Phylogenetic relationships of Pleistophora-like microsporidia based on small subunit ribosomal DNA sequences and implications for the source of trachipleistophora hominis infections

Mass mortality event of round sardinella Sardinella aurita Valenciennes associated with Glugea Thélohan, 1891 microsporidian infection off the southern Italian coast

Intracellular parasites of the genus Glugea Thélohan, 1891 (Microsporidia) comprise about 34 putative species capable of causing high morbidity and mortality in freshwater and marine teleost fishes. In this study, we report on the first mass mortality event associated with Glugea sp. infecting free-ranging round sardinella Sardinella aurita in the southern Tyrrhenian Sea (Italy). Here, we describe the ultrastructure of mature spores of this microsporidian and characterize it molecularly, as well as report its phylogenetic position. Most of the affected fish showed an irregular swelling of its abdomen. At necropsy, a variable number of xenomas, spherical to ellipsoidal in shape, were found in the peritoneal cavity strongly attached to the viscera of all fish. Histological analysis revealed varying severity of chronic inflammation along with occasional necrosis in visceral organs associated with multiple xenoma proliferation. These pathological findings were considered the main cause of this mass mortality event. Morphologically, the present material was closely related to G. sardinellesis and G. thunni. The phylogenetically closest taxa to the newly SSU rDNA sequence were G. thunni and an erroneusly identified  G. plecoglossi, which were very closely related to each other, also suggesting that all these sequences might belong to the same species.

Cambaraspora faxoni n. sp. (Microsporidia: Glugeida) from native and invasive crayfish in the USA and a novel host of Cambaraspora floridanus

Crayfishes are among the most widely introduced freshwater taxa and can have extensive ecological impacts. Knowledge of the parasites crayfish harbor is limited, yet co-invasion of parasites is a significant risk associated with invasions. In this study, we describe a novel microsporidium, Cambaraspora faxoni n. sp. (Glugeida: Tuzetiidae), from two crayfish hosts in the Midwest USA, Faxonius virilis and Faxonius rusticus. We also expand the known host range of Cambaraspora floridanus to include Procambarus spiculifer. Cambaraspora faxoni infects muscle and heart tissue of F. rusticus and develops within a sporophorous vesicle. The mature spore measures 3.22 ± 0.14 μm in length and 1.45 ± 0.13 μm in width, with 8-9 turns of the polar filament. SSU sequencing indicates the isolates from F. virilis and F. rusticus were identical (100%) and 93.49% similar to C. floridanus, supporting the erection of a new species within the Cambaraspora genus. The novel parasite was discovered within the native range of F. rusticus (Ohio, USA) and within a native congeneric (F. virilis) in the invasive range of F. rusticus (Wisconsin, USA). Faxonius virilis is invasive in other regions. This new parasite could have been introduced to Wisconsin with F. rusticus or it may be a generalist species with a broad distribution. In either case, this parasite infects two crayfish species that have been widely introduced to new drainages throughout North America and could have future effects on invasion dynamics or impacts.

Intraspecific genetic diversity of the fish-infecting microsporidian parasite Pseudokabatana alburnus (Microsporidia)

Pseudokabatana alburnus is a xenoma-forming fish microsporidium, firstly described from the liver of the Culter alburnus from Poyang Lake in China. In the present study, P. alburnus was firstly reported from the ovary of 6 other East Asian minnows, including Squaliobarbus curriculus, Hemiculter leucisculus, Cultrichthys erythropterus, Pseudolaubuca engraulis, Toxabramis swinhonis, and Elopichthys bambusa. Genetic analysis revealed high sequence diversity in the ribosomal internal transcribed spacer region (ITS) and the largest subunit of RNA polymerase II (Rpb1) loci of P. alburnus isolated from different hosts and locations. The variation of Rpb1 mainly occurred in the 1,477–1737 bp regions. The presence of a wide variety of Rpb1 haplotypes within a single fish host, together with evidence of genetic recombination suggested that P. alburnus may have the intergenomic variation and sexual reproduction might be present in other hosts (possibly freshwater shrimp). Phylogenetic analysis and population genetic analysis showed that there was no geographical population divergence for P. alburnus. Homogeneity and high variability of ITS sequences indicates that ITS may be a suitable molecular marker to distinguish different P. alburnus isolates. Our data confirm the broad geographical distribution and host range of P. alburnus in the middle and lower reaches of the Yangtze River. Additionally, we emendated the genus Pseudokabatana to exclude the infection site, liver as one of the taxonomic criteria, and proposed that fish ovary was be the general infection site of P. alburnus.

Microsporidia Ameson earli sp. n. and A. michaelis (Sprague 1965) infecting blue crabs Callinectes sapidus from shedding facilities in Louisiana

During a survey for pathogens and commensals of blue crabs in commercial soft shell shedding facilities in Louisiana, we discovered an occurrence of microsporidiosis in two of forty examined crabs. Judging from spore shape and size, tissue tropism and external signs of muscle pathology, the causative agent of infections was identified as Ameson michaelis, a muscle-infecting species that has been repeatedly detected in populations of Callinectes sapidus in Louisiana since 1965. However, retrospective ultrastructural examination revealed that in one of Ameson-infected crabs, infection was caused by a parasite with ultrastructural characters not completely compliant with the ones of A. michaelis. The major difference was the absence of microtubule-like appendages attached to the exospore, typical of A. michaelis and other Ameson spp. SSUrDNA-inferred pairwise evolutionary distances between the novel species and other Ameson spp. ranged from 0.006 to 0.051; it was 0.039 in the case of A. michaelis. Hence, we describe here a new species in the genus Ameson, and name it after Prof. Earl Weidner, our colleague and friend, an outstanding microsporidiologist and the author of pioneer papers on the ultrastructure and physiology of A. michaelis.

