Impaired NDRG1 functions in Schwann cells cause demyelinating neuropathy in a dog model of Charcot-Marie-Tooth type 4D

Mutations in the N-myc downstream-regulated gene 1 (NDRG1) cause degenerative polyneuropathy in ways that are poorly understood. We have investigated Alaskan Malamute dogs with neuropathy caused by a missense mutation in NDRG1. In affected animals, nerve levels of NDRG1 protein were reduced by more than 70% (p< 0.03). Nerve fibers were thinly myelinated, loss of large myelinated fibers was pronounced and teased fiber preparations showed both demyelination and remyelination. Inclusions of filamentous material containing actin were present in adaxonal Schwann cell cytoplasm and Schmidt-Lanterman clefts. This condition strongly resembles the human Charcot-Marie-Tooth type 4D. However, the focally folded myelin with adaxonal infoldings segregating the axon found in this study are ultrastructural changes not described in the human disease. Furthermore, lipidomic analysis revealed a profound loss of peripheral nerve lipids. Our data suggest that the low levels of mutant NDRG1 is insufficient to support Schwann cells in maintaining myelin homeostasis.

Granulomatous Uveitis Associated with Vaccination in the Atlantic Salmon

This study addressed histologic and immunopathologic changes in ocular tissues and investigated the distribution of major histocompatibility class II (MHC class II)-positive cells in Atlantic salmon ( Salmo salar) suffering from severe postvaccination disease. Twenty-nine fish with generalized inflammation, probably a result of vaccination, were investigated. One individual that had escaped vaccination was included in the study. Material was investigated by cultivation methods for fungi and bacteria. Histology using conventional staining procedures and immunohistochemistry with antisera against MHC class II β chain were performed. No growth was observed from the cultivation investigations. Histology revealed occlusion of the lumen in the larger choroid vessels and in the choriocapillaris, inflammatory infiltrations and loss of structure in the choroid rete, and, in some cases, aggregations of multinucleated giant cells (MGC) and Splendore-Hoeppli material. Immunohistochemistry demonstrated massive MHC class II+ cellular infiltrations in the uveal tract. Such infiltrations were also seen in the ventral ciliary cleft, a condition that is associated with glaucoma. Immunoreactive cells included dendritelike cells, epithelioid cells, and MGCs. The endothelia of smaller vessels were frequently MHC class II+, and immunoreactive infiltrations were seen in the optic nerve in several individuals. No pathologic changes were detected in the unvaccinated individual. In conclusion, generalized inflammatory reactions in fish may lead to severe ocular inflammation, occlusion of uveal vessels, and perivascular changes with MHC class II+ upregulation in cells in the uveal tract and optic nerve.

Mast cells in common wolffish Anarhichas lupus L.: ontogeny, distribution and association with lymphatic vessels

The morphology, ontogeny and tissue distribution of mast cells were studied in common wolffish(Anarhichas lupus L.) at the larval, juvenile and adult life stages using light and electron-microscopy and immunohistochemistry. Fish were sampled at 1 day, 1, 2, 3, 4, 8 and 12 weeks post-hatching in addition to 6 and 9 months and 2 years and older. From 8 weeks post-hatching, mast cells in common wolffish mainly appeared as oval or rounded cells 8-15 mm in diameter with an eccentrically placed, ovoid nucleus and filled with cytoplasmic granules up to 1.2 mm in diameter. Granules were refractile and eosinophilic to slightly basophilic in H&E and stained bright red with Martius-scarlet-blue and purple with pinacyanol erythrosinate in formalin-fixed tissues. Mast cells stained positive for piscidin 4 and Fc ε RI by immunohistochemistry. From 1 day to 4 weeks post-hatching, immature mast cell containing only a few irregularly sized cytoplasmic granules were observed by light and electron-microscopy in loose connective tissue of cranial areas. From 1 day post-hatching, these cells stained positive for piscidin 4 and Fc ε RI by immunohistochemistry. From 12 weeks post-hatching, mast cells showed a primarily perivascular distribution and were particularly closely associated with lymphatic vessels and sinuses. Mast cells were mainly located at the peripheral border of the adventitia of arteries and veins, while they were in intimate contact with the endothelium of the lymphatic vessels. Numerous mast cells were observed in the intestine. A stratum compactum, as described in salmonids, was not observed in wolffish intestine,nor were mast cells confined to a separate layer, a stratum granulosum. Lymphatic vessels consisting of endothelium, intimal connective tissue and a poorly developed basal lamina were observed in the intestine. Scanning electron microscopy was used to compare the structure and localization of intestinal mast cells of common wolffish and rainbow trout. Scanning electron microscopy also revealed endothelial surface features and confirmed the existence of three distinctly different types of vessels in the wolffish intestine. Rainbow trout mast cell granules appeared as intact globular structures while empty vacuoles were observed in common wolffish. Mast cells were closely associated with lymphatic vessels in common wolffish, but not in rainbow trout.

A Gly98Val mutation in the N-Myc downstream regulated gene 1 (NDRG1) in Alaskan Malamutes with polyneuropathy

