Viruses of parasites as actors in the parasite-host relationship: A "ménage à trois"

Microbial Matryoshka: Addressing the Relationship between Pathogenic Flagellated Protozoans and Their RNA Viral Endosymbionts (Family Totiviridae)

Three genera of viruses of the family Totiviridae establish endosymbiotic associations with flagellated protozoa responsible for parasitic diseases of great impact in the context of One Health. Giardiavirus, Trichomonasvirus, and Leishmaniavirus infect the protozoa Giardia sp., Trichomonas vaginalis, and Leishmania sp., respectively. In the present work, we review the characteristics of the endosymbiotic relationships established, the advantages, and the consequences caused in mammalian hosts. Among the common characteristics of these double-stranded RNA viruses are that they do not integrate into the host genome, do not follow a lytic cycle, and do not cause cytopathic effects. However, in cases of endosymbiosis between Leishmaniavirus and Leishmania species from the Americas, and between Trichomonasvirus and Trichomonas vaginalis, it seems that it can alter their virulence (degree of pathogenicity). In a mammalian host, due to TLR3 activation of immune cells upon the recognition of viral RNA, uncontrolled inflammatory signaling responses are triggered, increasing pathological damage and the risk of failure of conventional standard treatment. Endosymbiosis with Giardiavirus can cause the loss of intestinal adherence of the protozoan, resulting in a benign disease. The current knowledge about viruses infecting flagellated protozoans is still fragmentary, and more research is required to unravel the intricacies of this three-way relationship. We need to develop early and effective diagnostic methods for further development in the field of translational medicine. Taking advantage of promising biotechnological advances, the aim is to develop ad hoc therapeutic strategies that focus not only on the disease-causing protozoan but also on the virus.

Extracellular vesicles in parasitic protozoa: Impact of Leishmania exosomes containing Leishmania RNA virus 1 (LRV1) on Leishmania infectivity and disease progression

This chapter focuses on the interplay between Leishmania parasites and their host, particularly on Leishmania RNA virus (LRVs) and extracellular vesicles (EVs) in modulating host-pathogen interactions. Leishmania EVs have been shown to facilitate gene transfer, including drug-resistance genes, enhancing the parasites' survival and resistance to antileishmanial therapeutics. These EVs also play a significant role in host immune modulation by altering cytokine production in macrophages and promoting an anti-inflammatory environment that favours parasitic persistence. The presence of virulence factors such as GP63 within these EVs further underscores their role in the parasite's immunopathogenesis. Over the last few decades, LRVs have been established as drivers of the severity and persistence of leishmaniasis by exacerbating inflammatory responses and potentially influencing treatment outcomes. This chapter discusses the evolutionary origins and classification of these viruses, and explores their role in parasitic pathogenicity, highlighting their ubiquity across protozoan parasites and their impact on disease progression.

A parasite odyssey: An RNA virus concealed in Toxoplasma gondii

We are entering a 'Platinum Age of Virus Discovery', an era marked by exponential growth in the discovery of virus biodiversity, and driven by advances in metagenomics and computational analysis. In the ecosystem of a human (or any animal) there are more species of viruses than simply those directly infecting the animal cells. Viruses can infect all organisms constituting the microbiome, including bacteria, fungi, and unicellular parasites. Thus the complexity of possible interactions between host, microbe, and viruses is unfathomable. To understand this interaction network we must employ computationally assisted virology as a means of analyzing and interpreting the millions of available samples to make inferences about the ways in which viruses may intersect human health. From a computational viral screen of human neuronal datasets, we identified a novel narnavirus Apocryptovirus odysseus (Ao) which likely infects the neurotropic parasite Toxoplasma gondii. Previously, several parasitic protozoan viruses (PPVs) have been mechanistically established as triggers of host innate responses, and here we present in silico evidence that Ao is a plausible pro-inflammatory factor in human and mouse cells infected by T. gondii. T. gondii infects billions of people worldwide, yet the prognosis of toxoplasmosis disease is highly variable, and PPVs like Ao could function as a hitherto undescribed hypervirulence factor. In a broader screen of over 7.6 million samples, we explored phylogenetically proximal viruses to Ao and discovered nineteen Apocryptovirus species, all found in libraries annotated as vertebrate transcriptome or metatranscriptomes. While samples containing this genus of narnaviruses are derived from sheep, goat, bat, rabbit, chicken, and pigeon samples, the presence of virus is strongly predictive of parasitic Apicomplexa nucleic acid co-occurrence, supporting the fact that Apocryptovirus is a genus of parasite-infecting viruses. This is a computational proof-of-concept study in which we rapidly analyze millions of datasets from which we distilled a mechanistically, ecologically, and phylogenetically refined hypothesis. We predict that this highly diverged Ao RNA virus is biologically a T. gondii infection, and that Ao, and other viruses like it, will modulate this disease which afflicts billions worldwide.

