Identification of Microsporidia causing human disease

Adaptation to genome decay in the structure of the smallest eukaryotic ribosome

The evolution of microbial parasites involves the counterplay between natural selection forcing parasites to improve and genetic drifts forcing parasites to lose genes and accumulate deleterious mutations. Here, to understand how this counterplay occurs at the scale of individual macromolecules, we describe cryo-EM structure of ribosomes from Encephalitozoon cuniculi, a eukaryote with one of the smallest genomes in nature. The extreme rRNA reduction in E. cuniculi ribosomes is accompanied with unparalleled structural changes, such as the evolution of previously unknown molten rRNA linkers and bulgeless rRNA. Furthermore, E. cuniculi ribosomes withstand the loss of rRNA and protein segments by evolving an ability to use small molecules as structural mimics of degenerated rRNA and protein segments. Overall, we show that the molecular structures long viewed as reduced, degenerated, and suffering from debilitating mutations possess an array of compensatory mechanisms that allow them to remain active despite the extreme molecular reduction.

Many parasitic organisms contain molecular structures that are drastically smaller than analogous structures in non-parasitic organisms. Here the authors describe a cryo-EM structure of the ribosome from E. cuniculi that reveals that it compensated rRNA truncations by evolving the ability to use small molecules as ribosomal building blocks.

Silver nanoparticles are effective in controlling microsporidia

Many approaches and technologies have been developed as treatments for microsporidian, infections but effective, broad-spectrum, and sustainable therapeutic approaches have not been found. Silver nanoparticles (AgNPs) have antimicrobial activity and are widely used against many different pathogens. AgNPs provide an opportunity to develop formulations that will control microsporidia. In this study, we synthesized AgNPs via a chemical reduction method and evaluated their formation, morphology, and stability using transmission electron microscopy (TEM) and ultraviolet spectroscopy analysis. We verified that AgNPs could disrupt the spore cell membrane and spore germination of microsporidia Nosema bombycis. This resulted in the release of microsporidia nucleic acids, proteins, and respiratory chain enzymes. The anti-microsporidia activity of AgNPs was studied by measuring the silkworm larvae survival rate and spore genome replication after microsporidia infection. AgNPs have anti-microsporidian activity and could be effective components of formulations for treating or preventing microsporidia infection.

Transporter gene acquisition and innovation in the evolution of Microsporidia intracellular parasites

The acquisition of genes by horizontal transfer can impart entirely new biological functions and provide an important route to major evolutionary innovation. Here we have used ancient gene reconstruction and functional assays to investigate the impact of a single horizontally transferred nucleotide transporter into the common ancestor of the Microsporidia, a major radiation of intracellular parasites of animals and humans. We show that this transporter provided early microsporidians with the ability to steal host ATP and to become energy parasites. Gene duplication enabled the diversification of nucleotide transporter function to transport new substrates, including GTP and NAD⁺, and to evolve the proton-energized net import of nucleotides for nucleic acid biosynthesis, growth and replication. These innovations have allowed the loss of pathways for mitochondrial and cytosolic energy generation and nucleotide biosynthesis that are otherwise essential for free-living eukaryotes, resulting in the highly unusual and reduced cells and genomes of contemporary Microsporidia.

Molecular identification of Enterocytozoon bieneusi and Encephalitozoon spp. in immunodeficient patients in Ahvaz, Southwest of Iran

Microsporidia are often considered as an opportunistic infection in patients with impaired immune systems such as transplant recipients and patients with acquired immune deficiency syndrome (AIDS). Due to the increasing prevalence of parasitic infections and immunodeficiency diseases; the aim of the study is to evaluate molecular identification of Enterocytozoon bieneusi and Encephalitozoon spp. in immunodeficient patients in Ahvaz, southwest of Iran. At first, 310 stool samples were collected from patients with immunodeficiency. The specimens were stained by modified trichrome (weber) and were examined microscopically. The extracted DNA samples were evaluated by multiplex/nested PCR method. The products of multiplex/nested PCR were explored by RFLP method using the restriction enzyme of Mnl1. Of 310, 93 samples were suspected positive for microsporidia by the staining. Also, of 310, 88 samples were positive by the multiplex/nested-PCR test that 62 samples were positive for E. bieneusi as well as 26 were detected as Encephalitozoon species that including 3 E. cuniculi, 19 E. intestinalis and 4 E. hellem. Of 62 E. bieneusi, 45, 16 and 1 were detected as genotype D, M and WL11, respectively. Also, Of 3 E. cuniculi, 1 and 2 cases were identified as genotype I and II, respectively. All E. hellem samples were included genotype 1A. Our findings revealed a relatively high prevalence of microsporidia species in immunodeficient patients. The highest risk of this infection is at individuals with impaired immune systems that it can be life-threatening in people with immune system dysfunction. It is essential that the high-risk people should be receiving the information about the risk of direct contact with infected individuals and animals.