Microsporidia, a Highly Adaptive Organism and Its Host Expansion to Humans

Emerging infectious disease has become the center of attention since the outbreak of COVID-19. For the coronavirus, bats are suspected to be the origin of the pandemic. Consequently, the spotlight has fallen on zoonotic diseases, and the focus now expands to organisms other than viruses. Microsporidia is a single-cell organism that can infect a wide range of hosts such as insects, mammals, and humans. Its pathogenicity differs among species, and host immunological status plays an important role in infectivity and disease severity. Disseminated disease from microsporidiosis can be fatal, especially among patients with a defective immune system. Recently, there were two Trachipleistophora hominis, a microsporidia species which can survive in insects, case reports in Thailand, one patient had disseminated microsporidiosis. This review gathered data of disseminated microsporidiosis and T. hominis infections in humans covering the biological and clinical aspects. There was a total of 22 cases of disseminated microsporidiosis reports worldwide. Ten microsporidia species were identified. Maximum likelihood tree results showed some possible correlations with zoonotic transmissions. For T. hominis, there are currently eight case reports in humans, seven of which had Human Immunodeficiency Virus (HIV) infection. It is observed that risks are higher for the immunocompromised to acquire such infections, however, future studies should look into the entire life cycle, to identify the route of transmission and establish preventive measures, especially among the high-risk groups.

A severe microsporidian disease in cultured Atlantic Bluefin Tuna (Thunnus thynnus)

One of the most promising aquaculture species is the Atlantic bluefin tuna (Thunnus thynnus) with high market value; disease control is crucial to prevent and reduce mortality and monetary losses. Microsporidia (Fungi) are a potential source of damage to bluefin tuna aquaculture. A new microsporidian species is described from farmed bluefin tunas from the Spanish Mediterranean. This new pathogen is described in a juvenile associated with a highly severe pathology of the visceral cavity. Whitish xenomas from this microsporidian species were mostly located at the caecal mass and ranged from 0.2 to 7.5 mm. Light and transmission electron microscopy of the spores revealed mature spores with an average size of 2.2 × 3.9 μm in size and a polar filament with 13-14 coils arranged in one single layer. Phylogenetic analysis clustered this species with the Glugea spp. clade. The morphological characteristics and molecular comparison confirm that this is a novel microsporidian species, Glugea thunni. The direct life-cycle and the severe pathologies observed makes this parasite a hard risk for bluefin tuna cultures.

Hepatic microsporidiosis of mudskipper, Boleophthalmus dussumieri Valenciennes, 1837 (Perciformes: Gobiidae), due to Microgemma sp

The present study reports a case of hepatic microsporidiosis caused by Microgemma sp. in brackishwater fish, Boleophthalmus dussumieri (Valenciennes, 1837) (n = 60), from the west coast of India. An eight-month study from September 2017 to April 2018 revealed a prevalence of 11.7% for this parasite. The microsporidian showed tissue-specific infection and did not reveal any gross pathology in infected fish. Small whitish cysts containing microspores of size 0.3-0.5 mm were observed in the liver of fish. The range of pyriform microsporidian spore size varied from 2.9-3.77 × 1.85-2.67 µm. Scanning electron microscopy of the spores showed a distinct groove on the anterior end of the spore for polar tube extrusion. Polymerase chain reaction (PCR) amplification of the DNA extracted from the microsporidian-infected liver tissue using primers targeting small ribosomal subunit DNA (SSU rDNA) yielded ~ 1340 bp amplicon and the genetic distance analysis showed a 0.2% variation with the reported M. tilanpasiri. Accordingly, in the phylogenetic tree, the present species of Microgemma clustered with M. tilanpasiri. Even though, the morphomeristic characters of the present Microgemma sp. was marginally different from the reported M. tilanpsasiri; the SSU rDNA showed considerably higher similarity with M. tilanpasiri. Thus, we report the species of Microgemma as Microgemma aff. tilanpasiri from a new host. This is the first report of a microsporidian from B. dussumieri and the first record of the genus Microgemma from India.

Muscular microsporidian infection in Arctic char Salvelinus alpinus from two lakes in Nunavik, Quebec, Canada

Arctic char Salvelinus alpinus is an important cultural and subsistence resource for Inuit communities. Muscular infections by microsporidia were diagnosed for the first time in Arctic char originating from 2 different lakes in Nunavik (Quebec, Canada). The consumption of these infected fish was associated with digestive tract disorders in people. To better characterize microsporidiosis in these char populations, a cross-sectional study was conducted on 91 fish. The microsporidium was classified as a member of the Microsporidium collective genus by morphological evaluation and phylogenetic analysis using small subunit ribosomal DNA sequence data. The presence and severity of infection were determined histologically. Microsporidian infection occurred in 61% of the fish (56/91) and was significantly associated with an increase in their age, length and weight. The severity of infection (percentage of muscle area affected by microsporidia) was mild in most cases (<1% of the total muscle area). Based on multiple linear regression modeling, the severity of infection was significantly greater in females and negatively correlated with the body condition. Despite a high prevalence, the low pathogenicity of the infection suggests that microsporidiosis has little impact on these char populations. Moreover, since digestive-tract disorders following ingestion of fish infected by microsporidia have never been reported in humans, it seems unlikely that it was responsible for the reported clinical signs. Anisakid larvae are occasionally observed in these char populations. Digestive-tract infection associated with ingestion of these larvae should thus be considered as a potential differential diagnosis in these Inuit communities.

Microsporidial myositis in adult-onset immunodeficiency: case-based review

Polymyositis is a diagnosis of exclusion. In patients with odd features, it can be of infective etiology. A high index of suspicion is required for diagnosis. A 55-year-old gentleman presented with gradual-onset proximal muscle weakness. Examination revealed mild distal weakness but no rash. Muscle enzymes were raised and tests for autoantibodies were negative. Biopsy revealed microsporidiosis. In view of this unusual infection, immunodeficiency was considered and he was found to have lymphopenia which antedated his illness. Later, he developed cranial nerve palsies due to multiple lesions in the pons. In addition, he had Cytomegalovirus viremia. Literature was reviewed to identify 20 cases of microsporidial myositis, its presentation, underlying immunodeficient state, and clinical course. Infective polymyositis should be considered in a patient with paucity of clinical and serological autoimmune features. Lymphopenia can point to underlying immunodeficiency. CMV infection could be the contributor to or bystander-effect of idiopathic lymphopenia.

A Vavraia-like microsporidium as the cause of deadly infection in threatened and endangered Eurycea salamanders in the United States

Background

Eurycea sosorum (Barton Springs salamander) and Eurycea nana (San Macros salamander) are listed as endangered and threatened species, respectively, by the U.S. Fish and Wildlife Service (USFWS) with habitats restricted to small regions near Austin, Texas, USA. The conservation efforts with the Eurycea salamanders at the captive breeding program in San Marcos Aquatic Resources Center (SMARC), a USFWS facility, have seen an unexpected and increased mortality rate over the past few years. The clinical signs of sick or dead salamanders included erythema, tail loss, asymmetric gills or brachial loss, rhabdomyolysis, kyphosis, and behavior changes, suggesting that an infectious disease might be the culprit. This study aimed to identify the cause of the infection, determine the taxonomic position of the pathogen, and investigate the potential reservoirs of the pathogen in the environment.

