Tissue reactions to microsporidian infections in fish

Abstract. Histopathological studies on natural and experimental infections of nineteen microsporidian species from fishes distinguished two types of tissue reactions.
The first type is characteristic of infections with xenoma-inducing microsporidian species and comprises three successive stages: a weakly reactive stage, a productive stage with the formation of granulomas and a stage of granuloma involution. Following the first stage, tissue reactions are directed towards the isolation of the parasite and result in its complete elimination and host tissue repair. The extent of pathological changes probably depends on the number of parasite cells which initiated the infection.
The second type is represented by Pleistophora species infecting muscles or oocytes. Host tissue reaction is surprisingly slight during the schizogony and sporogony and does not tend to isolate the invaded muscle fibres. A slight lymphocytic infiltration of myosepta indicates the first stage of tissue reaction. The tissue reaction only reaches the productive stage when mature spores completely fill the contents of the infected muscle fibre. A thick wall of fibroblasts may be formed to demarcate the parasite mass as soon as it undergoes necrotic changes. The extent of pathological changes probably depends on the ability of early developmental stages of the parasite to spread the infection within the host.
In both types of tissue reaction, the spores are destroyed by complete digestion within host phagocytic cells.     

Eimeria branchiphila sp.nov. sporulating in the gill filaments of roach, Rutilus rutilus L.

Abstract. Eimeria branchiphila sp. nov. is described from the roach, Rutilus rutilus L., collected in Bulgaria. Sporulated oocysts were found in gill secondary lamellae and less frequently were associated with melano-macrophage centres in the spleen and in kidney interstitial tissue. In the gills, parasite cells identified as zygotes and sporulation stages were also encountered. This unusual site of sporulation represents a mechanism of sporocyst dispersal previously not recorded in fish coccidia.     

Tissue reaction of the three-spined stickleback Gasterosteus aculeatus L. to infection with Glugea anomala (Moniez, 1887)

Abstract. Studies on an experimental infection of the stickleback (Gasterosteus aculeatus L.) with the microsporidian Glugea anomala conducted until day 126 post infection confirmed that xenoparasitic formations typical of the intracellular development of this microsporidian were responsible for a marked tissue reaction in the host. After a single oral infection, xenoparasitic formations developed in the subepithelial connective tissue of the glandular part of the stomach. The course of xenoma development was asynchronous. Up to the 'cyst' stage (xenomas filled with mature spores), their growth and development caused a pressure atrophy in the surrounding tissue. Later, the response to the presence of the xenoparasitic formation was the development of a granulomatous inflammatory reaction. Locally, the host responded to the infection by phagocytosis of mature spores by locally derived macrophages. In massive infections, changes occurred in the subepithelial connective tissue of the glandular part of the stomach (often the complete disappearance of tubular glands), which may result in a permanent influence on the function of this organ.     

Histopathological changes in Trypanosoma danilewskyi Laveran & Mesnil, 1904 and Trypanoplasma borelli Laveran & Mesnil, 1902 infections of goldfish, Carassiw auratus (L.)

Abstract. Syringe passaged stocks of Trypanosoma danilewskyi and Trypanoplasma borelli derived from carp were used for experimental infections of goldfish. Infections of T. danilewskyi and T . borelli produced a heavy parasitaemia in the peripheral blood of goldfish and extensive tissue damage, mainly in haemopoietic organs. There was no inflammatory reaction or haemorrhage in trypanosome infected goldfish. Infection with trypanoplasms provoked more varied changes including vascular lesions and inflammatory changes. The extent of pathological changes occurring at rising and peak levels of parasitaemia could account for the high mortality (up to 100%) of the infected fish.     

Fish coccidia: critical notes on life cycles, classification and pathogenicity

Abstract. The present knowledge of oocyst morphology, life cycles, classification and pathogenicity of eimeriid coccidia infecting fishes is reviewed. Compared with typical Eimeria species from higher vertebrates, fish coccidia, currently classified as all belonging to the same genus, differ in having, as a rule, a thin oocyst wall and endogenous sporulation. Some species possess a bivalved sporocyst, a structure and consequently an excystation mechanism, essentially different from that of the genus Eimeria. An analysis of the life cycles of more than 120 recorded species of fish coccidia has shown six different types of developmental patterns. The life cycles offish coccidia are compared with the life cycles of coccidia in general. None of the fish coccidia having a sporocyst with a Stieda body sporulates exogenously and therefore do not display a true eimerian developmental pattern. In view of the importance of sporocyst structure and developmental patterns in taxonomy, the revalidation of Labbé's genera Goussia and Crystallospora is proposed along with the establishment of a new genus, Epieimeria n.g. Most of the species offish coccidia are left within the genus Eimeria until new data make possible their correct classification. Detailed data on histopathological changes are available only in infections by two carp-infecting species, E. carpelli and E. subepithelialis and E. funduli infections in killifishes. The potential threat of coccidiosis in fishes reared under intensive conditions requires a thorough study of the pathogenicity of further species infecting commercially important hosts.     

Notes on kidney-infecting species of the genus Sphaerospora Thélohan (Myxosporea), including a new species S. gobionis sp.nov., and on myxosporean life cycle stages in the blood of some freshwater fish

Abstract Freshwater fish in Czechoslovakia were examined for species of the genus Sphaerospora Thélohan, 1892 and for myxosporean life cycle stages in the blood. In addition to perch infected with S. pectinacea Bocharova & Donets, 1974, renal tubules of seven host species harboured thus far unidentified Sphaerospora species. A new species, S. gobionis sp.nov. is described from renal tubules of Gobio gobio. In populations of Gobio gobio, Tinea tinea and Rutilus rutilus harbouring infections with different Sphaerospora species, organisms identified as mobile myxosporean life cycle stages were detected in the blood, where they undergo a proliferative cycle. These organisms were reminiscent of stages in the blood of common carp fingerlings, supposedly identical with Sphaerospora renicola Dyková & Lorn. It is possible that the blood stages found in the three cyprinid hosts represent stages of the life cycle of their respective Sphaerospora species. If this is correct, further studies may show if the presence of proliferative stages in the bloodstream is a character distinctive of the genus Sphaerospora.