Survival of Bacterial and Parasitic Pathogens from Zebrafish (Danio rerio) After Cryopreservation and Thawing

Cryopreservation is a common method used to preserve the sperm of various animal species, and it is widely used with zebrafish (Danio rerio). As with other animals, there is a possibility of paternal pathogen transmission through sperm. We evaluated the ability of five common and important pathogens of zebrafish to survive cryopreservation as used with zebrafish sperm and freezing without cryopreservant. We evaluated Mycobacterium chelonae, Mycobacterium marinum, and Edwardsiella ictaluri, each originally isolated from zebrafish, eggs of Pseuodocapillaria tomentosa, and spores of Pseudoloma neurophilia. Each mycobacterial isolate showed relatively minimal reduction in survival after freezing and thawing, particularly when subjected to cryopreservation. E. ictaluri also showed survival after cryopreservation, but exhibited a several log reduction after freezing at -80°C without cryopreservant. With P. neurophilia, two separate experiments conducted 3 years apart yielded very similar results, showing some, but reduced, survival of spores by using three different viability assays: SYTOX stain, Fungi-Fluor stain, and presence of a spore vacuole. Eggs of P. tomentosa showed no survival based on larvation of eggs when subjected to either freezing method. Given that four of the five pathogens exhibited survival after cryopreservation, we recommend that sperm samples or donor male zebrafish fish be tested for pathogens when sperm are to be stored by using cryopreservation.

The roles of microsporidia spore wall proteins in the spore wall formation and polar tube anchorage to spore wall during development and infection processes

Microsporidia are highly specialized obligate intracellular, spore forming divergent fungi with a wide variety host range that includes most vertebrates and invertebrates. The resistant spores are surrounded by a rigid cell wall which consists of three layers: the electron-lucent chitin and protein inner endospore, the outer-electron-dense and mainly proteinaceous exospore and plasma membrane. Interestingly, microsporidia owns a special invasion organelle, called polar tube, coiled within the interior of the spore wall and attached to anchoring disk at the anterior end of spore. Spore wall and polar tube are the major apparatuses for mature spores adhering and infecting to the host cells. In this review, we summarize the research advances in spore wall proteins (SWPs) related to spore adherence and infection, and SWPs and deproteinated chitin spore coats (DCSCs) interaction associated with SWPs deposit processes and spore wall assembly. Furthermore, we highlight the SWPs-polar tube proteins (PTPs) interaction correlated to polar tube orderly orientation, arrangement and anchorage to anchoring disk. Based on results obtained, it is helpful to improve understanding of the spore wall assembly and polar tube orderly arrangement mechanisms and molecular pathogenesis of microsporidia infection. Also, such information will provide a basis for developing effective control strategies against microporidia.

Empirical evidence that metabolic theory describes the temperature dependency of within-host parasite dynamics

The complexity of host–parasite interactions makes it difficult to predict how host–parasite systems will respond to climate change. In particular, host and parasite traits such as survival and virulence may have distinct temperature dependencies that must be integrated into models of disease dynamics. Using experimental data from Daphnia magna and a microsporidian parasite, we fitted a mechanistic model of the within-host parasite population dynamics. Model parameters comprising host aging and mortality, as well as parasite growth, virulence, and equilibrium abundance, were specified by relationships arising from the metabolic theory of ecology. The model effectively predicts host survival, parasite growth, and the cost of infection across temperature while using less than half the parameters compared to modeling temperatures discretely. Our results serve as a proof of concept that linking simple metabolic models with a mechanistic host–parasite framework can be used to predict temperature responses of parasite population dynamics at the within-host level.

Host–parasite interactions are impacted by temperature, and climate change is altering the nature of these interactions. Measuring how a range of temperatures affects host and parasite traits and how this influences the outcome of infections is infeasible in most systems. The metabolic theory of ecology provides a powerful framework to predict biological rates in response to temperature. Using a Daphnia–parasite model system, we collected experimental data on host survival and parasite abundance across the host’s temperature range. We fitted thermal relationships based on the metabolic theory of ecology to separate host and parasite traits, including host mortality and aging as well as parasite growth and virulence. We then provide empirical evidence of the predictive power of linking these relationships in mechanistic within-host parasite models. This allows us to predict the outcome of individual infections continuously across a temperature gradient, as well as to gain a better understanding of the impact of temperature changes on disease dynamics. Due to its simplicity and generality, this framework could be a valuable approach for predicting the effects of climate change on infection outcomes for hosts and microparasites.

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.

Heterosporis anguillarum infections in farm cultured eels (Anguilla japonica) in Korea

Ten eels (Anguilla japonica) from a fish farm in Korea were examined and diagnosed with a Heterosporis infection. The gross lesions on the trunk were uneven and the concave parts were pasty. Histopathologically, lyses of the trunk muscles, degenerative muscle fibers and the scattered spores were observed. The sporophorocyst (SPC) contained several spores with a variety of shapes. Some SPC were disrupted and the spores in the SPC were scattered in the muscle tissues. Macrophages existed near the scattered spores. Electron microscopy revealed special structures such as sporophorocyst containing various developmental parasitic stages such as meronts, sporonts, sporophorous vesicles and spores.

Spores of two fish microsporidia (Pseudoloma neurophilia and Glugea anomala) are highly resistant to chlorine

Pseudoloma neurophilia (Microsporidia) is the most common pathogen found in zebrafish Danio rerio research facilities. The parasite is associated with marked emaciation. Zebrafish laboratories usually disinfect eggs to prevent transmission of pathogens, typically with chlorine at 25 to 50 ppm for 10 min. The ability of chlorine to kill spores of P. neurophilia and 2 other microsporidia, Glugea anomala and Encephalitozoon cuniculi, was evaluated using 2 viability stains. SYTOX Green was used to visualize dead spores, and live spores were identified by their ability to extrude polar tubes in Fungi-Fluor solution following UV exposure. Results with both stains were similar at various chlorine concentrations for P. neurophilia and G. anomala, but Fungi-Fluor was not useful for E. cuniculi, due to the much smaller spore size. Using the SYTOX stain, we found that 5 ppm chlorine for 10 min causes 100% death in spores of E. cuniculi, which was similar to findings in other studies. In contrast, the spores of P. neurophilia and G. anomala were much more resistant to chlorine, requiring >100 or 1500 ppm chlorine, respectively, to achieve >95% spore death. Repeating chlorine exposures with spores of P. neurophilia using solutions adjusted to pH 7 increased the efficacy of 100 ppm chlorine, achieving >99% spore inactivation. We corroborated our viability staining results with experimental exposures of zebrafish fry, achieving heavy infections in fry at 5 to 7 d post-exposure in fish fed spores treated at 50 ppm (pH 9). Some fish still became infected with spores exposed to 100 ppm chlorine (pH 9.5). This study demonstrates that spores of certain fish microsporidia are highly resistant to chlorine, and indicates that the egg disinfection protocols presently used by most zebrafish research facilities will not prevent transmission of P. neurophilia to progeny.