The first cases of early-onset progressive polyneuropathy appeared in the Alaskan Malamute population in Norway in the late 1970s. Affected dogs were of both sexes and were ambulatory paraparetic, progressing to non-ambulatory tetraparesis. On neurologic examination, affected dogs displayed predominantly laryngeal paresis, decreased postural reactions, decreased spinal reflexes and muscle atrophy. The disease was considered eradicated through breeding programmes but recently new cases have occurred in the Nordic countries and the USA. The N-myc downstream-regulated gene (NDRG1) is implicated in neuropathies with comparable symptoms or clinical signs both in humans and in Greyhound dogs. This gene was therefore considered a candidate gene for the polyneuropathy in Alaskan Malamutes. The coding sequence of the NDRG1 gene derived from one healthy and one affected Alaskan Malamute revealed a non-synonymous G>T mutation in exon 4 in the affected dog that causes a Gly98Val amino acid substitution. This substitution was categorized to be “probably damaging” to the protein function by PolyPhen2 (score: 1.000). Subsequently, 102 Alaskan Malamutes from the Nordic countries and the USA known to be either affected (n = 22), obligate carriers (n = 7) or healthy (n = 73) were genotyped for the SNP using TaqMan. All affected dogs had the T/T genotype, the obligate carriers had the G/T genotype and the healthy dogs had the G/G genotype except for 13 who had the G/T genotype. A protein alignment showed that residue 98 is conserved in mammals and also that the entire NDRG1 protein is highly conserved (94.7%) in mammals. We conclude that the G>T substitution is most likely the mutation that causes polyneuropathy in Alaskan Malamutes. Our characterization of a novel candidate causative mutation for polyneuropathy offers a new canine model that can provide further insight into pathobiology and therapy of human polyneuropathy. Furthermore, selection against this mutation can now be used to eliminate the disease in Alaskan Malamutes.

Polyclonal hypergammaglobulinemia and autoantibody production induced by vaccination in farmed Atlantic salmon

The introduction of oil-adjuvanted vaccines in salmon aquaculture made large-scale production feasible by reducing the impact of infections. Vaccines given intraperitoneally (ip) contain oil adjuvant such as mineral oil. However, in rodents, a single ip injection of adjuvant hydrocarbon oil induces lupus-like systemic autoimmune syndrome. We have recently reported that autoimmune disease in farmed salmon, characterized by production of various autoantibodies, immune complex glomerulonephritis, liver thrombosis, and spinal deformity, are previously unrecognized side effects of vaccination. In the present study, we examined whether vaccination-induced autoantibody production in farmed Atlantic salmon is a mere result of polyclonal B-cell activation. Sera were collected from 205 vaccinated and unvaccinated Atlantic salmon (experimental, 7 farms) and wild salmon. Total IgM levels and autoantibodies to salmon blood cell (SBC) extract in sera were measured by ELISA and the relationship between hypergammaglobulinemia and autoantibody production was analyzed. Comparison of endpoint titers vs levels/units using a single dilution of sera in detection of autoantibodies to SBC showed near perfect correlation, justifying the use of the latter for screening. Both total IgM and anti-SBC antibodies are increased in vaccinated salmon compared with unvaccinated controls, however, they do not always correlate well when compared between groups or between individuals, suggesting the involvement of antigen-specific mechanisms in the production of anti-SBC autoantibodies. The primary considerations of successful vaccine for aquaculture are cost-effectiveness and safety. Vaccination-induced autoimmunity in farmed Atlantic salmon may have consequences on future vaccine development and salmon farming strategy. Evaluation for polyclonal hypergamamglobulinemia and autoimmunity should be included as an important trait when vaccine efficacy and safety are evaluated in future.

Antigen-sampling cells in the salmonid intestinal epithelium

Antigen uptake has been shown to occur in the teleost intestine, but so far, limited information is available on the distribution and nature of cells involved in the process, and M cells, known for their antigen-sampling abilities in mammals, have not been identified. Here, different intestinal segments from salmonid fish were exposed to gold-BSA to identify antigen-sampling cells. Sections from exposed intestine were examined by light and electron microscopy. Uptake of gold-BSA was restricted to very few dendritic-like cells and to a limited number of epithelial cells located in the mucosal folds in the second segment of the mid-intestine. Gold-positive epithelial cells displayed diverging and electron-dense microvilli with channels intruding into the cytoplasm. A lectin binding experiment demonstrated the presence of cells with mammalian M-cell characteristics in the identical regions. As the identified epithelial cells shared some morphological similarities with immature mammalian M cells, this phenotype may represent evolutionary early antigen-sampling enterocytes.

Manifestations of systemic autoimmunity in vaccinated salmon

The development of systemic autoimmunity may result as an undesired side-effect following vaccination, and this condition was recently shown to occur in farmed salmon (Salmo salar). Several of previously reported side-effects following vaccination of fish should therefore be reviewed in the light of this condition. Here, organs and pathological changes in three separate groups of fish severely affected by vaccination were investigated by different morphological methods (n=84). Granulomas or microgranulomas were observed at the injection site and in several organs. Mott cells were observed in all tissues examined. Pannus-like changes with lymphocyte infiltrates were observed in spines. In conclusion, the reactions following vaccination were of a systemic nature that may be explained by a pathogenetic mechanism caused by systemic autoimmunity.

Identification and characterization of a novel intraepithelial lymphoid tissue in the gills of Atlantic salmon

In addition to being the respiratory organ in fish, the gills form a barrier against the external milieu. Innate and adaptive immune system components have been detected in the gills, but lymphoid cell accumulations similar to that seen in the mammalian mucosa have not been described. The present investigations revealed cell accumulations on the caudal edge of interbranchial septum at the base of the gill filaments in the Atlantic salmon. Cytokeratin immunohistochemical staining and identification of a basal membrane and desmosome cell junctions by electron microscopy showed that the cell accumulation was located intraepithelially. Major histocompatibility complex (MHC) class II+ cells were detected by immunohistochemistry, and laser capture micro-dissection and subsequent RT-PCR analysis revealed expression of T-cell receptor transcripts in the investigated tissue, suggesting the presence of T cells. The intraepithelial tissue reported here may be a suitable location for immune surveillance of gill infections, as well as a target site for new vaccine approaches and investigations of epithelial immunity. This is the first description of a lymphocyte cell aggregation within a teleostian gill epithelium network, illustrating a phylogenetically early form of leukocyte accumulations in a respiratory organ.

