

    CONCLUSIONS: The prevalence and species of Plasmodium varied among the wild and captive macaques, and between macaques at 4 sampling sites in Thailand. Macaca arctoides is a new natural host for P. knowlesi, P. inui, P. coatneyi and P. fieldi.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  6. Brown R, Chua TH, Fornace K, Drakeley C, Vythilingam I, Ferguson HM
    PLoS Negl Trop Dis, 2020 09;14(9):e0008617.
    PMID: 32886679 DOI: 10.1371/journal.pntd.0008617
    The zoonotic malaria parasite, Plasmodium knowlesi, is now a substantial public health problem in Malaysian Borneo. Current understanding of P. knowlesi vector bionomics and ecology in Sabah comes from a few studies near the epicentre of human cases in one district, Kudat. These have incriminated Anopheles balabacensis as the primary vector, and suggest that human exposure to vector biting is peri-domestic as well as in forest environments. To address the limited understanding of vector ecology and human exposure risk outside of Kudat, we performed wider scale surveillance across four districts in Sabah with confirmed transmission to investigate spatial heterogeneity in vector abundance, diversity and infection rate. Entomological surveillance was carried out six months after a cross-sectional survey of P. knowlesi prevalence in humans throughout the study area; providing an opportunity to investigate associations between entomological indicators and infection. Human-landing catches were performed in peri-domestic, farm and forest sites in 11 villages (3-4 per district) and paired with estimates of human P. knowlesi exposure based on sero-prevalence. Anopheles balabacensis was present in all districts but only 6/11 villages. The mean density of An. balabacensis was relatively low, but significantly higher in farm (0.094/night) and forest (0.082/night) than peri-domestic areas (0.007/night). Only one An. balabacensis (n = 32) was infected with P. knowlesi. Plasmodium knowlesi sero-positivity in people was not associated with An. balabacensis density at the village-level however post hoc analyses indicated the study had limited power to detect a statistical association due low vector density. Wider scale sampling revealed substantial heterogeneity in vector density and distribution between villages and districts. Vector-habitat associations predicted from this larger-scale surveillance differed from those inferred from smaller-scale studies in Kudat; highlighting the importance of local ecological context. Findings highlight potential trade-offs between maximizing temporal versus spatial breadth when designing entomological surveillance; and provide baseline entomological and epidemiological data to inform future studies of entomological risk factors for human P. knowlesi infection.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  7. Noordin NR, Lee PY, Mohd Bukhari FD, Fong MY, Abdul Hamid MH, Jelip J, et al.
    Am J Trop Med Hyg, 2020 09;103(3):1107-1110.
    PMID: 32618263 DOI: 10.4269/ajtmh.20-0268
    Asymptomatic and/or low-density malaria infection has been acknowledged as an obstacle to achieving a malaria-free country. This study aimed to determine the prevalence of asymptomatic and/or low-density malaria infection in previously reported malarious localities using nested PCR in four states, namely, Johor, Pahang, Kelantan, and Selangor, between June 2019 and January 2020. Blood samples (n = 585) were collected and were extracted using a QIAamp blood kit. The DNA was concentrated and subjected to nested PCR. Thin and thick blood smears were examined as well. Of the 585 samples collected, 19 were positive: 10 for Plasmodium knowlesi, eight for Plasmodium vivax, and one for Plasmodium ovale. Asymptomatic and/or low-density malaria infection is a threat to malaria elimination initiatives. Eliminating countries should develop guidance policy on the importance of low-density malaria infection which includes detection and treatment policy.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  8. Nuin NA, Tan AF, Lew YL, Piera KA, William T, Rajahram GS, et al.
    Malar J, 2020 Aug 27;19(1):306.
    PMID: 32854695 DOI: 10.1186/s12936-020-03379-2
    BACKGROUND: The monkey parasite Plasmodium knowlesi is an emerging public health issue in Southeast Asia. In Sabah, Malaysia, P. knowlesi is now the dominant cause of human malaria. Molecular detection methods for P. knowlesi are essential for accurate diagnosis and in monitoring progress towards malaria elimination of other Plasmodium species. However, recent commercially available PCR malaria kits have unpublished P. knowlesi gene targets or have not been evaluated against clinical samples.

