Dr. Murai Éva szerk.: Parasitologia Hungarica 19. (Budapest, 1986)

ed in fresh state; the remainder of the kidneys and ureter were divided into two parts, and fixed for histological examination inBouin's solution and 10% neutral formalin, respectively. Squash preparations were made from pieces of the kidney under coverslips. Mucus squeezed out from the ureter was also studied in fresh state under microscope. Organs fixed for histological examination were embedded in paraffin, sectioned, and the 4 to 8 um thick sections were stained with haematoxylin and eosin. RESULTS In fresh squash preparations made from the ureter of all the 12 common carp studied, large numbers of Myxosporean plasmodia 15 to 40 *m in size and situated freely in the lumen, stages identified by MOLNÁR, CSABA and KOVÁCS-GAYER (1986) with coelozoic forms of H. cyprini, were present. Mostly spherical foci 0. 1 to 0. 3 mm in diameter and free from parasites were demonstrable in the kidneys of all the fish examined. Renal tubular portions containing intracellular Hoferellus stages were found only for one fish exhibiting rather severe infection. By histological examination only few areas infected by typical Hoferellus trophozoites were found. In these sections Hoferellus trophozoites were located intracellularly in a syncytium formed of epithelial cells, in formations 100-180 x 170-200 urn in size. In most cases infection extended only to one side of the tubules, and on the other side intact epithelial cells were seen (Fig. 1). In the epithelial areas attacked by Hoferellus trophozoites a circumscribed tubulonephrosis, involving shorter or longer portions of the given tubule, developed. Epithelial cells transformed into cell syncytia were demarcated from the renal interstitium by a thin basement membrane, and towards the tubular lumen they were lined by an intact brush border. The cytoplasm of the syncytium was filled with masses of Hoferellus trophozoites which pushed the nuclei of injured epithelial cells to the basement membrane where they formed small clusters. In advanced stages of infection, the cytoplasm of the parasite-containing syncytium became degenerated, disintegrated, and the trophozoite-containing cytoplasm was expulsed, through the ruptured cell membrane, into the lumen of the tubules (Fig. 2). The remaining cytoplasm of the syncytium contained only the nuclei of infected epithelial cells Legend to the figures

: Fig. 1, Portion of a renal tubule infected by intracellular Hoferellus stages. Epithelial cells containing parasites have been transformed into syncytia. In certain parts of the tubule there still are intact epithelial cells. Haematoxylin and eosin, x 200 Fig. 2. Release of Hoferellus trophozoites into the lumen. Only the cell nuclei and a few trophozoites have remained in the degenerated syncytium. Most of the parasites are situated in the lumen. H. and E., x 200 Fig. 3. Release of Hoferellus trophozoites into the lumen. Note the mass of trophozoites and epithelial debris within the intact basement membrane. Remnants of the syncytium contain nuclei and trophozoites. In the distal efferent ducts there are Hoferellus Plasmodia. H. and E., x 200 Fig. 4. Section of a distal part of a tubular portion infected by Hoferellus. Intracellular and coelozoic trophozoites occur together, side by side. The trophozoites situated in the lumen contain secondary formations. H. and E., x 200 Fig. 5. Cross-sections of tubular portions with passed-off HofereUus infection. The lumen of the tubule is filled with tissue debris interwoven with fibroblasts. From the direction of the basement membrane the connective tissue becomes fibrillated. H. and E., x 200 Fig. 6. Advanced stage of regeneration. In the place of the lumen an amorphous debris, surrounded by fibrous connective tissue, can be seen. H. and E., x 200 Fig. 7. Focus formation in the place of the Hoferellus nodule. The fibrous focus is surrounded by epitheloid cells arranged in crescent shape. H. and E., x 200 Fig. 8. Hoferellus plasmodia in the lumen of the ureter. H. and E., x 100