Loma Salmonae Research Articles

Regulatory Effects of Water Temperature onLoma salmonae(Microspora) Development in Rainbow Trout

Abstract Water temperature, a pivotal factor influencing interactions between teleosts and pathogens, was examined to determine its effects on the kinetics of xenoma formation and dissolution subsequent to experimental exposure of rainbow trout Oncorhynchus mykiss to the microsporidian gill pathogen Loma salmonae. The permissive water temperature range in which xenomas developed was between 9° and 20°C. Parasite development was arrested at temperatures outside this range, as indicated by the absence of visible xenomas among exposed fish. In addition, when these trout were subsequently moved to temperatures within the permissive range, xenomas failed to develop. Water temperature, within the permissive range, had no significant effect on either the number of xenomas that formed or the proportion of fish that developed xenomas following gastric intubation with a standard dose of spores. The relationship between water temperature and xenoma onset-time was best described (R 2 = 88.3%) by polynomial regression...

Effect of water temperature manipulation on a thermal unit predictive model for Loma salmonae

Loma salmonae is an important microsporidian pathogen affecting the mariculture of Pacific salmon, Oncorhynchus tshawytscha (Walbaum). Clinical signs associated with infection arise when the parasite enters sporogony and forms xenoparasitic complexes (xenomas) within the gill. The present study tested a thermal unit (TU) model, which was devised to predict the timing of xenoma formation, under conditions in which water temperature changed during the course of infection. In vivo trials with juvenile trout showed that the model [TU for xenoma onset = (days post exposure) × ( °C above 7 °C)] accurately predicted the onset time for xenomas when fish were moved from either 11 or 5 °C to 15 °C at various intervals after exposure. These findings suggest that the TU model may allow aquaculturists to predict disease onset. However, the model failed when fish were moved from 15 to 5 °C at intervals after exposure. This finding suggests that the temperature‐constrained phase of the life‐cycle of L. salmonae occurs early on after the spore is ingested by the fish.

Iodophor treatment is not completely efficacious in preventing Loma salmonae (Microsporidia) transmission in experimentally challenged chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Journal of Fish DiseasesVolume 22, Issue 4 p. 311-313 Iodophor treatment is not completely efficacious in preventing Loma salmonae (Microsporidia) transmission in experimentally challenged chinook salmon, Oncorhynchus tshawytscha (Walbaum) R. W. Shaw, R. W. Shaw Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada Department of Fisheries and Oceans, Pacific Biological Station, Nanaimo, British Columbia, CanadaSearch for more papers by this authorM. L. Kent, M. L. Kent Department of Fisheries and Oceans, Pacific Biological Station, Nanaimo, British Columbia, CanadaSearch for more papers by this authorM. L. Adamson, M. L. Adamson Department of Zoology, University of British Columbia, Vancouver, British Columbia, CanadaSearch for more papers by this author R. W. Shaw, R. W. Shaw Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada Department of Fisheries and Oceans, Pacific Biological Station, Nanaimo, British Columbia, CanadaSearch for more papers by this authorM. L. Kent, M. L. Kent Department of Fisheries and Oceans, Pacific Biological Station, Nanaimo, British Columbia, CanadaSearch for more papers by this authorM. L. Adamson, M. L. Adamson Department of Zoology, University of British Columbia, Vancouver, British Columbia, CanadaSearch for more papers by this author First published: 18 January 2002 https://doi.org/10.1046/j.1365-2761.1999.00167.xCitations: 16 Ross W Shaw, 3190 Hammond Bay Road, Pacific Biological Station, Nanaimo, BC, Canada V9R 5K6 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume22, Issue4July 1999Pages 311-313 RelatedInformation

Resistance to reinfection in chinook salmon Oncorhynchus tshawytscha to Loma salmonae (Microsporidia).

Chinook salmon Oncorhynchus tshawytscha were experimentally infected per os with Loma salmonae and held in flow-through seawater tanks at 12 to 14 degrees C. The fish exhibited 100% infection when first examined at 7 wk post initial exposure (p.e.), and by 20 wk p.e. they had completely recovered from gill infections. The recovered fish were then re-exposed the following week. All of these fish showed strong protection to new L. salmonae infections, while naïve fish exposed to the same inoculum developed the infection. Most of the re-exposed fish exhibited a few free spores or spores within phagocytes in the kidney interstitium at 20 to 29 wk p.e., but xenomas were not detected in either the gills or visceral organs. The kidney is the primary site of reticulo-endothelial activity, and thus these spores were likely deposited in the kidney by entrapment by fixed macrophages. It is possible that these spores provide immunologic stimuli to reinforce the resistance to new L. salmonae infections.