Inference of parasite local adaptation using two different fitness components

Estimating parasite fitness is central to studies aiming to understand parasite evolution. Theoretical models generally use the basic reproductive rate R(0) to express fitness, yet it is very difficult to quantify R(0) empirically and experimental studies often use fitness components such as infection intensity or infectivity as substitutes. These surrogate measures may be biased in several ways. We assessed local adaptation of the microsporidium Ordospora colligata to its host, the crustacean Daphnia magna using two different parasite fitness components: infection persistence over several host generations in experimental populations and infection intensity in individual hosts. We argue that infection persistence is a close estimator of R(0), whereas infection intensity measures only a component of it. Both measures show a pattern that is consistent with parasite local adaptation and they correlate positively. However, several inconsistencies between them suggest that infection intensity may at times provide an inadequate estimate of parasite fitness.

Multiple losses of sex within a single genus of Microsporidia

Background

Most asexual eukaryotic lineages have arisen recently from sexual ancestors and contain few ecologically distinct species, providing evidence for long-term advantages of sex. Ancient asexual lineages provide rare exceptions to this rule and so can yield valuable information relating to the evolutionary forces underlying the maintenance of sex. Microsporidia are parasitic, unicellular fungi. They include many asexual species which have traditionally been grouped together into large, presumably ancient taxonomic groups. However, these putative ancient asexual lineages have been identified on the basis of morphology, life cycles and small subunit ribosomal RNA (16S rRNA) gene sequences, all of which hold questionable value in accurately inferring phylogenetic relationships among microsporidia.

Results

The hypothesis of a single, ancient loss of sex within the Nosema/Vairimorpha group of microsporidia was tested using phylogenetic analyses based on alignments of rRNA and RPB1 gene sequences from sexual and asexual species. Neither set of gene trees supported ancient asexuality, instead indicating at least two, recent losses of sex.

Conclusion

Sex has been lost on multiple, independent occasions within the Nosema/Vairimorpha group of microsporidia and there is no evidence for ancient asexual lineages. It appears therefore that sex confers important long-term advantages even upon highly simplified eukaryotes such as microsporidia. The rapid evolution of microsporidian life cycles indicated by this study also suggests that even closely related microsporidia cannot be assumed to have similar life cycles and the life cycle of each newly discovered species must therefore be completely described. These findings are relevant to the use of microsporidia as biological control agents, since several species under consideration as potential agents have life cycles that have been incompletely described.

Analogs of the Golgi complex in microsporidia: structure and avesicular mechanisms of function

Microsporidia are obligatory intracellular parasites, most species of which live in the host cell cytosol. They synthesize and then transport secretory proteins from the endoplasmic reticulum to the plasma membrane for formation of the spore wall and the polar tube for cell invasion. However, microsporidia do not have a typical Golgi complex. Here, using quick-freezing cryosubstitution and chemical fixation, we demonstrate that the Golgi analogs of the microsporidia Paranosema (Antonospora) grylli and Paranosema locustae appear as 300-nm networks of thin (25- to 40-nm diameter), branching or varicose tubules that display histochemical features of a Golgi, but that do not have vesicles. Vesicles are not formed even if membrane fusion is inhibited. These tubular networks are connected to the endoplasmic reticulum, the plasma membrane and the forming polar tube, and are positive for Sec13, gammaCOP and analogs of giantin and GM130. The spore-wall and polar-tube proteins are transported from the endoplasmic reticulum to the target membranes through these tubular networks, within which they undergo concentration and glycosylation. We suggest that the intracellular transport of secreted proteins in microsporidia occurs by a progression mechanism that does not involve the participation of vesicles generated by coat proteins I and II.

Pyruvate-converting activity in the spores of the microsporidian genus Paranosema (Antonospora)

Microsporidia, a large group of fungi-related protozoa with an obligate intracellular lifestyle, are characterized by a drastically reduced cell machinery and a unique metabolism. These parasites possess genes encoding glycolysis components and glycerol-phosphate shuttle, but lack typical mitochondria, Krebs cycle, respiratory chain and pyruvate-converting enzymes, except for two subunits of the E(1) enzyme of the pyruvate dehydrogenase complex. This study demonstrates that in spite of the above, destroyed spores of the microsporidian Paranosema (Antonospora) grylli and P. locustae deplete pyruvate content in the incubation medium. This activity is sensitive to heat, proportionally distributed between the soluble and the insoluble fractions and does not depend on additional ions or cofactors.

Recovery, bioaccumulation, and inactivation of human waterborne pathogens by the Chesapeake Bay nonnative oyster, Crassostrea ariakensis

The introduction of nonnative oysters (i.e., Crassostrea ariakensis) into the Chesapeake Bay has been proposed as necessary for the restoration of the oyster industry; however, nothing is known about the public health risks related to contamination of these oysters with human pathogens. Commercial market-size C. ariakensis triploids were maintained in large marine tanks with water of low (8-ppt), medium (12-ppt), and high (20-ppt) salinities spiked with 1.0 x 10(5) transmissive stages of the following human pathogens: Cryptosporidium parvum oocysts, Giardia lamblia cysts, and microsporidian spores (i.e., Encephalitozoon intestinalis, Encephalitozoon hellem, and Enterocytozoon bieneusi). Viable oocysts and spores were still detected in oysters on day 33 post-water inoculation (pwi), and cysts were detected on day 14 pwi. The recovery, bioaccumulation, depuration, and inactivation rates of human waterborne pathogens by C. ariakensis triploids were driven by salinity and were optimal in medium- and high-salinity water. The concentration of human pathogens from ambient water by C. ariakensis and the retention of these pathogens without (or with minimal) inactivation and a very low depuration rate provide evidence that these oysters may present a public health threat upon entering the human food chain, if harvested from polluted water. This conclusion is reinforced by the concentration of waterborne pathogens used in the present study, which was representative of levels of infectious agents in surface waters, including the Chesapeake Bay. Aquacultures of nonnative oysters in the Chesapeake Bay will provide excellent ecological services in regard to efficient cleaning of human-infectious agents from the estuarine waters.

