Trypanosoma brucei infection protects mice against malaria

SARS-CoV-2 decreases malaria severity in co-infected rodent models

Coronavirus disease 2019 (COVID-19) and malaria, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Plasmodium parasites, respectively, share geographical distribution in regions where the latter disease is endemic, leading to the emergence of co-infections between the two pathogens. Thus far, epidemiologic studies and case reports have yielded insufficient data on the reciprocal impact of the two pathogens on either infection and related diseases. We established novel co-infection models to address this issue experimentally, employing either human angiotensin-converting enzyme 2 (hACE2)-expressing or wild-type mice, in combination with human- or mouse-infective variants of SARS-CoV-2, and the P. berghei rodent malaria parasite. We now show that a primary infection by a viral variant that causes a severe disease phenotype partially impairs a subsequent liver infection by the malaria parasite. Additionally, exposure to an attenuated viral variant modulates subsequent immune responses and provides protection from severe malaria-associated outcomes when a blood stage P. berghei infection was established. Our findings unveil a hitherto unknown host-mediated virus-parasite interaction that could have relevant implications for disease management and control in malaria-endemic regions. This work may contribute to the development of other models of concomitant infection between Plasmodium and respiratory viruses, expediting further research on co-infections that lead to complex disease presentations.

Coinfection with Schistosoma mansoni Enhances Disease Severity in Human African Trypanosomiasis

Introduction

Human African trypanosomiasis (HAT) and schistosomiasis are neglected parasitic diseases found in the African continent. This study was conducted to determine how primary infection with Schistosoma mansoni affects HAT disease progression with a secondary infection with Trypanosoma brucei rhodesiense (T.b.r) in a mouse model.

Methods

Female BALB-c mice (6-8 weeks old) were randomly divided into four groups of 12 mice each. The different groups were infected with Schistosoma mansoni (100 cercariae) and Trypanosoma brucei rhodesiense (5.0 × 104) separately or together. Twenty-one days after infection with T.b.r, mice were sacrificed and samples were collected for analysis.

Results

The primary infection with S. mansoni significantly enhanced successive infection by the T.b.r; consequently, promoting HAT disease severity and curtailing host survival time. T.b.r-induced impairment of the neurological integrity and breach of the blood-brain barrier were markedly pronounced on coinfection with S. mansoni. Coinfection with S. mansoni and T.b.r resulted in microcytic hypochromic anemia characterized by the suppression of RBCs, hematocrit, hemoglobin, and red cell indices. Moreover, coinfection of the mice with the two parasites resulted in leukocytosis which was accompanied by the elevation of basophils, neutrophils, lymphocytes, monocytes, and eosinophils. More importantly, coinfection resulted in a significant elevation of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total bilirubin, creatinine, urea, and uric acid, which are the markers of liver and kidney damage. Meanwhile, S. mansoni-driven dyslipidemia was significantly enhanced by the coinfection of mice with T.b.r. Moreover, coinfection with S. mansoni and T.b.r led to a strong immune response characterized by a significant increase in serum TNF-α and IFN-γ. T.b.r infection enhanced S. mansoni-induced depletion of cellular-reduced glutathione (GSH) in the brain and liver tissues, indicative of lethal oxidative damage. Similarly, coinfection resulted in a significant rise in nitric oxide (NO) and malondialdehyde (MDA) levels.

Conclusion

Primary infection with S. mansoni exacerbates disease severity of secondary infection with T.b.r in a mouse model that is associated with harmful inflammatory response, oxidative stress, and organ injury.

Mechanistic insights into the interaction between the host gut microbiome and malaria

Malaria is a devastating infectious disease and significant global health burden caused by the bite of a Plasmodium-infected female Anopheles mosquito. Gut microbiota was recently discovered as a risk factor of severe malaria. This review entails the recent advances on the impact of gut microbiota composition on malaria severity and consequence of malaria infection on gut microbiota in mammalian hosts. Additionally, this review provides mechanistic insight into interactions that might occur between gut microbiota and host immunity which in turn can modulate malaria severity. Finally, approaches to modulate gut microbiota composition are discussed. We anticipate this review will facilitate novel hypotheses to move the malaria-gut microbiome field forward.