Vaccination-induced systemic autoimmunity in farmed Atlantic salmon

Over half of the salmon consumed globally are farm-raised. The introduction of oil-adjuvanted vaccines into salmon aquaculture made large-scale production feasible by preventing infections. The vaccines that are given i.p. contain oil adjuvant such as mineral oil. However, in rodents, a single i.p. injection of adjuvant hydrocarbon oil induces lupus-like systemic autoimmune syndrome, characterized by autoantibodies, immune complex glomerulonephritis, and arthritis. In the present study, whether the farmed salmon that received oil-adjuvanted vaccine have autoimmune syndrome similar to adjuvant oil-injected rodents was examined. Sera and tissues were collected from vaccinated or unvaccinated Atlantic salmon (experimental, seven farms) and wild salmon. Autoantibodies (immunofluorescence, ELISA, and immunoprecipitation) and IgM levels (ELISA) in sera were measured. Kidneys and livers were examined for pathology. Autoantibodies were common in vaccinated fish vs unvaccinated controls and they reacted with salmon cells/Ags in addition to their reactivity with mammalian Ags. Diffuse nuclear/cytoplasmic staining was common in immunofluorescence but some had more specific patterns. Serum total IgM levels were also increased in vaccinated fish; however, the fold increase of autoantibodies was much more than that of total IgM. Sera from vaccinated fish immunoprecipitated ferritin and approximately 50% also reacted with other unique proteins. Thrombosis and granulomatous inflammation in liver, and immune-complex glomerulonephritis were common in vaccinated fish. Autoimmunity similar to the mouse model of adjuvant oil-induced lupus is common in vaccinated farmed Atlantic salmon. This may have a significant impact on production loss, disease of previously unknown etiology, and future strategies of vaccines and salmon farming.

Pancreas disease in farmed Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), in Norway

The present paper describes, for the first time, clinical signs and pathological findings of pancreas disease (PD) in farmed Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), in sea water in Norway. Similarities and differences with reports of PD from Ireland and Scotland are discussed. Samples of 68 rainbow trout from disease outbreaks on 14 farms and from 155 Atlantic salmon from outbreaks on 20 farms collected from 1996 to 2004 were included in the present study. The histopathological findings of PD in Atlantic salmon and rainbow trout in sea water were similar. Acute PD, characterized by acute necrosis of exocrine pancreatic tissues, was detected in nine Atlantic salmon and three rainbow trout. Salmonid alphavirus (SAV) was identified in acute pancreatic necroses by immunohistochemistry. Most fish showed severe loss of exocrine pancreatic tissue combined with chronic myositis. Myocarditis was often but not consistently found. Kidneys from 40% and 64% of the rainbow trout and Atlantic salmon, respectively, had cells along the sinusoids that were packed with cytoplasmic eosinophilic granules. These cells resembled hypertrophied endothelial cells or elongated mast cell analogues. Histochemical staining properties and electron microscopy of these cells are presented. SAV was identified by RT-PCR and neutralizing antibodies against SAV were detected in blood samples.

Magnetic resonance imaging of the Harderian gland in piglets

The main purpose of the present study was to investigate the value and effectiveness of functional and morphological magnetic resonance imaging (MRI), in order to assess the extent of brain injury in a hypoxic-ischaemic piglet model, and further to validate that the ischaemic injury was successfully induced. In this way, we also characterized the Harderian gland. MRI was performed at 1.5 T in anaesthetized piglets (n = 10, 12-36 h of age). Magnetic resonance perfusion and diffusion imaging were performed at different time points, before, during and after the induction of hypoxia-ischaemia. The effects following bilateral clamping of the carotid arteries were also assessed by contrast-enhanced magnetic resonance angiography. Morphological assessment included T1- and T2-weighted imaging, and fat-suppressed T1-weighted imaging before and after contrast medium enhancement. Morphological MRI revealed a prominent, well-defined structure located at the eyeball. Magnetic resonance angiography reconstructed with volume rendering showed this structure to be partially enclosed by large venous sinuses. At dissection, when compared with the magnetic resonance images, the deep gland of the third eyelid, the Harderian gland, corresponded to this structure both in topography and in size. By contrast, the lacrimal gland proper presented as a small, soft and pale structure that was difficult to distinguish from the surrounding connective tissue. At histological examination, the Harderian gland consisted mainly of compact areas of tubuloacinar glands with abundant eosinophilic granules. The present MRI demonstration of the Harderian gland was an accidental finding during an investigation to assess the extent of brain injury in a hypoxic-ischaemic piglet model. The combination of MRI and histology made it possible to detect and describe the Harderian gland in pig. It has generally been studied in rodents and lower vertebrates and is reported to possess various endocrine and exocrine functions.

Osmotic cataract causes reduced vision in wild Atlantic salmon postsmolts

Osmotic cataracts were diagnosed in all of 191 Atlantic salmon Salmo salar L. postsmolts caught during 8 trawl hauls on the western side of the Vøringsplateau, Norwegian Sea, in June 2001. The changes varied from a hazy opacity in the anterior part of the lens to cataracts affecting the whole lens. Severely affected lenses appeared swollen and large vacuoles were visible in the opaque areas. Large vacuoles in otherwise clear lenses were diagnosed in 1 of 4 adult salmon examined. Histologically, widened sutures, vacuolation of lens epithelium and cortex, and proteinaceous lakes subjacent to the epithelium were the most frequent changes, while extensive cortical necroses and epithelial proliferation were seen in a few cases. UV-absorbance of the aqueous humor was determined and levels compared to plasma levels and also to levels in farmed Atlantic salmon of the same developmental stage. Wild salmon generally showed higher levels of protective factors than farmed fish. The osmotic type of cataract diagnosed leads to poor vision and is a potential cause of reduced survival in postsmolts. The cause of the cataracts could not be determined, but defective osmoregulation is suspected.