    METHODS: Two real-time PCR methods currently used in Sabah for confirmatory malaria diagnosis and surveillance reporting were evaluated: the QuantiFast™ Multiplex PCR kit (Qiagen, Germany) targeting the P. knowlesi 18S SSU rRNA; and the abTES™ Malaria 5 qPCR II kit (AITbiotech, Singapore), with an undisclosed P. knowlesi gene target. Diagnostic accuracy was evaluated using 52 P. knowlesi, 25 Plasmodium vivax, 21 Plasmodium falciparum, and 10 Plasmodium malariae clinical isolates, and 26 malaria negative controls, and compared against a validated reference nested PCR assay. The limit of detection (LOD) for each PCR method and Plasmodium species was also evaluated.

    RESULTS: The sensitivity of the QuantiFast™ and abTES™ assays for detecting P. knowlesi was comparable at 98.1% (95% CI 89.7-100) and 100% (95% CI 93.2-100), respectively. Specificity of the QuantiFast™ and abTES™ for P. knowlesi was high at 98.8% (95% CI 93.4-100) for both assays. The QuantiFast™ assay demonstrated falsely-positive mixed Plasmodium species at low parasitaemias in both the primary and LOD analysis. Diagnostic accuracy of both PCR kits for detecting P. vivax, P. falciparum, and P. malariae was comparable to P. knowlesi. The abTES™ assay demonstrated a lower LOD for P. knowlesi of ≤ 0.125 parasites/µL compared to QuantiFast™ with a LOD of 20 parasites/µL. Hospital microscopy demonstrated a sensitivity of 78.8% (95% CI 65.3-88.9) and specificity of 80.4% (95% CI 67.6-89.8) compared to reference PCR for detecting P. knowlesi.

    CONCLUSION: The QuantiFast™ and abTES™ commercial PCR kits performed well for the accurate detection of P. knowlesi infections. Although the QuantiFast™ kit is cheaper, the abTES™ kit demonstrated a lower LOD, supporting its use as a second-line referral-laboratory diagnostic tool in Sabah, Malaysia.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  9. Mahendran P, Liew JWK, Amir A, Ching XT, Lau YL
    Malar J, 2020 Jul 10;19(1):241.
    PMID: 32650774 DOI: 10.1186/s12936-020-03314-5
    BACKGROUND: Plasmodium knowlesi and Plasmodium vivax are the predominant Plasmodium species that cause malaria in Malaysia and play a role in asymptomatic malaria disease transmission in Malaysia. The diagnostic tools available to diagnose malaria, such as microscopy and rapid diagnostic test (RDT), are less sensitive at detecting lower parasite density. Droplet digital polymerase chain reaction (ddPCR), which has been shown to have higher sensitivity at diagnosing malaria, allows direct quantification without the need for a standard curve. The aim of this study is to develop and use a duplex ddPCR assay for the detection of P. knowlesi and P. vivax, and compare this method to nested PCR and qPCR.

    METHODS: The concordance rate, sensitivity and specificity of the duplex ddPCR assay were determined and compared to nested PCR and duplex qPCR.

    RESULTS: The duplex ddPCR assay had higher analytical sensitivity (P. vivax = 10 copies/µL and P. knowlesi = 0.01 copies/µL) compared to qPCR (P. vivax = 100 copies/µL and P. knowlesi = 10 copies/µL). Moreover, the ddPCR assay had acceptable clinical sensitivity (P. vivax = 80% and P. knowlesi = 90%) and clinical specificity (P. vivax = 87.84% and P. knowlesi = 81.08%) when compared to nested PCR. Both ddPCR and qPCR detected more double infections in the samples.

    CONCLUSIONS: Overall, the ddPCR assay demonstrated acceptable efficiency in detection of P. knowlesi and P. vivax, and was more sensitive than nested PCR in detecting mixed infections. However, the duplex ddPCR assay still needs optimization to improve the assay's clinical sensitivity and specificity.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  10. Lai MY, Ooi CH, Jaimin JJ, Lau YL
    Am J Trop Med Hyg, 2020 06;102(6):1370-1372.
    PMID: 32228783 DOI: 10.4269/ajtmh.20-0001
    The incidence of zoonotic malaria, Plasmodium knowlesi, infection is increasing and now is the major cause of malaria in Malaysia. Here, we describe a WarmStart colorimetric loop-mediated isothermal amplification (LAMP) assay for the detection of Plasmodium spp. The detection limit for this assay was 10 copies/µL for P knowlesi and Plasmodium ovale and 1 copy/µL for Plasmodium falciparum, Plasmodium vivax, and Plasmodium malariae. To test clinical sensitivity and specificity, 100 microscopy-positive and 20 malaria-negative samples were used. The WarmStart colorimetric LAMP was 98% sensitive and 100% specific. Amplification products were visible for direct observation, thereby eliminating the need for post-amplification processing steps. Therefore, WarmStart colorimetric LAMP is suitable for use in resource-limited settings.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  11. Hussin N, Lim YA, Goh PP, William T, Jelip J, Mudin RN
    Malar J, 2020 Jan 31;19(1):55.
    PMID: 32005228 DOI: 10.1186/s12936-020-3135-x
    BACKGROUND: To date, most of the recent publications on malaria in Malaysia were conducted in Sabah, East Malaysia focusing on the emergence of Plasmodium knowlesi. This analysis aims to describe the incidence, mortality and case fatality rate of malaria caused by all Plasmodium species between Peninsular Malaysia and East Malaysia (Sabah and Sarawak) over a 5-year period (2013-2017).