First data on parasites of the invasive brown bullhead Ameiurus nebulosus (Siluriformes: Ictaluridae) in Ukraine

This study describes the parasite community of non-native brown bullhead, Ameiurus nebulosus (Actinopterygii: Ictaluridae), collected at three sites in the river Vistula Basin (Lake Svitiaz, Lake Pisochne, and Lake on Plastova) and one site in the river Diester Basin (Lake Stryiska), in Ukraine. Our data represent the first comprehensive study of parasite community in this fish species in Europe. Sixteen parasite taxa were found, including species co-introduced from North America and species acquired in the European range. Maximum parasite richness (13 spp.) was recorded in Lake Svitiaz situated in a Natural Protected Area, while lowest species richness (3 spp.) was observed at Lake on Plastova, an artificial pond in the city of Lviv. Three co-introduced monogenean species, Gyrodactylus nebulosus, Ligictaluridus pricei and Ligictaluridus monticellii, are recorded in Ukraine for the first time, widening the knowledge of the European distribution of these North American parasites. Metric features for hard parts of invasive and native monogeneans showed overlap in ligictalurid parasites, but slightly smaller metrics in Ukrainian G. nebulosus, possibly reflecting water temperature during fish sampling. Though prevalence and abundance of acquired parasites was relatively low, infection parameters for metacercariae of Diplostomum spp. were relatively high at Lake Svitiaz and the natural Lake Stryiska in Lviv. In two lakes in the Vistula basin, we found high prevalence and abundance of Anguillicola crassus, an Asian nematode infecting eels, possibly supporting the invasional meltdown hypothesis. Our study confirms both further spread of non-native parasites in Europe and use of non-native fish as competent hosts for local native and introduced parasites.

The intracellular parasite Anncaliia algerae induces a massive miRNA down-regulation in human cells

Anncaliia algerae belongs to microsporidia, a group of obligate intracellular parasites related to fungi. These parasites are largely spread in water and food-webs and can infect a wide variety of hosts ranging from invertebrates to vertebrates including humans. In humans, microsporidian infections are mainly opportunistic as immunocompetent hosts can clear parasites naturally. Recent studies however have reported persistent microsporidian infections and have highlighted them as a risk factor in colon cancer. This may be a direct result of cell infection or may be an indirect effect of the infectious microenvironment and the host's response. In both cases, this raises the question of the effects of microsporidian infection at the host and host-cell levels. We aimed to address the question of human host intracellular response to microsporidian infection through a transcriptomic kinetic study of human foreskin fibroblasts (HFF) infected with A.algerae, a human infecting microsporidia with an exceptionally wide host range. We focused solely on host response studying both coding and small non-coding miRNA expression. Our study revealed a generalized down-regulation of cell miRNAs throughout infection with up to 547 different miRNAs downregulated at some timepoints and also transcriptomic dysregulations that could facilitate parasite development with immune and lipid metabolism genes modulation. We also hypothesize possible small nucleic acid expropriation explaining the miRNA downregulation. This work contributes to a better understanding of the dialogue that can occur between an intracellular parasite and its host at the cellular level, and can guide future studies on microsporidian infection biology to unravel the mode of action of these minimalist parasites at the tissue or host levels.We have also generated a kinetic and comprehensive transcriptomic data set of an infectious process that can help support comparative studies in the broader field of parasitology. Lastly, these results may warrant for caution regarding microsporidian exposure and persistent infections.