Occurrence of the microsporidian parasite Nucleospora salmonis in four species of salmonids from the Massif Central of France

Nucleospora salmonis (Hedrick, Groff et Baxa, 1991), an intranuclear microsporidian parasite of marine and freshwater fish, causes diseases mainly in salmonid species. Losses have been reported in stocks of salmonid fish reared in the region of Auvergne (France). The cause of chronic mortalities in the local host species raised in aquaculture and destined for supplementation of the river system Loire-Allier was examined. The presence of N. salmonis was confirmed by PCR and histology in Salmo salar L. previously and in newly investigated salmonid species, Salmo salar, Salmo trutta fario L., Thymallus thymallus (L.) and Salvelinus alpinus (L.), present in European streams. The infection by N. salmonis was consistent in all cases with characteristic symptoms of the disease in deceased or moribund fish. The small subunit ribosomal DNA from N. salmonis was partially sequenced and compared to previously characterised N. salmonis isolates. As a result, a genotype, or clonal entity, was attributed to N. salmonis among Atlantic salmon found along the Northern Atlantic coastal lines and other salmonid species co-inhabiting or co-cultivated in the Auvergne region.

[An effect of the microsporidian Vairimorpha ephestiae (Microsporidia: Burenellidae) on activity and spectrum of nonspecific esterases in different tissues of the greater wax moth galleria mellonella (Lepidoptera: Pyralidae) larvae]

The effect of the microsporidian Vairimorpha ephestiae Matted (Microsporidia: Burenellidae) on nonspecific esterases was studied in hemolymph, fat body and midgut of the larvae of Galleria mellonella L. (Lepidoptera: Pyralidae). Esterase patterns were analyzed by the polyacrylamide gel electrophoresis, the total esterase activity was detected spectrophotometrically. The increase of total esterase activity was registered in hemolymph of inflected larvae. An overexpression of esterase isozyme in hemolymph was already detected at the 3rd day post infection. No changes in esterases pattern were observed in the fat body's homogenates of the G. mellonella larvae possessing the symptoms of microsporidiosis. The degradation of esterase isozymes and the decrease of total esterase activity in the pattern of the midgut homogenates of infected larvae were registered during parasite sporogony. The greatest esterase activity in hemolymph and midgut tissues was registered during vegetative reproduction of parasite, but the least level of esterase activity was observed during mass sporogony of microsporidia.

Transmission and burden and the impact of temperature on two species of vertically transmitted microsporidia

Microsporidia are unusual amongst eukaryotic parasites in that they utilize both vertical and horizontal transmission and vertically transmitted species can cause sex ratio distortion in their host. Here we study vertical transmission in two species of feminising microsporidia, Nosema granulosis and Dictyocoela duebenum, infecting a single population of the crustacean host Gammarus duebeni and measure the effect of temperature on parasite transmission and replication. N. granulosis was vertically transmitted to 82% of the host embryos and D. duebenum was transmitted to 72% of host embryos. For both parasites, we report relatively low parasite burdens in developing host embryos. However, the parasites differ in their pattern of replication and burden within developing embryos. Whilst N. granulosis undergoes replication during host development, the burden of D. duebenum declines, leading us to propose that parasite dosage and feminisation efficiency underlie the different parasite frequencies in the field. We also examine the effect of temperature on parasite transmission and replication. Temperature does not affect the percentage of young that inherit the infection. However, low temperatures inhibit parasite replication relative to host cell division, resulting in a reduction in parasite burden in infected embryos. The reduced parasite burden at low temperatures may underpin reduced feminization at low temperatures and so limit the spread of sex ratio distorters through the host population.

In vitro cultivation and electron microscopy characterization of Trachipleistophora anthropophthera isolated from the cornea of an AIDS patient

We describe an in vitro culture technique for a microsporidian isolated from the corneal biopsy of an HIV-infected patient. The corneal biopsy was inoculated into a monolayer culture of fibroblasts derived from newborn mouse brain and incubated at 37 degrees C in an atmosphere of 5% CO2. Minimum essential medium supplemented with 2% fetal bovine serum appeared to be an optimum medium for growth and maintenance of the parasite and for production of large numbers of spores. This microsporidian was identified as Trachipleistophora anthropophthera based on ultrastructural features. It forms two types of sporophorous vesicles and two types of spores simultaneously: polysporous vesicle type I with eight or more oval spores, 3.7-4.0 microm by 2.0-2.3 microm, and bisporous vesicle type II with two round spores, 1.7-2.2 microm by 1.6-2.0 microm in size.

[Microsporidia: general characteristics, infections and laboratory diagnosis]

Microsporidia are single celled, obligate intracellular, spore forming microorganisms which were first described as a cause of human disease in 1959. They are capable of infecting a wide variety of vertebrate and invertebrate hosts. Among the numerous microsporidial genera, seven have been described in human diseases such as Enterocytozoon, Encephalitozoon, Nosema, Pleistophora, Trachipleistophora, Vittaforma, Brachiola. Among these, Enterocytozoon bieneusi is the most frequently identified microsporidian in the patients. Features used in identification include spore size, nuclear configuration of spores, the number of polar tubule coils and the parazite-host interaction. In the development of Microsporidia, there are two different phases, called as proliferative phase and sporogonic phase. The only stage of Microsporidia outside the host is infective spores. The microsporidial spore is highly specialized, environmentally resistant structure that varies in size and shape according to species. They can cause infections both in immunocompetent subjects and immunocompromised patients such as AIDS. Although it can cause self-limiting infections in immunocompetent patients, it can cause severe life threating infections especially AIDS patients. In this review, the basic biology, epidemiologic characteristics and immunopathogenesis of Microsporidia, together with the diagnosis and treatment of the infections have been discussed.

How do microsporidia invade cells?

Microsporidia are obligate intracellular eukaryotic parasites that utilize a unique mechanism to infect host cells. One of the main characteristics of all microsporidia is that they produce spores containing an extrusion apparatus that consists of a coiled polar tube ending in an anchoring disc at the apical part of the spore. With appropriate conditions inside a suitable host, the polar tube is discharged through the thin anterior end of the spore, thereby penetrating a new host cell for inoculating the infective sporoplasm into the new host cell. This method of invading new host cells is one of the most sophisticated infection mechanisms in biology and ensures that the microsporidia enter the host cell unrecognized and protected from the host defence reactions. Recent studies have shown that microsporidia gain access to host cells by phagocytosis as well. However, after phagocytosis, the special infection mechanism of the microsporidia is used to escape from the maturing phagosomes and to infect the cytoplasm of the cells. Gaining access to cells by endocytosis, and escaping destruction in the phago-/endo-/lysosome by egressing quickly from the phagocytic vacuole to multiply outside the lysosome, is a common phenomenon in biology that has been evolved several times during evolution. How this is put into execution by the microsporidia is an inimitable principle by which an obligate intracellular organism has managed this problem. The extrusion apparatus of the microsporidia has obviously ensured the success of this phylum during evolution, resulting in a group of obligate intracellular organisms, capable of infecting almost any type of host and cell.

