Can Babesia infections be used as a model for cerebral malaria?

Infections with certain species of Plasmodium and Babesia induce, among other symptoms, cerebral pathology. The finding of heavily parasitized cerebral capillaries upon postmortem examination has led to the assumption that blockage of capillaries with infected red blood cells caused the cerebral symptoms and subsequent death. As this type of cerebrovascular pathology is found both in humans dying from malaria and in cattle dying from babesiosis, the latter could possibly be used as an animal model for the study of human cerebral malaria. However, before such a model system is adopted, the experimental data concerning cerebral pathology of babesiosis needs critical evaluation. Here, Theo Schetters and Wijnand Eling review the pathological mechanisms in cerebral babesiosis and relate these to cerebral malaria. Finally, they discuss the use of animal model systems for specific aspects of the pathological picture.     

New insights into the altered adhesive and mechanical properties of red blood cells parasitized by Babesia bovis

Sequestration of parasite-infected red blood cells (RBCs) in the microvasculature is an important pathological feature of both bovine babesiosis caused by Babesia bovis and human malaria caused by Plasmodium falciparum. Surprisingly, when compared with malaria, the cellular and molecular mechanisms that underlie this abnormal circulatory behaviour for RBCs infected with B. bovis have been relatively ignored. Here, we present some novel insights into the adhesive and mechanical changes that occur in B. bovis-infected bovine RBCs and compare them with the alterations that occur in human RBCs infected with P. falciparum. After infection with B. bovis, bovine RBCs become rigid and adhere to vascular endothelial cells under conditions of physiologically relevant flow. These alterations are accompanied by the appearance of ridge-like structures on the RBC surface that are analogous, but morphologically and biochemically different, to the knob-like structures on the surface of human RBCs infected with P. falciparum. Importantly, albeit for a limited number of parasite lines examined here, the extent of these cellular and rheological changes appear to be related to parasite virulence. Future investigations to identify the precise molecular composition of ridges and the proteins that mediate adhesion will provide important insight into the pathogenesis of both babesiosis and malaria.     

Pathology of experimental Babesia microti infection in the Syrian hamster

Pathologic changes produced after 4 weeks of infection by Babesia microti in Syrian hamsters are described and compared to babesiosis of humans. Following intraperitoneal inoculation, both intravascular and extravascular hemolysis developed. Up to 70% of red blood cells were parasitized. The principal morphologic abnormalities were an increase in extramedullary hematopoiesis and hyperplasia of the mononuclear phagocytic cells of the red pulp manifested grossly as splenomegaly, marked renal tubular hemosiderosis and hypertrophy of Kupffer cells. The disease was not fatal to any hamsters during the 4 week study. The clinical signs and lesions were less severe than fatal babesiosis of asplenic humans and similar to severe, but nonfatal disease in spleen intact humans. The hamster may serve as an animal model for the studying the pathophysiology of human babesiosis and for studying potential chemotherapeutic agents.     

Canine babesiosis in Europe: how many diseases?

Babesiosis, recognized since ancient times as an important disease of livestock and more recently as an emerging disease in dogs worldwide, is caused by intraerythrocytic protozoa of the genus Babesia and is transmitted by ticks. The pathophysiology of canine babesiosis has been extensively studied but many questions remain unanswered, especially regarding the diversity of disease manifestations in different European countries. Continued investigation of the similarities and differences in host-parasite interplay in canine babesiosis in different European countries should lead to a better understanding of the disease process, potentially leading to better prediction of disease outcome and the development of new treatment modalities. From the European point of view it is important to conduct these studies on Babesia canis.     

Immunopathophysiology of Babesia bovis and Plasmodium falciparum infections

Babesia bovis and Plasmodium falciparum are both vector-borne parasites primarily infecting the erythrocytes of their respective hosts. They have obvious differences, yet the diseases caused by these parasites share many common features. Both have generated a considerable body of research but, perhaps because of the classical distinction between veterinary and medical parasitology, many of the similarities between the two have been neglected. As this review shows however, many of the pathophysiological changes in B. bovis infections are poorly described for P. falciparum - and vice versa. Examples are the roles of lipid peroxidation, neutrophil adhesion and production of tumour necrosis factor (TNF) in malaria, which have been largely unstudied in babesiosis, or conversely the roles of fibronectin, immune complexes, cryofibrinogen and the complement cascade in babesiosis, which have been little studied (partly for ethical reasons) in human malaria. To clarify such questions, it may be that each of these diseases may serve as a partial model for the other.     