Results

Histopathological examination indicated microsporidian infection (microsporidiosis) in the sick and dead Eurycea salamanders that was later confirmed by PCR detection. We also determined the near full-length small subunit ribosomal RNA (SSU rRNA) gene from the microsporidian pathogen, which allowed us to determine its phylogenetic position, and to design primers for specific and sensitive detection of the pathogen. Phylogenetic analysis indicated that this pathogen was closely related to the insect parasites Vavraia spp. and the human opportunistic pathogen, Trachipleistophora hominis. This Vavraia-like microsporidium was present in dead salamanders at SMARC archived between 2011 and 2015 (positive rates ranging between 52.0–88.9% by PCR detection), as well as in some aquatic invertebrates at the facility (e.g. snails and small crustaceans).

Conclusions

A Vavraia-like microsporidian was at least one of the major pathogens, if not solely, responsible for the sickness and mortality in the SMARC salamanders, and the pathogen had been present in the center for years. Environmental invertebrates likely served as a source and reservoir of the microsporidian pathogen. These observations provide new knowledge and a foundation for future conservation efforts for Eurycea salamanders including molecular surveys, monitoring of the pathogen, and discovery of effective treatments.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3369-z) contains supplementary material, which is available to authorized users.

First record of Tetramicra brevifilum in lumpfish (Cyclopterus lumpus, L.)

A microsporidian species with 98.3-98.4% nucleotide identity to Tetramicra brevifilum (Journal of Fish Diseases, 3, 1980, 495) was diagnosed in lumpfish (Cyclopterus lumpus, L.) broodstock held at a breeding and rearing facility in western Ireland. The fish were wild-caught from the west coast of Ireland, and the first case was diagnosed one year after capture. Clinical signs included severe bloating, lethargy, exophthalmos, anorexia, white patches on the cornea and externally visible parasitic cysts on skin and fins. Necropsy revealed severe ascites, white nodules and vacuoles in all the internal organs and partial liquefaction of the skeletal muscle. On histological examination, microsporidian xenomas were observed in all internal organs, the skin, skeletal muscle, gills and the eyes. The microsporidian species was identified by molecular analysis and transmission electron microscopy. This is the first record of T. brevifilum infecting lumpfish, and the disease is considered to be of potential significance to the rising aquaculture industry of this species.

Detection of a new microsporidium Perezia sp. in shrimps Penaeus monodon and P. indicus by histopathology, in situ hybridization and PCR

Samples of microsporidia-infected shrimps exhibiting clinical signs of cotton shrimp disease were collected from Madagascar, Mozambique, and the Kingdom of Saudi Arabia from 2005 to 2014. The tails of the infected shrimps appeared opaque and whitish; subsequent histological examination revealed the presence of cytoplasmic inclusions and mature spores in tissues of the muscle, hepatopancreas, gills, heart, and lymphoid organ. PCR analysis targeting the small subunit rDNA (SSU rDNA) from infected samples resulted in the amplification of a 1.2 kbp SSU rDNA sequence fragment 94% identical to the corresponding region in the genome of the microsporidian Perezia nelsoni, which infects populations of Penaeus setiferus in the USA. Its SSU rDNA sequence was 100% identical among isolates from Madagascar and Saudi Arabia, indicating that shrimps from the Red Sea and Indian Ocean were infected with the same microsporidium, the novel Perezia sp. A 443 bp fragment of the SSU rDNA sequence was cloned, labeled with digoxigenin and subjected to an in situ hybridization assay with tissue sections of Perezia sp.-infected Penaeus monodon from Madagascar and Mozambique, and P. indicus from Saudi Arabia. The probe hybridized to the mature spores in the hepatopancreas and muscle from which the spores had been obtained for DNA isolation. This assay was specific, showing no reaction to another microsporidium, Enterocytozoon hepatopenaei (EHP), infecting the hepatopancreas of shrimp P. stylirostris cultured in SE Asian countries. We also developed an SSU rDNA-based PCR assay, specific for the novel Perezia sp. This PCR did not react to EHP, nor to genomic DNA of shrimp and other invertebrates.

Distribution, prevalence, and pathology of a microsporidian infecting freshwater sculpins

Microsporidian infections are common in many fish species, yet detailed studies of these parasites in ecologically important wild populations are rare. Phylogenetic analysis using rDNA sequence data and parasite morphology indicate that mottled sculpin Cottus bairdii and slimy sculpin C. cognatus are hosts for Glugea sp. microsporidia in the northern USA. Glugea sp. is common in the Michigan populations sampled for this study, and prevalence was ≥ 70% in 4 of 6 infected populations (range -4 to 80%). Glugea sp. infection causes the formation of xenomas associated with the body wall, fat body, gonads, and kidneys. Infections range from mild to very heavy, with variable xenoma numbers and sizes. Female sculpin experience heavier infections and more frequent infection of the gonads relative to males. Glugea sp. is transmitted horizontally between hosts through ingestion of spores. Vertical transmission may also be possible, either by spores infecting eggs directly or by spores contaminating the surface of eggs in the ovary or in the nest. The frequency and route of vertical transmission requires further study, but if it occurs, it may partly explain the high prevalence of infection. Our study combined with previous research suggests that additional molecular data and cross-infection experiments should be conducted to clarify species designations in the genus Glugea.

