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The microsporidian genus Nosema is primarily known to infect insects of economic importance stimulating high research interest, while other hosts remain understudied. Nosema granulosis is one of the formally described Nosema species infecting amphipod crustaceans, being known to infect only two host species. Our first aim was to characterize Nosema spp. infections in different amphipod species from various European localities using the small subunit ribosomal DNA (SSU) marker. Second, we aimed to assess the phylogenetic diversity, host specificity and to explore the evolutionary history that may explain the diversity of gammarid-infecting Nosema lineages by performing a phylogenetic reconstruction based on RNA polymerase II subunit B1 (RPB1) gene sequences. For the host species Gammarus balcanicus, we also analyzed sex ratios of progenies to test for sex ratio distortion in relation with Nosema infection. We identified Nosema spp. in 316 individuals from nine amphipod species being widespread in Europe. The RPB1-based phylogenetic reconstruction using newly reported sequences and available data from other invertebrates identified 39 haplogroups being associated with amphipods. These haplogroups clustered into five clades (A-E) that did not form a single amphipod-infecting monophyletic group. Closely related sister clades C and D correspond to Nosema granulosis. Clades A, B and E might represent unknown Nosema species infecting amphipods. Host specificity seemed to be variable with some clades being restricted to single hosts, and some that could be found in several host species. We show that Nosema parasite richness in gammarid hosts is much higher than expected, illustrating the advantage of the use of RPB1 marker over SSU. Finally, we found no hint of sex ratio distortion in Nosema clade A infecting G. balcanicus. This study shows that Nosema spp. are abundant, widespread and diverse in European gammarids. Thus, Nosema is as diverse in aquatic as in terrestrial hosts. Author summary: The intracellular microsporidian parasites of the genus Nosema are important pathogens as they infect insects of economic importance such as pollinators or domestic silk moths. However, they have been overlooked in other groups of invertebrates such as crustaceans, where only few Nosema spp. were detected, including Nosema granulosis in two gammarid amphipod hosts. Here, using molecular tools, we detected infections by Nosema spp. in nine freshwater amphipod species from various European localities. These infections are common, widespread, and the phylogenetic analysis revealed that some Nosema lineages are specific to certain host species, while the others are not restricted to single hosts. We also confirms that there are several Nosema lineages infecting gammarid crustaceans, not only N. granulosis, that can be new candidate species of Nosema. We conclude that Nosema is as diverse in aquatic as in terrestrial hosts. [ABSTRACT FROM AUTHOR]

The flat oyster Ostrea edulis is an oyster species native to Europe. It has declined to functional extinction in many areas of the NE Atlantic for several decades. Factors explaining this decline include over-exploitation of natural populations and diseases like bonamiosis, regulated across both the EU and the wider world and caused by the intracellular protozoan parasite Bonamia ostreae. To date, very limited sequence data are available for this Haplosporidian species. We present here the first transcriptome of B. ostreae. As this protozoan is not yet culturable, it remains extremely challenging to obtain high-quality -omic data. Thanks to a specific parasite isolation protocol and a dedicated bioinformatic pipeline, we were able to obtain a high-quality transcriptome for an intracellular marine micro-eukaryote, which will be very helpful to better understand its biology and to consider the development of new relevant diagnostic tools. [ABSTRACT FROM AUTHOR]

• The occurrence of E. cuniculi in Apodemus spp. and Myodes glareolus was reported for the first time. • The highest infection rate was recorded for A. flavicollis. • E. cuniculi genotype II was the most frequently recorded. • Uncommon in rodents, E. cuniculi genotypes I and III, were also identified. Encephalitozoon spp. is an obligate intracellular microsporidian parasite that infects a wide range of mammalian hosts, including humans. This study was conducted to determine the prevalence of Encephalitozoon spp. in wild living rodents from Poland, the Czech Republic and Slovakia. Faecal and spleen samples were collected from individuals of Apodemus agrarius , Apodemus flavicollis , Apodemus sylvaticus , and Myodes glareolus (n = 465) and used for DNA extraction. PCR, targeting the ITS region of the rRNA gene was performed. The overall prevalence of microsporidia was 15.1%. The occurrence of Encephalitozoon cuniculi in the abovementioned host species of rodents has been presented for the first time, with the highest infection rate recorded for A. flavicollis. Sequence analysis showed that the most frequent species was E. cuniculi genotype II (92.5%). E. cuniculi genotypes I (1.5%) and III (6.0%) were also identified. [ABSTRACT FROM AUTHOR]