TNP‐470, the analogue of fumagillin‐DCH, controls PKX in naturally infected sockeye salmon, Oncorhynchus nerka (Walbaum), underyearlings

The use of fumagillin‐DCH, a natural product of Aspergillus fumigatus, has proven successful for the control of microsporidian infections, including Nucleospora salmonis Hedrick, Groff & Baxa (Hedrick, Groff & Baxa 1991) and Loma salmonae (Putz, Hoffmann & Dunbar) (Kent & Dawe 1994). Fumagillin has also been used to treat various myxosporean diseases of fishes, including proliferative kidney disease (PKD), which is caused by the PKX organism (Molnár, Baska & Székely 1987; Hedrick, Groff, Foley & McDowell 1988; Székely, Molnár & Baska 1988; Wishkovsky, Groff, Laurén, Toth & Hedrick 1990; Yokoyama, Ogawa & Wakabayashi 1990; El‐Matbouli & Hoffmann 1991; Sitjá‐Bobadilla & Alvarez‐Pellitero 1992; Higgins & Kent 1996). An analogue of fumagillin, TNP‐470, has been shown to be effective in in vitro studies against the mammalian microsporidian pathogens Encephalitozoon intestinalis (Cali, Kotler & Orenstein), Vittaforma corneae (Shadduck, Meccoli, Davis & Font) (Didier 1997), E. cuniculi Levaditi, Nicolau & Schoen and E. hellem Didier, Didier, Freidberg, Stenson, Orenstein, Yee, Tio, Davis, Vossbrinck, Millichamp & Shadduck (Coyle, Kent, Tanowitz, Wittner & Weiss 1998). Higgins, Kent, Moran, Weiss & Dawe (1998) tested TNP‐470 against two microsporidian diseases of salmonids, N. salmonis and L. salmonae, and showed a significant reduction in parasitism after oral treatment with 0.1 or 1.0 mg kg‐1 fish day‐1 for 5 weeks. Therefore, the present authors investigated the efficacy of TNP‐470 against the PKX myxosporean in naturally exposed sockeye salmon, Oncorhynchus nerka (Walbaum). This host was chosen as it has been found to be particularly susceptible to the infection.

Quinine hydrochloride treatment delays xenoma formation and dissolution in rainbow trout challenged with Loma salmonae

An experiment was designed to study the effect of dietary quinine hydrochloride (61 mg/kg of fish/day), on the rate of xenoma formation in the gills of Loma salmonae-infected juvenile rainbow trout maintained at a water temperature of 15 degrees C. Almost all (90.9%) control fish had developed xenomas by week 6 post-exposure (PE), but significantly fewer (18.2%) of the medicated fish were similarly affected (P < 0.0001). By week 8 PE, 100% of control fish had xenomas, but only 57.5% of quinine-treated had xenomas (P < 0.0001). However, by week 9 there was no difference between treated and control fish. Xenoma dissolution and branchitis, two crucial events in the pathogenesis of L. salmonae infection in farm-reared Pacific salmon, were present at week 10 in control fish. In contrast, comparable lesions did not develop in treated fish until week 14. These findings are of potential significance for the control of L. salmonae infection in farmed salmon.

Loma salmonae‐associated growth rate suppression in rainbow trout, Oncorhynchus mykiss (Walbaum), occurs during early onset xenoma dissolution as determined by in situ hybridization and immunohistochemistry

AbstractExperimental infection of rainbow trout, Oncorhynchus mykiss (Walbaum), juveniles with Loma salmonae at a water temperature of 15 °C yielded detectable parasite DNA within the gills by week 2 post‐exposure (PE) and detectable spore‐wall antigen within developing xenomas by week 3 PE, as determined by in situ hybridization and monoclonal antibody (Mab) based immunohistochemistry, respectively. The microsporidian was most commonly located within endothelial cells of lamellar basal channels. Whereas the onset of xenoma formation appeared to be relatively synchronous, as expected from previous studies, xenoma dissolution followed an unexpected biphasic pattern with peaks at weeks 4 and 9 PE. The onset of significant growth rate suppression, at week 4 PE in exposed fish, was temporally associated with the appearance of gill lesions which, in turn, were centred about sites of premature xenoma dissolution. The latter was determined by the detection of spore‐wall antigen within lesions. Co‐habitant control fish began developing xenomas by week 10, indicating the infective potential of those spores released from the principal fish during early xenoma dissolution. Although infection with L. salmonae significantly affects fish growth rates, the time‐course of this suppression is limited, and as an unexpected finding, growth rate recovery commences prior to the infection’s resolution.

