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Concept: Plasmodium knowlesi


The simian parasite Plasmodium knowlesi is a common cause of human malaria in Malaysian Borneo and threatens the prospect of malaria elimination. However, little is known about the emergence of P. knowlesi, particularly in Sabah. We reviewed Sabah Department of Health records to investigate the trend of each malaria species over time.

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Apicomplexa, Malaysia, Plasmodium knowlesi


Plasmodium is the causal parasite of malaria, infectious disease responsible for the death of up to one million people each year. Glycerophospholipid and consequently membrane biosynthesis are essential for the survival of the parasite and are targeted by a new class of antimalarial drugs developed in our lab. In order to understand the highly redundant phospholipid synthethic pathways and eventual mechanism of resistance to various drugs, an organism specific kinetic model of these metabolic pathways need to be developed in Plasmodium species.

Concepts: Infectious disease, Metabolism, Biology, Organism, Malaria, Plasmodium, Species, Plasmodium knowlesi


Background. Plasmodium knowlesi commonly causes severe malaria in Malaysian Borneo, with high case-fatality rates reported. We compared risk and spectrum of severe disease from P.knowlesi, P.falciparum and P.vivax and outcomes following introduction of protocols for early referral and intravenous artesunate for all severe malaria.Methods. From September 2010-October 2011 we prospectively assessed non-pregnant patients ≥12 years-old admitted to Queen Elizabeth Hospital (QEH), Sabah, with PCR-confirmed Plasmodium monoinfection. Standardized referral (4+ parasite-density and/or any severity-criterion) and pre-referral intravenous artesunate were instituted at district hospitals.Results. Severe malaria (modified-WHO 2010 criteria) occurred in 38/130 (29%) patients with P.knowlesi, 13/122 (11%) with P.falciparum and 7/43 (16%) with P.vivax. Most common severity criteria in knowlesi malaria included parasitemia>100,000/µL (n=18), jaundice (n=20), respiratory distress (n=14), hypotension (n=13), and acute kidney injury (n=9). On multivariate analysis, P. knowlesi was associated with a 2.96 (95%CI:1.19-7.38)-fold greater risk of severity than P. falciparum (p=0.020); only parasitemia and schizontemia >10%, but not age, independently predicted knowlesi severity. Risk of severe knowlesi malaria increased 11-fold with parasitemia >20,000/µL, and 28-fold with parasitemia >100,000/µL. Nearly all (92%) knowlesi malaria patients received oral artemisinin-therapy; 36/38 (95%) and 39/92 (42%) with severe and non-severe disease also received ≥1 dose of intravenous artesunate. For all species, median parasite clearance-time was two days and no deaths occurred.Conclusions. P.knowlesi is the commonest cause of severe malaria at QEH, with parasitemia the major risk-factor for severity. Early referral and treatment with artesunate was highly effective for severe malaria from all species and associated with zero mortality.

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Apicomplexa, Artemisinin, Plasmodium knowlesi


Plasmodium knowlesi was initially identified in the 30s as a natural Plasmodium of Macaca fascicularis monkey also capable of experimentally infecting humans. It gained a relative notoriety in the mid-30s as an alternative to Plasmodium vivax in the treatment of the general paralysis of the insane (neurosyphilis). In 1965 the first natural human infection was described in a US military surveyor coming back from the Pahang jungle of the Malaysian peninsula. P. knowlesi was again brought to the attention of the medical community when in 2004, Balbir Singh and his co-workers reported that about 58% of malaria cases observed in the Kapit district of the Malaysian Borneo were actually caused by P. knowlesi. In the following years several reports showed that P. knowlesi is much more widespread than initially thought with cases reported across Southeast Asia. This infection should also be considered in the differential diagnosis of any febrile travellers coming back from a recent travel to forested areas of Southeast Asia. P. knowlesi can cause severe malaria with a rate of 6-9% and with a case fatality rate of 3%. Respiratory distress, acute renal failure, shock and hyperbilirubinemia are the most frequently observed complications of severe P. knowlesi malaria. Chloroquine is considered the treatment of choice of uncomplicated malaria caused by P. knowlesi.

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Southeast Asia, Plasmodium vivax, Plasmodium malariae, Malaysia, Plasmodium knowlesi


Bangladesh is one of the four major malaria-endemic countries in South-East Asia having approximately 34% of its population at risk of malaria. This paper aims at providing an overview of the malaria situation in this country. Relevant information was retrieved from published articles and reports in PubMed and Google Scholar. Malaria in Bangladesh is concentrated in 13 districts with a prevalence ranging between 3.1% and 36%, and is mostly caused by Plasmodium falciparum. Geographical conditions pose a potential risk for Plasmodium knowlesi malaria. Resistance to a number of drugs previously recommended for treatment has been reported. Low socio-economic status, poor schooling and close proximity to water bodies and forest areas comprise important risk factors. Despite the significant steps in Long Lasting Insecticide Net (LLIN)/Insecticide Treated Net (ITN) coverage in Bangladesh, there are still many challenges including the extension of malaria support to the remote areas of Bangladesh, where malaria prevalence is higher, and further improvements in the field of referral system and treatment.

Concepts: Epidemiology, Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Apicomplexa, Plasmodium knowlesi


Plasmodium knowlesi is typically found in macaques and has recently been recognized as the fifth Plasmodium species to cause malaria in humans. Several cases of P. knowlesi malaria have been reported in people in Southeast Asia. Most cases are simple but approximately one in 10 patients develops complications. The morphology of P. knowlesi parasites in human infections closely resembles that of Plasmodium malariae or Plasmodium falciparum, so a molecular method is the optimum diagnostic procedure. The treatment of choice for uncomplicated P. knowlesi malaria is oral chloroquine, whereas severe infection should be treated with intravenous quinine.

