Whirling disease: host specificity and interaction between the actinosporean stage of Myxobolus cerebralis and rainbow trout Oncorhynchus mykiss.
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Scanning electron microscopic studies were conducted on rainbow trout Oncorhynchus mykiss in the first 60 min after their exposure to the triactinomyxon spores of Myxobolus cerebralis. The results demonstrated that as early as 1 min post exposure the whole process, from the attachment of the triactinomyxon spores to the complete penetration of their sporoplasm germs, had occurred. The triactinomyxon spores sought out the secretory openings of mucous cells of the epidermis, the respiratory epithelium and the buccal cavity of trout and used them as portals of entry. Exposure experiments of the triactinomyxon spores of M. cerebralis to non-salmonid fish, such as goldfish Carassius auratus, carp Cyprinus carpio, nose Chondrostoma nasus, medaka Oryzias latipes, guppy Poecilia reticulata and also the amphibian tadpole Rana pipiens as well as to rainbow trout fry indicated a specificity for salmonids. Attempts to activate the triactinomyxon spores by exposure to mucus prepared from cyprinid and salmonid fish showed no significant differences from those conducted in tap water. The results suggest that the simultaneous presence of both mechano- and chemotactic stimuli was required for finding the salmonid fish host. (+info)
Pathogenicity of Ichthyophonus hoferi for laboratory-reared Pacific herring Clupea pallasi and its early appearance in wild Puget Sound herring.
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Laboratory-reared pathogen-free Pacific herring were exposed to pure cultures of Ichthyophonus hoferi, and reproduced the disease seen in naturally infected fish--thus fulfilling Koch's Postulates. Pathogen-free herring used in this study were reared from artificially spawned eggs incubated in filtered, UV-sterilized seawater, eliminating the variables associated with multiple infections, which are common in wild herring. Wild free-ranging herring were captured monthly from June through October by dip net from 'herring balls' located in the northern Puget Sound. I. hoferi infections were identified in these fish soon after metamorphoses, about 4 mo post-hatch. The prevalence increased from 5 to 6% in 0-yr fish to 24% in 1-yr-old fish to 50 to 70% in fish over 2 yr old, with no associated increase in mortality. The route of natural transmission to wild herring was not determined, but carnivorous fish became infected and died when they were experimentally fed tissues infected with the organism. In vitro culture of tissues was the most sensitive method for identifying both clinical and subclinical infections. (+info)
Nosema notabilis (Microsporidia), its ultrastructure and effect on the myxosporean host Ortholinea polymorpha.
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Nosema notabilis Kudo, 1939 produces chain-forming meronts with a dense cell coat in direct contact with the host cell cytoplasm. Cytoplasmic microtubules and membranaceous whorls could be observed in meront cytoplasm. Sporonts differ in that they have a thicker cell wall and more conspicuous endoplasmic reticulum (ER) cisternae. Sporoblasts have an externally ridged cell wall. Spores have an apically located anchoring disc, an isofilar polar tube with 6 to 9 turns and polyribosomal strands in the sporoplasm. Diplokarya occur in all stages. Heavily infected plasmodia of Ortholinea polymorpha (Davis, 1917) reveal marked pathological signs. The most prominent are reduction of surface projections and/or pinocytosis, inflated mitochondria with altered inner structures, affected vegetative nuclei, damage to generative cells and occurrence of various anomalous formations in the plasmodium cytoplasm. The damage may result in complete disintegration of the plasmodium. However, the development of the microsporidian is affected by a remarkably high percentage of teratological stages revealing membranaceous and tubular structures. (+info)
Molecular characterization of the myxosporean associated with parasitic encephalitis of farmed Atlantic salmon Salmo salar in Ireland.
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During seasonal epizootics of neurologic disease and mass mortality in the summers of 1992, 1993 and 1994 on a sea-farm in Ireland, Atlantic salmon Salmo salar smolts suffered from encephalitis associated with infection by a neurotropic parasite. Based on ultrastructural studies, this neurotropic parasite was identified as an intercellular presporogonic multicellular developmental stage of a histozoic myxosporean, possibly a Myxobolus species. In order to generate sequence data for phylogenetic comparisons to substantiate the present morphological identification of this myxosporean in the absence of detectable sporogony, polymerase chain reaction (PCR), Southern blot hybridization, dideoxynucleotide chain-termination DNA sequencing, and in situ hybridization (ISH) were used in concert to characterize segments of the small subunit ribosomal RNA (SSU rRNA) gene. Oligonucleotide primers were created from sequences of the SSU rRNA gene of M. cerebralis and were employed in PCR experiments using DNA extracted from formalin-fixed paraffin-embedded tissue sections of brains from Atlantic salmon smolts in which the myxosporean had been detected by light microscopy. Five segments of the SSU rRNA gene of the myxosporean, ranging in length from 187 to 287 base pairs, were amplified, detected by hybridization with sequence-specific probes, and sequenced. Consensus sequences from these segments were aligned to create a partial sequence of the SSU rRNA gene of the myxosporean. Assessments of sequence identity were made between this partial sequence and sequences of SSU rRNA genes from 7 myxosporeans, including Ceratomyxa shasta, Henneguya doori, M. arcticus, M. cerebralis, M. insidiosus, M. neurobius, and M. squamalis. The partial SSU rRNA gene sequence from the myxosporean had more sequence identity with SSU rRNA gene sequences from neurotropic and myotropic species of Myxobolus than to those from epitheliotropic species of Myxobolus or Henneguya, or the enterotropic species of Ceratomyxa, and was identical to regions of the SSU rRNA gene of M. cerebralis. Digoxigenin-labeled oligonucleotide DNA probes complementary to multiple segments of the SSU rRNA gene of M. cerebralis hybridized with DNA of the parasite in histologic sections of brain in ISH experiments, demonstrating definitively that the segments of genome amplified were from the organisms identified by histology and ultrastructural analysis. Based on sequence data derived entirely from genetic material of extrasporogonic stages, the SSU rDNA sequence identity discovered in this study supports the hypothesis that the myxosporean associated with encephalitis of farmed Atlantic salmon smolts is a neurotropic species of the genus Myxobolus, with sequences identical to those of M. cerebralis. (+info)
Development of a polymerase chain reaction diagnostic assay for Ceratomyxa shasta, a myxosporean parasite of salmonid fish.