Public health importance of Brachiola algerae (Microsporidia)--an emerging pathogen of humans

Brachiola algerae, a parasite of Anopheles mosquitoes, has also been isolated from a human cornea, a cutaneous nodule and deep muscle tissue. All three human isolates of B. algerae are morphologically, serologically, and genetically similar to the mosquito-derived isolates including the original isolate of Vavra and Undeen. All of these isolates grew well in mammalian cell cultures at 37 degrees C and produced spores. Transmission electron microscopy revealed that all developmental stages including meronts, sporoblasts and spores were diplokaryotic and developed in direct contact with the host cell cytoplasm, a feature characteristic of the genus Brachiola. Spores of all isolates reacted well, in the immunofluorescence assay, with the rabbit anti-B. algerae serum. In the immunoblot assay, although the overall banding patterns of the human and mosquito isolates were similar, minor differences could be discerned. Sequencing of the PCR products of the amplified SSU rRNA gene revealed the existence of two distinct genotypes; the original mosquito (Undeen) isolate belonged to genotype 1 and the isolate from cornea and that from the deep muscle biopsy to genotype 2, whereas the isolates from a mosquito and one of the other two human isolates (one from skin abscess) had both genotypes, 1 and 2. It is known that spores of mosquito-derived B. algerae can not only proliferate in mammalian cell cultures at 37 degrees C but also can infect mice when injected into footpads or deposited on the corneal surface. These observations indicate that the spores have potential to be a risk factor for humans, especially those with immunodeficiency.

In Vitro Cultivation of an Insect Microsporidian Tubulinosema ratisbonensis in Mammalian Cells

Tubulinosema ratisbonensis is a microsporidian pathogen of Drosophila melanogaster belonging to the family Tubulinosematidae. The microsporidia in this family mainly cause infections in invertebrate hosts, but two members of this family, Brachiola vesicularum and Brachiola algerae, have been found to cause infections in humans as well. Moreover, B. algerae can be transmitted to immunodeficient mice and grows in mammalian cell cultures. Thus, the examination of the opportunistic properties of other members of the family Tubulinosematidae is important. Spores of T. ratisbonensis, isolated from infected fruit flies, were used to inoculate mammalian and insect cell cultures. Parasite growth was only seen in human lung fibroblasts. No growth was seen in Vero cells or insect cell cultures. Comparison of growth kinetics at 31 degrees C and 37 degrees C showed that there were fewer and smaller parasitic foci in cultures incubated at 37 degrees C. Transmission electron microscopy revealed the typical ultrastructure of T. ratisbonensis, and scanning electron microscopy showed oval or slightly pyriform spores, with some spores having extruded their polar tubes. The PCR-amplified sequences of rDNA fragments from infected cell cultures were 100% identical to the original T. ratisbonensis rRNA sequence. As T. ratisbonensis is able to proliferate in mammalian cell cultures, it may have the opportunistic properties of other members of the family Tubulinosematidae.

Review of microsporidia-mosquito relationships: from the simple to the complex

Microsporidia in mosquitoes can be divided into two categories based on their life cycles and host-parasite relationships. Some species of microsporidia exhibit simple life cycles with one spore type responsible for oral (horizontal) transmission. They affect only one generation of the mosquito and are not usually host or tissue specific. Brachiola algerae and Vavraia culicis are examples of species isolated from mosquitoes with relatively straightforward life cycles (one spore type) and simple host-parasite relationships. B. algerae and a close relative of V. culicis have also been isolated from a vertebrate (human) host but sources for these infections are unknown. In contrast to B. algerae and V. culicis, polymorphic (heterosporous) microsporidia in mosquitoes are characterized by complex life cycles involving multiple spore types responsible for horizontal and vertical transmission. They affect two generations of the mosquito and some involve an obligate intermediate host. These microsporidia are generally very host and tissue specific with complex developmental sequences comprised of unique stages and events. The microsporidium Edhazardia aedis is a pathogen of Aedes aegypti and does not require an intermediate host. The developmental cycle of E. aedis is characterized by four sporulation sequences, two in the parental host and two in the filial generation. Recent speculation relative to the source of B. algerae human infection have implicated infected mosquitoes and raised concerns about the safety of mosquito microsporidia in general. The subject of this review is to compare and contrast three species of microsporidia from mosquitoes, two with broad host ranges (B. algerae and V. culicis) and one specific to mosquitoes (E. aedis). This review describes features that distinguish mosquito-parasitic microsporidia with simple life cycles and broad host ranges from truly mosquito-specific microsporidian parasites with complex life cycles.

Microsporidian xenomas in fish seen in wider perspective

The history of understanding xenoparasitic complexes or xenomas provoked in the host cell by various protists and especially by microsporidia is outlined. Microsporidia have been known to produce xenomas in oligochaetes (e.g., genera Bacillidium, Burkea, Hrabyeia, Jirovecia, species of the collective group Microsporidium), crustaceans (e.g., Abelspora, Mrazekia), insects (e.g., Polydispyrenia, Thelohania) and poikilothermic vertebrates, mostly fish (Alloglugea, Amazonspora, Glugea, Ichthyosporidium, Loma, Microfilum, Microgemma, Neonosemoides, Pseudoloma, Spraguea, Tetramicra). An overview of characters of xenomas caused by species of these genera is presented. The study of microsporidia causing xenomas in fish offers an insight into cell pathology and is of interest since many of these species are important agents of diseases in commercial fish. Xenomas produced from a few types of target cell display a complete change of organisation of the host cell and differ, according to the agent, in their structure. Recent data show that proliferation of the parasite may have already started in the cells transporting the parasites to the final site of xenoma formation. However, these are preliminary revelations and most of the facets of the life cycle are still to be clarified. Curiously, xenoma-forming microsporidia do not seem to be strictly host specific. The salient features of fish microsporidian xenomas are discussed, such as role of the xenoma, whether its features are host- or microsporidium-dependent, development and demise of the xenoma in the course of time, and host reaction phenomena. The need of further research is emphasised.