Potaspora aequidens n. sp. (Microsporidia, Tetramicridae), a parasite infecting the freshwater fish Aequidens plagiozonatus (Teleostei, Cichlidae) from Brazil

Morphological and molecular procedures were used to describe a new species of microsporidian that infects the muscles of the sub-opercular region and the caudal fins of the freshwater Aequidens plagiozonatus in Brazil. This microsporidian forms whitish xenomas containing variable number of spores, reaching up to ~0.4 mm in diameter. The mature spores, pyriformin shape, with slightly round ends, measured 3.4 ± 0.5 μm long and 1.9 ± 0.3 μm wide (n = 50) and showed characteristics typical of Microsporidia. The average thickness of the spore wall was 100 (96-108) nm (n = 50), and the spore wall was composed of two layers, a thin, electron-dense exospore and a thick electron-transparent endospore. The exospore was surrounded by a thin, irregular layer of granular material. The anchoring disc was mushroom-like, located in the apical region of the spore in an eccentric position relative to the spore axis, rendering bilateral asymmetry to the spore. The anterior part of the polar filament (PF) (manubrium) measured approximately 125 (122-128) nm thick (n = 30), and the angle of tilt between the anterior PF and the spore axis was ~45°; the posterior part was packed in 8-9 coils. Phylogenetic analysis showed a strongly supported clade containing family Spragueidae Weissenberg, 1976, family Tetramicridae Matthews and Matthews, 1980, Microsporidium sp. RBS1, and Kabatana spp. In conclusion, the available morphological, ultrastructural, and molecular data shows that this microsporidian is a new species belonging to group 4, classified as Potaspora aequidens n. sp. This is the second species described in the genus Potaspora.

Description of microsporidia in simulids: molecular and morphological characterization of microsporidia in the larvae of Simulium pertinax Kollar (Diptera: Simuliidae)

INTRODUCTION

Microsporidia constitute the most common black fly pathogens, although the species' diversity, seasonal occurrence and transmission mechanisms remain poorly understood. Infections by this agent are often chronic and non-lethal, but they can cause reduced fecundity and decreased longevity. The objective of this study was to identify microsporidia infecting Simulium (Chirostilbia) pertinax (Kollar, 1832) larvae from Caraguatatuba, State of São Paulo, Brazil, by molecular and morphological characterization.

METHODS

Larvae were collected at a single point in a stream in a rural area of the city and were kept under artificial aeration until analysis. Polydispyrenia spp. infection was characterized by the presence of at least 32 mononuclear spores measuring 6.9 ± 1.0 × 5.0 ± 0.7 µm in persistent sporophorous vesicles. Similarly, Amblyospora spp. were characterized by the presence of eight uninucleate spores measuring 4.5 × 3.5 µm in sporophorous vesicles.

RESULTS

The molecular analysis confirmed the presence of microsporidian DNA in the 8 samples (prevalence of 0.51%). Six samples (Brazilian larvae) were related to Polydispyrenia simulii and Caudospora palustris reference sequences but in separate clusters. One sample was clustered with Amblyospora spp. Edhazardia aedis was the positive control taxon.

CONCLUSIONS

Samples identified as Polydispyrenia spp. and Amblyospora spp. were grouped with P. simulii and Amblyospora spp., respectively, corroborating previous results. However, the 16S gene tree showed a considerable distance between the black fly-infecting Amblyospora spp. and the mosquito-infecting spp. This distance suggests that these two groups are not congeneric. Additional genomic region evaluation is necessary to obtain a coherent phylogeny for this group.

The genome of the obligate intracellular parasite Trachipleistophora hominis: new insights into microsporidian genome dynamics and reductive evolution

The dynamics of reductive genome evolution for eukaryotes living inside other eukaryotic cells are poorly understood compared to well-studied model systems involving obligate intracellular bacteria. Here we present 8.5 Mb of sequence from the genome of the microsporidian Trachipleistophora hominis, isolated from an HIV/AIDS patient, which is an outgroup to the smaller compacted-genome species that primarily inform ideas of evolutionary mode for these enormously successful obligate intracellular parasites. Our data provide detailed information on the gene content, genome architecture and intergenic regions of a larger microsporidian genome, while comparative analyses allowed us to infer genomic features and metabolism of the common ancestor of the species investigated. Gene length reduction and massive loss of metabolic capacity in the common ancestor was accompanied by the evolution of novel microsporidian-specific protein families, whose conservation among microsporidians, against a background of reductive evolution, suggests they may have important functions in their parasitic lifestyle. The ancestor had already lost many metabolic pathways but retained glycolysis and the pentose phosphate pathway to provide cytosolic ATP and reduced coenzymes, and it had a minimal mitochondrion (mitosome) making Fe-S clusters but not ATP. It possessed bacterial-like nucleotide transport proteins as a key innovation for stealing host-generated ATP, the machinery for RNAi, key elements of the early secretory pathway, canonical eukaryotic as well as microsporidian-specific regulatory elements, a diversity of repetitive and transposable elements, and relatively low average gene density. Microsporidian genome evolution thus appears to have proceeded in at least two major steps: an ancestral remodelling of the proteome upon transition to intracellular parasitism that involved reduction but also selective expansion, followed by a secondary compaction of genome architecture in some, but not all, lineages.

Microsporidians are enormously successful obligate intracellular parasites of animals, including humans. Despite their economic and medical importance, there are major gaps in our understanding of how microsporidians have made the transition from a free-living organism to one that can only complete its life cycle by living inside another cell. We present the larger genome of Trachipleistophora hominis isolated from a human patient with HIV/AIDS. Our analyses provide insights into the gene content, genome architecture and intergenic regions of a known opportunistic pathogen, and will facilitate the development of T. hominis as a much-needed model species that can also be grown in co-culture. The genome of T. hominis has more genes than other microsporidians, it has diverse regulatory motifs, and it contains a variety of transposable elements coupled with the machinery for RNA interference, which may eventually allow experimental down-regulation of T. hominis genes. Comparison of the genome of T. hominis with other microsporidians allowed us to infer properties of their common ancestor. Our analyses predict an ancestral microsporidian that was already an intracellular parasite with a reduced core proteome but one with a relatively large genome populated with diverse repetitive elements and a complex transcriptional regulatory network.

Ultrastructural and molecular studies of Microgemma carolinus n. sp. (Microsporidia), a parasite of the fish Trachinotus carolinus (Carangidae) in Southern Brazil

A new species of Microsporidia Microgemma carolinus n. sp. found in the marine teleost Trachinotus carolinus collected in Florianópolis, Brazil was described based on light, ultrastructural and phylogenetic studies. This parasite developed in the liver forming whitish xenomas that contained different developmental stages with monokaryotic nuclei. The periphery of the xenoma presented some vacuolization and possessed several small projections in the membrane. The mature spores, measuring 3·8 ± 0·4 μm in length and 2·4 ± 0·4 μm in width, were slightly pyriform to ellipsoidal and had rounded ends. The polaroplast was bipartite and the isofilar polar filament was coiled with 8 – 9 turns in a single or double row at the posterior end of the spore. The nucleus was voluminous and in a central position, measuring ∼0·9 μm in diameter. A large posterior vacuole appeared as a pale area, occupying about a third of the spore length. The SSU rRNA gene was sequenced and analysed using maximum parsimony, maximum likelihood and neighbour-joining methods. This study allowed us to conclude that this was a new species of the genus Microgemma, being the first description of this genus from among South America fauna.