[Display omitted] • One third of adult mosquitoes were positive for microsporidian DNA. • Central European mosquitoes are exposed to at least 13 microsporidian species. • Microsporidians infecting mosquitoes seems to be polyxenic parasites. • Some microsporidians co-occurring in the same host mutually affect each other. Microsporidians (Microsporidia) are a diverse group of obligate and intracellular parasites of eukaryotes. There is evidence that the real species diversity in the phylum could be greatly underestimated, especially for microsporidians parasitic on invertebrates. Mosquitoes (Culicidae) are among very important microsporidian host groups. However, to date, no extensive survey on the prevalence of microsporidians in European mosquitoes has been performed. Here, we used mosquitoes collected in west-central Poland and a metabarcoding approach to examine the prevalence and diversity of microsporidian species among European mosquitoes. We found that up to one-third of mosquitoes in Europe may be infected with at least 13 microsporidian species belonging to the genera Amblyospora , Hazardia , Encephalitozoon , Enterocytospora , and Nosema and the holding genus Microsporidium. The lack of a difference in microsporidian prevalence between mosquito sexes implies that other factors, e.g., temperature or humidity, affect microsporidian occurrence in adult mosquitoes. Each microsporidian species was found in at least three mosquito species, which suggests that these microsporidians are polyxenic rather than monoxenic parasites. The co-occurrence of at least two different microsporidian species was found in 3.6% of host individuals. The abundance of microsporidian DNA sequences suggests interactions between co-occurring parasites; however, these results should be confirmed by microscopic and quantitative methods. In addition, further histological research is required to describe Microsporidium sp. PL01 or match its DNA to that of an already described species. [ABSTRACT FROM AUTHOR]

Rickettsiae, obligate intracellular Gram-negative bacteria, responsible for mild to severe diseases in humans are associated with arthropod vectors. Dermacentor marginatus and Dermacentor reticulatus are known vectors of Rickettsia slovaca and Rickettsia raoultii distributed across Europe. A total of 794 D. marginatus, D. reticulatus and Ixodes ricinus adult ticks were collected from the vegetation, removed from horses, sheep, goats and dogs in Slovakia. The DNA of Rickettsia sp. was found in 229 ticks by PCR amplifying parts of gltA, ompA and sca4 genes. Next analyses of Rickettsia-positive samples by PCR-RFLP and/or sequencing showed D. reticulatus ticks were more infected with R. raoultii and D. marginatus were more infected with R. slovaca. The prevalence of R. raoultii was 8.1-8.6% and 22.3-27% in D. marginatus and D. reticulatus, respectively. The prevalence of R. slovaca was 20.6-24.3% in D. marginatus and 1.7-3.4% in D. reticulatus. Intracellular growth of R. raoultii isolate from D. marginatus tick was evaluated by rOmpA-based quantitative SybrGreen PCR assay. The highest point of multiplication was recorded on the 7th and 8th day postinfection in Vero and L929 cells, respectively. R. raoultii was transmitted during feeding of R. raoultii-positive ticks to guinea pigs and subsequently rickettsial infection was recorded in all organs, the highest infection was in spleen, liver and heart. Our study describes the detection and isolation of tick-borne pathogens R. raoultii and R. slovaca, show that they are spread in Slovakia and highlight their risk for humans. [ABSTRACT FROM AUTHOR]

L. monocytogenes is a widespread facultative intracellular pathogen. The range of natural hosts that supporting L. monocytogenes persistence in the environment has not been fully established yet. In this study, we were interested in the potential of L. monocytogenes to infect cells of bats, which are being increasingly recognized as a reservoir for microorganisms that are pathogenic to humans and domestic animals. A stable epithelial cell line was developed from the kidneys of Pipistrellus nathusii, a small bat widely distributed across Europe. The wild-type L. monocytogenes strain EGDe infected this cell line with an invasion efficiency of 0.0078 ± 0.0009%. Once it entered bat cells, L. monocytogenes doubled within about 70 min. When L. monocytogenes lacked either of the major invasion factors, InlA and InlB, invasion efficiency decreased by a factor of 10 and 25 respectively (p < 0.000001). The obtained results suggest that bat epithelial cells are susceptible to L. monocytogenes infection and that L. monocytogenes invasion of bat cells depends on the major invasion factors InlA and InlB. These results constitute the first report on in vitro studies of L. monocytogenes infection in bats. [ABSTRACT FROM AUTHOR]