Interactions of Cryptosporidium parvum, Giardia lamblia, vaccinal poliovirus type 1, and bacteriophages phiX174 and MS2 with a drinking water biofilm and a wastewater biofilm

Biofilms colonizing surfaces inside drinking water distribution networks may provide a habitat and shelter to pathogenic viruses and parasites. If released from biofilms, these pathogens may disseminate in the water distribution system and cause waterborne diseases. Our study aimed to investigate the interactions of protozoan parasites (Cryptosporidium parvum and Giardia lamblia [oo]cysts) and viruses (vaccinal poliovirus type 1, phiX174, and MS2) with two contrasting biofilms. First, attachment, persistence, and detachment of the protozoan parasites and the viruses were assessed with a drinking water biofilm. This biofilm was allowed to develop inside a rotating annular reactor fed with tap water for 7 months prior to the inoculation. Our results show that viable parasites and infectious viruses attached to the drinking water biofilm within 1 h and persisted within the biofilm. Indeed, infectious viruses were detected in the drinking water biofilm up to 6 days after the inoculation, while viral genome and viable parasites were still detected at day 34, corresponding to the last day of the monitoring period. Since viral genome was detected much longer than infectious particles, our results raise the question of the significance of detecting viral genomes in biofilms. A transfer of viable parasites and viruses from the biofilm to the water phase was observed after the flow velocity was increased but also with a constant laminar flow rate. Similar results regarding parasite and virus attachment and detachment were obtained using a treated wastewater biofilm, suggesting that our observations might be extrapolated to a wide range of environmental biofilms and confirming that biofilms can be considered a potential secondary source of contamination.     

Survival of protozoan intracellular parasites in host cells

The most common human diseases are caused by pathogens. Several of these microorganisms have developed efficient ways in which to exploit host molecules, along with molecular pathways to ensure their survival, differentiation and replication in host cells. Although the contribution of the host cell to the development of many intracellular pathogens (particularly viruses and bacteria) has been unequivocally established, the study of host-cell requirements during the life cycle of protozoan parasites is still in its infancy. In this review, we aim to provide some insight into the manipulation of the host cell by parasites through discussing the hurdles that are faced by the latter during infection.     

昆虫抗菌肽基因工程研究进展

昆虫抗菌肽对细菌、真菌、病毒和原虫都具有杀灭作用 ,甚至对肿瘤细胞也具有杀伤作用。昆虫抗菌肽并且有独特的作用机制 ,成为众多表达系统外源导入基因的侯选对象之一 ,综述了昆虫抗菌肽的种类及其在微生物转基因工程和植物转基因工程中的进展。     

Nitric oxide: an antiparasitic molecule of invertebrates

Since Furchgott, Ignarro and Murad won the Nobel prize in 1998 for their work on the role of nitric oxide (NO) as a signaling molecule, many reports have shown the seemingly limitless range of body functions controlled by this compound. In vertebrates, the role of NO as a defense against infection caused by viruses, bacteria, and protozoan and metazoan parasites has been known for several years. New evidence, however, shows that NO is also important in defending invertebrates against parasites. This discovery is a breakthrough in the understanding of how the invertebrate immune system works, and it has implications for the emerging field of invertebrate ecological immunology.     

Role of gregarine parasite Ascogregarina culicis (Apicomplexa: Lecudinidae) in the maintenance of Chikungunya virus in vector mosquito

Ascogregarina culicis and Ascogregarina taiwanensis are common gregarine parasites of Aedes aegypti and Aedes albopictus mosquitoes, respectively. These mosquito species are also known to transmit dengue and Chikungunya viruses. The sporozoites of these parasites invade the midgut epithelial cells and develop intracellularly and extracellularly in the gut to complete their life cycles. The midgut is also the primary site for virus replication in the vector mosquitoes. Therefore, studies were carried out with a view to determine the possible role of these gregarines in the vertical transmission of dengue and Chikungunya viruses from larval to adult stage. Experiments were performed by exposing first instar mosquito larvae to suspensions containing parasite oocysts and viruses. Since Ascogregarina sporozoites invade the midgut of first instar larvae, the vertical transmission was determined by feeding the uninfected first instar larvae on the freshly prepared homogenates from mosquitoes, which were dually infected with viruses and the parasite oocysts. Similarly, the role of protozoan parasites in the vertical transmission of viruses was determined by exposing fresh first instar larvae to the dried pellets of homogenates prepared from the mosquitoes dually infected with viruses and the parasite oocysts. Direct vertical transmission and the vertical transmission of CHIK virus through the oocyst of the parasites were observed in the case of Ae. aegypti mosquitoes. It is suggested that As. culicis may have an important role in the maintenance of CHIK virus during the inter-epidemic period.     