Ultrastructure and molecular phylogenetics of a new isolate of Pleistophora pagri sp. nov. (Microsporidia, Pleistophoridae) from Pagrus pagrus in Egypt

The spore morphology and molecular systematic of a new microsporidian which was isolated from the common sea bream Pagrus pagrus (F: Sparidae Linnaeus, 1758) from the Red Sea, Egypt have been studied. Fifty-six out of 300 (18.7%) of this fish were infected with microsporidian parasites. The infection was appeared as whitish, ellipsoid, round, or elongated nodules embedded in the epithelial lining of the peritoneum and also in the intestinal epithelium. Light microscopic study revealed that nodules were encapsulated by a fibrous layer encircling numerous mature spores measuring 1.7 ± 0.6 (1.5-2.7 μm) × 1.5 ± 0.3 μm (1.2-1.8 μm) in size. Ultrastructure of spores was characteristic for the genus Pleistophora: dimorphic, uninucleate spores (each spore possesses three to five polar filament coils) and a posterior vacuole. Also, the early recognizable stages of the parasite within nodules include uninucleated, binucleated, and multinucleated meronts followed by detachment of the plasmalemma of the sporont producing sporoblasts which mature to spores that consist of a spore coat and spore contents. Also, we analyzed the small subunit ribosomal gene (SSUrDNA) using PCR and sequencing specimens from the marine populations of P. pagrus fish from the Red Sea. From blast searches, sequence analysis, and phylogenetic analysis, we did not find corresponding GenBank entries to our species. Comparison of the nucleotide sequences showed that the sequence of our microsporidium was most similar to five Pleistophora species with degrees of identity (>91.5%). It was most similar (97.8% identity) to that of Pleistophora hyphessobryconis (account no. GU126672) differing in 19 nucleotide positions and with lower divergence value, Pleistophora ovariae (96.2% identity, account no. AJ252955), Pleistophora hippoglossoideos (91.9% identity, account no. AJ252953), Pleistophora mulleri (91.9% identity, account no. EF119339), and Pleistophora typicalis (91.9% identity, account no. AJ252956). So, they likely represent new species named Pleistophora pagri sp. n. with accession number JF797622 and a GC content of 53%.

Morphological and molecular biological characterization of Pleistophora aegyptiaca sp. nov. infecting the Red Sea fish Saurida tumbil

One hundred three out of 225 (45.8%) of the Red Sea fish Saurida tumbil were infected with microsporidian parasites. The infection was recorded as tumor-like masses (whitish macroscopic cysts) or xenomas often up to 2 cm in diameter and embedded in the peritoneal cavity. Generally, the infection was increased during winter 63.8% (86 out of 135) and fall to 18.9% (17 out of 90) in summer. Light microscopic study revealed that xenomas were encapsulated by a fibrous layer encircling numerous sporophorous vesicles filled with mature spores measuring 1.7 ± 0.6 (1.5-2.7 μm) × 1.5 ± 0.3 μm (1.2-1.8 μm) in size. Ultrastructural microscopic study showed the presence of smooth membranes of the sarcoplasmic reticulum forming a thick, amorphous coat surrounding various developmental stages of the parasite. The various recognizable stages of the parasite were uninuclear, binucleated, and multinucleated meronts followed by detachment of the plasmalemma of the sporont from the sporophorous vesicle producing sporoblasts. Mature spores consist of a spore coat and spore contents. The spore contents consist of the uninucleated sporoplasm and a posterior vacuole located at the posterior end. The polar tube consists of a straight shaft and a coiled region (26-32 coils) arranged in many rows along the inside periphery of the spore. The polaroplast consisted of an anterior region of closely and loosely packed membranes. Molecular analysis based on the small subunit rDNA gene was performed to determine the phylogenetic position of the present species. The percentage identity between this species and a range of other microsporidia predominantly from aquatic hosts demonstrated a high degree of similarity (>92%) with eight Pleistophora species. Comparison of the nucleotide sequences and divergence showed that the sequence of the present microsporidium was most similar to that of Pleistophora anguillarum (99.8% identity) differing in 13 nucleotide positions. So, the present species was recorded and phylogenetically positioned as a new species of Pleistophora.

A new Encephalitozoon species (Microsporidia) isolated from the lubber grasshopper, Romalea microptera (Beauvois) (Orthoptera: Romaleidae)

We describe a new microsporidian species, Encephalitozoon romaleae n. sp., isolated from an invertebrate host, the grasshopper Romalea microptera, collected near Weeks Island, Louisiana, and Jacksonville, Florida. This microsporidian is characterized by specificity to the gastric caecae and midgut tissues of the host and a life cycle that is nearly identical to that of Encephalitozoon hellem and Encephalitozoon cuniculi. Mature spores are larger (3.97 x 1.95 microm) than those of other Encephalitozoon species. Polar filament coils number 7 to 8 in a single row. Analysis of the small subunit (SSU) rDNA shows that E. romaleae fits well into the Encephalitozoon group and is a sister taxon to E. hellem. This is the first Encephalitozoon species that has been shown to complete its life cycle in an invertebrate host.

A new microsporidian parasite, Potaspora morhaphis n. gen., n. sp. (Microsporidia) infecting the Teleostean fish, Potamorhaphis guianensis from the River Amazon. Morphological, ultrastructural and molecular characterization

A fish-infecting Microsporidia Potaspora morhaphis n. gen., n. sp. found adherent to the wall of the coelomic cavity of the freshwater fish, Potamorhaphis guianensis, from lower Amazon River is described, based on light microscope and ultrastructural characteristics. This microsporidian forms whitish xenomas distinguished by the numerous filiform and anastomosed microvilli. The xenoma was completely filled by several developmental stages. In all of these stages, the nuclei are monokaryotic and develop in direct contact with host cell cytoplasm. The merogonial plasmodium divides by binary fission and the disporoblastic pyriform spores of sporont origin measure 2·8±0·3×1·5±0·2 μm. In mature spores the polar filament was arranged into 9–10 coils in 2 layers. The polaroplast had 2 distinct regions around the manubrium and an electron-dense globule was observed. The small subunit, intergenic space and partial large subunit rRNA gene were sequenced and maximum parsimony analysis placed the microsporidian described here in the clade that includes the genera Kabatana, Microgemma, Spraguea and Tetramicra. The ultrastructural morphology of the xenoma, and the developmental stages including the spores of this microsporidian parasite, as well as the phylogenetic analysis, suggest the erection of a new genus and species.