    METHODS: This is a secondary data review of all diagnosed and reported malaria confirmed cases notified to the Ministry of Health, Malaysia between January 2013 and December 2017.

    RESULTS: From 2013 to 2017, a total of 16,500 malaria cases were notified in Malaysia. The cases were mainly contributed from Sabah (7150; 43.3%) and Sarawak (5684; 34.4%). Majority of the patients were male (13,552; 82.1%). The most common age group in Peninsular Malaysia was 20 to 29 years (1286; 35.1%), while Sabah and Sarawak reported highest number of malaria cases in age group of 30 to 39 years (2776; 21.6%). The top two races with malaria in Sabah and Sarawak were Bumiputera Sabah (5613; 43.7%) and Bumiputera Sarawak (4512; 35.1%), whereas other ethnic group (1232; 33.6%) and Malays (1025; 28.0%) were the two most common races in Peninsular Malaysia. Plasmodium knowlesi was the commonest species in Sabah and Sarawak (9902; 77.1%), while there were more Plasmodium vivax cases (1548; 42.2%) in Peninsular Malaysia. The overall average incidence rate, mortality rate and case fatality rates for malaria from 2013 to 2017 in Malaysia were 0.106/1000, 0.030/100,000 and 0.27%, respectively. Sarawak reported the highest average incidence rate of 0.420/1000 population followed by Sabah (0.383/1000). Other states in Peninsular Malaysia reported below the national average incidence rate with less than 0.100/1000.