Vaccination induces major histocompatibility complex class II expression in the Atlantic salmon eye

The aim of the study was to investigate the presence, distribution and density of major histocompatibility complex (MHC) class II+ cells in the ocular tissues of the Atlantic salmon, Salmo salar, prior to and following vaccination. Eyes were collected 14 days prior to and at 4, 11, 25 and 39 days and 4 months subsequent to vaccination with a commercial fish vaccine. A quantitative analysis was performed in sections on the number of immunopositive cells in the retinal layers. In all groups, MHC class II+ cells were detected in the area of the limbus but not in the central parts of the cornea. In the uvea, immunopositive cells were present in unvaccinated and vaccinated fish. Abundant immunopositive cells were identified in the choroid rete (or choroid gland) in all groups as well as in the ventral ciliary cleft, where macrophage-like MHC class II+ cells were seen. Quantitative histology of the retina revealed a significant increase in MHC class II+ cells in the outer plexiform layer (OPL) and the inner nuclear layer (INL) 4 days following vaccination. Positive cells were detected in all layers of the retina with the exception of the photoreceptor layer.

Production of rabbit antisera against recombinant MHC class II beta chain and identification of immunoreactive cells in Atlantic salmon (Salmo salar)

In the present work, rabbit antisera recognising the Atlantic salmon (Salmo salar) MHC class II beta chain polypeptide were produced and used in immunoblotting, immunohistochemistry and immunogold electron microscopy. A construct encoding the beta1 and beta2 domains fused to the E. coli protein thioredoxin was used to express the recombinant MHC class II beta chain. Immunoblotting revealed a band of approximately 30kDa in total protein samples from head kidney, spleen, gills, thymus and blood leukocytes, while being absent in muscle. The distribution of MHC class II positive cells was immunohistochemically demonstrated in Atlantic salmon epithelial and haemopoietic tissues. Ultrastructural demonstration of immunoreactive organelles in mid-kidney cells was performed by immunogold electron microscopy. The results indicate expression in lymphocytes, macrophages, epithelial cells and endritic-like cells. This is the first study to address morphological MHC class II expression in a fish species.

Redescription of Neospora caninum and its differentiation from related coccidia

Neospora caninum is a protozoan parasite of animals, which before 1984 was misidentified as Toxoplasma gondii. Infection by this parasite is a major cause of abortion in cattle and causes paralysis in dogs. Since the original description of N. caninum in 1988, considerable progress has been made in the understanding of its life cycle, biology, genetics and diagnosis. In this article, the authors redescribe the parasite, distinguish it from related coccidia, and provide accession numbers to its type specimens deposited in museums.

Subclinical herpesvirus infection in farmed turbot Scophthalmus maximus

Subclinical infections with a herpesvirus were detected by light and electron microscopic examination of juvenile turbot collected during a national surveillance programme. Virions detected in the epidermis of skin and in the epithelium of gills had a morphology consistent with those of Herpesvirus scophthalmi described from turbot in the United Kingdom and Denmark. This is the first report of herpesvirus infection in turbot in Norway.

The anatomy of the oesophagus, stomach and intestine in common wolffish (Anarhichas lupus L.): a basis for diagnostic work and research

The alimentary canal of laboratory-reared common wolffish (Anarhichas lupus L.) was studied using light and electron microscopy. In the oesophagus, a simple columnar microvillous epithelium with transport characteristics was observed in addition to the main striated squamous epithelium. An osmoregulatory function is proposed for the simple columnar epithelium, which was supported by wide, thin-walled vessels. In the stomach, a separate type of neck cells was observed leading into the acinar gastric glands, which morphologically consist of one cell type: chief cells. The intestine was divided into a proximal and distal segment by an intestinal valve. Pyloric caeca were not present. We propose that shallow, crypt-like structures in the intestinal mucosa are the sites of epithelial-cell proliferation in juveniles and adults. The length of microvilli decreased from approximately 4 microns in the cranial part of the proximal intestine, to 1.5 microns in the distal intestine. In the distal intestine, rod-shaped bacteria were observed between microvilli. An extensive system of thin-walled vessels was observed in the submucosa of juvenile and adult wolffish stomach and intestine. Eosinophilic granular cells were numerous in the perivascular connective tissue in the gastric and intestinal submucosa of adults and juveniles, but were not observed in larvae.

An outbreak of cataract with lens rupture and nuclear extrusion in wolf-fish (Anarhicas spp.)

Eight spotted (Anarhicas minor Olafsen) and five common wolf-fish (Anarhicas Lupus L), developed cataracts shortly after an episode of increased water temperature and decreased salinity 5 years prior to examination. On clinical examination, the cataracts were mostly bilateral and complete, and a majority of the lenses were lobulated. Inflammatory reaction was, apart from one eye with severe inflammation, limited to iris atrophy. Of the 14 eyes collected for pathomorphological examination, eight had lens rupture with extrusion of the nucleus to the posterior chamber, two showed partly dislocated nuclei with posterior protrusion and two lenses were morgagnian. A multilayered squamous epithelium with abundant desmosomes had developed on the surface of seven of the extruded nuclei. The main cause of the cataracts was considered to be the rapid decrease in water salinity, causing osmotic changes within the eyes with secondary swelling of lens fibers and rupture of the lens capsules.

The anatomy of the oesophagus, stomach and intestine in common wolffish (Anarhichas lupus L.): a basis for diagnostic work and research

The alimentary canal of laboratory-reared common wolffish (Anarhichas lupus L.) was studied using light and electron microscopy. In the oesophagus, a simple columnar microvillous epithelium with transport characteristics was observed in addition to the main striated squamous epithelium. An osmoregulatory function is proposed for the simple columnar epithelium, which was supported by wide, thin-walled vessels. In the stomach, a separate type of neck cells was observed leading into the acinar gastric glands, which morphologically consist of one cell type: chief cells. The intestine was divided into a proximal and distal segment by an intestinal valve. Pyloric caeca were not present. We propose that shallow, crypt-like structures in the intestinal mucosa are the sites of epithelial-cell proliferation in juveniles and adults. The length of microvilli decreased from approximately 4 microns in the cranial part of the proximal intestine, to 1.5 microns in the distal intestine. In the distal intestine, rod-shaped bacteria were observed between microvilli. An extensive system of thin-walled vessels was observed in the submucosa of juvenile and adult wolffish stomach and intestine. Eosinophilic granular cells were numerous in the perivascular connective tissue in the gastric and intestinal submucosa of adults and juveniles, but were not observed in larvae.