Trachipleistophora extenrec n. sp. a new microsporidian (fungi: microsporidia) infecting mammals

A new microsporidian Trachipleistophora extenrec n. sp. was isolated from a muscle lesion of the streaked tenrec Hemicentetes semispinosus Cuvier, 1798 (Mammalia, Tenrecidae), an insectivore endemic to Madagascar. The spores isolated from the tenrec were infectious to severe combined immunodeficient (SCID) mice by intramuscular injection. Material obtained from muscular lesions in mice was used for the parasite description. All developmental stages of the microsporidian were covered by a dense coat, which during sporogony changed into the sporophorous vesicle wall. Eight, 16, 32, or more spores were formed inside the sporophorous vesicle as the result of the division by plasmotomy and sequential fission of a multinucleate sporogonial plasmodium. Spores were ovoid, 4.7 x 2.8 microm in size, had a large posterior vacuole, and had an isofilar polar tube with 15-16 coils. Although the fine structure and the developmental pattern of the organism were in some respects similar to the genus Vavraia, molecular phylogeny based on the gene sequences of the small subunit rRNA and RNA polymerase subunit II indicated that the organism belongs to the genus Trachipleistophora. The diagnostic characters of the genera Trachipleistophora and Vavraia are discussed as well as the discrepancies between the phylogenies of these two microsporidian genera based on morphology and molecules.

A case of bilateral microsporidial keratitis from Bangladesh – infection by an insect parasite from the genus Nosema

An HIV-negative patient from Bangladesh with bilateral keratitis was found to be infected with a microsporidian parasite belonging to the genus Nosema. Significantly, the patient had bathed in a rural pond 7 days prior to the development of ocular symptoms. Nosema parasites are common insect parasites and the source of this microsporidial infection was possibly from mosquito larvae developing in the pond in which the patient bathed. The reduced temperature of the human eye and its immune status may have allowed a poikilothermic insect parasite to establish infection in the cornea of a homeothermic human host. This case highlights the opportunistic potential of insect microsporidial parasites to infect immunocompetent humans as well as those who are immunodeficient.

Establishment of Liebermannia dichroplusae n. comb. on the Basis of Molecular Characterization of Perezia dichroplusae Lange, 1987 (Microsporidia)

Perezia dichroplusae Lange, 1987 is a parasite of the Malpighian tubules of an Argentine grasshopper, Dichroplus elongatus (Orthoptera, Acrididae, Melanoplinae). In order to determine relationships of this microsporidium with Perezia nelsoni and with other microsporidia, we sequenced its small subunit ribosomal RNA gene (SSU rDNA) (GenBank Accession No. EF016249) and performed phylogenetic analysis of the novel sequence against 17 microsporidian SSU rDNA sequences from GenBank, using neighbor-joining (NJ), maximum-parsimony (MP), and maximum-likelihood (ML) methods. This analysis revealed the highest similarity (96%) of the new sequence to Liebermannia patagonica, a parasite of gut epithelium cells of another grasshopper from Argentina, versus only 65% similarity to P. nelsoni, a parasite of muscles of paenaeid shrimps. In phylogenetic trees inferred from SSU rDNA sequences, the microsporidium from D. elongatus is sister taxon to L. patagonica and both cluster with Orthosomella operophterae. At the higher hierarchical level, the Liebermania-Orthosomella branch forms a clade with the Endoreticulatus-Cystosporogenus-Vittaforma group and with Enterocytozoon bieneusi. Perezia nelsoni falls into another large clade together with Nosema and Ameson species. We propose transferring P. dichroplusae to the genus Liebermannia and creating a new combination Liebermannia dichroplusae n. comb., based both on SSU rDNA sequence analysis and on common characters between P. dichroplusae and L. patagonica, which include the presence of elongated multinuclear sporonts, sporoblastogenesis by a similar process of sequentially splitting off sporoblasts, ovocylindrical spores of variable size, tissue tropism limited to epithelial cells, Orthoptera as hosts, and geographical distribution of hosts in the southern temperate region of Argentina. We argue that the condition of the nuclei in spores (i.e. diplokaryotic in L. patagonica or monokaryotic in L. dichroplusae) cannot be used to distinguish genera. Therefore, we remove the statement about the presence of diplokaryotic spores from the revised diagnosis of the genus Liebermannia.

Systenostrema alba Larsson 1988 (Microsporidia, Thelohaniidae) in the Dragonfly Aeshna viridis (Odonata, Aeshnidae) from South Siberia: morphology and molecular characterization

An octospore microsporidium was found in the nymphs of Aeshna viridis, collected in intermittent streams near Novosibirsk, Siberia, Russia in 2003. Spores were uninucleate and measured 6.1+/-0.07 x 3.0+/-0.04 microm on fresh smears. The polar filament was anisofilar having 10-11 anterior coils (thicker filament diam.) and 10-11 posterior (thinner filament diam.) coils. Sporophorous vesicles were persistent and measured 12.3+/-0.23 x 11.9+/-0.20 microm. The infection was restricted to the adipose tissue and caused the formation of whitish "cysts" containing mature octospores. Based on ultrastructural similarity we consider this Siberian isolate to be Systenostrema alba, a species described from Aeshna grandis collected in Sweden (Larsson 1988). Maximum likelihood, neighbor joining, and maximum parsimony analyses of the small subunit rDNA all placed Systenostrema alba (Accession no. AY953292) as the sister taxon to a clade consisting of Thelohania solenopsae, Tubulinosema ratisbonensis, and Tubulinosema acridophagus.

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.

