RESUMO

The development of genetic manipulation of Plasmodium falciparum in the 1980s was key to study malaria biology. Genetically modified parasites have been used to study several aspects of the disease, such as red blood cell invasion, drug resistance mechanisms, gametocyte development and mosquito transmission. However, biological and genetic differences between P. falciparum and the other human malaria parasites make P. falciparum a poor model to study different species. The lack of robust systems of long-term in vitro culture of P. vivax and the other human malaria parasites lagged the genetic manipulation of these species. Here we review the efforts to generate genetically modified non-falciparum human malaria parasites, in vivo and in vitro. Using in vivo models - infection of non-human primates such as rhesus macaques and saimiri monkeys - researchers were able to generate transgenic lines of P. knowlesi, P. cynomolgi, and P. vivax. The development of long-term in vitro culture of P. knowlesi in the 2000's, using rhesus and human red blood cells, created a platform to genetically manipulate non-falciparum malaria parasites. Recently, the use of CRISPR/Cas9 technology to genome edit P. knowlesi provides another tool to non-falciparum malaria research, extending the possibilities and allowing researchers to study different aspects of the biology of these parasites and understand the differences between these species and P. falciparum.

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RESUMO

La malaria es causada por parásitos del género Plasmodium y trasmitida por la picadura de mosquitos hembras de género Anopheles. De las 120 especies del género Plasmodium, cuatro infectan al hombre: Plasmodium falciparum, P. vivax, P. ovale y P. malariae, que producen las fiebres terciana maligna, tercianas benignas y cuartana respectivamente. La enfermedad se manifiesta clínicamente como un síndrome febril aguda o crónico, anemia, mialgias, cefalea, espleno y hepatomegalia. La malaria continua siendo la enfermedad parasitaria más importante en el mundo, ya que afecta a 294 millones de personas por año y se estima que provoca 1,1 millones de muertes por año, sola o en combinación. En Venezuela para el 2012 , se registraron 51.050 casos.(AU)

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RESUMO

The first reported case of natural transmission of Plasmodium knowlesi to humans was published in 1965. In Southeast Asia, the atypical presentation of malaria cases, the changes in the distribution of the Plasmodium species diagnosed and their atypical morphology prompted several studies that confirmed natural infections in humans by this protozoon which naturally infects different species of apes which are endemic in the forests of this region. Recent studies suggest that P. knowlesi malaria is not an emerging disease in humans but was rather being misdiagnosed due to its morphological similarity with P. malariae and P. falciparum, hampering its correct diagnosis by microscopic examination. Currently, the diagnosis can be confirmed by polymerase chain reaction using P. knowlesi specific primers. Malaria by P. knowlesi has lead to fatal outcomes in humans and poses several challenges such as the development of useful diagnostic tools for endemic areas, the study of the vectors involved and the therapeutic efficacy of the drugs for its treatment. In the jungle regions of South America it is imperative to monitor the parasites of simian malaria and the vectors that have the potential to transmit this zoonosis.

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RESUMO

El campo de las enfermedades infecciosas ha tenido un crecimiento acelerado en el mundo en las últimas 3 décadas. La emergencia o el descubrimiento de múltiples agentes infecciosos, como el del virus de la inmunodeficiencia humana, los priones asociados con la enfermedad de Creutzfeldt-Jakob y otras enfermedades del ser humano, los coronavirus causantes del síndrome respiratorio agudo grave o el de Plasmodium knowlesi, quinta especie causal de malaria en humanos, son tan solo algunos ejemplos de los nuevos retos a los que se enfrentan los profesionales que trabajan en el campo de la infectología y disciplinas relacionadas. Para afrontarlos, la investigación y la difusión del conocimiento científico en aspectos epidemiológicos, diagnósticos, terapéuticos y preventivos han tenido que incrementarse.