Genetic markers linked to neuronal ceroid lipofuscinosis in English setter dogs

The neuronal ceroid lipofuscinoses (NCL) are a group of fatal autosomal recessive neurodegenerative diseases occurring in human and some domesticated animal species. A canine form of the disease (CNCL) has been extensively studied in a Norwegian colony of inbred English setters since 1960. A resource family developed for genetic mapping and comprising 170 individuals was typed for 103 genetic markers. Linkage analysis showed three genetic markers to be linked to the disease locus with the closest marker at a distance of about 3 CM. Two other loci were linked with these markers making a linkage group of five genetic markers. The linkage group spanned a distance of 54 CM. Two genes for human forms of the disease, CLN2 and CLN3, have been identified and mapped to human chromosome 11p15 and 16p12, respectively. The present study did not indicate any linkage between CNCL and the canine CLN3 homologue or to homologues of markers for genes that map close to human CLN2.

Cataract development in Atlantic salmon (Salmo salar L) in fresh water

Irreversible bilateral cataracts were diagnosed by slit-lamp biomicroscopy in 178 of 200 farm-raised Atlantic salmon (Salmo salar L) fed a standard diet over a five-month period. Initial changes were anterior polar opacities, progressing to involve both the anterior and posterior cortex before changes in the lens nucleus were seen. The lens changes were recorded and given scores according to the severity of the cataracts. At each of 3 samplings, after 2, 4 and 5 months, 200 fish were measured, weighed and examined by slit-lamp biomicroscopy. At all 3 samplings, there was a significant correlation between body length and both cataract incidence and cataract severity. There was also a significant correlation between body weight and cataract incidence and severity for the 2 last samplings. There was a significant correlation between K-factor as a measure of the shape of the fish, and both cataract incidence and severity, at all 3 samplings. Evaluation of specific growth rate in the periods between the examinations showed that the rapidly-growing fish were most susceptible to cataract formation. After cataract developed, however, the growth rate slowed. Follow-up examination of severely affected fish 3 months after transfer to sea water showed a normal cortical zone in the periphery of the lens in 24 out of 28 fish.

Neospora caninum infection in a litter of Labrador retriever dogs in Denmark

Neospora caninum is a recently recognized cyst-forming coccidian parasite associated with severe encephalomyelitis and myositis in dogs of different breeds and ages (Bjerkås et al 1984, Bjerkås & Presthus 1988, Dubey et al. 1988), but has for many years been misdiagnosed as Toxoplasma gondii. In some dogs, the main clinical sign has been attributed to polyradiculoneuritis (Dubey et al. 1988, Cuddon et al. 1992). Furthermore, ulcerative dermatitis (Dubey et al. 1988) and megaoesophagus have been reported (Wolf et al. 1991). The life cycle of the parasite and mode of infection have not been clarified, but transplacental infection seems so far to be the natural route of transmission between intermediate hosts (Dubey & Lindsay 1989). It has been speculated that the disease in young and adult dogs might be due to reactivation of a persistent infection because corticosteroid therapy can activate a latent N. caninum infection (Dubey & Lindsay 1993).

Extraglomerular lesions in kidneys of mink with encephalitozoonosis

Extraglomerular renal lesions were studied by light and electron microscopy in 13 farmed mink which showed cataractous eyes associated with spontaneous encephalitozoonosis. The extraglomerular renal lesions consisted of multiple renal cysts, multifocal-to-coalescing interstitial nephritis and vasculitis. Tubular cysts of varying size were present in the corticomedullary junction and medulla. The inflammatory infiltrates were composed mostly of lymphocytes and plasma cells and usually accompanied an interstitial fibrosis. Vasculitis, perivasculitis and sclerotic arteries were frequently seen.

Extraglomerular lesions in kidneys of mink with encephalitozoonosis

Extraglomerular renal lesions were studied by light and electron microscopy in 13 farmed mink which showed cataractous eyes associated with spontaneous encephalitozoonosis. The extraglomerular renal lesions consisted of multiple renal cysts, multifocal-to-coalescing interstitial nephritis and vasculitis. Tubular cysts of varying size were present in the corticomedullary junction and medulla. The inflammatory infiltrates were composed mostly of lymphocytes and plasma cells and usually accompanied an interstitial fibrosis. Vasculitis, perivasculitis and sclerotic arteries were frequently seen.

Brain and spinal cord lesions in encephalitozoonosis in mink

Central nervous system lesions were studied by light microscopy in 43 farmed mink, aged 5 months to 2 1/2 years, with spontaneous encephalitozoonosis and showing cataractous eye changes. Lesions were found in the brain and spinal cord of all animals examined but were generally mild and chronic. The lesions were consistent with those previously described in spontaneous encephalitozoonosis in other carnivores. Parasites in parasitophorous vacuoles and free or phagocytosed in necrotic and granulomatous lesions were demonstrated in animals aged 5 months to 1 year. The occurrence of arterial lesions of the polyarteritis nodosa type found in the youngest animals probably indicates fetal infection. In animals aged 1 1/2 and 2 1/2 years active lesions were usually lacking and the changes were characterized by arterial sclerosis, sometimes with aneurysmal formations, small perivascular lympho-plasmacytic cuffings and focal gliosis.