Characterization and phylogenetic relationships among microsporidia infecting silkworm, Bombyx mori, using inter simple sequence repeat (ISSR) and small subunit rRNA (SSU-rRNA) sequence analysis

This study is the first report on the genetic characterization and relationships among different microsporidia infecting the silkworm, Bombyx mori, using inter simple sequence repeat PCR (ISSR-PCR) analysis. Six different microsporidians were distinguished through molecular DNA typing using ISSR-PCR. Thus, ISSR-PCR analysis can be a powerful tool to detect polymorphisms and identify microsporidians, which are difficult to study with microscopy because of their extremely small size. Of the 100 ISSR primers tested, only 28 primers had reproducibility and high polymorphism (93%). A total of 24 ISSR primers produced 55 unique genetic markers, which could be used to differentiate the microsporidians from each other. Among the 28 SSRs tested, the most abundant were (CA)n, (GA)n, and (GT)n repeats. The degree of band sharing was used to evaluate genetic similarity between different microsporidian isolates and to construct a phylogenetic tree using Jaccard's similarity coefficient. The results indicate that the DNA profiles based on ISSR markers can be used as diagnostic tools to identify different microsporidia with considerable accuracy. In addition, the small subunit ribosomal RNA (SSU-rRNA) sequence gene was amplified, cloned, and sequenced from each of the 6 microsporidian isolates. These sequences were compared with 20 other microsporidian SSU-rRNA sequences to develop a phylogenetic tree for the microsporidia isolated from the silkworms. This method was found to be useful in establishing the phylogenetic relationships among the different microsporidians isolated from silkworms. Of the 6 microsporidian isolates, NIK-1s revealed an SSU-rRNA gene sequence similar to Nosema bombycis, indicating that NIK-1s is similar to N. bombycis; the remaining 5 isolates, which differed from each other and from N. bombycis, were considered to be different variants belonging to the species N. bombycis.Key words: microsporidia, Nosema, silkworm, Bombyx mori, inter simple sequence repeat PCR, small subunit rRNA, phylogeny.

Microgemma vivaresi n. sp. (Microsporidia, Tetramicridae), infecting liver and skeletal muscle of sea scorpions, Taurulus bubalis (Euphrasen 1786) (Osteichthyes, Cottidae), an inshore, littoral fish

The ultrastructure of a new microsporidian species Microgemma vivaresi n. sp. causing liver cell xenoma formation in sea scorpions, Taurulus bubalis, is described. Stages of merogony, sporogony, and sporogenesis are mixed in the central cytoplasm of developing xenomas. All stages have unpaired nuclei. Uninucleate and multinucleate meronts lie within vacuoles formed from host endoplasmic reticulum and divide by binary or multiple fission. Sporonts, no longer in vacuoles, deposit plaques of surface coat on the plasma membrane that cause the surface to pucker. Division occurs at the puckered stage into sporoblast mother cells, on which plaques join up to complete the surface coat. A final binary fission gives rise to sporoblasts. A dense globule, thought to be involved in polar tube synthesis, is gradually dispersed during spore maturation. Spores are broadly ovoid, have a large posterior vacuole, and measure 3.6 microm x 2.1 microm (fresh). The polar tube has a short wide anterior section that constricts abruptly, then runs posteriad to coil about eight times around the posterior vacuole with granular contents. The polaroplast has up to 40 membranes arranged in pairs mostly attached to the wide region of the polar tube and directed posteriorly around a cytoplasm of a coarsely granular appearance. The species is placed alongside the type species Microgemma hepaticusRalphs and Matthews 1986 within the family Tetramicridae, which is transferred from the class Dihaplophasea to the class Haplophasea, as there is no evidence for the occurrence of a diplokaryotic phase.

Epidemiology of microsporidiosis: sources and modes of transmission

Microsporidia are single-celled, obligate intracellular parasites that were recently reclassified from protozoa to fungi. Microsporidia are considered a cause of emerging and opportunistic infections in humans, and species infecting humans also infect a wide range of animals, raising the concern for zoonotic transmission. Persistent or self-limiting diarrhea are the most common symptoms associated with microsporidiosis in immune-deficient or immune-competent individuals, respectively. Microsporidian spores appear to be relatively resistant under environmental conditions, and species of microsporidia infecting humans and animals have been identified in water sources, raising concern about water-borne transmission. Sensitive and specific immunomagnetic bead separation and PCR-based methods are being developed and applied for detecting microsporidia in infected hosts and water sources for generating more reliable prevalence data. The most effective drugs for treating microsporidiosis in humans currently include albendazole, which is effective against the Encephalitozoon species but not against Enterocytozoon bieneusi, and fumagillin, which has broader anti-microsporidia activity but is toxic in mammals, suggesting a need to identify better drugs. Strategies to capture and disinfect microsporidia in water are being developed and include filtration, coagulation, chlorination, gamma-irradiation, and ozonation.

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.

Ultrastructural examination of two cases of stromal microsporidial keratitis

Two cases with chronic stromal keratitis are described in immunocompetent hosts where the diagnosis was originally thought to be herpetic or adenoviral disease. Light microscopy and ultrastructural examination of corneal tissue by electron microscopy were performed following penetrating keratoplasty (case 1) and corneal biopsy (case 2). Specimens from both cases were analysed for viral identification by PCR. Two different species of Microsporidia were identified. Case 1 represents the fourth reported case of corneal stromal Vittaforma corneae where the spores measured 3.3 x 1.4 microm, arranged in characteristic linear groups of about four to eight. Each spore contained a diplokaryotic nucleus and a single row of ten polar tube coils. By contrast, case 2 is the first reported case of stromal keratitis caused by Trachipleistophora hominis. In this case, spores measured 4 x 2.4 microm, located typically within packets. In this species, the polar tube was arranged as a single row of about 10-13 profiles. Viral DNA could not be amplified by PCR. In conclusion, microsporidial stromal keratitis should be considered in culture-negative cases refractory to medical therapy. As microbiological culture techniques are unsuccessful, diagnosis may only be established following histopathological and ultrastructural examination of corneal tissue.

Resolution of a taxonomic conundrum: an ultrastructural and molecular description of the life cycle of Pleistophora mulleri (Pfeiffer 1895; Georgevitch 1929)

The classification of a microsporidian parasite observed in the abdominal muscles of amphipod hosts has been repeatedly revised but still remains inconclusive. This parasite has variable spore numbers within a sporophorous vesicle and has been assigned to the genera Glugea, Pleistophora, Stempellia, and Thelohania. We used electron microscopy and molecular evidence to resolve the previous taxonomic confusion and confirm its identification as Pleistophora mulleri. The life cycle of P. mulleri is described from the freshwater amphipod host Gammarus duebeni celticus. Infection appeared as white tubular masses within the abdominal muscle of the host. Light and transmission electron microscope examination revealed the presence of an active microsporidian infection that was diffuse within the muscle block with no evidence of xenoma formation. Paucinucleate merogonial plasmodia were surrounded by an amorphous coat immediately external to the plasmalemma. The amorphous coat developed into a merontogenetic sporophorous vesicle that was present throughout sporulation. Sporogony was polysporous resulting in uninucleate spores, with a bipartite polaroplast, an anisofilar polar filament and a large posterior vacuole. SSU rDNA analysis supported the ultrastructural evidence clearly placing this parasite within the genus Pleistophora. This paper indicates that Pleistophora species are not restricted to vertebrate hosts.