The field of infectious diseases has seen an accelerated growth in the world over the last 3 decades. The emergence or discovery of multiple infectious agents, such as the human immunodeficiency virus, prions associated with Creutzfeldt-Jakob disease and other human diseases, coronaviruses causing severe acute respiratory syndrome or Plasmodium knowlesi, the fifth species causing malaria in humans, are just some examples of the new challenges faced by professionals working in the field of infectious diseases and related disciplines. To face them, research and dissemination of scientific knowledge in epidemiological, diagnostic, therapeutic and preventive aspects have had to increase.

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RESUMO

El primer caso informado de transmisión natural de Plasmodium knowlesi en humanos se publicó en 1965. En el sureste de Asia la presentación atípica de casos de malaria, tanto por cambios en la distribución de las especies diagnosticadas de Plasmodium, como por su morfología, motivó diversos estudios que han confirmado la infección en humanos por este plasmodio que infecta naturalmente distintas especies de simios, que son endémicos de las selvas de esta región. Los estudios recientes sugieren que la malaria por P. knowlesi no es una enfermedad emergente en humanos sino que no estaba siendo diagnosticada, debido a la similitud morfológica de este plasmodio con P. malariae y P. falciparum, lo cual dificulta su reconocimiento mediante examen microscópico. Actualmente, se puede confirmar el diagnóstico mediante reacción en cadena de la polimerasa que permite identificar cebadores específicos de P. knowlesi. La malaria por P. knowlesi ha ocasionado desenlaces fatales en humanos, lo que plantea diversos retos como la búsqueda de métodos operativos de diagnóstico para las zonas endémicas, el estudio de los vectores involucrados y la eficacia terapéutica de los medicamentos para su tratamiento. En las regiones selváticas de Suramérica se hace imperativa la vigilancia de parásitos y vectores de la malaria en simios, que potencialmente puedan ocasionar esta zoonosis.

The first reported case of natural transmission of Plasmodium knowlesi to humans was published in 1965. In Southeast Asia, the atypical presentation of malaria cases, the changes in the distribution of the Plasmodium species diagnosed and their atypical morphology prompted several studies that confirmed natural infections in humans by this protozoon which naturally infects different species of apes which are endemic in the forests of this region. Recent studies suggest that P. knowlesi malaria is not an emerging disease in humans but was rather being misdiagnosed due to its morphological similarity with P. malariae and P. falciparum, hampering its correct diagnosis by microscopic examination. Currently, the diagnosis can be confirmed by polymerase chain reaction using P. knowlesi specific primers. Malaria by P. knowlesi has lead to fatal outcomes in humans and poses several challenges such as the development of useful diagnostic tools for endemic areas, the study of the vectors involved and the therapeutic efficacy of the drugs for its treatment. In the jungle regions of South America it is imperative to monitor the parasites of simian malaria and the vectors that have the potential to transmit this zoonosis.

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RESUMO

After examining the most recent scientific evidences, which assessed the role of some malaria plasmodia that have monkeys as natural reservoirs, the authors focus their attention on Plasmodium knowlesi. The infective foci attributable to this last Plasmodium species have been identified during the last decade in Malaysia, in particular in the states of Sarawak and Sabah (Malaysian Borneo), and in the Pahang region (peninsular Malaysia). The significant relevance of molecular biology assays (polymerase chain reaction, or PCR, performed with specific primers for P. knowlesi), is underlined, since the traditional microscopic examination does not offer distinguishing features, especially when the differential diagnosis with Plasmodium malariae is of concern. Furthermore, Plasmodium knowlesi disease may be responsible of fatal cases, since its clinical presentation and course is more severe compared with those caused by P. malariae, paralleling a more elevated parasitemia. The most effective mosquito vector is represented by Anopheles latens; this mosquito is a parasite of both humans and monkeys. Among primates, the natural hosts are Macaca fascicularis, M. nemestina, M. inus, and Saimiri scirea. When remarking the possible severe evolution of P. knowlesi malaria, we underline the importance of an early recognition and a timely management, especially in patients who have their first onset in Western Hospitals, after journeys in Southeast Asian countries, and eventually participated in trekking excursions in the tropical forest. When malaria-like signs and symptoms are present, a timely diagnosis and treatment become crucial. In the light of its emerging epidemiological features, P. knowlesi may be added to the reknown human malaria parasites, whith includes P. vivax, P. ovale, P. malariae, and P. falciparum, as the fifth potential ethiologic agent of human malaria. Over the next few years, it will be mandatory to support an adequate surveillance and epidemiological network. In parallel with epidemiological and health care policy studies, also an accurate appraisal of the clinical features of P. knowlesi-affected patients will be strongly needed, since some preliminary experiences seem to show an increased disease severity, associated with increased parasitemia, in parallel with the progressive increase of inter-human infectious passages of this emerging Plasmodium.