Genetic linkage and association analyses for trait mapping in Plasmodium falciparum

Genetic studies of Plasmodium falciparum laboratory crosses and field isolates have produced valuable insights into determinants of drug responses, antigenic variation, disease virulence, cellular development and population structures of these virulent human malaria parasites. Full-genome sequences and high-resolution haplotype maps of SNPs and microsatellites are now available for all 14 parasite chromosomes. Rapidly increasing genetic and genomic information on Plasmodium parasites, mosquitoes and humans will combine as a rich resource for new advances in our understanding of malaria, its transmission and its manifestations of disease.     

TLR-mediated cell signaling by malaria GPIs

Proinflammatory responses to malaria have crucial roles in controlling parasite growth and disease pathogenesis. The glycosylphosphatidylinositol (GPI) of Plasmodium falciparum is thought to be an important factor in the induction of proinflammatory responses. The GPI induces host cellular responses mainly through Toll-like receptor (TLR)2/MyD88-mediated signaling. Knowledge of the parasite-host factors involved in activating and regulating innate immune responses and of the associated signaling mechanisms is likely to provide insights into the modulation of parasite-specific adaptive immunity and offer targets for the development of novel therapeutics or a vaccine for malaria. This article focuses on the malaria GPI-mediated cell-signaling mechanisms.     

Endemic Burkitt's lymphoma: a polymicrobial disease?

Endemic Burkitt's lymphoma is the most common childhood cancer in equatorial Africa. Two ubiquitous human pathogens are thought to be responsible for the aetiology of this disease: Epstein-Barr virus and Plasmodium falciparum malaria. New data suggest how these two pathogens might interact to result in disease and provide insights into the emerging concepts of polymicrobial disease pathogenesis.     

Evolution of the human genome under selective pressure from malaria: applications for control

Research on the molecular basis for resistance of humans to malaria has been vigorous during the last 10 years, with new discoveries and extension of work from previous decades. Much of the work has important implications both for understanding pathogenesis and for applications for control of disease.     

Babesiosis: recent insights into an ancient disease

Ever since the discovery of parasitic inclusions in erythrocytes of cattle in Romania by Victor Babes at the end of the 19th century, newly recognised babesial pathogens continue to emerge around the world and the substantial public health impact of babesiosis on livestock and man is ongoing. Babesia are transmitted by ixodid ticks and infection of the host causes a host-mediated pathology and erythrocyte lysis, resulting in anemia, hyperbilirubinuria, hemoglobinuria, and possibly organ failure. Recently obtained molecular data, particularly for the 18S rRNA gene, has contributed significantly to a better understanding of the sometimes puzzling phylogenetic situation of the genus Babesia and new information has been added to help determine the taxonomic position of many species. Moreover, it seems that owing to higher medical awareness the number of reported cases in humans is rising steadily. Hitherto unknown zoonotic babesias are now being reported from geographical areas where babesiosis was not known to occur and the growing numbers of immunocompromised individuals suggest that the frequency of cases will continue to rise. This review covers recent insights into human babesiosis with regard to phylogeny, diagnostics and treatment in order to provide new information on well known as well as recently discovered parasites with zoonotic potential.     

Erythrocyte variants and the nature of their malaria protective effect

The malaria threat to global health is exacerbated by widespread drug resistance in the Plasmodium parasite and its insect vector, and the lack of an efficacious vaccine. Infection with Plasmodium parasites can cause a wide spectrum of pathologies, from a transient mild form of anaemia to a severe and rapidly fatal cerebral disease. Epidemiological studies in humans and experiments in animal models have shown that genetic factors play a key role in the onset, progression, type of disease developed and ultimate outcome of malaria. The protective effect of polymorphic variants in erythrocyte-specific structural proteins or metabolic enzymes against the blood-stage of the disease is one of the clearest illustrations of this genetic modulation, and has suggested co-evolution of the Plasmodium parasite with its human host in areas of endemic disease. Here, we present a brief overview of erythrocyte polymorphisms with biological relevance to malaria pathogenesis, and current work on the mechanism(s) by which these mediate their protective effect. The recent addition of erythrocyte pyruvate kinase to this group of protective genes will also be discussed.     