Detection of Encephalitozoon spp. from human diarrheal stool and farm soil samples in Korea

Microsporidia are eukaryotic organisms that cause zoonosis and are major opportunistic pathogens in HIV-positive patients. However, there is increasing evidence that these organisms can also cause gastrointestinal and ocular infections in immunocompetent individuals. In Korea, there have been no reports on human infections with microsporidia to date. In the present study, we used real-time PCR and nucleotide sequencing to detect Encephalitozoon intestinalis infection in seven of 139 human diarrheal stool specimens (5%) and Encephalitozoon hellem in three of 34 farm soil samples (8.8%). Genotype analysis of the E. hellem isolates based on the internal transcribed spacer 1 and polar tube protein genes showed that all isolates were genotype 1B. To our knowledge, this is the first report on human E. intestinalis infection in Korea and the first report revealing farm soil samples as a source of E. hellem infection. Because microsporidia are an important public health issue, further large-scale epidemiological studies are warranted.

In vitro growth of the microsporidian Heterosporis saurida in the eel kidney EK-1 cell line

Heterosporis saurida is an intracellular microsporidian that infects lizardfish Saurida undosquamis. Although some attempts have been introduced to clarify microsporidian host-pathogen interactions, development of novel strategies to combat fish diseases is still needed. Here we present an in vitro cultivation model for fish microsporidia based on an eel kidney cell line (EK-1), which is susceptible to infection by H. saurida. Spores were isolated from infected lizardfish and used to inoculate EK-1 cells. H. saurida were propagated in the eel kidney EK-1 cell line and detected by immunofluorescence. Developmental stages of H. saurida were seen in EK-1 cells by transmission electron microscopy. Identity of the parasite was confirmed by partial sequencing of the 16S rDNA gene. Our cell culture model provides a valuable means to explore molecular and immunological events and will facilitate development of effective treatment strategies.

Animal cell cultures in microsporidial research: their general roles and their specific use for fish microsporidia

The use of animal cell cultures as tools for studying the microsporidia of insects and mammals is briefly reviewed, along with an in depth review of the literature on using fish cell cultures to study the microsporidia of fish. Fish cell cultures have been used less often but have had some success. Very short-term primary cultures have been used to show how microsporidia spores can modulate the activities of phagocytes. The most successful microsporidia/fish cell culture system has been relatively long-term primary cultures of salmonid leukocytes for culturing Nucleospora salmonis. Surprisingly, this system can also support the development of Enterocytozoon bienusi, which is of mammalian origin. Some modest success has been achieved in growing Pseudoloma neurophilia on several different fish cell lines. The eel cell line, EP-1, appears to be the only published example of any fish cell line being permanently infected with microsporidia, in this case Heterosporis anguillarum. These cell culture approaches promise to be valuable in understanding and treating microsporidia infections in fish, which are increasingly of economic importance.

A novel route for ATP acquisition by the remnant mitochondria of Encephalitozoon cuniculi

Mitochondria use transport proteins of the eukaryotic mitochondrial carrier family (MCF) to mediate the exchange of diverse substrates, including ATP, with the host cell cytosol. According to classical endosymbiosis theory, insertion of a host-nuclear-encoded MCF transporter into the protomitochondrion was the key step that allowed the host cell to harvest ATP from the enslaved endosymbiont. Notably the genome of the microsporidian Encephalitozoon cuniculi has lost all of its genes for MCF proteins. This raises the question of how the recently discovered microsporidian remnant mitochondrion, called a mitosome, acquires ATP to support protein import and other predicted ATP-dependent activities. The E. cuniculi genome does contain four genes for an unrelated type of nucleotide transporter used by plastids and bacterial intracellular parasites, such as Rickettsia and Chlamydia, to import ATP from the cytosol of their eukaryotic host cells. The inference is that E. cuniculi also uses these proteins to steal ATP from its eukaryotic host to sustain its lifestyle as an obligate intracellular parasite. Here we show that, consistent with this hypothesis, all four E. cuniculi transporters can transport ATP, and three of them are expressed on the surface of the parasite when it is living inside host cells. The fourth transporter co-locates with mitochondrial Hsp70 to the E. cuniculi mitosome. Thus, uniquely among eukaryotes, the traditional relationship between mitochondrion and host has been subverted in E. cuniculi, by reductive evolution and analogous gene replacement. Instead of the mitosome providing the parasite cytosol with ATP, the parasite cytosol now seems to provide ATP for the organelle.