Assuntos

RESUMO

After examining the most recent scientific evidences, which assessed the role of some malaria plasmodia that have monkeys as natural reservoirs, the authors focus their attention on Plasmodium knowlesi. The infective foci attributable to this last Plasmodium species have been identified during the last decade in Malaysia, in particular in the states of Sarawak and Sabah (Malaysian Borneo), and in the Pahang region (peninsular Malaysia). The significant relevance of molecular biology assays (polymerase chain reaction, or PCR, performed with specific primers for P. knowlesi), is underlined, since the traditional microscopic examination does not offer distinguishing features, especially when the differential diagnosis with Plasmodium malariae is of concern. Furthermore, Plasmodium knowlesi disease may be responsible of fatal cases, since its clinical presentation and course is more severe compared with those caused by P. malariae, paralleling a more elevated parasitemia. The most effective mosquito vector is represented by Anopheles latens; this mosquito is a parasite of both humans and monkeys. Among primates, the natural hosts are Macaca fascicularis, M. nemestina, M. inus, and Saimiri scirea. When remarking the possible severe evolution of P. knowlesi malaria, we underline the importance of an early recognition and a timely management, especially in patients who have their first onset in Western Hospitals, after journeys in Southeast Asian countries, and eventually participated in trekking excursions in the tropical forest. When malaria-like signs and symptoms are present, a timely diagnosis and treatment become crucial. In the light of its emerging epidemiological features, P. knowlesi may be added to the reknown human malaria parasites, whith includes P. vivax, P. ovale, P. malariae, and P. falciparum, as the fifth potential ethiologic agent of human malaria. Over the next few years, it will be mandatory to support an adequate surveillance and epidemiological network. In parallel with epidemiological and health care policy studies, also an accurate appraisal of the clinical features of P. knowlesi-affected patients will be strongly needed, since some preliminary experiences seem to show an increased disease severity, associated with increased parasitemia, in parallel with the progressive increase of inter-human infectious passages of this emerging Plasmodium.

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RESUMO

The translationally controlled tumor protein (TCTP) is conserved in all eukaryotes studied thus far. Recent evidence points to an important role for TCTP in the induction of cell proliferation in animals through an interaction with G proteins. TCTP may also constitute an intercellular secreted signal that modulates the immune response in the vertebrates. Because of its sequence conservation and ubiquity, the analysis of its amino acid sequence divergence between different taxa may provide insight into the structural constraints on the evolution of this protein. In the present study, we analyzed the phylogeny of TCTP sequences from a wide range of organisms and found that, with some exceptions, the groupings formed were consistent with the evolutionary history. Indeed, at the level of lower-order taxa, the groupings are in agreement with their established phylogeny, thus indicating that the substitution rates of the TCTP residues varied evenly between members of the same clade. Predicted three-dimensional structures of representative TCTPs, based on the reported 3D structure of Schizosaccharomyces pombe, indicated that these proteins are highly conserved among diverse taxonomic groups. However, analysis of the primary structure indicated subtle differences in the domain-forming pocket that potentially interacts with G proteins, particularly among Diplomonadidae, Apicomplexa, and other parasites of vertebrates. These differences support the notion that these specific TCTPs could block the normal immune response by acting as dominant negative mutants. Structural differences were also observed in a reported sequence of TCTP from Plasmodium knowlesi, in which the presence of an extra alpha-helix could also interfere in the interaction with G proteins.

