Ultrastructural details of the xenoma of Loma myrophis (phylum Microsporidia) and extrusion of the polar tube during autoinfection

Abstract

Xenomas of the recently described new microsporidian species Loma myrophis parasitizing the gut tissue of the Amazonian fish Myrophis platyrhynchus (family Ophichthidae) were described by light-and transmission-electron microscopy. The xenoma consisted of a thin fibrillar wall that surrounded a hypertrophic host cell cytoplasm containing numerous microsporidian developmental stages and spores. Several spores showed different stages of natural extrusion of the polar tube. Numerous longitudinal and transverse sections of the extruded polar tubes were observed in developing life-cycle stages (spores excepted), the nucleus of hypertrophic host cell, the xenoma wall and surrounding fibroblasts. The extruded polar tubes were projected in all directions with no preferential orientation. These aspects suggested that autoinfection occurred within this xenoma.KEY WORDS: Ultrastructure · Microsporidian · Xenoma · Extrusion · Polar tube · Loma myrophis · ParasiteResale or republication not permitted without written consent of the publisher Dis Aquat Org 54: 203-207, 2003 In this paper, we describe both light and electron microscope observations of a microsporidian xenoma, with special reference to the ultrastructural aspects of the natural extrusion of the polar tube, suggestive of causing autoinfection. MATERIALS AND METHODSSpecimens of the freshwater fish Myrophis platyrhynchus Breder, 1927 (family Ophichthidae) (Brazilian common name: Cutuca) were collected in the Amazon River (00°35' 38'' S, 47°35' 00'' W), near the city of Belém, Brazil. The internal organs were examined to detect the parasites, which appeared as a whitish xenoma in the subepithelial tissue of the midgut, containing the recently described microsporidian species Loma myrophis Azevedo and Matos, 2002 (family Glugeidae). For transmission electron microscopy (TEM), the xenoma and surrounding cells were fixed in 5% glutaraldehyde in 0.2 M sodium cacodylate buffer (pH 7.2) for 10 h at 4°C, washed overnight in the same buffer at 4°C, and post-fixed in 2% OsO 4 , buffered with the same buffer and at the same temperature for 8 h. After dehydration in an ethanol series (5 to 6 h in each change) and propylene oxide, the xenomas were embedded in Epon. For light microscopy (LM), semithin sections were stained with methylene blue azure II. For TEM, the ultrathin sections were contrasted with both aqueous uranyl acetate and lead citrate, and observed in a JEOL 100CXII at TEM operated at 60 kV. RESULTS Light microscope studiesThe xenomas, small whitish nodules located in the connective tissues of the intestine, were observed after dissection. They were broadly spherical and well delimited by the xenoma wall ( Fig. 1). After disruption, the spores contained within the xenomas were identified as belonging to the microsporidian species Loma myrophis. No overt behavioral or external morphological signs or symptoms of disease were observed in the infected fish. Electron microscope studiesThe wall was externally surrounded by several concentric layers of compre...

Ultrastructural evidence of autoinfection in the gills of Atlantic cod Gadus morhua infected with Loma sp. (phylum Microsporidia)

“…Similar observations have been interpreted as evidence of autoinfection for Loma myrophis in the Amazonian fish Myrophis platyrhynchus (Matos et al 2003). The possibility of microsporidian autoinfection in fish has been indicated by some authors as a very limited mechanism for transmitting infection (Lom & Dyková 1992).…”

“…cod study, and previous observations for Loma sp. in rainbow trout (Rodriguez et al 2002(Rodriguez et al , 2003 and an Amazonian fish (Matos et al 2003), suggest that autoinfection could be a common way for establishing a secondary infestation in the host by Loma sp., as was previously proposed in fish exposed to L. salmonae (Shaw et al 1998). …”

“…Everted polar tubes originating from xenomas and confined within originating xenoma have recently been reported for L. salmonae in rainbow trout Oncorhynchus mykiss (Rodriguez-Tovar et al 2003). Both intra-and extraxenomal everted polar tubes have been reported for L. myrophis in the Amazonian fish Myrophis platyrhynchus (Matos et al 2003). The objective of the present report is to describe the ultrastructural features of xenoma formed by Loma sp.…”

“…To date, there is no information in the literature regarding RBCs as possible transport vehicle. Some consider the presence of multiple parasites in different stages of development, and everted polar tubes within a xenoma, as evidence for autoinfection of itself (Cali & Owen 1990, Matos et al 2003. Reasons for re-infecting the same host cell are still unknown.…”

Xenomas in Crassostrea rhizophorae (Ostreidae) from Camamu Bay, Bahia, Brazil

“…Xenomas are formed when intracellular parasites accumulate within host cells, causing hypertrophy of the cell and its nucleus. In fish, the xenomas are commonly caused by microsporidians (Matos et al, 2003), but in the oyster Crassostrea virginica (Gmelin) they are caused by ciliates, genus Sphenophrya (Bower et al, 1994;Winstead et al, 2004;Scarpa et al, 2006). In Brazil, Nascimento et al (1986) observed such organisms in C. rhizophorae from Todos os Santos Bay (Bahia), but these authors didn't make reference to xenoma formation.…”