A Diverse Virome Is Identified in Parasitic Flatworms of Domestic Animals in Xinjiang, China

Parasitic flatworms infect diverse vertebrates and are major threats to animal and even human health; however, little is known about the virome of these lower life forms. Using viral metagenomic sequencing, we characterized the virome of the parasitic flatworms collected from major domestic animals, including Dicrocoelium lanceatum and Taenia hydatigena, Echinococcus granulosus sensu stricto and Echinococcus multilocularis. Seven and three different viruses were discovered from D. lanceatum and T. hydatigena, respectively, and no viral sequences were found in adult tapeworms and protoscoleces of E. granulosus sensu stricto and E. multilocularis. Two out of the five parasitic flatworm species carry viruses, showing a host specificity of these viruses. These viruses belong to the Parvoviridae, Circoviridae, unclassified circular, Rep-encoding single-stranded (CRESS) DNA virus, Rhabdoviridae, Endornaviridae, and unclassified RNA viruses. The presence of multiple highly divergent RNA viruses, especially those that cluster with viruses found in marine animals, implies a deep evolutionary history of parasite-associated viruses. In addition, we found viruses with high identity to common pathogens in dogs, including canine circovirus and canine parvovirus 2. The presence of these viruses in the parasites implies that they may infect parasitic flatworms but does not completely exclude the possibility of contamination from host intestinal contents. Furthermore, we demonstrated that certain viruses, such as CRESS DNA virus may integrate into the genome of their host. Our results expand the knowledge of viral diversity in parasites of important domestic animals, highlighting the need for further investigations of their prevalence among other parasites of key animals. IMPORTANCE Characterizing the virome of parasites is important for unveiling the viral diversity, evolution, and ecology and will help to understand the "Russian doll" pattern among viruses, parasites, and host animals. Our data indicate that diverse viruses are present in specific parasitic flatworms, including viruses that may have an ancient evolutionary history and viruses currently circulating in parasite-infected host animals. These data also raise the question of whether parasitic flatworms acquire and/or carry some viruses that may have transmission potential to animals. In addition, through the study of virus-parasite-host interactions, including the influence of viral infection on the life cycle of the parasite, as well as its fitness and pathogenicity to the host, we could find new strategies to prevent and control parasitic diseases.

A potential role for Giardia chaperone protein GdDnaJ in regulating Giardia proliferation and Giardiavirus replication

BACKGROUND

Giardia duodenalis (referred to as Giardia) is a flagellated binucleate protozoan parasite, which causes one of the most common diarrheal diseases, giardiasis, worldwide. Giardia can be infected by Giardiavirus (GLV), a small endosymbiotic dsRNA virus belongs to the Totiviridae family. However, the regulation of GLV and a positive correlation between GLV and Giardia virulence is yet to be elucidated.

METHODS

To identify potential regulators of GLV, we performed a yeast two-hybrid (Y2H) screen to search for interacting proteins of RdRp. GST pull-down, co-immunoprecipitation and bimolecular fluorescence complementation (BiFC) assay were used to verify the direct physical interaction between GLV RdRp and its new binding partner. In addition, their in vivo interaction and colocalization in Giardia trophozoites were examined by using Duolink proximal ligation assay (Duolink PLA).

RESULTS

From Y2H screen, the Giardia chaperone protein, Giardia DnaJ (GdDnaJ), was identified as a new binding partner for GLV RdRp. The direct interaction between GdDnaJ and GLV RdRp was verified via GST pull-down, co-immunoprecipitation and BiFC. In addition, colocalization and in vivo interaction between GdDnaJ and RdRp in Giardia trophozoites were confirmed by Duolink PLA. Further analysis revealed that KNK437, the inhibitor of GdDnaJ, can significantly reduce the replication of GLVs and the proliferation of Giardia.

CONCLUSION

Taken together, our results suggested a potential role of GdDnaJ in regulating Giardia proliferation and GLV replication through interaction with GLV RdRp.

Insights into the Biology of Leucocytozoon Species (Haemosporida, Leucocytozoidae): Why Is There Slow Research Progress on Agents of Leucocytozoonosis?