A hyperparasitic microsporidian infecting the salmon louse, Lepeophtheirus salmonis: an rDNA-based molecular phylogenetic study

The sea louse, Lepeophtheirus salmonis, is an obligate ectoparasitic copepod that lives on the external surface of salmonid fish. It is the most common ectoparasite of marine cage-reared salmonids, causing major economic loss to the aquaculture industry. During a sea louse monitoring programme, samples of L. salmonis were found to harbour an unreported microsporidian parasite. The microsporidian was observed in pre-adult and adult stages of both male and female copepods, with a prevalence of up to 5%. Unfixed spores were slightly pyriform in shape measuring 2.34 microm by 1.83 microm (+/- 0.01 microm) and were not observed to be enclosed by a sporophorous vesicle. The microsporidian infection was observed in all areas of the copepods' body, xenoma-like cysts forming directly under the cuticle in the epidermal tissue layer. In the present study, rDNA (530f-580r) sequence data gathered from the unidentified microsporidian parasite isolated from infected sea lice were compared with equivalents available in the databases in an attempt to identify its systematic position. The microsporidian was found to group within the phylogenetic clade containing the family Enterocytozoonidae, being most similar to members of the intranuclear genus Nucleospora. This is the first report of a hyperparasitic microsporidian infecting a caligid copepod.

Fish microsporidia: fine structural diversity and phylogeny

Structural diversity of fish microsporidian life cycle stages and of the host-parasite interface is reviewed. In the infected cell of the fish host, microsporidia may either cause serious degradation of the cytoplasm and demise of the cell, or they may elicit host cell hypertrophy, producing a parasite-hypertrophic host cell complex, the xenoma. The structure of the xenoma and of its cell wall may differ according to the genus of the parasite, and seems to express properties of the parasite rather than those of the host. In merogony, the parasite cell surface interacts with the host cell in diverse ways, the most conspicuous being the production of thick envelopes of different types. Sporogony stages reveal different types of walls or membranes encasing the sporoblasts and later the spores and these envelopes may be of host or parasite origin. Nucleospora differs from all other fish microsporidia by its unique process of sporogony. Except for the formation of conspicuous xenomas, there are no essentially different structures in fish-infecting microsporidia compared with microsporidia from other hosts. Although the structures associated with the development of fish microsporidia cannot be attributed importance in tracing the phylogeny, they are relevant for practical determination and assessing the relation to the host. The possibility of the existence of an intermediate host is discussed. Higher-level classification of Microsporidia is briefly discussed and structure and evolutionary rates in microsporidian rDNA are reviewed. Discussion of rDNA molecular phylogeny of fish-infecting microsporidia is followed by classification of these parasites. Most form a rather cohesive clade. Outside this clade is the genus Nucleospora, separated at least at the level of Order. Within the main clade, however, there are six species infecting hosts other than fish. Based on data available for analysis, a tentative classification of fish-infecting microsporidia into five groups is proposed. Morphologically defined groups represent families, others are referred to as clades. Group 1, represented by family Pleistophoridae, includes Pleistophora, Ovipleistophora and Heterosporis; Vavraia and Trachipleistophora infect non-fish hosts. Group 2, represented by family Glugeidae, is restricted to genus Glugea and Tuzetia weidneri from crustaceans. Group 3 comprises three clades: Loma and a hyperparasitic microsporidian from a myxosporean; Ichthyosporidium and Pseudoloma clade and the Loma acerinae clade. For the latter species a new genus has to be established. Group 4 contains two families, Spragueidae with the genus Spraguea and Tetramicridae with genera Microgemma and Tetramicra, and the Kabatana and Microsporidium seriolae clade. Group 5 is represented by the family Enterocytozoonidae with the genus Nucleospora and mammal-infecting genus Enterocytozoon.

Mouse antibody response to a microsporidian parasite following inoculation with a gene coding for parasite ribosomal RNA

This study found that a plasmid construct encoding the small-subunit ribosomal RNA (SSUrRNA) of the microsporidian Microgemma caulleryi generates a humoral response upon intramuscular inoculation in mice. The plasmid used was pCMV, following preliminary trials indicating efficient beta-galactosidase gene expression in mouse muscle cells transfected with pCMV/beta-Gal. The antibodies produced after inoculation with pCMV/SSUDNA recognized parasite spore antigens and reached maximum levels at 30 days postinoculation, subsequently remaining stable for at least 120 days. Due to the highly conserved sequence of the SSUrDNA in different microsporidian species, these results open up interesting prospects for broad-spectrum vaccination.

Ultrastructural aspects of a new species, Vavraia mediterranica (Microsporidia, Pleistophoridae), parasite of the French Mediterranean shrimp, Crangon crangon (Crustacea, Decapoda)

The life cycle stages of a new species of the genus Vavraia (Microsporidia, Pleistophoridae), which parasitizes the shrimp Crangon crangon (Crustacea, Decapoda), were examined by light and electron microscopy. This parasite was monomorphic with polysporous sporogony and developed in the skeletal muscle of the host. The multinucleate sporogonial plasmodium divided by plasmotomy and multiple division into uninucleate sporoblasts. All stages were surrounded by a thick and amorphous dense coat external to the plasmalemma. This structure gradually became a merontogenetic sporophorous vacuole (MSV) where the sporonts developed into sporoblasts. The MSV was filled with episporontal granular secretory products and eventually contained up to 50 uninucleate spores. During spore morphogenesis, these episporontal granular products within the MSV became organized as episporontal tubular-like structures. In transverse sections, these structures showed a mean diameter of 1.0 microm, but disappeared during the final phase of the spore maturation. Mature spores were ellipsoidal to slightly pyriform and measured 2.30 x 1.41 microm. The polar filament was anisofilar and consisted of a single coil with six to seven turns (rarely five). This new species is named Vavraia mediterranica n. sp.