Microsporidiosis: an emerging and opportunistic infection in humans and animals

Microsporidia have emerged as causes of infectious diseases in AIDS patients, organ transplant recipients, children, travelers, contact lens wearers, and the elderly. These organisms are small single-celled, obligate intracellular parasites that were considered to be early eukaryotic protozoa but were recently reclassified with the fungi. Of the 14 species of microsporidia currently known to infect humans, Enterocytozoon bieneusi and Encephalitozoon intestinalis are the most common causes of human infections and are associated with diarrhea and systemic disease. Species of microsporidia infecting humans have been identified in water sources as well as in wild, domestic, and food-producing farm animals, raising concerns for waterborne, foodborne, and zoonotic transmission. Current therapies for microsporidiosis include albendazole which is a benzimidazole that inhibits microtubule assembly and is effective against several microsporidia, including the Encephalitozoon species, but is less effective against E. bieneusi. Fumagillin, an antibiotic and anti-angiogenic compound produced by Aspergillus fumigatus, is more broadly effective against Encephalitozoon spp. and Enterocytozoon bieneusi but is toxic when administered systemically to mammals. Gene target studies have focused on methionine aminopeptidase 2 (MetAP2) for characterizing the mechanism of action and for identifying more effective, less toxic fumagillin-related drugs. Polyamine analogues have shown promise in demonstrating anti-microsporidial activity in culture and in animal models, and a gene encoding topoisomerase IV was identified in Vittaforma corneae, raising prospects for studies on fluoroquinolone efficacy against microsporidia.

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.

A primary culture of haemocytes isolated from Gryllus bimaculatus (Orthoptera, Gryllidae) and their interactions with two intracellular parasites--Paranosema grylli (Microsporidia) and Adelina grylli (Coccidia)

Cricket haemocytes were derived from either haemolymph or haemopoietic organs (lymph glands) of insects and introduced to a primary culture. Varied isolation protocols, tissue culture vessels, media compositions and cell densities were tested to determine the optimal conditions for in vitro maintenance of haemocytes, and for subsequent light and electron microscopic analysis of monolayers. Freshly prepared Mitsuhashi and Maramorosh (MM;Sigma, Steinheim, Germany) insect medium (420 mOsm), buffered with sodium bicarbonate (pH 7.2) and supplemented with 10 % FCS, was found to be most appropriate for haemocyte maintenance. All tested tissue culture vessels (FLEXiperm units, multiwell plates and Thermanox slides, with the exception of Melineux agar plates), were suitable for cell attachment and haemocyte monolayers formation. Viability of cultured cells was confirmed by LIVE/DEAD Viability/Cytotoxity Kit for Eukaryotic Cells. Free circulating haemocytes were cultivated up to 27 days and then degraded. Infection with the microsporidian Paranosema grylli or the coccidian Adelina grylli caused noticeable swelling of host lymph glands (haemopoietic tissue) and increase in the number of cells comprising the glands. The cells derived from haemopoietic tissue were maintained for maximum 5 days; thereafter multiplication of bacteria normally inhabiting cricket lymph glands destroyed monolayers and killed the cells. Microsporidian and coccidian invasive stages (spores and sporozoites, respectively) were isolated from infected tissues, resuspended in MM medium and added to haemocyte monolayers in ratios 1 zoite per haemocytes or 10 spores per 1 haemocyte. Actively moving zoites contacted and penetrated the cultured cells. Unlike coccidian zoites, microsporidian spores were phagocytized by haemocytes. Application of fluorescent LIVE/DEAD kit allowed to visualize internalized parasites inside host cells as clearly shaped dark areas. The present study has demonstrated that 1) cricket haemocytes from both circulating haemolymph and lymph glands can be short-term cultivated on tissue culture vessel surfaces which made possible their further light and electron microscopic analysis; 2) short-term haemocyte cultures may be employed to study host-parasite interactions, in particular, to follow the initial steps of parasite internalization inside host cell; 3) Fluorescent assay with Viability/Cytotoxity Kit for Eukaryotic Cells (Molecular Probes, Oregon) allows to observe penetration of these parasites into cultured cells.

Predictive Modelling of Post-onset Xenoma Growth During Microsporidial Gill Disease (Loma salmonae) of Salmonids

Loma salmonae, an obligate intracellular microsporidian parasite, is the causal agent of microsporidial gill disease of salmon (MGDS), characterized by the production, growth and eventual rupture of spore-filled xenomas. MGDS in farmed chinook salmon remains occult until xenoma rupture, at which time the infected fish respond with intense branchitis and high rates of mortality. The present study showed that in experimentally infected fish the rate of change of xenoma diameter could be modelled through regression analysis, particularly through the period of 4-9 weeks post-infection, yielding the predictive equation: xenoma diameter=-42.9 microns +15.3 microns x (number of weeks post-infection). This provides a tool for diagnosticians to predict the time to xenoma rupture and hence to the initiation of the clinical phase of MGDS.

Experimental infection of severe combined immunodeficient (SCID) mice with the human microsporidian Trachipleistophora hominis

Different courses of microsporidiosis, related to the route of infection, were observed in severe combined immunodeficient (SCID) mice inoculated with spores of the human microsporidian Trachipleistophora hominis (Phylum Microspora). After eye contamination by spores the mice became moribund within 7 to 8 weeks, showing severe infection in the conjunctiva and cornea, and lighter infections in the urinary bladder, liver and spleen. The mean survival time of intramuscularly inoculated SCID mice was 12 weeks, when heavy infection was found in muscles around the site of inoculation, and also in several viscera. Subcutaneously inoculated SCID mice developed skin lesions around the inoculation sites, and heavy urinary bladder infection, and died 6 or 7 weeks after inoculation. Intracerebrally inoculated SCID mice became moribund 5 or 6 weeks after inoculation with massive infection in the urinary bladder and liver, but none in the brain. Intraperitoneally inoculated SCID mice survived for 13 weeks and the urinary bladder and liver were the most heavily infected organs. The SCID mice, inoculated perorally and examined after 23 weeks, were uninfected. Infection was not detected in the brain of any of the inoculated SCID mice. Our results show that T. hominis has very little tissue specificity. Peroral infection seems to be ineffective in T. hominis, but eye conta mination or insect bite (as mimicked by injection) are suggested as possible routes of infection under natural conditions.