Concepts: Immune system, Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Quinine, Apicomplexa, Plasmodium knowlesi


Plasmodium knowlesi is a zoonotic parasite transmitted from macaques causing malaria in humans in Southeast Asia. Plasmodium parasites bind to red blood cell (RBC) surface receptors, many of which are sialylated. While macaques synthesize the sialic acid variant N-glycolylneuraminic acid (Neu5Gc), humans cannot because of a mutation in the enzyme CMAH that converts N-acetylneuraminic acid (Neu5Ac) to Neu5Gc. Here we reconstitute CMAH in human RBCs for the reintroduction of Neu5Gc, which results in enhancement of P. knowlesi invasion. We show that two P. knowlesi invasion ligands, PkDBPβ and PkDBPγ, bind specifically to Neu5Gc-containing receptors. A human-adapted P. knowlesi line invades human RBCs independently of Neu5Gc, with duplication of the sialic acid-independent invasion ligand, PkDBPα and loss of PkDBPγ. Our results suggest that absence of Neu5Gc on human RBCs limits P. knowlesi invasion, but that parasites may evolve to invade human RBCs through the use of sialic acid-independent pathways.

Concepts: Evolution, Blood, Malaria, Plasmodium falciparum, Plasmodium, Red blood cell, Sickle-cell disease, Plasmodium knowlesi


Human malaria parasite species were originally acquired from other primate hosts and subsequently became endemic, then spread throughout large parts of the world. A major zoonosis is now occurring with Plasmodium knowlesi from macaques in Southeast Asia, with a recent acceleration in numbers of reported cases particularly in Malaysia. To investigate the parasite population genetics, we developed sensitive and species-specific microsatellite genotyping protocols and applied these to analysis of samples from 10 sites covering a range of >1,600 km within which most cases have occurred. Genotypic analyses of 599 P. knowlesi infections (552 in humans and 47 in wild macaques) at 10 highly polymorphic loci provide radical new insights on the emergence. Parasites from sympatric long-tailed macaques (Macaca fascicularis) and pig-tailed macaques (M. nemestrina) were very highly differentiated (FST = 0.22, and K-means clustering confirmed two host-associated subpopulations). Approximately two thirds of human P. knowlesi infections were of the long-tailed macaque type (Cluster 1), and one third were of the pig-tailed-macaque type (Cluster 2), with relative proportions varying across the different sites. Among the samples from humans, there was significant indication of genetic isolation by geographical distance overall and within Cluster 1 alone. Across the different sites, the level of multi-locus linkage disequilibrium correlated with the degree of local admixture of the two different clusters. The widespread occurrence of both types of P. knowlesi in humans enhances the potential for parasite adaptation in this zoonotic system.

Concepts: Genetics, Malaria, Plasmodium, Macaque, Primate, Cercopithecine monkeys, Crab-eating Macaque, Plasmodium knowlesi


Malaria cases caused by the zoonotic parasite Plasmodium knowlesi are being increasingly reported throughout Southeast Asia and in travelers returning from the region. To test for evidence of signatures of selection or unusual population structure in this parasite, we surveyed genome sequence diversity in 48 clinical isolates recently sampled from Malaysian Borneo and in five lines maintained in laboratory rhesus macaques after isolation in the 1960s from Peninsular Malaysia and the Philippines. Overall genomewide nucleotide diversity (π = 6.03 × 10(-3)) was much higher than has been seen in worldwide samples of either of the major endemic malaria parasite species Plasmodium falciparum and Plasmodium vivax. A remarkable substructure is revealed within P. knowlesi, consisting of two major sympatric clusters of the clinical isolates and a third cluster comprising the laboratory isolates. There was deep differentiation between the two clusters of clinical isolates [mean genomewide fixation index (FST) = 0.21, with 9,293 SNPs having fixed differences of FST = 1.0]. This differentiation showed marked heterogeneity across the genome, with mean FST values of different chromosomes ranging from 0.08 to 0.34 and with further significant variation across regions within several chromosomes. Analysis of the largest cluster (cluster 1, 38 isolates) indicated long-term population growth, with negatively skewed allele frequency distributions (genomewide average Tajima’s D = -1.35). Against this background there was evidence of balancing selection on particular genes, including the circumsporozoite protein (csp) gene, which had the top Tajima’s D value (1.57), and scans of haplotype homozygosity implicate several genomic regions as being under recent positive selection.

Concepts: DNA, Gene, Genetics, Natural selection, Malaria, Plasmodium falciparum, Plasmodium, Plasmodium knowlesi


Infection by the simian malaria parasite, Plasmodium knowlesi, can lead to severe and fatal disease in humans, and is the most common cause of malaria in parts of Malaysia. Despite being a serious public health concern, the geographical distribution of P. knowlesi malaria risk is poorly understood because the parasite is often misidentified as one of the human malarias. Human cases have been confirmed in at least nine Southeast Asian countries, many of which are making progress towards eliminating the human malarias. Understanding the geographical distribution of P. knowlesi is important for identifying areas where malaria transmission will continue after the human malarias have been eliminated.

Concepts: Immune system, Malaria, Plasmodium falciparum, Africa, Plasmodium, Plasmodium vivax, Apicomplexa, Plasmodium knowlesi