    CONCLUSIONS: There were different trends and characteristics of notified malaria cases in Peninsular Malaysia and Sabah and Sarawak. They provide useful information to modify current prevention and control measures so that they are customised to the peculiarities of disease patterns in the two regions in order to successfully achieve the pre-elimination of human-only species in the near future.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  12. Davidson G, Chua TH, Cook A, Speldewinde P, Weinstein P
    Ecohealth, 2019 12;16(4):594-610.
    PMID: 30675676 DOI: 10.1007/s10393-019-01395-6
    Defining the linkages between landscape change, disease ecology and human health is essential to explain and predict the emergence of Plasmodium knowlesi malaria, a zoonotic parasite residing in Southeast Asian macaques, and transmitted by species of Anopheles mosquitos. Changing patterns of land use throughout Southeast Asia, particularly deforestation, are suggested to be the primary drivers behind the recent spread of this zoonotic parasite in humans. Local ecological changes at the landscape scale appear to be increasing the risk of disease in humans by altering the dynamics of transmission between the parasite and its primary hosts. This paper will focus on the emergence of P. knowlesi in humans in Malaysian Borneo and the ecological linkage mechanisms suggested to be playing an important role.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  13. Stark DJ, Fornace KM, Brock PM, Abidin TR, Gilhooly L, Jalius C, et al.
    Ecohealth, 2019 12;16(4):638-646.
    PMID: 30927165 DOI: 10.1007/s10393-019-01403-9
    Land-use changes can impact infectious disease transmission by increasing spatial overlap between people and wildlife disease reservoirs. In Malaysian Borneo, increases in human infections by the zoonotic malaria Plasmodium knowlesi are hypothesised to be due to increasing contact between people and macaques due to deforestation. To explore how macaque responses to environmental change impact disease risks, we analysed movement of a GPS-collared long-tailed macaque in a knowlesi-endemic area in Sabah, Malaysia, during a deforestation event. Land-cover maps were derived from satellite-based and aerial remote sensing data and models of macaque occurrence were developed to evaluate how macaque habitat use was influenced by land-use change. During deforestation, changes were observed in macaque troop home range size, movement speeds and use of different habitat types. Results of models were consistent with the hypothesis that macaque ranging behaviour is disturbed by deforestation events but begins to equilibrate after seeking and occupying a new habitat, potentially impacting human disease risks. Further research is required to explore how these changes in macaque movement affect knowlesi epidemiology on a wider spatial scale.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  14. Zaw MT, Lin Z
    J Microbiol Immunol Infect, 2019 Oct;52(5):679-684.
    PMID: 31320238 DOI: 10.1016/j.jmii.2019.05.012
    Plasmodium knowlesi is now regarded as the fifth malaria parasite causing human malaria as it is widely distributed in South-East Asian countries especially east Malaysia where two Malaysian states namely Sabah and Sarawak are situated. In 2004, Polymerase Chain Reaction (PCR) was applied for diagnosing knowlesi malaria in the Kapit Division of Sarawak, Malaysia, so that human P. knowlesi infections could be detected correctly while blood film microscopy diagnosed incorrectly as Plasmodium malariae. This parasite is transmitted from simian hosts to humans via Anopheles vectors. Indonesia is the another country in South East Asia where knowlesi malaria is moderately prevalent. In the last decade, Sarawak and Sabah, the two states of east Malaysia became the target of P. knowlesi research due to prevalence of cases with occasional fatal infections. The host species of P. knowlesi are three macaque species namely Macaca fascicularis, Macaca nemestrina and Macaca leonina while the vector species are the Leucosphyrus Complex and the Dirus Complex of the Leucophyrus Group of Anopheles mosquitoes. Rapid diagnostic tests (RDT) are non-existent for knowlesi malaria although timely treatment is necessary for preventing complications, fatality and drug resistance. Development of RDT is essential in dealing with P. knowlesi infections in poor rural healthcare services. Genetic studies of the parasite on possibility of human-to-human transmission of P. knowlesi were recommended for further studies.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  15. Fong MY, Lau YL, Jelip J, Ooi CH, Cheong FW
    J Genet, 2019 Sep;98.
    PMID: 31544794
    Plasmodium knowlesi contributes to the majority of human malaria incidences in Malaysia. Its uncontrollable passage among the natural monkey hosts can potentially lead to zoonotic outbreaks. The merozoite of this parasite invades host erythrocytes through interaction between its erythrocyte-binding proteins (EBPs) and their respective receptor on the erythrocytes. The regionII of P. knowlesi EBP, P. knowlesi beta (PkβII) protein is found to be mediating merozoite invasion into monkey erythrocytes by interacting with sialic acid receptors. Hence, the objective of this study was to investigate the genetic diversity, natural selection and haplotype grouping of PkβII of P. knowlesi isolates in Malaysia. Polymerase chain reaction amplifications of PkβII were performed on archived blood samples from Malaysia and 64 PkβII sequences were obtained. Sequence analysis revealed length polymorphism, and its amino acids at critical residues indicate the ability of PkβII to mediate P. knowlesi invasion into monkey erythrocytes. Low genetic diversity (π = 0.007) was observed in the PkβII of Malaysia Borneo compared to Peninsular Malaysia (π = 0.015). The PkβII was found to be under strong purifying selection to retain infectivity in monkeys and it plays a limited role in the zoonotic potential of P. knowlesi. Its haplotypes could be clustered into Peninsular Malaysia and Malaysia Borneo groups, indicating the existence of two distinct P. knowlesi parasites in Malaysia as reported in an earlier study.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  16. Chua TH, Manin BO, Vythilingam I, Fornace K, Drakeley CJ
    Parasit Vectors, 2019 Jul 25;12(1):364.
    PMID: 31345256 DOI: 10.1186/s13071-019-3627-0
    BACKGROUND: We investigated the effect of five common habitat types on the diversity and abundance of Anopheles spp. and on the biting rate and time of Anopheles balabacensis (currently the only known vector for Plasmodium knowlesi in Sabah) at Paradason village, Kudat, Sabah. The habitats were forest edge, playground area, longhouse, oil palm plantation and shrub-bushes area. Sampling of Anopheles was done monthly using the human landing catch method in all habitat types for 14 months (October 2013 to December 2014, excluding June 2014). The Anopheles species were morphologically identified and subjected to PCR assay for the detection of Plasmodium parasites. Generalised linear mixed models (GLMM) were applied to test the variation in abundance and biting rates of An. balabacensis in different habitat types.