Modes of transmission of Glugea plecoglossi (Microspora) via the skin and digestive tract in an experimental infection model using rainbow trout, Oncorhynchus mykiss (Walbaum)

Glugea plecoglossi (Microspora) is a significant cause of economic loss in cultured ayu, Plecoglossus altivelis, in Japan, due to the unsightly appearance of infected fish harbouring xenomas in the body cavity. Modes of transmission of G. plecoglossi via the skin and digestive tract were studied in an experimental infection model using rainbow trout, Oncorhynchus mykiss. Combined with Uvitex 2B and in situ hybridization (ISH) assays, the early development of G. plecoglossi was successfully traced. Following a bath exposure of fish Uvitex 2B-labelled G. plecoglossi spores were observed to attach to microscopic injuries (trypan blue-positive sites) of fish skin, after which ISH-positive sporoplasms were found to invade the epidermis as early as 5 min post-infection (PI), migrating rapidly to the subdermis. It was also shown that G. plecoglossi entering via the skin does not spread into the internal organs but develops into subdermal xenomas. After rainbow trout were exposed to G. plecoglossi spores by oral intubation, spores germinated in the intestinal lumen, followed by penetration of sporoplasms into the gut mucosal epithelium 5 min PI. In vitro trials determining stimulation factors (fish mucus, changes in pH, digestive enzymes) for the extrusion of the polar tube were inconclusive. The present study indicates that skin wounds and the gut epithelium can be portals of entry of G. plecoglossi and that natural infection in fish seems to occur perorally rather than via the skin.

Virulence reaction norms across a food gradient

Host-parasite interactions involve competition for nutritional resources between hosts and the parasites growing within them. Consuming part of a host's resources is one cause of a parasite's virulence, i.e. part of the fitness cost imposed on the host by the parasite. The influence of a host's nutritional conditions on the virulence of a parasite was experimentally tested using the mosquito Aedes aegypti and the microsporidian parasite Vavraia culicis. A condition-dependent expression of virulence was found and a positive relation between virulence and transmissibility was established. Spore production was positively influenced by host food availability, indicating that the parasite's within-host growth is limited by host condition. We also investigated how the fitness of each partner varied across the nutritional gradient and demonstrated that the sign of the correlation between host fitness and parasite fitness depended on the amount of nutritional resources available to the host.

Within-host dynamics of a microsporidium with horizontal and vertical transmission: Octosporea bayeri in Daphnia magna

The fresh-water crustacean Daphnia magna may acquire an infection with the microsporidium Octosporea bayeri either by ingesting spores from the water (horizontally), or directly from its mother (vertically). Due to differences in the time and mechanisms of transmission, horizontal and vertical infections may lead to differences in the growth of the parasite within the host. This may influence parasite virulence, transmission to new hosts, and, consequently, epidemiology and evolution. Here we describe the within-host dynamics of 3 spore-types of O. bayeri from infections that were acquired either horizontally or vertically. In all treatments the number of spores increased exponentially until spore density reached a plateau, suggesting density-dependent within-host growth. The spore types seen differ in their growth dynamics, suggesting different roles in the parasite life-cycle. Horizontally-infected hosts harboured significantly fewer spores than vertically-infected hosts. Further, host survival was affected by infection route, with mortality being higher in horizontal infections than in vertical infections. Our results suggest that different routes of infection have an immediate effect on within-host parasite growth and thus on parasite fitness and epidemiology.

Thelohania montirivulorum sp. nov. (Microspora: Thelohaniidae), a parasite of the Australian freshwater crayfish, Cherax destructor (Decapoda: Parastacidae): fine ultrastructure, molecular characteristics and phylogenetic relationships

Thelohania montirivulorum sp. nov., a new species of microsporidian parasite, was found in a highland population of the Australian yabby, Cherax destructor. Data are presented on fine ultrastructure, developmental morphology and DNA sequence of the small subunit ribosomal DNA (SSU rDNA) and internal transcribed spacer region. The phylogenetic relationships of T. montrivulorum sp. nov. and other crayfish parasites in the genus Thelohania, based on the SSU rDNA sequence, are investigated. Fine ultrastructure, patterns of sporogony and SSU rDNA sequence similarities indicate T. montirivulorum sp. nov. is congeneric with T. parastaci, a parasite of lowland populations of C. destructor, and with T. contejeani, a parasite of European freshwater crayfish. SSU rDNA data suggests Thelohania species found in crustacean hosts are more closely related to the Vairimorpha/ Nosema clade of species from insect and crustacean hosts than to the fire ant parasites, T. solenopsae and Thelohania sp.

Life cycle and epizootiology of Amblyospora ferocis (Microspora: Amblyosporidae) in the mosquito Psorophora ferox (Diptera: Culicidae)

A natural population of Psorophora ferox (Humbold, 1820) infected with the microsporidium Amblyospora ferocis Garcia et Becnel, 1994 was sampled weekly during a seven-month survey in Punta Lara, Buenos Aires Province, Argentina. The sequence of development of A. ferocis in larvae of P. ferox leading to the formation of meiospores followed the developmental pathway previously reported for various species of Amblyospora. The natural prevalence of A. ferocis in the larval population of P. ferox ranged from 0.4% to 13.8%. Spores were detected in the ovaries of field-collected females of P. ferox and were shown to be responsible for transovarial transmission of A. ferocis to the next generation of mosquito larvae in laboratory tests. These spores were binucleate and slightly pyriform in shape. The prevalence of A. ferocis in the adult population ranged from 2.7% to 13.9%. Data on effects of the infection on female fecundity showed that infected field-collected adults of P. ferox laid an average of 47.6 +/- 6.5 eggs of which 35.8% +/- 4.1% hatched. Uninfected field-collected adults of P. ferox laid 82.8 +/- 6.8 eggs of which 64.1% +/- 5.5% hatched. Six species of copepods living together with P. ferox were fed meiospores from field-infected larvae but none became infected. Horizontal transmission of A. ferocis to P. ferox larvae remains unknown.

Thelohania parastaci sp. nov. (Microspora: Thelohaniidae), a parasite of the Australian freshwater crayfish, Cherax destructor (Decapoda: Parastacidae)

Thelohania parastaci sp. nov. infects the Australian freshwater crayfish, Cherax destructor. Data on morphology, developmental patterns and sequences from the small subunit (SSU) and internal transcribed spacer (ITS) regions of the ribosomal DNA (rDNA) of T. parastaci sp. nov. are described. The ultrastructural features of different life cycle stages are very similar to those of the European crayfish parasite Thelohania contejeani. T. parastaci sp. nov. exhibits simultaneous dimorphic sporogony in muscle tissue. Meronts, sporonts and spores are found in muscle tissue, within haemocytes in the hepatopancreas, and in the intestinal wall of infected crayfish. T. parastaci sp. nov. shows 92% sequence identity with T. contejeani and only 67% sequence identity with the fire ant pathogen T. solenopsae, when SSU rDNA sequences are compared. Analysis of SSU rDNA and ITS sequences of T. parastaci sp. nov. from crayfish from Victoria, Western Australia, and New South Wales indicate that the parasite has a wide geographical distribution in Australia.