First detection and genotyping of human-associated microsporidia in pigeons from urban parks

Microsporidia are ubiquitous opportunistic parasites in nature infecting all animal phyla, and the zoonotic potential of this parasitosis is under discussion. Fecal samples from 124 pigeons from seven parks of Murcia (Spain) were analyzed. Thirty-six of them (29.0%) showed structures compatible with microsporidia spores by staining methods. The DNA isolated from 26 fecal samples (20.9%) of microsporidia-positive pigeons was amplified with specific primers for the four most frequent human microsporidia. Twelve pigeons were positive for only Enterocytozoon bieneusi (9.7%), 5 for Encephalitozoon intestinalis (4%), and one for Encephalitozoon hellem (0.8%). Coinfections were detected in eight additional pigeons: E. bieneusi and E. hellem were detected in six animals (4.8%); E. bieneusi was associated with E. intestinalis in one case (0.8%); and E. hellem and E. intestinalis coexisted in one pigeon. No positive samples for Encephalitozoon cuniculi were detected. The internally transcribed spacer genotype could be completed for one E. hellem-positive pigeon; the result was identical to the genotype A1 previously characterized in an E. hellem Spanish strain of human origin. To our knowledge, this is the first time that human-related microsporidia have been identified in urban park pigeons. Moreover, we can conclude that there is no barrier to microsporidia transmission between park pigeons and humans for E. intestinalis and E. hellem. This study is of environmental and sanitary interest, because children and elderly people constitute the main visitors of parks and they are populations at risk for microsporidiosis. It should also contribute to the better design of appropriate prophylactic measures for populations at risk for opportunistic infections.

Zoonotic potential of the microsporidia

Microsporidia are long-known parasitic organisms of almost every animal group, including invertebrates and vertebrates. Microsporidia emerged as important opportunistic pathogens in humans when AIDS became pandemic and, more recently, have also increasingly been detected in otherwise immunocompromised patients, including organ transplant recipients, and in immunocompetent persons with corneal infection or diarrhea. Two species causing rare infections in humans, Encephalitozoon cuniculi and Brachiola vesicularum, had previously been described from animal hosts (vertebrates and insects, respectively). However, several new microsporidial species, including Enterocytozoon bieneusi, the most prevalent human microsporidian causing human immunodeficiency virus-associated diarrhea, have been discovered in humans, raising the question of their natural origin. Vertebrate hosts are now identified for all four major microsporidial species infecting humans (E. bieneusi and the three Encephalitozoon spp.), implying a zoonotic nature of these parasites. Molecular studies have identified phenotypic and/or genetic variability within these species, indicating that they are not uniform, and have allowed the question of their zoonotic potential to be addressed. The focus of this review is the zoonotic potential of the various microsporidia and a brief update on other microsporidia which have no known host or an invertebrate host and which cause rare infections in humans.

Trachipleistophora hominis infection in the myocardium and skeletal muscle of a patient with AIDS

OBJECTIVES

To review the literature relevant to microsporidial infection of muscle and to describe a case of human microsporidial infection involving both skeletal and cardiac muscle.

METHODS

Samples from an AIDS patient with myositis have been examined by light and electron microscopy.

RESULTS

We describe the findings at autopsy of a 47 year old Australian male with late stage AIDS, who had skeletal and cardiac muscle involvement with the microsporidian Trachipleistophora hominis. This is the third definitively identified case of human T. hominis infection and the first to describe infection of the myocardium.

CONCLUSIONS

Microsporidial infection of muscle is rare in humans, but more work is needed to elucidate both the organisms and routes of transmission of this group of parasitic protozoa.

Intraspecies genotype variability of the microsporidian parasite Encephalitozoon hellem

Seven isolates of Encephalitozoon hellem from human immunodeficiency virus-positive patients were genotyped through a series of markers: the internal transcribed spacer (ITS) of ribosomal DNA, the polar tube protein (PTP) gene, and two intergenic spacers (IGS-TH and IGS-HZ) whose polymorphism is newly reported. The genome markers were all analyzed at three levels: PCR amplification followed by polyacrylamide gel electrophoresis, single-strand conformation analysis (SSCA), and DNA sequencing. The polymorphisms detected involve insertions/deletions and point mutations. SSCA can distinguish any pair of sequences, even those differing by a single base pair. The different isolates studied fit into the previously described ITS genotype 1A, except one which seems to be a 2A derivative variant (2D). When PTP and the new markers IGS-TH and IGS-HZ were analyzed, most of the isolates displayed different genotypes, demonstrating that E. hellem has a strong intraspecies variability. A set of markers such as those used here may be very useful in genotyping of clinical samples and in the assessment of epidemiological relationships among E. hellem strains.