    RESULTS: A total of 1599 Anopheles specimens were collected in the village, of which about 90% were An. balabacensis. Anopheles balabacensis was present throughout the year and was the dominant Anopheles species in all habitat types. The shrub bushes habitat had the highest Anopheles species diversity while forest edge had the greatest number of Anopheles individuals caught. GLMM analysis indicated that An. balabacensis abundance was not affected by the type of habitats, and it was more active during the early and late night compared to predawn and dawn. PCR assay showed that 1.61% of the tested An. balabacensis were positive for malaria parasites, most of which were caught in oil palm estates and infected with one to two Plasmodium species.

    CONCLUSIONS: The identification of infected vectors in a range of habitats, including agricultural and farming areas, illustrates the potential for humans to be exposed to P. knowlesi outside forested areas. This finding contributes to a growing body of evidence implicating environmental changes due to deforestation, expansion of agricultural and farming areas, and development of human settlements near to forest fringes in the emergence of P. knowlesi in Sabah.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  17. Jiram AI, Ooi CH, Rubio JM, Hisam S, Karnan G, Sukor NM, et al.
    Malar J, 2019 May 02;18(1):156.
    PMID: 31046769 DOI: 10.1186/s12936-019-2786-y
    BACKGROUND: Malaysia has declared its aim to eliminate malaria with a goal of achieving zero local transmission by the year 2020. However, targeting the human reservoir of infection, including those with asymptomatic infection is required to achieve malaria elimination. Diagnosing asymptomatic malaria is not as straightforward due to the obvious lack of clinical manifestations and often subpatent level of parasites. Accurate diagnosis of malaria is important for providing realistic estimates of malaria burden and preventing misinformed interventions. Low levels of parasitaemia acts as silent reservoir of transmission thus remains infectious to susceptible mosquito vectors. Hence, the aim of this study is to investigate the prevalence of asymptomatic submicroscopic malaria (SMM) in the District of Belaga, Sarawak.

    METHODS: In 2013, a total of 1744 dried blood spots (DBS) were obtained from residents of 8 longhouses who appeared healthy. Subsequently, 251 venous blood samples were collected from residents of 2 localities in 2014 based on the highest number of submicroscopic cases from prior findings. Thin and thick blood films were prepared from blood obtained from all participants in this study. Microscopic examination were carried out on all samples and a nested and nested multiplex PCR were performed on samples collected in 2013 and 2014 respectively.

    RESULTS: No malaria parasites were detected in all the Giemsa-stained blood films. However, of the 1744 samples, 29 (1.7%) were positive for Plasmodium vivax by PCR. Additionally, of the 251 samples, the most prevalent mono-infection detected by PCR was Plasmodium falciparum 50 (20%), followed by P. vivax 39 (16%), P. knowlesi 9 (4%), and mixed infections 20 (8%).

    CONCLUSIONS: This research findings conclude evidence of Plasmodium by PCR, among samples previously undetectable by routine blood film microscopic examination, in local ethnic minority who are clinically healthy. SMM in Belaga district is attributed not only to P. vivax, but also to P. falciparum and P. knowlesi. In complementing efforts of programme managers, there is a need to increase surveillance for SMM nationwide to estimate the degree of SMM that warrant measures to block new transmission of malaria.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  18. Gamalo LE, Dimalibot J, Kadir KA, Singh B, Paller VG
    Malar J, 2019 Apr 24;18(1):147.
    PMID: 31014342 DOI: 10.1186/s12936-019-2780-4
    BACKGROUND: Macaca fascicularis (long-tailed macaque) is the most widespread species of macaque in Southeast Asia and the only species of monkey found naturally in the Philippines. The species is the natural host for the zoonotic malaria species, Plasmodium knowlesi and Plasmodium cynomolgi and for the potentially zoonotic species, Plasmodium inui. Moreover, other Plasmodium species such as Plasmodium coatneyi and Plasmodium fieldi are also natural parasites of M. fascicularis. The aims of this study were to identify and determine the prevalence of Plasmodium species infecting wild and captive long-tailed macaques from the Philippines.

    METHODS: A total of 95 blood samples from long-tailed macaques in the Philippines were collected from three locations; 30 were from captive macaques at the National Wildlife Rescue and Rehabilitation Center (NWRRC) in Luzon, 25 were from captive macaques at the Palawan Wildlife Rescue and Conservation Center (PWRCC) in Palawan and 40 were from wild macaques from Puerto Princesa Subterranean River National Park (PPSRNP) in Palawan. The Plasmodium spp. infecting the macaques were identified using nested PCR assays on DNA extracted from these blood samples.

