Kidney Disease In Rainbow Trout Research Articles

Dysregulation of B Cell Activity During Proliferative Kidney Disease in Rainbow Trout.

Proliferative kidney disease (PKD) is a widespread disease caused by the endoparasite Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea). Clinical disease, provoked by the proliferation of extrasporogonic parasite stages, is characterized by a chronic kidney pathology with underlying transcriptional changes indicative of altered B cell responses and dysregulated T-helper cell-like activities. Despite the relevance of PKD to European and North American salmonid aquaculture, no studies, to date, have focused on further characterizing the B cell response during the course of this disease. Thus, in this work, we have studied the behavior of diverse B cell populations in rainbow trout (Oncorhynchus mykiss) naturally infected with T. bryosalmonae at different stages of preclinical and clinical disease. Our results show a clear upregulation of all trout immunoglobulins (Igs) (IgM, IgD, and IgT) demonstrated by immunohistochemistry and Western blot analysis, suggesting the alteration of diverse B cell populations that coexist in the infected kidney. Substantial changes in IgM, IgD, and IgT repertoires were also identified throughout the course of the disease further pointing to the involvement of the three Igs in PKD through what appear to be independently regulated mechanisms. Thus, our results provide strong evidence of the involvement of IgD in the humoral response to a specific pathogen for the first time in teleosts. Nevertheless, it was IgT, a fish-specific Ig isotype thought to be specialized in mucosal immunity, which seemed to play a prevailing role in the kidney response to T. bryosalmonae. We found that IgT was the main Ig coating extrasporogonic parasite stages, IgT+ B cells were the main B cell subset that proliferated in the kidney with increasing kidney pathology, and IgT was the Ig for which more significant changes in repertoire were detected. Hence, although our results demonstrate a profound dysregulation of different B cell subsets during PKD, they point to a major involvement of IgT in the immune response to the parasite. These results provide further insights into the pathology of PKD that may facilitate the future development of control strategies.

What goes around comes around: an investigation of resistance to proliferative kidney disease in rainbow trout Oncorhynchus mykiss (Walbaum) following experimental re-exposure.

Rainbow trout Oncorhynchus mykiss surviving proliferative kidney disease (PKD) are reported not to develop the disease upon re-exposure. However, the mechanisms involved in the immune response to re-exposure are unknown. We examined disease susceptibility and the immune response of naive 1+ rainbow trout when first exposed to Tetracapsuloides bryosalmonae in comparison with that of 1+ rainbow trout re-exposed to T.bryosalmonae. PKD pathogenesis, parasite burden and transcriptional signatures of the host immune response were assessed at 10, 25 and 40 d.p.e (days post-exposure). In addition, we evaluated the presence of IgM+ B cells in the blood and the posterior kidney. The exposure of 1+ rainbow trout to T.bryosalmonae for the first time resulted in 100% infection prevalence, high parasite burdens and severe clinical PKD, while re-exposed fish were either able to avoid reinfection completely or mount an earlier and more efficient adaptive-type immune response. This response was characterized by a greater amount of IgM+ B cells in the blood and elevated mRNA levels of secretory IgM in the posterior kidney which minimized pathogen burden and kidney inflammation. Our findings suggest that rainbow trout is able to develop immune protection against T.bryosalmonae.

Proliferative kidney disease in rainbow trout (Oncorhynchus mykiss) under intensive breeding conditions: Pathogenesis and haematological and immune parameters

Proliferative kidney disease (PKD) is an endoparasitic disease of salmonid fish caused by Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea). This study presents a comprehensive view on PKD development in rainbow trout (Oncorhynchus mykiss) reared at an intensive fish breeding facility, with focus on mortality, pathology/histopathology, haematological findings and immune functions. Diseased and reference fish were sampled monthly and time course of natural infection was followed up from the onset of clinical signs (September 2014) to full recovery (January 2015). PKD- associated cumulative mortality was 30% with a peak value in October, while immunohistochemical testing indicated a continuous significant decrease in T. bryosalmonae numbers from September to December; with no parasites detected in January. During peak clinical infection, a significant decrease in red blood cell counts, haematocrit values, haemoglobin concentration, along with a reduction in lymphocytes and a significant phagocyte elevation corresponding with an increase in phagocyte oxidative burst were measured in comparison to control animals. Complement activity and total immunoglobulin plasma concentrations were also elevated, though only during the initial monitoring period (September). Individuals surviving PKD, recovered and were able to fully regenerate both renal structure and haematopoietic parameters to normal levels. Changes in the red blood cell parameters indicate anaemia and a decreased oxygen transportation capacity during the clinical disease phase. Together with an increased oxygen demand at higher temperatures and decreased oxygen solubility this could lead to decompensation and elevated mortality. The stimulation of immune parameters, and especially oxidative phagocytic burst, is likely to have had a strong effect on both, regeneration and elimination of the pathogenic agent.