Blood parasites of the genus Leucocytozoon (Leucocytozoidae) only inhabit birds and represent a readily distinct evolutionary branch of the haemosporidians (Haemosporida, Apicomplexa). Some species cause pathology and even severe leucocytozoonosis in avian hosts, including poultry. The diversity of Leucocytozoon pathogens is remarkable, with over 1400 genetic lineages detected, most of which, however, have not been identified to the species level. At most, approximately 45 morphologically distinct species of Leucocytozoon have been described, but only a few have associated molecular data. This is unfortunate because basic information about named and morphologically recognized Leucocytozoon species is essential for a better understanding of phylogenetically closely related leucocytozoids that are known only by DNA sequence. Despite much research on haemosporidian parasites during the past 30 years, there has not been much progress in taxonomy, vectors, patterns of transmission, pathogenicity, and other aspects of the biology of these cosmopolitan bird pathogens. This study reviewed the available basic information on avian Leucocytozoon species, with particular attention to some obstacles that prevent progress to better understanding the biology of leucocytozoids. Major gaps in current Leucocytozoon species research are discussed, and possible approaches are suggested to resolve some issues that have limited practical parasitological studies of these pathogens.

Cryptosporidium uses CSpV1 to activate host type I interferon and attenuate antiparasitic defenses

Cryptosporidium infects gastrointestinal epithelium and is a leading cause of infectious diarrhea and diarrheal-related death in children worldwide. There are no vaccines and no fully effective therapy available for the infection. Type II and III interferon (IFN) responses are important determinants of susceptibility to infection but the role for type I IFN response remains obscure. Cryptosporidium parvum virus 1 (CSpV1) is a double-stranded RNA (dsRNA) virus harbored by Cryptosporidium spp. Here we show that intestinal epithelial conditional Ifnar1^-/- mice (deficient in type I IFN receptor) are resistant to C. parvum infection. CSpV1-dsRNAs are delivered into host cells and trigger type I IFN response in infected cells. Whereas C. parvum infection attenuates epithelial response to IFN-γ, loss of type I IFN signaling or inhibition of CSpV1-dsRNA delivery can restore IFN-γ-mediated protective response. Our findings demonstrate that type I IFN signaling in intestinal epithelial cells is detrimental to intestinal anti-C. parvum defense and Cryptosporidium uses CSpV1 to activate type I IFN signaling to evade epithelial antiparasitic response.

An Overview of Mucosa-Associated Protozoa: Challenges in Chemotherapy and Future Perspectives

Parasitic infections caused by protozoans that infect the mucosal surfaces are widely neglected worldwide. Collectively, Entamoeba histolytica, Giardia lamblia, Cryptosporidium spp. and Trichomonas vaginalis infect more than a billion people in the world, being a public health problem mainly in developing countries. However, the exact incidence and prevalence data depend on the population examined. These parasites ultimately cause pathologies that culminate in liver abscesses, malabsorption syndrome, vaginitis, and urethritis, respectively. Despite this, the antimicrobial agents currently used to treat these diseases are limited and often associated with adverse side effects and refractory cases due to the development of resistant parasites. The paucity of drug treatments, absence of vaccines and increasing problems of drug resistance are major concerns for their control and eradication. Herein, potential candidates are reviewed with the overall aim of determining the knowledge gaps and suggest future perspectives for research. This review focuses on this public health problem and focuses on the progress of drug repositioning as a potential strategy for the treatment of mucosal parasites.

Identification and Molecular Characterization of Novel Mycoviruses in Saccharomyces and Non-Saccharomyces Yeasts of Oenological Interest

Wine yeasts can be natural hosts for dsRNA, ssRNA viruses and retrotransposon elements. In this study, high-throughput RNA sequencing combined with bioinformatic analyses unveiled the virome associated to 16 Saccharomyces cerevisiae and 8 non-Saccharomyces strains of oenological interest. Results showed the presence of six viruses and two satellite dsRNAs from four different families, two of which-Partitiviridae and Mitoviridae-were not reported before in yeasts, as well as two ORFan contigs of viral origin. According to phylogenetic analysis, four new putative mycoviruses distributed in Totivirus, Cryspovirus, and Mitovirus genera were identified. The majority of commercial S. cerevisiae strains were confirmed to be the host for helper L-A type totiviruses and satellite M dsRNAs associated with the killer phenotype, both in single and mixed infections with L-BC totiviruses, and two viral sequences belonging to a new cryspovirus putative species discovered here for the first time. Moreover, single infection by a narnavirus 20S-related sequence was also found in one S. cerevisiae strain. Considering the non-Saccharomyces yeasts, Starmerella bacillaris hosted four RNAs of viral origin-two clustering in Totivirus and Mitovirus genera, and two ORFans with putative satellite behavior. This study confirmed the infection of wine yeasts by viruses associated with useful technological characteristics and demonstrated the presence of complex mixed infections with unpredictable biological effects.