Evidence for an increased risk of transmission of simian immunodeficiency virus and malaria in a rhesus macaque coinfection model

In sub-Saharan Africa, HIV-1 infection frequently occurs in the context of other coinfecting pathogens, most importantly, Mycobacterium tuberculosis and malaria parasites. The consequences are often devastating, resulting in enhanced morbidity and mortality. Due to the large number of confounding factors influencing pathogenesis in coinfected people, we sought to develop a nonhuman primate model of simian immunodeficiency virus (SIV)-malaria coinfection. In sub-Saharan Africa, Plasmodium falciparum is the most common malaria parasite and is responsible for most malaria-induced deaths. The simian malaria parasite Plasmodium fragile can induce clinical symptoms, including cerebral malaria in rhesus macaques, that resemble those of P. falciparum infection in humans. Thus, based on the well-characterized rhesus macaque model of SIV infection, this study reports the development of a novel rhesus macaque SIV-P. fragile coinfection model to study human HIV-P. falciparum coinfection. Using this model, we show that coinfection is associated with an increased, although transient, risk of both HIV and malaria transmission. Specifically, SIV-P. fragile coinfected macaques experienced an increase in SIV viremia that was temporarily associated with an increase in potential SIV target cells and systemic immune activation during acute parasitemia. Conversely, primary parasitemia in SIV-P. fragile coinfected animals resulted in higher gametocytemia that subsequently translated into higher oocyst development in mosquitoes. To our knowledge, this is the first animal model able to recapitulate the increased transmission risk of both HIV and malaria in coinfected humans. Therefore, this model could serve as an essential tool to elucidate distinct immunological, virological, and/or parasitological parameters underlying disease exacerbation in HIV-malaria coinfected people.     

Cytoadherence, pathogenesis and the infected red cell surface in Plasmodium falciparum.

The particular virulence of Plasmodium falciparum compared with the other malaria species which naturally infect humans is thought to be due to the way in which the parasite modifies the surface of the infected red cell. Approximately 16 hours into the asexual cycle, parasite encoded proteins appear on the red cell surface which mediate adherence to a variety of host tissues. Binding of infected red cells to vascular endothelium, a process which occurs in all infections, is thought to be an important factor in the pathogenesis of severe disease where concentration of organisms in particular organs such as the brain occurs. Binding to uninfected red cells to form erythrocyte rosettes, a property of some isolates, is linked to disease severity. Here we summarise the data on the molecular basis of these interactions on both the host and parasite surfaces and review the evidence for the involvement of particular receptors in specific disease syndromes. Finally we discuss the relevance of these data to the development of new treatments for malaria.     

Sphingosine kinase and sphingosine-1-phosphate in liver pathobiology

Over 20?years ago, sphingosine-1-phosphate (S1P) was discovered to be a bioactive signaling molecule. Subsequent studies later identified two related kinases, sphingosine kinase 1 and 2, which are responsible for the phosphorylation of sphingosine to S1P. Many stimuli increase sphingosine kinase activity and S1P production and secretion. Outside the cell, S1P can bind to and activate five S1P-specific G protein-coupled receptors (S1PR1–5) to regulate many important cellular and physiological processes in an autocrine or paracrine manner. S1P is found in high concentrations in the blood where it functions to control vascular integrity and trafficking of lymphocytes. Obesity increases blood S1P levels in humans and mice. With the world wide increase in obesity linked to consumption of high-fat, high-sugar diets, S1P is emerging as an accomplice in liver pathobiology, including acute liver failure, metabolic syndrome, control of blood lipid and glucose homeostasis, nonalcoholic fatty liver disease, and liver fibrosis. Here, we review recent research on the importance of sphingosine kinases, S1P, and S1PRs in liver pathobiology, with a focus on exciting insights for new therapeutic modalities that target S1P signaling axes for a variety of liver diseases.     