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The schizont maturation assay for in vitro drug sensitivity tests has been a standard method employed in the global baseline assessment and monitoring of drug response in Plasmodium falciparum. This test is limited in its application to synchronous plasmodial infections because it evaluates the effect of drug on the maturation of parasite especially from ring to schizont stage and therefore synchronized P. falciparum cultures are required. On the other hand, P. knowlesi, a simian malaria parasite has a unique 24-h periodicity and maintains high natural synchronicity in monkeys. The present report presents the results of a comparative study on the course of in vitro maturation of sorbitol synchronized P. falciparum and naturally synchronous P. knowlesi. Ring stage parasites were incubated in RPMI medium supplemented with 10-15% pooled homologous serum in flat-bottomed 96-well micro plates using a candle jar at 37 degrees C. The results suggest that the ideal time for harvesting the micro-assay plates for in vitro drug sensitivity test for sorbitol-synchronized P. falciparum and naturally synchronous P. knowlesi are from 26 to 30 h and from 22 to 25 h, respectively. The advantages of using P. knowlesi in chemotherapeutic studies are discussed.

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RESUMO

The schizont maturation assay for in vitro drug sensitivity tests has been a standard method employed in the global baseline assessment and monitoring of drug response in Plasmodium falciparum. This test is limited in its application to synchronous plasmodial infections because it evaluates the effect of drug on the maturation of parasite especially from ring to schizont stage and therefore synchronized P. falciparum cultures are required. On the other hand, P. knowlesi, a simian malaria parasite has a unique 24-h periodicity and maintains high natural synchronicity in monkeys. The present report presents the results of a comparative study on the course of in vitro maturation of sorbitol synchronized P. falciparum and naturally synchronous P. knowlesi. Ring stage parasites were incubated in RPMI medium supplemented with 10-15 percent pooled homologous serum in flat-bottomed 96-well micro plates using a candle jar at 37°C. The results suggest that the ideal time for harvesting the micro-assay plates for in vitro drug sensitivity test for sorbitol-synchronized P. falciparum and naturally synchronous P. knowlesi are from 26 to 30 h and from 22 to 25 h, respectively. The advantages of using P. knowlesi in chemotherapeutic studies are discussed

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RESUMO

The apical membrane antigen (AMA-1) family of malaria merozoite proteins is characterised by a high degree of inter-species conservation. Evidence that the protein (PK66/AMA-1) from the simian parasite Plasmodium knowlesi was protective in rhesus monkeys suggested that the 83kDa P. falciparum equivalent (PF83/AMA-1) should be investigated for protective effects in humans. Here we briefly review pertinent comparative data, and describe the use of an eukaryotic full length recombinant PF83/AMA-1 molecule to develop a sensitive ELISA for the determination of serological responses in endemic populations. The assay has revealed surprisingly high levels of humoral response to this quantitatively minor antigen. We also show that PK66/AMA-1 inhibitory mAb's are active against merozoites subsequent to release from schizont-infected red cells, further implicating AMA-1 molecules in red cell invasion.

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RESUMO

The apical membrane antigen (AMA-1) family of malaria merozoite proteins is characterised by a high degree of inter-species conservation. Evidence that the protein (PK66/AMA-1) from the simian parasite Plasmodium knowlesi was protective in rhesus monkeys suggested that the 83kDa P. falciparum equivalent (PF83/AMA-1) should be investigated for protective effects in humans. Here we briefly review pertinent comparative data, and describe the use of an eukaryotic full length recombinant PF83/AMA-1 molecule to develop a sensitive ELISA for the determination of serological responses in endemic populations. The assay has revealed surprisingly high levels of humoral response to this quantitatively minor antigen. We also show that PK66/AMA-1 inhibitory mAb's are active against merozoites subsequent to release from schizont-infected red cells, further implicating AMA-1 molecules in red cell invasion.

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