Ultrastructural study of the late stages of Loma salmonae development in the gills of experimentally infected rainbow trout

The main objective of this investigation was to examine the ultrastructural features of gills from rainbow trout experimentally infected with Loma salmonae to determine the morphological events that occur during the late stages of development of this parasite. Peripheral distribution of the mature parasites inside round xenomas was observed at weeks 5 and 6 postexposure (PE), but eventually the parasite occupied the entire xenoma. Degenerative changes were observed only in immature parasites at week 7 PE, and eventually an inflammatory reaction with a cellular infiltration was directed against mature spores. Round, flattened, and irregular shaped xenomas were observed at week 8 PE. The round xenomas showed a severe inflammatory response with disintegration of the xenoma membrane. This event was accompanied by eversion of polar tubes within the attacked xenoma and by the simultaneous presence of 2 tubular appendages, the type I and II tubules. Flattened xenomas were observed below the endothelium of gill lamella arteries. The irregular xenomas were located in the connective tissue of the gill filament and showed multiple projections occupied by spores. Both flattened and irregular xenomas showed no evidence of inflammatory reaction. An earlier proposed hypothesis is expanded to explain how L. salmonae is implanted beneath lamellar endothelium and within filament connective tissue.

Ultrastructure and development of Pleistophora ronneafiei n. sp., a microsporidium (Protista) in the skeletal muscle of an immune-compromised individual

This report provides a detailed ultrastructural study of the life cycle, including proliferative and sporogonic developmental stages, of the first Pleistophora species (microsporidium) obtained from an immune-incompetent patient. In 1985, the organism obtained from a muscle biopsy was initially identified as belonging to the genus Pleistophora, based on spore morphology and its location in a sporophorous vesicle. Since that initial report, at least two new microsporidial genera, Trachipleistophora and Brachiola, have been reported to infect the muscle tissue of immunologically compromised patients. Because Trachipleistophora development is similar to Pleistophora, and as Pleistophora was only known to occur in cold-blooded hosts, the question of the proper classification of this microsporidium arose. The information acquired in this study makes it possible to compare Pleistophora sp. (Ledford et al. 1985) to the known human infections and properly determine its correct taxonomic position. Our ultrastructural data have revealed the formation of multinucleate sporogonial plasmodia, a developmental characteristic of the genus Pleistophora and not Trachipleistophora. A comparison with other species of the genus supports the establishment of a new species. This parasite is given the name Pleistophora ronneafiei n. sp.

[Crepidula beklemishevi gen. et sp. n. and Dimeiospora palustris gen. et sp. n. (Microspora: Amblyosporidae)--new microsporidian genera and species from blood-sucking mosquitoes (Diptera: Culicidae) from the south of the western Siberia]

Microsporidia parasitizing the adipose body of mosquito larvae of Anopheles beklemishevi and Aedes punctor has been studied. Two new genera of microsporidia are described based on lightmicroscopic and ultrastructural characteristics of spores and sporogony stages. The spore wall of Crepidula beklemishevi gen. n. et sp. n. is formed by two-membrane exospore, thick exospore, bilayer endospore and thin plasmolemma. Spores with single nucleus, polar filament anisofilar, with 6-7 coils (2+ 4-5), polaroplast consisting of three parts: macrochelicoidal, microhelicoidal and lamellar. Fixed spores 4.2 +/- 0.22 x 2 +/- 0.01 microns. The sporogony of Dimeiospora palustris gen. et. n. results in spore formation of two different types. Spores of the first type are oviform, with thick wall, single-nuclear, 6.1 x 4.9 microns. Spore wall with three layers, about 370 nm. Exospore electron-dense, subexospore moderately electrondense. Exospore and subexospore irregularly pleated on the almost spore surface and slightly thinner on anterior end only. Endospore electron-translucent. Polar filament anisofilar, with 9 coils (3 + 6). Polaroplas consists of three parts: lamellar, fine bubbled, and coarse bubbled. Spores of the second type broad-ovate, with apical pole narrower, distal pole concave, 4.6 x 3.7 microns. Spore wall with three layer, 355 nm. Exospore on the apical end irregularly pleated, consists of thin electrondense exospore, subexospore of variable electron density, endospore electron-translucent. Polar filament anisofilar, with 13 coils (3 + 10). Polaroplast has two parts: lamellar and vesicular.

The impact of a vertically transmitted microsporidian, Nosema granulosis on the fitness of its Gammarus duebeni host under stressful environmental conditions

Although purely vertically transmitted parasites are predicted to cause low pathogenicity in their hosts, the effects of such parasites on host fitness under stressful environmental conditions have not previously been assessed. Here, we investigate the effects of Nosema granulosis, a vertically transmitted, microsporidian parasite of the brackish water amphipod Gammarus duebeni, on host growth and survival under conditions of host-host competition and limited food. The parasite had no effect on host survival, but caused a reduction in juvenile growth. Stressful environmental conditions also led to a reduction in G. duebeni growth. However, we found no evidence to support the prediction that parasitized hosts would suffer a greater reduction in fitness than uninfected hosts under adverse environmental conditions. We interpret our results in the context of selection for successful vertical parasite transmission.

Microsporidia: biology and evolution of highly reduced intracellular parasites

Microsporidia are a large group of microbial eukaryotes composed exclusively of obligate intracellular parasites of other eukaryotes. Almost 150 years of microsporidian research has led to a basic understanding of many aspects of microsporidian biology, especially their unique and highly specialized mode of infection, where the parasite enters its host through a projectile tube that is expelled at high velocity. Molecular biology and genomic studies on microsporidia have also drawn attention to many other unusual features, including a unique core carbon metabolism and genomes in the size range of bacteria. These seemingly simple parasites were once thought to be the most primitive eukaryotes; however, we now know from molecular phylogeny that they are highly specialized fungi. The fungal nature of microsporidia indicates that microsporidia have undergone severe selective reduction permeating every level of their biology: From cell structures to metabolism, and from genomics to gene structure, microsporidia are reduced.

