Review of the genus Endoreticulatus (Microsporidia, Encephalitozoonidae) with description of a new species isolated from the grasshopper Poecilimon thoracicus (Orthoptera: Tettigoniidae) and transfer of Microsporidium itiiti Malone to the genus

Metabarcoding reveals low prevalence of microsporidian infections in castor bean tick (Ixodes ricinus)

BACKGROUND

Microsporidia is a large group of eukaryotic obligate intracellular spore-forming parasites, of which 17 species can cause microsporidiosis in humans. Most human-infecting microsporidians belong to the genera Enterocytozoon and Encephalitozoon. To date, only five microsporidian species, including Encephalitozoon-like, have been found in hard ticks (Ixodidae) using microscopic methods, but no sequence data are available for them. Furthermore, no widespread screening for microsporidian-infected ticks based on DNA analysis has been carried out to date. Thus, in this study, we applied a recently developed DNA metabarcoding method for efficient microsporidian DNA identification to assess the role of ticks as potential vectors of microsporidian species causing diseases in humans.

METHODS

In total, 1070 (493 juvenile and 577 adult) unfed host-seeking Ixodes ricinus ticks collected at urban parks in the city of Poznan, Poland, and 94 engorged tick females fed on dogs and cats were screened for microsporidian DNA. Microsporidians were detected by PCR amplification and sequencing of the hypervariable V5 region of 18S rRNA gene (18S profiling) using the microsporidian-specific primer set. Tick species were identified morphologically and confirmed by amplification and sequencing of the shortened fragment of cytochrome c oxidase subunit I gene (mini-COI).

RESULTS

All collected ticks were unambiguously assigned to I. ricinus. Potentially zoonotic Encephalitozoon intestinalis was identified in three fed ticks (3.2%) collected from three different dogs. In eight unfed host-seeking ticks (0.8%), including three males (1.1%), two females (0.7%) and three nymphs (0.7%), the new microsporidian sequence representing a species belonging to the genus Endoreticulatus was identified.

CONCLUSIONS

The lack of zoonotic microsporidians in host-seeking ticks suggests that I. ricinus is not involved in transmission of human-infecting microsporidians. Moreover, a very low occurrence of the other microsporidian species in both fed and host-seeking ticks implies that mechanisms exist to defend ticks against infection with these parasites.

Identification and characterization of three microsporidian genera concurrently infecting a silkworm, Bombyx mori, in Brazil

Microsporidia are important entomopathogens known for infecting insects such as the silkworm (Bombyx mori) thus impairing global silk production. This study aimed to identify and characterize the microsporidia isolated from a diseased larva of silkworm, collected from a sericulture farm in southern Brazil. Identification was performed by phylogenetic analysis of the nucleotide sequences of the SSU rRNA genes. Characterization was performed by analyzing spore sizes, tissue tropism, internal and external symptoms, and pathogenicity against B. mori. Microsporidia belonging to three different genera were identified, namely, Endoreticulatus, Nosema and Tubulinosema. After inoculation of the mixed spores of the microsporidian isolates into B. mori larvae, a high prevalence of Tubulinosema spp. was observed. This isolate showed high prevalence on the silk glands and a late mortality, initially of around 10% until the 20th day post-inoculation but reaching 91.5% upon pupation. Therefore, we demonstrated that Tubulinosema spp. causes chronic infection with slow pathogenicity. We identified for the first time three different microsporidians concurrently infecting B. mori in Brazil. Tubulinosema is of particular interest because of its potential threat to silk production; it affects the formation of silk glands in B. mori while not presenting distinguishable external symptoms or causing the immediate death of these insects. Further studies focusing on this species, mainly regarding its life cycle within the host and the sublethal effects of surviving individuals, demonstrate the importance of describing it as a new species and improving the characterization of the disease in order to prevent its spread.