Stronger population differentiation at infection-sensing than infection-clearing innate immune loci in songbirds: Different selective regimes for different defenses

Parasite-mediated selection is widespread at loci involved in immune defense, but different defenses may experience different selective regimes. For defenses involved in clearing infections, purifying selection favoring a single most efficacious allele likely predominates. However, for defenses involved in sensing and recognizing infections, evolutionary arms races may make positive selection particularly important. This could manifest primarily within populations (e.g., balancing selection maintaining variation) or among them (e.g., spatially varying selection enhancing population differences in allele frequencies). We genotyped three toll-like receptors (TLR; involved in sensing infections) and three avian beta-defensins (involved in clearing infections) in 96 song sparrows (Melospiza melodia) from three breeding populations that differ in disease resistance. Variation-based indicators of selection (proportion of variable sites, proportion of nonsynonymous SNPs, proportion of sites bearing signatures of positive or purifying selection, rare allele frequencies) did not differ appreciably between the two locus types. However, differentiation was generally higher at infection-sensing than infection-clearing loci. Allele frequencies differed markedly at TLR3, driven by a variant predicted to alter protein function. Geographically structured variants at infection-sensing loci may reflect local adaptation to spatially heterogeneous parasite communities. Selective regimes experienced by infection-sensing versus infection-clearing loci may differ primarily due to parasite-mediated population differentiation.

Vector-borne zoonotic blood parasites in wildlife from Ecuador: A report and systematic review

Background and Aim:

Ecuador is a hugely diverse country, but information on infectious diseases in local wild animals is scarce. The aim of this study was to screen the presence of blood parasites in free-ranging wild animals admitted to the Wildlife Hospital at Universidad San Francisco de Quito, from April 2012 to January 2019.

Materials and Methods:

We identified blood parasites by microscopic observation of blood smears from free-ranging wildlife species that attended the Wildlife Hospital of Universidad San Francisco de Quito (Ecuador) from April 2012 to January 2019.

Results:

The microscopic evaluations of animals as potential reservoirs for vector-borne zoonotic blood parasites revealed the presence of Anaplasma spp., Babesia spp., Ehrlichia spp., Hepatozoon spp., microfilaria, Mycoplasma spp., and Trypanosoma spp. in previously unreported wildlife species. In addition, we performed a systematic review to understand the current knowledge gaps in the context of these findings.

Conclusion:

Our data contribute to the knowledge of blood parasites in wildlife from Ecuador. Furthermore, the potential transmission of these parasites to humans and domestic animals, current anthropogenic environmental changes in the region, and the lack of information on this suggest the importance of our results and warrant further investigations on infectious diseases in animals and humans and their relationship with environmental health as key domains of the One Health concept.

Giardiavirus: an update

Giardiavirus is the only virus that infects Giardia duodenalis, a highly prevalent parasite worldwide, especially in low-income and developing countries. This virus belongs to the Totiviridae family, being a relative of other viruses that infect fungi and protozoa. It has a simple structure with only two proteins encoded in its genome and it appears that it can leave the cell without lysis. All these characteristics make it an interesting study model; however, its research has unfortunately made little progress in recent years. Thus, in this review, we summarize the currently available data on Giardiavirus, from their structure, genome and main proteins, to the uses that have been given to them and the possible health applications for the future.