Experimental pestivirus infections in pregnant goats

Fifty pregnant goats, inoculated intramuscularly at different gestational stages with a non-cytopathic ovine pestivirus or a cytopathic bovine pestivirus, all developed pestivirus-neutralizing antibodies within 5 weeks of inoculation. The incidence of reproductive failure was similar for the two agents. Parturition at term with only healthy kids occurred in 13 (26 per cent) of the goats. Viable kids were not born to any of the 17 goats inoculated at about day 40 of gestation. Three of the 17 delivered dead or weak kids, seven aborted and three of seven which were necropsied during pregnancy had markedly underdeveloped and autolysed or mummified fetuses in utero, while four were barren. When inoculated at around the 60th day of gestation, two of 18 animals gave birth to only healthy kids, 12 to dead and/or weak kids, two aborted and, at necropsy, a small, decomposed fetus was found in one goat while one other was barren. In this group, one kid was ataxic and seven others had body tremors characteristic of border disease. One of the latter kids was viable. Of 15 goats inoculated at around day 100 of gestation, 11 gave birth to healthy kids only, three to dead and/or weak kids and one aborted. In 23 progeny, histological changes in the central nervous system (CNS) consisted mainly of cerebral white matter necrosis, cerebellar dysplasia, hypercellular areas in white matter and lymphocytic perivascular cuffings. All seven weak-born kids with signs of border disease had CNS lesions, particularly cerebellar dysplasia and/or hypercellular areas. Non-cytopathic pestivirus was isolated from tissues from all eight progeny examined in the 40-day inoculation group, from tissues and/or serum from 10 of 23 progeny in the 60-day group, and from four of 24 in the 100-day group. Persistent infection was demonstrated in a healthy kid, in a viable shaker and in two other kids which appeared normal at birth. Examination of offspring before ingestion of colostrum revealed pestivirus antibodies in one kid in each of the 40- and 60-day inoculation groups and in five kids in the 100-day group.

Outbreaks of border disease in goats induced by a pestivirus-contaminated orf vaccine, with virus transmission to sheep and cattle

Five herds with a total of 276 female goats experienced severe outbreaks of reproductive failure due to a pestivirus-contaminated experimental orf vaccine given early in the breeding season. The reproductive failures comprised barrenness in 42 goats, abortion in 53 and, in 118, the birth of dead or weak kids. The incidence of female goats with such failures was 82 per cent overall, herd incidence rates ranging from 79 to 96 per cent. No progeny showed characteristic signs of border disease (BD). Microscopic lesions in the CNS were moderate, mostly characterized by hypercellularity, cell disorganization and decreased myelin content. Non-cytopathic strains of pestivirus were demonstrated in tissue or serum from two weak-born and two apparently healthy kids. Neutralizing antibodies against a bovine pestivirus were found in all 254 goats examined about 4 months after vaccination. At the end of the breeding season, all kids were removed and 74 young kids were introduced from presumably normal herds. Approximately 8 months later, 64 (86 per cent) of the bought-in kids had pestivirus antibodies. Two years after the outbreaks, such antibodies were found in all but three of 127 vaccinated goats still alive, and another 2 years later, in all 22 vaccinated goats in one of the herds. Sheep also were kept on the same five farms and cattle on one. Sheep in two of the flocks showed reproductive failure probably caused by pestivirus transmitted from infected goat offspring. A pair of twin lambs showed nervous signs and brain lesions characteristic of BD, while 17 other lambs had a very low growth rate. Virus was not isolated from any lamb. The prevalence rates of ewes with pestivirus antibodies in the two affected flocks were 33 and 72 per cent, respectively. One of nine cows aborted a pestivirus-infected foetus, and all were antibody-positive.

Neuropathology and host-parasite relationship of acute experimental toxoplasmosis of the blue fox (Alopex lagopus)

The neuropathology and host-parasite relationship of experimental infection with the RH-strain of Toxoplasma gondii were studied in 27 blue foxes (Alopex lagopus) aged 0 to 23 days, using light microscopy, including immunohistochemical staining, and transmission and scanning electron microscopy. All cases displayed multifocal necrotic lesions with numerous parasitic tachyzoites in the brain and spinal cord. The gray matter and the meninges were most seriously affected. Although a wide variety of cell types were parasitized, neurons and astrocytes seemed to be the main target cells. Individual parasitophorous vacuoles usually contained only a few tachyzoites, with rosette formations as a prominent feature. The present ultrastructural study supports the theory that the parasites actively invade the host cells by mechanisms that are different from those of phagocytosis. This is apparently the first report indicating that the formation of the network of tubular structures within the parasitophorous vacuole of T. gondii is associated with a transient, sack-like formation in the posterior end of the tachyzoites.

Ultrastructural findings in spongy degeneration of white matter in silver foxes (Vulpes vulpes). A naturally occurring demyelinating disease with oligodendrocyte vacuolation

Spongy degeneration of white matter in silver foxes is a naturally occurring, hereditary disorder. We report ultrastructural findings in the upper cervical cord of five perfusion-fixed foxes that were examined between 5 weeks and 2 1/4 years after the onset of clinical signs. Large cytoplasmic vacuoles in oligodendrocytes were present in the foxes examined 5, 12 and 20 weeks after the onset. Other early features of the disease were severe vacuolation of myelin sheaths, demyelination, expansion of extracellular spaces and hypertrophy of astrocytes. Evidence of partial demyelination as well as demyelination of entire internodes was found. In the later stages of the disease, the vacuolation was largely resolved but a marked astrogliosis persisted and numerous remyelinated axons were present in the gliotic areas. Vacuolation of oligodendrocytes and partial demyelination has not previously been seen together in a single disease process. The relationship between oligodendrocyte vacuolation, myelin sheath vacuolation and demyelination is discussed. It is concluded that the present condition is due to a primary damage to oligodendrocytes; however, the underlying biochemical lesion is not known.