Survey of Salmonid Pathogens in Ocean-Caught Fishes in British Columbia, Canada

Abstract A survey of wild fishes captured around marine net-pen salmon farms and from open waters for certain salmonid pathogens was conducted in the coastal waters of British Columbia. Viral hemorrhagic septicemia virus was detected in Pacific herring Clupea pallasi, shiner perch Cymatogaster aggregata, and threespine sticklebacks Gasterosteus aculeatus. Infectious hematopoietic necrosis (IHN) virus was detected in one Pacific herring (collected well away from the farms) and in tube-snouts Aulorhynchus flavidus and shiner perch collected from a farm experiencing an IHN outbreak. Renibacterium salmoninarum was observed in moribund Pacific hakes Merluccius productus collected from within a net-pen and was also detected in several ocean-caught salmon. Aeromonas salmonicida subsp. salmonicida (typical strain) was isolated from a juvenile chinook salmon Oncorhynchus tshawytscha, whereas the atypical strain of this organism was isolated from a lingcod Ophiodon elongatus. Loma salmonae (Microsporea) was observe...

Induced resistance in rainbow trout, Oncorhynchus mykiss (Walbaum), to gill disease associated with the microsporidian gill parasite Loma salmonae.

Branchial xenomas were detected by week 5 and disappeared by week 10 after naive juvenile rainbow trout, held at 14.5 °C, were fed or intubated with Loma salmonae-infected gill tissue preparations. Upon re-challenge with L. salmonae, these fish were protected from disease and branchial xenomas did not develop. Branchial xenomas were never detected in naive fish held at 10 °C and exposed to L. salmonae. When these fish were re-challenged with L. salmonae at 14.5 °C, they were also protected from the disease. Branchial xenomas also developed after naive fish, held at 14.5 °C, were injected intraperitoneally with a semipurified preparation of fresh spores, but generally did not develop after intraperitoneal injection with a preparation of spores subjected to freezing and thawing before use. Fish that had received fresh spores intraperitoneally were completely resistant to disease when re-challenged via oral delivery of spores, whereas those that had received frozen spores were incompletely, but significantly, protected from disease compared with naive fish. We conclude that infection with L. salmonae induces strong protection towards the disease upon re-exposure to spores, and that the protection does not depend on the completion of the parasite's life cycle, thus establishing the basis for further research on vaccine development for this disease.

Efficacy of the fumagillin analog TNP-470 for Nucleospora salmonis and Loma salmonae infections in chinook salmon Oncorhynchus tshawytscha.

Oral treatment with fumagillin is effective for controlling various microsporean and myxosporean infections in fish. We tested a synthetic analog of fumagillin, TNP-470 (Takeda Chemical Industries), for its efficacy against 2 microsporean pathogens of salmon: Loma salmonae and Nucleospora salmonis. Chinook salmon Oncorhynchus tshawytscha were experimentally infected with either L. salmonae (per os) or N. salmonis (intraperitoneal, i.p., injection) and held in fresh water at 15 degrees C. Fish were then divided into 3 replicate groups: untreated or treated orally at 1.0 mg or at 0.1 mg drug kg-1 fish d-1. With L. salmonae, the high dose fish had 0.32 xenomas mm-2 of gill tissue compared to controls at 24.5 xenomas per mm2. With N. salmonis infections, untreated fish exhibited 100% infection, showed prominent clinical signs (e.g. renal swelling, anaemia), and high mortality. In contrast, fish treated at 1.0 mg kg-1 showed no clinical signs, and 16% of those treated at 0.1 mg kg-1 showed only mild gross pathological changes. With the treated groups, over 50% of the fish exhibited extremely light infections, even with high dose treatments, but no mortalities were attributed to N. salmonis infections. Uninfected fish treated at 1.0 mg drug kg-1 fish d-1 for 5 wk appeared clinically normal and showed no reduction in growth. However, about half of these fish exhibited atrophy of the renal interstitial hematopoietic tissue.

Modes of transmission of Loma salmonae (Microsporidia).

Loma salmonae (Putz, Hoffman and Dunbar, 1965) Morrison and Sprague, 1981 (Microsporidia) causes prominent gill disease in pen-reared chinook salmon Oncorhynchus tshawytscha in the Pacific Northwest. Transmission of the parasite was examined by exposing Pacific salmon Oncorhynchus spp. to infectious spores by various routes: per os, intraperitoneal, intramuscular, and intravascular injection, by cohabitation with infected fish, and by placement of spores directly on the gill. All exposure methods led to infections except placement of spores on the gill. Putative sporoplasms were visible in epithelial cells of the alimentary canal within 24 h of per os exposure. L. salmonae may initially infect alimentary epithelial cells and then migrate into the lamina propia to access the blood stream. Positive results obtained by intravascular injection suggest that autoinfection from spores of ruptured xenomas in the endothelium may also occur. The cohabitation experiment demonstrates that fish may become infected by spores released from live fish.