Prevalence rates of microsporidia in locusts and grasshoppers in South-Western Russia

Locusts and grasshoppers are dangerous polyphagous pests of agricultural crops. In the present paper, results of screening of Acridoidea populations in the South-Western Russia for microsporidia infections including locusts Locusta migratoria, Dociostaurus maroccanus, and Calliptamus italicus and grasshoppers Chorthippus loratus, Oedipoda caerulescens, and Acrida bicolor, are presented. Microsporidia prevalence rates were estimated using light microscopy of fresh smears. Out of 179 specimens of L. migratoria sampled between 2002 and 2019 in Krasnodar Territory, Astrakhan and Rostov Regions, none was infected with microsporidia. Similarly, 95 specimens of D. marrocanus from Krasnodar Territory (2017) and Dagestan Republic (2009) were also negative for microsporidia. Meanwhile, one positive case was detected for C. italicus corresponding to 0.5 % for the total amount of 192 exemplars collected from 2002 to 2019 in Krasnodar Territory, Astrakhan and Rostov Regions. As for grasshoppers, all Ch. loratus samplings in Krasnodar Territory in 2017-2019 were infected at the prevalence rates of 2.2-15 %, though no infection was found in 40 specimens in Crimea in 2019. In 56 individuals of O. caerulescens collected from Rostov Region and Krasnodar Territory, the microsporidia prevalence rate was 1.8 %. Among 96 specimens of A. bicolor, none was infected. In total, the microsporidia prevalence rates were higher in grasshoppers as compared to locusts, the difference being statistically significant at p<0.01.

Infection of Chorthippus loratus (Orthoptera: Acrididae) with Liebermannia sp. (Microsporidia) in South-Western Russia

Chorthippus loratus collected in Krasnodar Territory in 2017 was infected at 15% rate with a microsporidium possessing ovocylindrical binucleate spores, 2.6 × 1.2 μm in size. SSU RNA gene typing (Genbank accession # MH396491) showed its allocation to the genus Liebermannia. Degenerate primers based upon largest subunit RNA polymerase II (RPB1) sequences of closest relatives allowed amplifying the respective gene fragment of Liebermannia sp. (# MH396492). The present finding indicates worldwide distribution of the Liebermannia genus and parasitism in hosts with nonoverlapping geographic ranges (representing Neotropical versus Palearctic fauna), while previous observations were restricted to Acridoidea endemic for South America.

Molecular surveillance of Vittaforma-like microsporidia by a small-volume procedure in drinking water source in Taiwan: evidence for diverse and emergent pathogens

Vittaforma corneae belongs to microsporidia, which include over 1500 species of opportunistic obligate intracellular fungi infecting almost all known animal taxa. Although outbreaks of ocular infections caused by waterborne V. corneae have been reported in recent years, little is known about the occurrence of this pathogen in aquatic environments. In this study, 50 water samples from rivers and reservoirs around Taiwan in two seasons were analyzed to explore the presence of this pathogen in natural aquatic environments. A high detection rate of Vittaforma-like amplicons (94%; 47/50) was observed in the water samples when examined by nested PCR with primer pairs specific to the small ribosomal subunit (SSU) rRNA gene. After electrophoresis, many lanes showed multiband patterns with expected molecular weights. After confirmation by DNA sequencing and by sequence alignment in the NCBI database, we identified a variety of Vittaforma-like microsporidia with weak sequence similarity, with approximately 85% identity to V. corneae, thus indicating high diversity of microsporidia in aquatic environments. Phylogenetic analysis showed clear-cut microsporidian clade classification and indicated that the most Vittaforma-like microsporidia in this study belong to clade IV and cluster into four major groups. The first group is similar to the microsporidia associated with ocular microsporidiosis. The second group is associated with the diarrheal pathogens, whereas the third and fourth groups are a novel group and a zoonotic group, respectively. This study provides abundant sequencing information, which will be useful for future molecular biological studies on microsporidia. Because microsporidia are important pathogens of animals and humans, it is urgently necessary to determine via a survey whether there are species with potential threats that have not yet been revealed.