Experimental pestivirus infections in newborn goat kids

Two experiments were carried out in which 37 healthy newborn goat kids were inoculated with a non-cytopathic ovine (BDV) or a cytopathic bovine pestivirus (BVDV) by intramuscular or intracerebral injection. No kids showed signs of disease or gross lesions which could be attributed to these viruses, but inoculated kids had lower mean growth rates than the controls. Significant histological changes in the CNS of 14 kids were restricted largely to the white matter and consisted mainly of hypercellular foci comprising microglial/histiocytic cells and mild perivascular infiltration by mononuclear cells. Varying degrees of infiltration of the myocardium by lymphocytes and plasma cells were observed. All kids remained negative for neutralizing antibodies against pestivirus until 2 to 3 weeks after infection. Titres increased during the following weeks. Pestiviruses were recovered from kids necropsied 10 days after inoculation, but not from any kids killed 20 days after inoculation or later. Non-cytopathic virus was isolated from various tissues of four kids that had received BDV and three kids that had been given BVDV. Cytopathic viruses were not recovered from any kids. Mean white blood cell counts in all kids were within the normal range at 4 and 8 weeks after inoculation. The lymphocyte response to stimulation by phytohaemagglutinin was significantly increased on both sampling occasions in the BDV-inoculated kids, while in the BVDV-inoculated animals, a similar increase was seen only at 8 weeks.

Spongy degeneration of white matter in the central nervous system of silver foxes (Vulpes vulpes)

A disorder of central nervous white matter in Norwegian-bred silver foxes is described from the case histories of 21 clinically affected foxes. The main presenting sign of this disorder was caudal limb ataxia, which appeared between 2 1/2 and 4 months of age and progressed over the next 4-8 weeks. Only four affected foxes were allowed to live beyond this period, but they showed moderate to marked improvement. Light microscopic examination of specimens from 16 affected foxes necropsied between 3 1/2 and 6 1/2 months of age revealed lesions that were restricted to the white matter of brain and spinal cord. The lesions were characterized by a symmetrical spongy change with vacuoles of varying sizes and included significant myelin deficiency. There was a relative preservation of axons and nerve cells and no significant inflammation or vascular reaction. An astrocytic hypertrophy was usually associated with the spongy change. Ultrastructural examination of central nervous tissue from two, perfusion-fixed, 6-month-old foxes showed intramyelin vacuoles resulting from splitting of the myelin lamellae at the intraperiod line and was interpreted as indicating myelin edema. Expanded extracellular spaces and watery astrocytic processes also contributed to the vacuolar appearance. Astrocytic processes in affected areas were hypertrophic and contained abundant filaments. Although the 16 silver foxes had severe clinical signs, their lesions had features in common with the juvenile form of Canavan's disease in children and a spongy degeneration reported in Labrador Retrievers; however, the clinical course in the foxes was not uniformly progressive.

Brain and spinal cord lesions in encephalitozoonosis in mink

Central nervous system lesions were studied by light microscopy in 43 farmed mink, aged 5 months to 2 1/2 years, with spontaneous encephalitozoonosis and showing cataractous eye changes. Lesions were found in the brain and spinal cord of all animals examined but were generally mild and chronic. The lesions were consistent with those previously described in spontaneous encephalitozoonosis in other carnivores. Parasites in parasitophorous vacuoles and free or phagocytosed in necrotic and granulomatous lesions were demonstrated in animals aged 5 months to 1 year. The occurrence of arterial lesions of the polyarteritis nodosa type found in the youngest animals probably indicates fetal infection. In animals aged 1 1/2 and 2 1/2 years active lesions were usually lacking and the changes were characterized by arterial sclerosis, sometimes with aneurysmal formations, small perivascular lympho-plasmacytic cuffings and focal gliosis.

The neuropathology in toxoplasmosis-like infection caused by a newly recognized cyst-forming sporozoon in dogs

The pathomorphological changes in the central nervous system associated with an infection with a previously reported, Toxoplasma-like, cyst-forming sporozoon were studied by means of light microscopy, including immunohistochemistry, and transmission electron microscopy in seven dogs, aged 4 months to 2 years. Tachyzoites (endozoites) within parasitophorous vacuoles were found in neurons, astrocytes, macrophages, vascular pericytes and probably also in fibroblasts, while cyst stages were only observed in cells showing features of neurons. Proliferating tachyzoites were associated with lesions of a necrotic/granulomatous type. Perivascular accumulations of lymphocytes and plasma cells, together with an activation of astrocytes and perivascular fibroblasts resulting in marked sclerosis, were prominent features in all cases. The grey matter was most seriously affected in the brain, while the white matter was most often the site of inflammation in the spinal cord. The structural similarity to the newly reported Neospora caninum suggests that we are dealing here with the same parasite. However, the present infection and toxoplasmosis have so many features in common, including the light microscopical morphology of the organisms and host/parasite relationship, that a definite etiological diagnosis should be based on ultrastructural and/or immunohistochemical examinations.

Immuno-histochemical and ultrastructural characteristics of a cyst-forming sporozoon associated with encephalomyelitis and myositis in dogs

Light-microscopy, including immuno-histochemical staining, and transmission and scanning electron microscopy were applied for the characterization of a Toxoplasma-like parasite associated with encephalomyelitis and myositis in dogs of the boxer breed. Most parasites were tachyzoites, occurring in clusters, up to 60 micron in diameter, in parasitophorous vacuoles of host cells. Cyst stages with a definite cyst wall were few, but could be demonstrated in all cases. Immunostaining with antiserum against Toxoplasma gondii was negative, while both tachyzoites and bradyzoites were stained with serum from affected dogs. Ultrastructurally, the parasite was characterized by a great number of rhoptries, few amylopectin granules, lack of micropores in the tachyzoites, and the occurrence of numerous dense bodies in the bradyzoites. Numerous intravacuolar tubules were present in the space of the parasitophorous vacuole. The cyst wall resembled that of T. gondii. Until a definite host is found, the parasite may be regarded as an "orphan", cyst-forming sporozoon that is ultrastructurally different from other known protozoan parasites. It has a light-microscopical similarity to T. gondii but is antigenically different.