Alterations in carbohydrate and fatty acid levels of Lymantria dispar larvae caused by a microsporidian infection and potential adverse effects on a co-occurring endoparasitoid, Glyptapanteles liparidis

Infection of Lymantria dispar host larvae by the entomopathogenic microsporidium Vairimorpha sp. has a negative impact on the performance of the endoparasitic braconid Glyptapanteles liparidis. To investigate possible causes for this effect, we studied to what extent nutritional host suitability is altered by the microsporidium. Therefore, we analyzed carbohydrates and fatty acids in host larvae after Vairimorpha infection and/or parasitism by G. liparidis. Trehalose levels were significantly reduced in the hemolymph of infected hosts. After day five post infection, it was detected only in traces. Four to six days later, the glycogen resources were depleted in infected larvae. Parasitism by G. liparidis, on the other hand, led to increased hemolymph trehalose levels during the early endoparasitic phase but to a significant decrease at the end of its larval development. No effect of parasitism on the glycogen content was ascertained. Hemolymph levels of the fatty acids analyzed, such as palmitic, stearic, oleic, linoleic, and linolenic acid, were significantly reduced in microsporidia-infected L. dispar. Vairimorpha sp. develops as an intracellular parasite in the fat body of the host larva and synthesis of trehalose and fatty acids may be disturbed. Moreover, microsporidia may also harness metabolites or energy produced by host cells. We conclude that the microsporidia-induced decrease in hemolymph carbohydrates and fatty acids adversely affects growth and development of parasitoid larvae.

Infection of Gammarus duebeni populations by two vertically transmitted microsporidia; parasite detection and discrimination by PCR-RFLP

We screened a population of the brackish water crustacean Gammarus duebeni from the Isle of Cumbrae for the presence of vertically transmitted microsporidia. We compared 2 screening techniques; light microscopy and PCR-based detection using generic 16S rDNA microsporidian primers. Fifty percent of females from this population tested positive for vertically transmitted microsporidia. The PCR screen was 100% efficient in comparison with existing LM based screening. In addition, the PCR screen produced bands of 2 sizes suggesting that more than 1 species of microsporidian was present. Sequencing revealed 2 distinct species of vertically transmitted microsporidia; 33% of females were infected with the feminizer Nosema granulosis and 17% were infected with a new species which we provisionally designate Microsporidium sp. On the basis of sequence information, we developed a discriminatory PCR-RFLP test based on MspI and HaeIII digests. This screen allows rapid detection and discrimination of vertically transmitted microsporidia in natural field populations. We applied the PCR-RFLP screen to a second G. duebeni population from the Isle of Man. This population also hosted these 2 parasite species. In total 45% of females harboured N. granulosis and 10% harboured Microsporidium sp. No dual-infected individuals were found in either population. The occurrence of 2 vertically transmitted parasites within a population has implications for our understanding of parasite-host relationships in the field and we discuss factors affecting the dynamics of parasite-parasite competition and coexistence.

Life cycle, ultrastructure and molecular phylogeny of Hyalinocysta chapmani (Microsporidia: Thelohaniidae), a parasite of Culiseta melanura (Diptera: Culicidae) and Orthocyclops modestus (Copepoda: Cyclopidae)

The complete life cycle of the microsporidium Hyalinocysta chapmani is described from the primary mosquito host Culiseta melanura and the intermediate copepod host Orthocyclops modestus. Infections are initiated in larval C. melanura following the oral ingestion of uninucleate spores from infected copepods. Spores germinate within the lumen of the midgut and directly invade fat body tissue where all development occurs. Uninucleated schizonts undergo binary division (schizogony) followed by karyokinesis (nuclear division) to form diplokaryotic meronts. Merogony is by synchronous binary division. The onset of sporogony is characterized by the simultaneous secretion of a sporophorous vesicle and meiotic division of the diplokaryon resulting in the formation of eight ovoid meiospores enclosed within a sporophorous vesicle. Most infected larvae die during the fourth stadium and there is no evidence of a developmental sequence leading to vertical transmission. Hyalinocysta chapmani is horizontally transmitted to O. modestus via oral ingestion of meiospores. Infections become established within ovarian tissue of females and all parasite development is haplophasic. Uninucleate schizonts divide by binary division during an initial schizogonic cycle. Newly formed uninucleate cells produce a thin sporophorous vesicle and undergo repeated nuclear division during sporogony to produce a rosette-shaped, multinucleated sporogonial plasmodium with up to 18 nuclei. This is followed by cytoplasmic cleavage, sporogenesis, and disintegration of the sporophorous vesicle to form membrane-free uninucleate spores. Infected females eventually die and there is no egg development. The small subunit rDNA sequence of H. chapmani isolated from meiospores from C. melanura was identical to the small subunit rDNA sequence obtained from spores from O. modestus, corroborating the laboratory transmission studies and confirming the intermediary role of O. modestus in the life cycle. Phylogenetic analysis was conducted with closely related microsporidia from mosquitoes. Hyalinocysta chapmani did not cluster within described Amblyospora species and can be considered a sister group, warranting separate genus status.

In vitro cultivation of microsporidia of clinical importance

Although attempts to develop methods for the in vitro cultivation of microsporidia began as early as 1937, the interest in the culture of these organisms was confined mostly to microsporidia that infect insects. The successful cultivation in 1969 of Encephalitozoon cuniculi, a microsporidium of mammalian origin, and the subsequent identification of these organisms as agents of human disease heightened interest in the cultivation of microsporidia. I describe the methodology as well as the cell lines, the culture media, and culture conditions used in the in vitro culture of microsporidia such as Brachiola (Nosema) algerae, Encephalitozoon cuniculi, E. hellem, E. intestinalis, Enterocytozoon bieneusi, Trachipleistophora hominis, and Vittaforma corneae that cause human disease.

Ultrastructural study of the early development and localization of Loma salmonae in the gills of experimentally infected rainbow trout

The early ultrastructural stages of Loma salmonae were studied in the gills of experimentally infected rainbow trout. No parasitic stages were identified during the first 2 wk of the infection. By week 3 postexposure (PE), uninucleate and binucleate meronts were recognized within host cells (no xenomas) associated with the capillary channels of secondary lamellae and lamellar arteries. An inflammatory reaction was absent. In secondary lamellae, infected cells were isolated from the capillary lumen, and some were recognized as pillar cells. In lamellar arteries, infected cells were localized beneath the endothelium and not in the lumen. Inflammatory reaction and destruction of parasites inside blood cells in the lumen of secondary lamellae were observed by week 4 PE. Three hypotheses, i.e., isolation, internalization, and evasion, are proposed to explain the localization of the infected cells in the gills. It is concluded that meronts are the earliest parasitic stage observed by week 3 PE, pillar cells are secondarily infected by phagocytosis of infected cells in the blood, endothelial cells of gills are not infected, and inflammatory response to the parasite starts by week 4 PE.