Animal models of rheumatoid arthritis

Animal models of arthritis are used to study pathogenesis of disease and to evaluate potential anti-arthritic drugs for clinical use. Therefore morphological similarities to human disease and capacity of the model to predict efficacy in humans are important criteria in model selection. Animal models of rheumatoid arthritis (RA) with a proven track record of predictability for efficacy in humans include: rat adjuvant arthritis, rat type II collagen arthritis, mouse type II collagen arthritis and antigen-induced arthritis in several species. Agents currently in clinical use (or trials) that are active in these models include: corticosteroids, methotrexate, nonsteroidal anti-inflammatory drugs, cyclosporin A, leflunomide interleukin-1 receptor antagonist (IL-1ra) and soluble TNF receptors. For some of these agents, the models also predict that toxicities seen at higher doses for prolonged dosing periods would preclude dosing in humans at levels that might provide disease modifying effects. Data, conduct and features of the various models of these commonly utilized models of RA as well as some transgenic mouse models and less commonly utilized rodent models will be discussed with emphasis on their similarities to human disease.     

Regulation of immunity to Plasmodium: Implications from mouse models for blood stage malaria vaccine design

Malaria, a disease caused by the protozoan parasite Plasmodium, remains a serious healthcare problem in developing countries worldwide. While the host-parasite relationship in humans has been difficult to determine, the pliability of murine malaria models has enabled valuable contributions to the understanding of the pathogenesis of disease. Although no single model reflects precisely malaria infection of the human, different models collectively provide important information on the mechanisms of protective immunity and immunopathogenesis. This review summarizes progress towards understanding the broad spectrum of immune responsiveness to the blood stages of the malaria parasite during experimental infections in mice and highlights how examination of murine malarias sheds light on the factors involved in the modulation of vaccine-potentiated immunity.     

A mouse model for cerebral babesiosis

Clinical symptoms and pathology observed in the cattle infected with Babesia bovis are quite similar to those of human cerebral malaria. Mechanisms involved in the pathogenesis of cerebral babesiosis, however, are still poorly understood because of the lack of a suitable experimental animal model. In this report, Masayoshi Tsuji and his colleagues describe B. bovis infection in severe combined immunodeficiency (SCID) mice, whose circulating red blood cells (RBCs) have been substituted with bovine RBCs (Bo-RBC-SCID mice). The infected mice not only develop a substantial level of parasitemia, but also show nerve symptoms and pathology similar to those observed in infected cattle.     

Modelling malaria pathogenesis

Almost 20 years after the development of models of malaria pathogenesis began, we are beyond the 'proof-of-concept' phase and these models are no longer abstract mathematical exercises. They have refined our knowledge of within-host processes, and have brought insights that could not easily have been obtained from experimentation alone. There is much potential that remains to be realized, however, both in terms of informing the design of interventions and health policy, and in terms of addressing lingering questions about the basic biology of malaria. Recent research has begun to iterate theory and data in a much more comprehensive way, and the use of statistical techniques for model fitting and comparison offers a promising approach for providing a quantitative understanding of the pathogenesis of such a complex disease.     

The role of tumour necrosis factor-alpha in the pathogenesis of complicated falciparum malaria

Plasmodium falciparum malaria is the most important parasitic infection of humans and is one of the most serious health problems facing the inhabitants of developing countries. It is responsible for about 2 million deaths every year. To date there is no specific treatment for the disease apart from anti-malarials. The declining sensitivity to these drugs is a serious therapeutic problem, while no safe and effective vaccine is likely to be available for general use in the near future. There is now abundant laboratory and clinical evidence to suggest that tumour necrosis factor-alpha (TNF-alpha) plays a major role in the pathogenesis of complicated falciparum malaria. Modulation of TNF-alpha response in combination with the current anti-malarial drugs, may represent a novel approach to the treatment of the serious complications associated with the disease.     

慢病毒载体法制备遗传工程猴和小型猪的现状及应用前景展望

较小鼠等啮齿类动物而言,猴和小型猪等大型实验动物在亲缘关系上与人类更为接近,在解剖、生理生化代谢及疾病发病机制等多方面与人类更接近,使它们在复制人类疾病模型,研究疾病发病机制和新药研发等中有无可替代的应用。而制备遗传工程大动物可以更深入地解析人类疾病,并可为器官移植和新药研发提供更充分的实验材料。基于慢病毒介导的转基因方法近几年已越来越多地被用来制备遗传工程猴和小型猪。与传统的原核显微注射方法和体细胞核移植法相比,慢病毒介导的转基因方法转基因效率高,操作更简单。因此,构筑基于慢病毒介导的转基因方法制备遗传工程猴和小型猪的技术平台将对生物医学研究产生巨大推动作用。