Biological and molecular features of Nosema rachiplusiae sp. n., a microsporidium isolated from the neotropical moth Rachiplusia nu (Guenée) (Lepidoptera: Noctuidae)

Light, electron microscopy and DNA analyses were performed to characterize a microsporidium infecting Rachiplusia nu larvae from a laboratory rearing in Argentina. Diplokaryotic spores were oval and measured 3.61 ± 0.29 × 1.61 ± 0.14 μM (fresh). The spore wall was composed of an electron-dense exospore and an electron-lucent endospore, ca. 30 nm and 100-120 nm thick, respectively. The polar filament was arranged in a single rank of 10-12 coils (typically 11). Microsporidian cells were found in the cytoplasm, next to the endoplasmic reticulum (especially the prespore stages) and generally surrounded by electron-lucent spaces. The infection was polyorganotropic; the fat body appeared as the most heavily invaded tissue, followed by tracheal matrix and epidermis. A molecular phylogeny based on the small (SSU) and large subunit (LSU) ribosomal RNA genes clearly placed the new isolate within the "Nosema bombycis clade". Considering both SSU and LSU concatenated partial sequences, the microsporidium from R. nu showed 99.5% nucleotide similarity with N. bombycis and 99.8% with its closest relative, a microsporidium isolated from Philosamia cynthia. According to its genetic and biological features, the R. nu isolate is proposed as the new species Nosema rachiplusiae sp. n., expanding the limited knowledge on microsporidia associated to endemic South-American moths.

Natural occurrence of microsporidia infecting Lepidoptera in Bulgaria

We examined 34 lepidopteran species belonging to 12 families to determine presence and prevalence of microsporidian pathogens. The insects were collected from May 2009 to July 2012 from 44 sites in Bulgaria. Nosema species were isolated from Archips xylosteana, Tortrix viridana, Operophtera brumata, Orthosia cerasi, and Orthosia cruda. Endoreticulatus sp. was isolated from Eilema complana. The prevalence of all isolates in their hosts was low and ranged from 1.0% to 5.3%. Phylogenetic analyses of the new isolates based on SSU rDNA are presented.

Ultrastructural characterization of Pleistophora macrozoarcidis Nigerelli 1946 (Microsporidia) infecting the ocean pout Macrozoarces americanus (Perciformes, Zoarcidae) from the gulf of Maine, MA, USA

Pleistophora macrozoarcidis a microsporidian parasite infecting the muscle tissue of the ocean pout Macrozoarces americanus collected from the Gulf of Maine of the Atlantic Ocean, MA, USA, was morphologically described on the basis of ultrastructural features. Infection was detected as opaque white or rusty brown lesions scattered throughout the musculature of the fish mainly in the region anterior to anus. Transmission electron microscopy showed that in individual parasitized muscle cells, the infection progresses within parasite formed vesicles which are in direct contact with muscle cell elements. The earliest observed parasitic stages are the globular multinucleated proliferative cells or plasmodia limited by a highly tortuous plasmalemma with intervesicular finger-like digitations projecting into the parasite cytoplasm. These cells divided through the invagination of the plasmalemma and the amorphous coat producing daughter-cells. Fine electron-dense secretion is deposited on the plasmalemma that causes its thickening which is a sign of commencement of the sporogonic phase. This phase is carried out by cytokinesis of the sporonts and results in the formation of sporoblasts and finally spores. Mature spore has a thin electron-dense exospore, a thick electron-lucent endospore, and the plasma membrane which encloses the spore contents. A single nucleus is centrally located with the posterior region containing a posterior vacuole. The majority of spores have 7-13 coils in 1-2 rows, and a small group of spores had about 23 coils forming two rows. Events of polar filament extrusion for penetration of uninfected cells were studied. The polaroplast membranes were expanded and occupy most of the length of the spore. The coils are dislocated from the sides of the spore to throughout the entire sporoplasm. The polar filament everts and extrudes through the polar cap with a sufficient force to pierce adjacent sporophorous vesicle walls. After eversion, the polar filament is referred to as a polar tubule, as it forms a tube through which the sporoplasm travels. It pierces anything in its path and deposits the sporoplasm at a new location to begin another infective cycle.