Newly identified Cryptosporidium parvum virus-1 from newborn calf diarrhoea in Turkey

Cryptosporidium is a common enteric parasite that primarily affects those immunocompromised susceptible individuals and newborns. Detailed investigations have revealed that Cryptosporidium (C.) oocysts contain dsRNA segments which are recently classified under the Partitiviridae family. The relationship between parasite and virus whether or not affect the clinical outcomes of newborn calf diarrhoea is not apparent. The aim of this study was the identification and characterization of Cryptosporidium parvum virus-1 (CSpV1) from newborn calves. We also aimed to understand that parasite-virus symbiont relationship role in the severity of disease cases. Parasitic screening was performed with the help of morphological examinations, immunoassay and molecular polymerase chain reaction (PCR) methods. To further identification of C. parvum oocysts, confocal laser, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) image analysis were used for the morphological investigations. Software-based in silico comparison and identity analyses were conducted from the CSpV1 genome for the genomic sequence characterizations. Cryptosporidium prevalence was 56.2% in newborn calf diarrhoeal cases. Virus dsRNA segments isolated from purified and clarified oocysts. Sequence results showed that we have successfully isolated CSpV1 from C. parvum oocysts. Virus RNA-dependent RNA polymerase (RdRp) was found to be highly variable and showed a species-specific relationship with their carriers. We also identified that CSpV1 frequency was around 8.8% from diarrhoea-showing newborn calves. Cryptosporidium was strongly associated with diarrhoea at early ages of newborns, but the parasite and CSpV1 relationship is not associated with the severity of newborn calf diarrhoea. The current study provides the first report and molecular characterization of CSpV1 in Turkey.

Viruses of protozoan parasites and viral therapy: Is the time now right?

Infections caused by protozoan parasites burden the world with huge costs in terms of human and animal health. Most parasitic diseases caused by protozoans are neglected, particularly those associated with poverty and tropical countries, but the paucity of drug treatments and vaccines combined with increasing problems of drug resistance are becoming major concerns for their control and eradication. In this climate, the discovery/repurposing of new drugs and increasing effort in vaccine development should be supplemented with an exploration of new alternative/synergic treatment strategies. Viruses, either native or engineered, have been employed successfully as highly effective and selective therapeutic approaches to treat cancer (oncolytic viruses) and antibiotic-resistant bacterial diseases (phage therapy). Increasing evidence is accumulating that many protozoan, but also helminth, parasites harbour a range of different classes of viruses that are mostly absent from humans. Although some of these viruses appear to have no effect on their parasite hosts, others either have a clear direct negative impact on the parasite or may, in fact, contribute to the virulence of parasites for humans. This review will focus mainly on the viruses identified in protozoan parasites that are of medical importance. Inspired and informed by the experience gained from the application of oncolytic virus- and phage-therapy, rationally-driven strategies to employ these viruses successfully against parasitic diseases will be presented and discussed in the light of the current knowledge of the virus biology and the complex interplay between the viruses, the parasite hosts and the human host. We also highlight knowledge gaps that should be addressed to advance the potential of virotherapy against parasitic diseases.

Mucosal microbial parasites/symbionts in health and disease: an integrative overview

Microbial parasites adapted to thrive at mammalian mucosal surfaces have evolved multiple times from phylogenetically distant lineages into various extracellular and intracellular life styles. Their symbiotic relationships can range from commensalism to parasitism and more recently some host-parasites interactions are thought to have evolved into mutualistic associations too. It is increasingly appreciated that this diversity of symbiotic outcomes is the product of a complex network of parasites-microbiota-host interactions. Refinement and broader use of DNA based detection techniques are providing increasing evidence of how common some mucosal microbial parasites are and their host range, with some species being able to swap hosts, including from farm and pet animals to humans. A selection of examples will illustrate the zoonotic potential for a number of microbial parasites and how some species can be either disruptive or beneficial nodes in the complex networks of host-microbe interactions disrupting or maintaining mucosal homoeostasis. It will be argued that mucosal microbial parasitic diversity will represent an important resource to help us dissect through comparative studies the role of host-microbe interactions in both human health and disease.

Novel RNA viruses associated with Plasmodium vivax in human malaria and Leucocytozoon parasites in avian disease