Babesia microti alleviates disease manifestations caused by Plasmodium berghei ANKA in murine co-infection model of complicated malaria

Malaria remains one of the most significant health issues worldwide, accounting for 2.6% of the total global disease burden, and efforts to eliminate this threat continue. The key focus is to develop an efficient and long-term immunity to this disease via vaccination or therapeutic approach, and innovative strategies would enable us to achieve this target. Previously, using a mouse co-infection disease model, cross-protection was illustrated between Babesia microti and Plasmodium chabaudi. Hence, this study was planned to elucidate the impact of acute B. microti Peabody mjr and Plasmodium berghei ANKA co-infection on the consequence of complicated malaria in the C57BL/6J mouse model of malaria. Furthermore, immune response and pathological features were analyzed, and the course of the disease was compared among experimental groups. Our study established that acute B. microti infection activated immunity which was otherwise suppressed by P. berghei. The immunosuppressive tissue microenvironment was counteracted as evidenced by the enhanced immune cell population in co-infected mice, in contrast to P. berghei-infected control mice. Parasite sequestration in the brain, liver, lung, and spleen of co-infected mice was significantly decreased and tissue injury was ameliorated. Meanwhile, the serum levels of IFN-γ, TNF-α, and IL-12p70 were reduced while the secretion of IL-10 was promoted in co-infected mice. Eventually, co-infected mice showed an extended rate of survival. Hereby, the principal cytokines associated with the severity of malaria by P. berghei infection were TNF-α, IFN-γ, and IL-12p70. Moreover, it was evident from our flow cytometry results that innate immunity is crucial and macrophages are at the frontline of immunity against P. berghei infection. Our study recommended further investigations to shed light on the effects of babesiosis in suppressing malaria with the goal of developing Babesia-based therapy against malaria.

Impact of Dietary Protein Restriction on the Immunogenicity and Efficacy of Whole-Sporozoite Malaria Vaccination

Malaria remains one of the world’s most prevalent infectious diseases. Several vaccination strategies currently under investigation aim at hampering the development of the Plasmodium parasite during the clinically silent liver stage of its life cycle in the mammalian host, preventing the subsequent disease-associated blood stage of infection. Immunization with radiation-attenuated sporozoites (RAS), the liver-infecting parasite forms, can induce sterile protection against malaria. However, the efficacy of vaccine candidates in malaria-naïve individuals in high-income countries is frequently higher than that found in populations where malaria is endemic. Malnutrition has been associated with immune dysfunction and with a delay or impairment of the immune response to some vaccines. Since vaccine efficacy depends on the generation of competent immune responses, and malaria-endemic regions are often associated with malnutrition, we hypothesized that an inadequate host nutritional status, specifically resulting from a reduction in dietary protein, could impact on the establishment of an efficient anti-malarial immune response. We developed a model of RAS immunization under low protein diet to investigate the impact of a reduced host protein intake on the immunogenicity and protective efficacy of this vaccine. Our analysis of the circulating and tissue-associated immune compartments revealed that a reduction in dietary protein intake during immunization resulted in a decrease in the frequency of circulating CD4+ T cells and of hepatic NK cells. Nevertheless, the profile of CD8+ T cells in the blood, liver and spleen was robust and minimally affected by the dietary protein content during RAS immunization, as assessed by supervised and in-depth unsupervised X-shift clustering analysis. Although mice immunized under low protein diet presented higher parasite liver load upon challenge than those immunized under adequate protein intake, the two groups displayed similar levels of protection from disease. Overall, our data indicate that dietary protein reduction may have minimal impact on the immunogenicity and efficacy of RAS-based malaria vaccination. Importantly, this experimental model can be extended to assess the impact of other nutrient imbalances and immunization strategies, towards the refinement of future translational interventions that improve vaccine efficacy in malnourished individuals.

Parasite co-infection: an ecological, molecular and experimental perspective

Laboratory studies of pathogens aim to limit complexity in order to disentangle the important parameters contributing to an infection. However, pathogens rarely exist in isolation, and hosts may sustain co-infections with multiple disease agents. These interact with each other and with the host immune system dynamically, with disease outcomes affected by the composition of the community of infecting pathogens, their order of colonization, competition for niches and nutrients, and immune modulation. While pathogen-immune interactions have been detailed elsewhere, here we examine the use of ecological and experimental studies of trypanosome and malaria infections to discuss the interactions between pathogens in mammal hosts and arthropod vectors, including recently developed laboratory models for co-infection. The implications of pathogen co-infection for disease therapy are also discussed.

Excreted Trypanosoma brucei proteins inhibit Plasmodium hepatic infection

Malaria, a disease caused by Plasmodium parasites, remains a major threat to public health globally. It is the most common disease in patients with sleeping sickness, another parasitic illness, caused by Trypanosoma brucei. We have previously shown that a T. brucei infection impairs a secondary P. berghei liver infection and decreases malaria severity in mice. However, whether this effect requires an active trypanosome infection remained unknown. Here, we show that Plasmodium liver infection can also be inhibited by the serum of a mouse previously infected by T. brucei and by total protein lysates of this kinetoplastid. Biochemical characterisation showed that the anti-Plasmodium activity of the total T. brucei lysates depends on its protein fraction, but is independent of the abundant variant surface glycoprotein. Finally, we found that the protein(s) responsible for the inhibition of Plasmodium infection is/are present within a fraction of ~350 proteins that are excreted to the bloodstream of the host. We conclude that the defence mechanism developed by trypanosomes against Plasmodium relies on protein excretion. This study opens the door to the identification of novel antiplasmodial intervention strategies.