Endobiont Viruses Sensed by the Human Host – Beyond Conventional Antiparasitic Therapy

Wide-spread protozoan parasites carry endosymbiotic dsRNA viruses with uncharted implications to the human host. Among them, Trichomonas vaginalis, a parasite adapted to the human genitourinary tract, infects globally ∼250 million each year rendering them more susceptible to devastating pregnancy complications (especially preterm birth), HIV infection and HPV-related cancer. While first-line antibiotic treatment (metronidazole) commonly kills the protozoan pathogen, it fails to improve reproductive outcome. We show that endosymbiotic Trichomonasvirus, highly prevalent in T. vaginalis clinical isolates, is sensed by the human epithelial cells via Toll-like receptor 3, triggering Interferon Regulating Factor -3, interferon type I and proinflammatory cascades previously implicated in preterm birth and HIV-1 susceptibility. Metronidazole treatment amplified these proinflammatory responses. Thus, a new paradigm targeting the protozoan viruses along with the protozoan host may prevent trichomoniasis-attributable inflammatory sequelae.     

Genomes and genome projects of protozoan parasites

Protozoan parasites are causing some of the most devastating diseases world-wide. It has now been recognised that a major effort is needed to be able to control or eliminate these diseases. Genome projects for the most important protozoan parasites have been initiated in the hope that the read-out of these projects will help to understand the biology of the parasites and identify new targets for urgently needed drugs. Here, I will review the current status of protozoan parasite genome projects, present findings obtained as a result of the availability of genomic data and discuss the potential impact of genome information on disease control.     

Transgenic mice and the study of cytokine function in infection

Most information about the involvement of the different cytokines in immunity to infection has been obtained by the administration to infected animals of recombinant molecules or of antibodies against them. Now another approach to the study of cytokine function, in vivo, is available in the form of transgenic mice that express a transgene encoding a particular cytokine, and of 'knockout' animals, in which a cytokine gene, or a gene for its receptor (which usually comes to the same thing), have been rendered inactive by targeted disruption. While a few of these lines of mice have been analysed for their response to infection by protozoan parasites or worms, more have been tested for their ability to withstand intracellular infections by bacteria or viruses. In this review, Janice Taverne outlines those described to date in which the immune (or immunopathological mechanisms concerned may be relevant to parasitic diseases.     

Naturally occurring antibodies that react with protozoan parasites

In this paper, Eiji Konishi reviews general features of naturally occurring (natural) antibodies that react with protozoan parasites. Several functions of natural antibodies have been identified in relation to their multireactivity, but reports on protozoan infection have dealt mainly with the role of natural antibodies in the innate immunity of the host, These antibodies lyse cells in the presence of complement and have opsonizing activity, in vitro. Studies of their origin have shown the possibilities of (1) continuous polyclonal stimulation by gastrointestinal bacteria, and (2) there being multireactive antibodies secreted by CD5(+) B cells. The protective functions of natural antibodies are important in the interpretation of the host range, the mode of infection, and the course of the disease of certain protozoan parasites.     

Protozoan parasites: programmed cell death as a mechanism of parasitism

Programmed cell death (PCD) is a potent mechanism to remove parasitized cells, but it has also been shown that protozoan parasites can induce or inhibit apoptosis in host cells. In recent years, it has become clear that unicellular parasites can also undergo PCD, meaning that they commit suicide in response to various stimuli. This review focuses on the role of protozoan PCD and on the interaction between protozoan parasites and the host cell death machinery from the perspective of parasite survival strategies.     

Cytoplasmic polyhedrosis viruses in Phlebotomus papatasi inhibit development of Leishmania major

Cytoplasmic polyhedrosis viruses (CPV's) were observed in wild-caught and laboratory-reared Phlebotomus papatasi. Chronic CPV pathology of the midgut, characterized by structural aberrations in the epithelium and the peritrophic membrane, interfered with blood digestion and rendered the sand flies refractory to Leishmania major infections. Rates of natural and artificial L. major infections were inversely correlated to the incidence of CPV infections. The interaction between viruses and protozoan parasites in an insect host is of basic biological interest and in this case may be of significance in the epidemiology of cutaneous leishmaniasis.     

Indirect interactions in the microbial world: specificities and similarities to plant–insect systems

Trophic interactions between bacteria, viruses, and protozoan predators play crucial roles in structuring aquatic microbial communities and regulating microbe-mediated ecosystem functions (biogeochemical processes). In this microbial food web, protozoan predators and viruses share bacteria as a common resource, and protozoan predators can kill viruses [intraguild predation (IGP)] and vice versa, even though these latter processes are probably of less importance. However, protozoan predators (IG predator) and viruses (IG prey) generally occur together in various environments, and this cannot be fully explained by the classic IGP models. In addition, controlled experiments have often demonstrated that protozoan predators have apparently positive effects on viral activity. These surprising patterns can be explained by indirect interactions between them via induced trait changes in bacterial assemblages, which can be compared with trait-mediated indirect interactions (TMIIs) in terrestrial plant–insect systems. Here, we review some trait changes in bacterial assemblages that may positively affect the activities and abundance of viruses. It has been suggested that in bacterial assemblages, protozoan predation may enhance growth conditions for individual bacteria and induce both phenotypic trait changes at the individual (e.g., filament-forming bacteria) and group level as a result of changes in bacterial community composition (e.g., species dominance). We discuss the specificities of aquatic microbial systems and attempt find functional similarities between aquatic microbial systems and terrestrial plant–insect systems with regard to TMII function.     

