Sporogony of Tetracapsuloides bryosalmonae in the brown trout Salmo trutta and the role of the tertiary cell during the vertebrate phase of myxozoan life cycles

Abstract

Tetracapsuloides bryosalmonae is the myxozoan that causes the commercially and ecologically important proliferative kidney disease of salmonid fish species. Immunohistochemistry and electron microscopy were used to examine the development of this parasite within the kidney of the brown trout Salmo trutta. The main replicative phase of T. bryosalmonae is a cell doublet composed of a primary cell and a single secondary cell. Engulfment of one secondary cell by another to form a secondary-tertiary doublet (S-T doublet) heralded the onset of sporogony whereupon the parasite migrated to the kidney tubule lumen. Within the tubule, the parasite transformed into a pseudoplasmodium and anchored to the tubule epithelial cells via pseudopodial extensions. Within each pseudoplasmodium developed a single spore, composed of 4 valve cells, 2 polar capsules and 1 sporoplasm. The pseudoplasmodia formed clusters suggesting that large numbers of spores develop within the fish. This examination of T. bryosalmonae suggests that the main replicative phase of freshwater myxozoans within vertebrates is via direct replication of cell doublets rather than through the rupturing of extrasporogonic stages, while tertiary cell formation relates only to sporogony. Taken in conjunction with existing phylogenetic data, 5 distinct sporogonial sequences are identified for the Myxozoa.

Light and electron microscopic studies on turbot Psetta maxima infected with Enteromyxum scophthalmi: histopathology of turbot enteromyxosis

“…Zschokkella mugilis and Tetracapsuloides bryosalmonae form similar folds and windings between intraepithelial plasmodia and the surrounding epithelial cells (Sitjà-Bobadilla & Álvarez-Pellitero 1993, Morris & Adams 2008. These structures together with their junctions play roles in attachment and communication with host cells.…”

Molecular characterization of Sphaerospora molnari (Myxozoa), the agent of gill sphaerosporosis in common carp Cyprinus carpio carpio

“…The need to reanalyze these Sphaerospora spp. has already been highlighted in studies dealing with myxozoan phylogeny and the relations between their development and phylogenetic data (Fiala 2006, Morris & Adams 2008, Bartošová et al 2011. By hybridization of specific oligonucleotide probes to target DNA in histological sections (in situ hybridization [ISH]) we were able to identify erroneously ascribed Sphaerospora sp.…”

Transmission Biology of the Myxozoa

“…They are about 12 × 7 μm in size and bear two polar capsules with 4 to 6 turns of their polar filament, one sporoplasm and four valve cells (Kent et al, 2000, Hedrick et al, 2004, Morris & Adams, 2008. Apparently, only few fishmalacospores are released at a time by T. bryosalmonae-infected fish, because only small numbers of spores were found in urine samples from infected fish over a prolonged period of time (Hedrick et al, 2004).…”