Hematological consequences of malaria in mice previously treated for visceral leishmaniasis

Background: Polyparasitism is commonplace in countries where endemicity for multiple parasites exists, and studies in animal models of coinfection have made significant inroads into understanding the impact of often competing demands on the immune system. However, few studies have addressed how previous exposure to and treatment for one infection impacts a subsequent heterologous infection.   Methods: We used a C57BL/6 mouse model of drug-treated Leishmania donovani infection followed by experimental Plasmodium chabaudi AS malaria, focusing on hematological dysfunction as a common attribute of both infections. We measured parasite burden, blood parameters associated with anemia and thrombocytopenia, and serum thrombopoietin. In addition, we quantified macrophage iNOS expression through immunohistological analysis of the liver and spleen.   Results: We found that the thrombocytopenia and anemia that accompanies primary L. donovani infection was rapidly reversed following single dose AmBisome® treatment, along with multiple other markers associated with immune activation (including restoration of tissue microarchitecture and reduced macrophage iNOS expression). Compared to naive mice, mice cured of previous L. donovani infection showed comparable albeit delayed clinical responses (including peak parasitemia and anemia) to P. chabaudi AS infection. Thrombocytopenia was also evident in these sequentially infected mice, consistent with a decrease in circulating levels of thrombopoietin. Architectural changes to the spleen were also comparable in sequentially infected mice compared to those with Plasmodium infection alone. Conclusions: Our data suggest that in this sequential infection model, previously-treated L. donovani infection has limited impact on the subsequent development of Plasmodium infection, but this issue deserves further attention in models of more severe disease or through longitudinal population studies in humans.

Hematological consequences of malaria infection in mice previously treated for visceral leishmaniasis

Background: Polyparasitism is commonplace in countries where endemicity for multiple parasites exists, and studies in animal models of coinfection have made significant inroads into understanding the impact of often competing demands on the immune system. However, few studies have addressed how previous exposure to and treatment for one infection impacts a subsequent heterologous infection.   Methods: We used a C57BL/6 mouse model of drug-treated Leishmania donovani infection followed by experimental Plasmodium chabaudi AS malaria, focusing on hematological dysfunction as a common attribute of both infections. We measured parasite burden, blood parameters associated with anemia and thrombocytopenia, and serum thrombopoietin. In addition, we quantified macrophage iNOS expression through immunohistological analysis of the liver and spleen.   Results: We found that the thrombocytopenia and anemia that accompanies primary L. donovani infection was rapidly reversed following single dose AmBisome® treatment, along with multiple other markers associated with immune activation (including restoration of tissue microarchitecture and reduced macrophage iNOS expression). Compared to naive mice, mice cured of previous VL showed comparable albeit delayed clinical responses (including peak parasitemia and anemia) to P. chabaudi AS infection. Thrombocytopenia was also evident in these sequentially infected mice, consistent with a decrease in circulating levels of thrombopoietin. Architectural changes to the spleen were also comparable in sequentially infected mice compared to those with malaria alone. Conclusions: Our data suggest that in this sequential infection model, previously-treated VL has limited impact on the subsequent development of malaria, but this issue deserves further attention in models of more severe disease or through longitudinal population studies in humans.

Possible influence of Plasmodium/Trypanosoma co-infections on the vectorial capacity of Anopheles mosquitoes

Objective

In tropical Africa, trypanosomiasis is present in endemic areas with many other diseases including malaria. Because malaria vectors become more anthropo-zoophilic under the current insecticide pressure, they may be exposed to trypanosome parasites. By collecting mosquitoes in six study sites with distinct malaria infection prevalence and blood sample from cattle, we tried to assess the influence of malaria-trypanosomiasis co-endemicity on the vectorial capacity of Anopheles.

Results

Overall, all animal infections were due to Trypanosoma vivax (infection rates from 2.6 to 10.5%) in villages where the lowest Plasmodium prevalence were observed at the beginning of the study. An. gambiae s.l. displayed trophic preferences for human-animal hosts. Over 84 mosquitoes, only one was infected by Plasmodium falciparum (infection rate: 4.5%) in a site that displayed the highest prevalence at the beginning of the study. Thus, Anopheles could be exposed to Trypanosoma when they feed on infected animals. No Plasmodium infection was observed in the Trypanosoma-infected animals sites. This can be due to an interaction between both parasites as observed in mice and highlights the need of further studies considering Trypanosoma/Plasmodium mixed infections to better characterize the role of these infections in the dynamic of malaria transmission and the mechanisms involved.