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A diagnostic procedure based on the polymerase chain reaction (PCR) was developed for the myxosporean parasite Ceratomyxa shasta. Three sets of oligonucleotide primers were designed to specifically amplify C. shasta ribosomal RNA genes and several parameters of the assay were tested and optimised. A simple protocol for the processing of fish tissue samples was also developed. In a single round, 20 microliters volume reaction the optimised procedure allows the detection of 50 fg of purified C. shasta genomic DNA, or 0.01 spore from a seeded fish intestine sample. This protocol is considerably faster, cheaper and more reliable than any previous diagnostic procedure for a myxosporean parasite, and can be an invaluable tool for the monitoring of early and/or subclinical C. shasta infections in wild and cultured salmon populations. (+info)
Ichthyophthiriasis in carp Cyprinus carpio: infectivity of trophonts prematurely exiting both the immune and non-immune host.
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Ichthyophthirius multifiliis exposed to naturally immunised carp established short-term infections, the majority of parasites actively emerging within 2 h of entering the epidermis. A small, but significant, number of these expelled parasites were shown to retain theront-like properties with the capacity to directly re-invade a further fish host. Infectivity fell rapidly with time in the host and was comparable to that of trophonts of a similar age artificially induced to emerge from non-immune hosts with the aid of MEM (minimal essential medium). Trophonts recovered with MEM from immune carp 2 to 8 h post infection rarely established infections upon exposure to susceptible new hosts and no infections resulted from older trophonts recovered after 8 to 24 h exposure; older trophonts, however, represented only a small percentage of the original parasite population. A low level of infectivity was recorded in trophonts collected with the aid of MEM from non-immune carp after up to 24 h of infection. The results are discussed in relation to theront transformation and evasion of the host immune response. (+info)
Molecular evidence that the proliferative kidney disease organism unknown (PKX) is a myxosporean.
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The proliferative kidney organism unknown (PKX), a serious salmonid fish pathogen, is considered to be a myxosporean on the basis of ultrastructural studies, but its real taxonomic position has never been confirmed. In order to ascertain its position, genomic DNA was extracted from PKX and small subunit (SSU) ribosomal DNA was amplified by PCR, cloned and sequenced. A phylogenetical analysis on SSU rDNA from 76 or 128 eucaryotic species was carried out. Whatever the tree reconstruction methods used, PKX was found to be a sister group of the Myxozoa phylum, providing the first molecular evidence for its membership in this phylum. (+info)
Demonstration of Tritrichomonas foetus in the external genitalia and of specific antibodies in preputial secretions of naturally infected bulls.
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Portions of penis and prepuce were collected from 24 bulls with current or recent Tritrichomonas foetus infection. Epididymides were collected from seven of the bulls, and seminal vesicles and prostate were collected from four. Following immunohistochemical staining with two monoclonal antibodies (34.7C4.4 and TF1.15) prepared against T. foetus surface antigens, trichomonads were identified in sections from 15 of the bulls. Organisms were most often located in penile crypts in the midshaft and caudal regions and less often in preputial crypts. Trichomonads were not observed in sections from other genitalia or in subepithelial tissue. T. foetus antigen, however, was present in the cytoplasm of some epithelial cells and the cytoplasm of some mononuclear cells in subepithelial lymphoid aggregates and follicles. Preputial smegma was collected from 16 T. foetus-infected bulls and from 16 control bulls with negative T. foetus cultures. Preputial antibody levels to TF1.17, a surface antigen of T. foetus, were determined by an enzyme-linked immunosorbent assay. Preputial secretions from infected bulls contained specific antibody of each isotype and subisotype tested. IgG1 responses were the greatest, IgM and IgA responses were approximately equal, and IgG2 responses were low. Each isotype and subisotype response in infected bulls was significantly greater than that in the controls. These results confirm previous speculation concerning anatomical sites of infection and suggest that parasite antigen can be taken up and processed locally, resulting in deposition of specific IgG1, IgG2, IgA, and IgM antibodies in the preputial cavity. (+info)