    RESULTS: All 40 of the wild macaques from PPSRNP in Palawan and 5 of 25 captive macaques from PWRCC in Palawan were Plasmodium-positive; while none of the 30 captive macaques from the NWRRC in Luzon had any malaria parasites. Overall, P. inui was the most prevalent malaria parasite (44.2%), followed by P. fieldi (41.1%), P. cynomolgi (23.2%), P. coatneyi (21.1%), and P. knowlesi (19%). Mixed species infections were also observed in 39 of the 45 Plasmodium-positive macaques. There was a significant difference in the prevalence of P. knowlesi among the troops of wild macaques from PPSRNP.

    CONCLUSION: Wild long-tailed macaques from the island of Palawan, the Philippines are infected with P. knowlesi, P. inui, P. coatneyi, P. fieldi and P. cynomolgi. The prevalence of these Plasmodium spp. varied among the sites of collection and among troops of wild macaques at one site. The presence of these simian Plasmodium parasites, especially P. knowlesi and P. cynomolgi in the long-tailed macaques in Palawan presents risks for zoonotic transmission in the area.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  19. Davidson G, Chua TH, Cook A, Speldewinde P, Weinstein P
    Malar J, 2019 Mar 08;18(1):66.
    PMID: 30849978 DOI: 10.1186/s12936-019-2693-2
    Plasmodium knowlesi is a zoonotic malaria parasite normally residing in long-tailed and pig-tailed macaques (Macaca fascicularis and Macaca nemestrina, respectively) found throughout Southeast Asia. Recently, knowlesi malaria has become the predominant malaria affecting humans in Malaysian Borneo, being responsible for approximately 70% of reported cases. Largely as a result of anthropogenic land use changes in Borneo, vectors which transmit the parasite, along with macaque hosts, are both now frequently found in disturbed forest habitats, or at the forest fringes, thus having more frequent contact with humans. Having access to human hosts provides the parasite with the opportunity to further its adaption to the human immune system. The ecological drivers of the transmission and spread of P. knowlesi are operating over many different spatial (and, therefore, temporal) scales, from the molecular to the continental. Strategies to prevent and manage zoonoses, such as P. knowlesi malaria require interdisciplinary research exploring the impact of land use change and biodiversity loss on the evolving relationship between parasite, reservoir hosts, vectors, and humans over multiple spatial scales.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  20. Grigg MJ, William T, Barber BE, Rajahram GS, Menon J, Schimann E, et al.
    Clin Infect Dis, 2018 07 18;67(3):350-359.
    PMID: 29873683 DOI: 10.1093/cid/ciy065
    Background: Plasmodium knowlesi is increasingly reported in Southeast Asia, but prospective studies of its clinical spectrum in children and comparison with autochthonous human-only Plasmodium species are lacking.

    Methods: Over 3.5 years, we prospectively assessed patients of any age with molecularly-confirmed Plasmodium monoinfection presenting to 3 district hospitals in Sabah, Malaysia.

    Results: Of 481 knowlesi, 172 vivax, and 96 falciparum malaria cases enrolled, 44 (9%), 71 (41%), and 31 (32%) children aged ≤12 years. Median parasitemia was lower in knowlesi malaria (2480/μL [interquartile range, 538-8481/μL]) than in falciparum (9600/μL; P < .001) and vivax malaria. In P. knowlesi, World Health Organization-defined anemia was present in 82% (95% confidence interval [CI], 67%-92%) of children vs 36% (95% CI, 31%-41%) of adults. Severe knowlesi malaria occurred in 6.4% (95% CI, 3.9%-8.3%) of adults but not in children; the commenst severity criterion was acute kideny injury. No patient had coma. Age, parasitemia, schizont proportion, abdominal pain, and dyspnea were independently associated with severe knowlesi malaria, with parasitemia >15000/μL the best predictor (adjusted odds ratio, 16.1; negative predictive value, 98.5%; P < .001). Two knowlesi-related adult deaths occurred (fatality rate: 4.2/1000 adults).

    Conclusions: Age distribution and parasitemia differed markedly in knowlesi malaria compared to human-only species, with both uncomplicated and severe disease occurring at low parasitemia. Severe knowlesi malaria occurred only in adults; however, anemia was more common in children despite lower parasitemia. Parasitemia independently predicted knowlesi disease severity: Intravenous artesunate is warranted initially for those with parasitemia >15000/μL.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
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