Development of an immunomagnetic separation-polymerase chain reaction (IMS-PCR) assay specific for Enterocytozoon bieneusi in water samples

AIMS

Microsporidia have become widely recognized as important human pathogens. Among Microsporidia, Enterocytozoon bieneusi is responsible for severe gastrointestinal disease. To date, no current therapy has been proven effective. Their mode of transmission and environmental occurrence are poorly documented because of the lack of detection methods that are both species-specific and sensitive. In this study, we developed a sensitive and specific molecular method to detect E. bieneusi spores in water samples.

METHODS AND RESULTS

The molecular assay combined immunomagnetic separation (IMS) and polymerase chain reaction (PCR) amplification to detect E. bieneusi spores. A comparison was made of IMS magnetic beads coated with two different monoclonal antibodies, one specific for the Encephalitozoon genus that cross-reacts with E. bieneusi and the other specific only for the E. bieneusi species itself.

CONCLUSIONS

Immunotech beads coated with the antibody specific for E. bieneusi were found to be the most effective combination.

SIGNIFICANCE AND IMPACT OF THE STUDY

The highly specific IMS-PCR assay developed in this study provides a rapid and sensitive means of screening water samples for the presence of E. bieneusi spores.

Inter-strain variability of insertion/deletion events in the Encephalitozoon cuniculi genome: a comparative KARD-PFGE analysis

We applied a two-dimensional pulsed-field gel electrophoresis procedure to the genomes of two karyotype variants assigned to two different strains of the microsporidian Encephalitozoon cuniculi, termed D (strain III) and F (strain II). Data obtained for BssHII and MluI restriction fragment length polymorphisms in each chromosome are compiled and compared to the reference strain I variant A. Six Insertion/Deletion (InDels) are found in subterminal position, some of these being characteristic of either D or F. Like in strain 1, the terminal fragments extending between each telomere and rDNA locus are conserved in length for each chromosome. They are however smaller than in reference variant. This size reduction is estimated to be 2.5 kbp for the strain III isolate and 3.5 kbp for the strain II isolate. We hypothesize that for the three E. cuniculi strains, all chromosome extremities are prone to a constant process of sequence homogenization through mitotic recombination between conserved regions.

Microsporidia: emerging advances in understanding the basic biology of these unique organisms

Microsporidia are long-known parasites of a wide variety of invertebrate and vertebrate hosts. The emergence of these obligate intracellular organisms as important opportunistic pathogens during the AIDS pandemic and the discovery of new species in humans renewed interest in this unique group of organisms. This review summarises recent advances in the field of molecular biology of microsporidia which (i) contributed to the understanding of the natural origin of human-infecting microsporidia, (ii) revealed unique genetic features of their dramatically reduced genome and (iii) resulted in the correction of their phylogenetic placement among eukaryotes from primitive protozoans to highly evolved organisms related to fungi. Microsporidia might serve as new intracellular model organisms in the future given that gene transfer systems will be developed.

Cryptosporidia and microsporidia--waterborne diseases in the immunocompromised host

Cryptosporidia and microsporidia are emerging parasitic pathogens in immunocompetent and immunocompromised individuals. Cryptosporidium infects several wild and domestic animals that excrete oocysts into the environment and contaminated water represents the major source of infection for humans. Waterborne transmission of Cryptosporidium is a major risk for humans and appropriate measures have to be taken to protect immunocompetent and immunocompromised individuals to become infected. For microsporidia, the sources and ways of transmission are not well documented. Although several animal hosts have been identified recently, the relevant reservoirs of human microsporidia are still unknown. Also, the routes of spreading are unknown. Is microsporidiosis a zoonotic disease that will be transmitted through close contact with infected animals or is contaminated surface water responsible for transmission and represents a relevant reservoir? This review is designed to give information on these two emerging intestinal parasites in a format that will be useful to clinical microbiologists, physicians interested in infectious diseases, and public health personnel.

Evidence of actin in the cytoskeleton of microsporidia

Using transmission electron microscopy, immuno-electron microscopy, and biochemical techniques such as 2-D electrophoresis and immunoblotting, actin was found in all biological stages of the microsporidia Encephalitozoon hellem and Encephalitozoon cuniculi.