The occurrence of Loma salmonae (Protozoa: Microspora) in farmed rainbow trout, Oncorhynchus mykiss Walbaum, in Scotland

A systemic infection of Loma salmonae is described from a farmed rainbow trout, Oncorhynchus mykiss Walbaum, population reared in fresh water in Scotland. Intact xenomas were associated with the blood vessels and pillar system of the gill lamellae and other organs. The secondary gill lamellae were hyperplastic with little evidence of fibrosis or inflammatory infiltrate. Uninucleate oval spores characteristic of L. salmonae are described. A low mortality was attributed to this outbreak which is believed to be the first occurrence in Scotland.

Efficacy of Fumagillin DCH against experimentally induced Loma salmonae (Microsporea) infections in chinook salmon Oncorhynchus tshawytscha

Efficacy of Fumagillin DCH against experimentally induced Loma salmonae (Microsporea) infections in chinook salmon Oncorhynchus tshawytscha

Loma salmonae (Protozoa: Microspora) infections in seawater reared coho salmon Oncorhynchus kisutch

Loma salmonae (Putz et al., 1965) infections were observed in five groups of coho salmon, Oncorhynchus kisutch, reared in seawater net-pens in Washington State, U.S.A. in 1984–1986. Ultrastructural characteristics, size of spores, tissues and host infected, and geographical location identified the microsporidium as Loma salmonae. Preserved spores measured 4.4×2.3 (4–5.6×2–2.4) μm and exhibited 14–17 turns of the polar filament. Infections were evident in the gills of some fish before seawater entry, but few parasites were observed and they caused little tissue damage. Infections observed in fish after transfer to seawater were associated with significant pathological changes in the gills. A mixed inflammatory infiltrate was associated with ruptured microsporidian xenomas within the vessels and interstitium of the primary lamellae. Microsporidian spores were dispersed throughout the lesions and were often seen inside phagocytes. The parasite was also observed in the heart, spleen, kidney and pseudobranchs; however, the inflammatory lesions were common only in the heart. Monthly examination of fish after transfer to seawater showed peak prevalences (33–65%) of gill infections during the summer. Although moribund fish were often infected with other pathogens, the high prevalence of L. salmonae infections and the severity of the lesions it caused, suggested that this parasite significantly contributed to the recurrent summer mortalities observed at this net-pen site.

Distribution of the flagellate Hexamita salmonis Moore, 1922 and the microsporidian Loma salmonae Putz, Hoffman and Dunbar, 1965 in brown trout, Salmo trutta L., and rainbow trout, Salmo gairdneri Richardson, in the River Itchen (U.K.) and three of its fish farms

The occurrence of Hexamita salmonis Moore, 1922 and Loma salmonae Putz, Hoffman and Dunbar, 1965 was investigated at 10 sites on the R. Itchen (five for brown trout only, three for rainbow trout only, and two for both brown trout and rainbow trout) and at three of its nine fish farms (two for rainbow trout, one for brown trout). Hexamita salmonis was recorded in brown trout from three river sites and the farm, and in rainbow trout from both farms and four river sites. Prevalence of Hexamita salmonis in farmed rainbow trout was higher than in farmed brown trout and was consistent with the former species being more susceptible to infection. H. salmonis was at significantly higher prevalence in rainbow trout from farm no. 5 than farm no. 2 for three size classes of fish. In wild brown trout and feral rainbow trout, the highest prevalences of H. salmonis were recorded at sites in the vicinity of farm no. 2. This distribution was consistent with an area of naturally high infection levels, and with infected fish unintentionally released from farm no. 2 serving as a source of infection, the infection subsequently becoming established in the river fish. Loma salmonae was recorded in wild brown trout and in rainbow trout from both farms. This appears to be the first recording of this parasite from British salmonids and also the first recording of the parasite from brown trout. The distribution of the parasite (particularly the prevalence being higher at farm no. 2 than farm no. 5) was consistent with it being introduced into the R. Itchen via rainbow trout from farm no. 2 (and probably no. 3) much of whose stock derived from imported Californian ‘Shasta’ rainbow trout.

Loma salmonae (Putz, Hoffman and Dunbar, 1965) in the rainbow trout, Salmo gairdneri Richardson, and L. fontinalis sp. nov. (Microsporida) in the brook trout, Salvelinus fontinalis (Mitchill)

Abstract. Loma salmonae (Putz, Hoffman and Dunbar, 1965), Morrison &amp; Sprague, 1981, in the rainbow trout, Salmo gairdneri Richardson, was studied with the electron microscope. It is morphologically very similar to L. morhua Morrison and Sprague, 1981, in the Atlantic cod, Gadus morhua L., having only minor differences. Loma sp. Morrison and Sprague, 1981, in the brook trout, Salvelinus fontinalis (Mitchill), is more like L. salmonae than the other species of Loma, but was deemed to be distinct. It was named L. fontinalis sp. nov.