What can GPI do for you?

Various functions for glycosylphosphatidylinositol (GPI) protein anchors have been described in mammalian and protozoan systems. These data suggest that some functions are common to higher and lower eukaryotes, whereas others may represent adaptations that are specifically advantageous to either unicellular or metazoan organisms. In this article, Mike Ferguson discusses the current theories of GPI function that have relevance to protozoan parasites and their mammalian hosts.     

Parasites, people and policy: infectious diseases and the Millennium Development Goals

Here, I briefly review past history and present patterns in the interactions between parasites (defined broadly to include viruses and bacteria along with protozoan, helminth and arthropod parasites) and human populations in developed and developing countries. Against this background, I offer thoughts on current public health initiatives at national and international levels, with particular reference to the Millennium Development Goals. The news is both good and bad: mortality and morbidity from infectious diseases in the developing world are significantly lower than they were 50 years ago, but we should and could be doing better, particularly in relation to neglected tropical diseases.     

An enzyme-release assay for the assessment of the lytic activities of complement or antimicrobial peptides on extracellular Toxoplasma gondii

A method is described which allows the evaluation of the membrane lytic activity of either complement or antimicrobial peptides against the extracellular stage of the human protozoan parasite Toxoplasma gondii. The assay is based on lacZ transgenic parasites, determining the activity of released cytoplasmic beta-galactosidase into the culture supernatant upon membrane disintegration. This method was used to evaluate the lytic activities of (i) complement which is a natural defense mechanism in infected hosts against extracellular parasites, and (ii) antimicrobial peptides which have not been evaluated against T. gondii before. The results show that the assay provides a simple and convenient way to assess the membrane lytic activity of such compounds and that T. gondii, like other protozoan parasites, is vulnerable to the membrane-lytic effect of antimicrobial peptides.     

Protozoan parasite-specific carbohydrate structures

The carbohydrate moieties displayed by pathogenic protozoan parasites exhibit many unusual structural features and their expression is often developmentally regulated. These unique structures suggest a specific relationship between such carbohydrates and parasite pathogenicity. Studies of infected humans indicate that immune responses to protozoan parasites are elicited by glycan determinants on cell-surface or secreted molecules. Infections by protozoa are a major worldwide health problem, and no vaccines or efficacious treatments exist to date. Recent progress has been made in elucidating the structure and function of carbohydrates displayed by major protozoan parasites that infect man. These structures can be used as prototypes for the chemical or combined chemo-enzymatic synthesis of new compounds for diagnosis and vaccine development, or as inhibitors specifically designed to target parasite glycan biosynthesis.     

The roles of intramembrane proteases in protozoan parasites

Intramembrane proteolysis is widely conserved throughout different forms of life, with three major types of proteases being known for their ability to cleave peptide bonds directly within the transmembrane domains of their substrates. Although intramembrane proteases have been extensively studied in humans and model organisms, they have only more recently been investigated in protozoan parasites, where they turn out to play important and sometimes unexpected roles. Signal peptide peptidases are involved in endoplasmic reticulum (ER) quality control and signal peptide degradation from exported proteins. Recent studies suggest that repurposing inhibitors developed for blocking presenilins may be useful for inhibiting the growth of Plasmodium, and possibly other protozoan parasites, by blocking signal peptide peptidases. Rhomboid proteases, originally described in the fly, are also widespread in parasites, and are especially expanded in apicomplexans. Their study in parasites has revealed novel roles that expand our understanding of how these proteases function. Within this diverse group of parasites, rhomboid proteases contribute to processing of adhesins involved in attachment, invasion, intracellular replication, phagocytosis, and immune evasion, placing them at the vertex of host–parasite interactions. This article is part of a Special Issue entitled: Intramembrane Proteases.     

Parasites and phytoplankton, with special emphasis on dinoflagellate infections

Planktonic members of most algal groups are known to harbor intracellular symbionts, including viruses, bacteria, fungi, and protozoa. Among the dinoflagellates, viral and bacterial associations were recognized a quarter century ago, yet their impact on host populations remains largely unresolved. By contrast, fungal and protozoan infections of dinoflagellates are well documented and generally viewed as playing major roles in host population dynamics. Our understanding of fungal parasites is largely based on studies for freshwater diatoms and dinoflagellates, although fungal infections are known for some marine phytoplankton. In freshwater systems, fungal chytrids have been linked to mass mortalities of host organisms, suppression or retardation of phytoplankton blooms, and selective effects on species composition leading to successional changes in plankton communities. Parasitic dinoflagellates of the genus Amoebophrya and the newly described Perkinsozoa, Parvilucifera infectans, are widely distributed in coastal waters of the world where they commonly infect photosynthetic and heterotrophic dinoflagellates. Recent work indicates that these parasites can have significant impacts on host physiology, behavior, and bloom dynamics. Thus, parasitism needs to be carefully considered in developing concepts about plankton dynamics and the flow of material in marine food webs.