Molecular techniques for detection, species differentiation, and phylogenetic analysis of microsporidia

Microsporidia are obligate intracellular protozoan parasites that infect a broad range of vertebrates and invertebrates. These parasites are now recognized as one of the most common pathogens in human immunodeficiency virus-infected patients. For most patients with infectious diseases, microbiological isolation and identification techniques offer the most rapid and specific determination of the etiologic agent. This is not a suitable procedure for microsporidia, which are obligate intracellular parasites requiring cell culture systems for growth. Therefore, the diagnosis of microsporidiosis currently depends on morphological demonstration of the organisms themselves. Although the diagnosis of microsporidiosis and identification of microsporidia by light microscopy have greatly improved during the last few years, species differentiation by these techniques is usually impossible and transmission electron microscopy may be necessary. Immunfluorescent-staining techniques have been developed for species differentiation of microsporidia, but the antibodies used in these procedures are available only at research laboratories at present. During the last 10 years, the detection of infectious disease agents has begun to include the use of nucleic acid-based technologies. Diagnosis of infection caused by parasitic organisms is the last field of clinical microbiology to incorporate these techniques and molecular techniques (e.g., PCR and hybridization assays) have recently been developed for the detection, species differentiation, and phylogenetic analysis of microsporidia. In this paper we review human microsporidial infections and describe and discuss these newly developed molecular techniques.

Evaluation of methodologies including immunofluorescent assay (IFA) and the polymerase chain reaction (PCR) for detection of human pathogenic microsporidia in water

Microsporidia is a term used to describe a group of emerging protozoan pathogens whose environmental occurrence has only recently been documented due to lack of detection methodologies. This study evaluates and describes current methods for detection of microsporidia in water. Standard methods, for the collection and processing of large volumes of water to detect protozoa, showed only a 4.8% recovery, of microsporidia spores, from 100 l volumes of tap. Immunofluorescent assay (IFA) analysis was assessed using two different antibodies specific for human pathogenic microsporidia. Results indicated that the use of IFA for routine screening of water for microsporidia was not an acceptable approach. The antibodies tested for the IFA resulted in false positives and false negatives and did not react with Enterocytozoon bieneusi, which is an important human pathogenic microsporidia. Finally, the small sizes of the human pathogenic microsporidia prevent confirmation and species determination by light microscopic methods. Two methods for isolating microsporidia DNA from water for use in polymerase chain reaction (PCR) amplification of microsporidia target sequences were assessed. Both of these DNA isolation methods when combined with the PCR showed the ability to detect less than ten spores in purified water concentrates. Thus, this study represents the first documentation and evaluation of current methods for the detection of human pathogenic microsporidia in water.

Determination of types of Enterocytozoon bieneusi strains isolated from patients with intestinal microsporidiosis

To determine the types of Enterocytozoon bieneusi strains associated with intestinal microsporidiosis, we developed a rapid and efficient approach for typing parasites obtained from stool specimens by PCR-restriction fragment length polymorphism (PCR-RFLP). Typing was based on DNA polymorphism of the ribosomal DNA internal transcribed spacer (ITS) region of E. bieneusi. RFLPs generated with two restriction enzymes (NlaIII and Fnu4HI) in PCR-amplified ITS products were used to classify strains into different lineages. This approach was successfully used to differentiate 78 strains that had been obtained from the stools of 65 patients with intestinal microsporidiosis. Among the 78 strains, we found four genetically unrelated lineages, showing the genetic diversity of E. bieneusi. Type I strains of E. bieneusi were found in a majority of the samples, accounting for 51 (78%) of the 65 microsporidiosis cases. In contrast, type II, III, and IV strains were found in only 8 (12%), 3 (5%), and 3 (5%) cases, respectively. All strains of E. bieneusi we have tested so far fall into one of four different lineages, and this study shows that human intestinal microsporidiosis is most often associated with type I strains. PCR-RFLP analysis of the ITS region of E. bieneusi should be useful for epidemiological studies.

Mechanisms of microsporidial cell division: ultrastructural study on Encephalitozoon hellem

The mitotic process in microsporidian Encephalitozoon hellem, a known human pathogen, has been studied with the aim of elucidating some ultrastructural aspects of its nuclear division. The presence of a nuclear spindle, of "electrondense spindle plaques" associated with the nuclear envelope and of cytoplasmic double walled vesicles are reported. We suggest that these "electrondense spindle plaques" serve as foci for intranuclear and cytoplasmic microtubule arrangements, similar to the microtubule organizing centers within the centrosomes of animal cells. The extent to which the microsporidial division process is comparable with that of more familiar eukaryotes such as yeast cells is discussed.