Brain and spinal cord lesions in encephalitozoonosis in blue foxes. Transmission and scanning electron microscopic studies

The brains and spinal cords from 3 young blue foxes suffering from acute to subacute encephalitozoonosis, were examined by transmission and scanning electron microscopy. Parasitophorous vacuoles (PV) were demonstrated more frequently in vascular smooth muscular cells than in endothelial cells. The present study also indicated that the parasite has great affinity for neurons, including their processes. In addition, PV occurred in macrophages and probably also in intravascular monocytes. PV were readily differentiated from phagosomes by the bleb formations of the limiting membrane. An accumulation of host cell mitochondria near the PV in areas where developmental stages were attached, was a most striking feature. The inflammatory lesions, mainly of the granulomatous type, were almost constantly associated with the presence of released parasites, both in vascular walls and the nervous tissue. Phagocytosed parasites were probably killed by the lysosomal enzymes, although the spores were only slowly degraded.

Brain and spinal cord lesions in encephalitozoonosis in the blue fox

The central nervous system lesions in encephalitozoonosis were studied in 11 naturally infected blue foxes. Immunohistochemical staining was employed in the demonstration of the parasites and identification of host cells. Consistent findings in acute to subacute stages included granulomatous meningoencephalomyelitis and vasculitis, with arterial lesions similar to polyarteritis nodosa. Chronic stages were dominated by arteriosclerosis, perivascular mononuclear infiltrations and gliosis, with less prominent granulomatous reaction. Parasites were almost constantly observed in association with active lesions both in vessels and nervous tissue. Parasitophorous vacuoles (PV) occurred in endothelial cells and in the medial layer of arteries. Neurons, including even their processes, were widely parasitized, a fact that may account for the brain being an important target organ. PV also occurred in ependymal cells of the choroid plexus and occasionally in macrophages. A great number of parasites was demonstrated in phagolysosomes of macrophages, a fact that probably reflects a relative resistance to digestion, and may consequently contribute to the development of the prominent granulomatous reaction. It was concluded that the brain lesions, except in chronic stages of mild infections, seem to be pathognomonic for encephalitozoonosis in the blue fox.

Identification of Toxoplasma gondii and Encephalitozoon cuniculi by immunoperoxidase techniques and electron microscopy, in stored, formalin-fixed, paraffin-embedded tissue

The peroxidase-anti-peroxidase (PAP), avidin-biotin-complex (ABC) techniques, and electron microscopy, were used to identify protozoan parasites in formalin-fixed material from routine necropsy cases. The material comprised paraffin blocks, that had been stored for up to 18 years, from 18 cases of suspected toxoplasmosis and encephalitozoonosis. With the ABC method a higher dilution of primary antibody could be used than with the PAP method. However, with both methods, a distinct reaction occurred with appropriate dilutions. The age of the material did not seem to effect the result. Frequently, phagocytized and necrotic parasites were also stained. Gystozoites (bradyzoites) of T. gondii were stained faintly compared to the endozoites (tachyzoites). A Toxoplasma-like parasite from a dog did not react with anti-Toxoplasma serum, and ultrastructurally it proved to be consistent with an unidentified cyst-forming sporozoan parasite previously reported in dogs. Electron microscopy based on paraffin-embedded tissue, seems to be a valuable method for identification of protozoan parasites, and thus provide a supplement or alternative to the immunoperoxidase methods.

Hereditary lethal arthrogryposis ("muscle contracture") in horses

In 4 female foals of the Norwegian horse breed, "Fjord Horse", congenital arthrogryposis of the limbs are described. The disorder was mainly limited to the hind limbs and associated with polydactylia and partly with brachygnathia superior and cleft palate. The defective foals were paternal halfsisters of 4 normal foals (1 female + 3 males), sired by the stallion "Bingo" 1804, which was phenotypically quite normal. The disorder being lethal, is possibly caused by a sex-limited or a strongly sex-influenced dominant gene.

[Disseminated candidiasis (moniliasis) in a dog. A case report]

A case of systemic candidiasis (Candida albicans) in a 1 1/2 year old dog is reported. Clinically, the first manifestation was enlargement of a superficial inguinal lymph node. Later several peripheral lymph nodes were affected and a fistulous opening appeared, communicating with an inflammatory process in the right humerus. Necropsy revealed gross lesions in the kidneys, pancreas and multiple lymph nodes. In addition, microscopic lesions were observed in the myocardium and the bone marrow of the right humerus. The lesions, which contained large fungal colonies, were mainly granulomatous with numerous multinuclear giant and epitheloid cells, but necrosis and suppuration were also evident. The site of invasion is not known. However, a previous perianal and abdominal dermatitis, which was treated locally with antibiotics and corticoids, could possibly have been a mycotic infection.

Hereditary "cavitating" leucodystrophy in Dalmation dogs. Light and electron microscopic studies

A recently recognised progressive disorder of central myelin in Dalmatian dogs is described. The disease is probably transmitted by autosomal recessive inheritance. The symptoms started at the age of 3-6 months and were dominated by visual deficiency and/or progressive locomotive abnormalities. Pathologically, the most consistent lesions were found bilaterally in the region of the centrum semiovale. The optic nerves were also frequently affected, the basal ganglia and spinal cord were affected infrequently. The main lesions were confined to myelin, while axons and nerve cells were spared, particularly in the early stages of the lesions. Numerous phagocytes were observed which contained engulfed myelin and other lipid breakdown products. Ultrastructurally and histochemically the disease differs from previously described types of leucodystrophy.