Eukaryotes of the genus Plasmodium cause malaria, a parasitic disease responsible for substantial morbidity and mortality in humans. Yet, the nature and abundance of any viruses carried by these divergent eukaryotic parasites is unknown. We investigated the Plasmodium virome by performing a meta-transcriptomic analysis of blood samples taken from patients suffering from malaria and infected with P. vivax, P. falciparum or P. knowlesi. This resulted in the identification of a narnavirus-like sequence, encoding an RNA polymerase and restricted to P. vivax samples, as well as an associated viral segment of unknown function. These data, confirmed by PCR, are indicative of a novel RNA virus that we term Matryoshka RNA virus 1 (MaRNAV-1) to reflect its analogy to a "Russian doll": a virus, infecting a parasite, infecting an animal. Additional screening revealed that MaRNAV-1 was abundant in geographically diverse P. vivax derived from humans and mosquitoes, strongly supporting its association with this parasite, and not in any of the other Plasmodium samples analyzed here nor Anopheles mosquitoes in the absence of Plasmodium. Notably, related bi-segmented narnavirus-like sequences (MaRNAV-2) were retrieved from Australian birds infected with a Leucocytozoon—a genus of eukaryotic parasites that group with Plasmodium in the Apicomplexa subclass hematozoa. Together, these data support the establishment of two new phylogenetically divergent and genomically distinct viral species associated with protists, including the first virus likely infecting Plasmodium parasites. As well as broadening our understanding of the diversity and evolutionary history of the eukaryotic virosphere, the restriction to P. vivax may be of importance in understanding P. vivax-specific biology in humans and mosquitoes, and how viral co-infection might alter host responses at each stage of the P. vivax life-cycle.

While parasites are a major cause of human disease, they can themselves be infected by viruses. We asked whether three of the major malaria-causing parasites in humans—Plasmodium vivax, P. falciparum and P. knowlesi—were also infected by viruses. To this end we performed total RNA-Sequencing (“meta-transcriptomics”) on human blood samples infected with these Plasmodium species. This resulted in the discovery of an abundant bi-segmented virus—Matryoshka RNA virus 1 (MaRNAV-1)—in all P. vivax samples tested (but no other Plasmodium species) that contains a replicase segment related to those of narnaviruses, arguably the simplest type of RNA viruses discovered to date. By screening for MaRNAV-1 in a larger set of Plasmodium species we revealed a strong specificity between this virus and P. vivax, as well as the presence of a related virus—MaRNAV-2—in avian Leucocytozoon hematozoa parasites. This is the first discovery of a Plasmodium-associated virus and will assist in revealing the deep evolutionary history of RNA viruses and our understanding of Plasmodium biology and disease processes.

Protective or Detrimental? Understanding the Role of Host Immunity in Leishmaniasis

The intracellular protozoan parasites of the genus Leishmania are the causative agents of leishmaniasis, a vector-borne disease of major public health concern, estimated to affect 12 million people worldwide. The clinical manifestations of leishmaniasis are highly variable and can range from self-healing localized cutaneous lesions to life-threatening disseminated visceral disease. Once introduced into the skin by infected sandflies, Leishmania parasites interact with a variety of immune cells, such as neutrophils, monocytes, dendritic cells (DCs), and macrophages. The resolution of infection requires a finely tuned interplay between innate and adaptive immune cells, culminating with the activation of microbicidal functions and parasite clearance within host cells. However, several factors derived from the host, insect vector, and Leishmania spp., including the presence of a double-stranded RNA virus (LRV), can modulate the host immunity and influence the disease outcome. In this review, we discuss the immune mechanisms underlying the main forms of leishmaniasis, some of the factors involved with the establishment of infection and disease severity, and potential approaches for vaccine and drug development focused on host immunity.

Diversity and distribution of Maize-associated totivirus strains from Tanzania

Typically associated with fungal species, members of the viral family Totiviridae have recently been shown to be associated with plants, including important crop species, such as Carica papaya (papaya) and Zea mays (maize). Maize-associated totivirus (MATV) was first described in China and more recently in Ecuador, where it has been found to co-occur with other viruses known to elicit maize lethal necrosis disease (MLND). In a survey for maize-associated viruses, 35 samples were selected for Illumina HiSeq sequencing, from the Tanzanian maize producing regions of Mara, Arusha, Manyara, Kilimanjaro, Morogoro and Pwani. Libraries were prepared using an RNA-tag-seq methodology. Taxonomic classification of the resulting datasets showed that 6 of the 35 samples from the regions of Arusha, Kilimanjaro, Morogoro and Mara, contained reads that were assigned to MATV reference sequences. This was confirmed with PCR and Sanger sequencing. Read assembly of the six MATV-associated datasets yielded partial MATV genomes, two of which were selected for further characterization, using RACE. This yielded two full-length MATV genomes, one of which is divergent from other available MATV genomes.