Proliferative kidney disease in rainbow trout: time- and temperature-related renal pathology and parasite distribution

Proliferative kidney disease is a parasitic infection of salmonid fishes caused by Tetracapsuloides bryosalmonae. The main target organ of the parasite in the fish is the kidney. To investigate the influence of water temperature on the disease in fish, rainbow trout Oncorhynchus mykiss infected with T bryosalmonae were kept at 12 degrees C and 18 degrees C. The number of parasites, the type and degree of lesions in the kidney and the mortality rate was evaluated from infection until full development of disease. While mortality stayed low at 12 degrees C, it reached 77% at 18 degrees C. At 12 degrees C, pathological lesions were dominated by a multifocal proliferative and granulomatous interstitial nephritis. This was accompanied by low numbers of T. bryosalmonae, mainly located in the interstitial lesions. With progression of the disease, small numbers of parasites appeared in the excretory tubuli, and parasite DNA was detected in the urine. Parasite degeneration in the interstitium was observed at late stages of the disease. At 18 degrees C, pathological lesions in kidneys were more severe and more widely distributed, and accompanied by significantly higher parasite numbers. Distribution of parasites in the renal compartments, onset of parasite degeneration and time course of appearance of parasite DNA in urine were not clearly different from the 12 degrees C group. These findings indicate that higher mortality at 18 degrees C compared to 12 degrees C is associated with an enhanced severity of renal pathology and increased parasite numbers.

Development of proliferative kidney disease in rainbow trout, Oncorhynchus mykiss (Walbaum), following short‐term exposure to Tetracapsula bryosalmonae infected bryozoans

The initial site of infection in the fish host for Tetracapsula bryosalmonae, causative agent of proliferative kidney disease (PKD) is poorly understood. Following the recent recognition that freshwater bryozoans harbour the infective stages to salmonid fish, experimental transmission studies were undertaken to investigate (1) the route of entry of the parasite into the fish host and (2) the minimum exposure time required to induce clinical signs of PKD. In‐situ hybridization (ISH) studies were carried out on naïve rainbow trout exposed to the naturally infected bryozoan Fredericella sultana for up to 90 min. The sporoplasm of T. bryosalmonae was detected entering the fish via mucous cells in the skin epithelium within the first minute of exposure. In addition, T. bryosalmonae cells were infrequently detected in the skeletal musculature of exposed experimental fish up to 72 h post‐exposure. The route of migration through the fish to the kidney and spleen was not determined. All fish exposed to infected, disrupted bryozoans for 10, 30 and 90 min and maintained for up to 8 weeks developed clinical PKD.

Malachite green: a pharmacokinetic study in rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. Pharmacokinetic studies on uptake, distribution and climination of malachite green in rainbow trout, Oncorhynchus mykiss (Walbaum), are described. All three processes were found to be temperature‐dependent, with levels and rates increasing with increases in water temperature. Tissues investigated were serum, liver, kidney, muscle and viscera. First‐order kinetics were found to apply and, in particular, kidney was observed to be a deep compartment. The long‐term persistence of kidney residues may explain the efficacy of malachite green for the control of proliferative kidney disease in rainbow trout. Residue levels in muscle were never excessive and an extrapolation from the experimental data suggests that a suitable withholding period might be 600 degree days.

Malachite green therapy of proliferative kidney disease in rainbow trout: field trials.

The results of a series of experiments to investigate the use of the arylmethane dye, malachite green, for the control of proliferative kidney disease in rainbow trout (Salmo gairdneri Richardson) are described. Under field conditions using the bath application method the dye gave good control of the disease with treatments at 1.6 ppm for 40 minutes repeated at seven, 14 and 21 day intervals. Flush treatments were also successful using the same treatment intervals and beginning with 3.2 ppm malachite green. The problems of toxicity and of standardising the exposure of the fish to the dye with flush treatments are discussed.

A study of the sequential clinical and pathological changes during proliferative kidney disease in rainbow trout, Salmo gairdneri Richardson

Abstract. A histological study of 0+ rainbow trout, exposed to proliferative kidney disease (PKD) on an infected farm, showed evidence of infection from the beginning of June, gross pathological changes from the beginning of July, and clinical signs from mid‐July. Evidence of healing was present in some samples from the second week of August. Kidney samples were divided into five grades (0–4) representing increasing severity of pathology. A sixth grade (H) was applied to kidneys showing signs of healing. The most frequent clinical signs were abdominal distension and exophthalmos. Melanosis, corneal cloudiness and ecchymoses were observed occasionally. Apart from renal enlargement, other internal gross pathological changes included ascites, gill and liver pallor, oedema, petechiation, and splenic enlargement. The majority of clinical signs and internal changes were only seen in fish with advanced renal swelling (grades 3 and 4). Histopathology was most marked in the kidney and was of three types: haemopoietic hyperplasia, vascular pathology and diffuse inflammatory change. Vascular changes, including occlusion of blood vessels in several organs and apparent haemoglobin crystallization, and destruction of renal excretory structures within areas of chronic diffuse inflammation were marked features of the histopathology in fish with clinical signs. The pathogenesis of PKD is discussed with reference to the histopathological changes.

Ultrastructural aspects of PKX, the causative agent of proliferative kidney disease in rainbow trout, Salmo gairdneri Richardson

Ultrastructural aspects of PKX, the causative agent of proliferative kidney disease in rainbow trout, <i>Salmo gairdneri</i> Richardson

The immune response during proliferative kidney disease in rainbow trout: A case history

Young-of-the-year rainbow trout clinically affected by proliferative kidney disease (PKD), a systemic protozoan infection, exhibit a massive proliferation of small lymphocytes in the posterior kidney and spleen, a decrease in erythrocyte packed cell volume, hemoglobin, and serum albumins and an increase in beta-globulins. Electronphotomicrographs of the causative agent indicate that it is engulfed within a macrophage which is surrounded by small lymphocytes. Fish having survived a clinical episode are completely refractory to subsequent infection. Their serum electrophoretic patterns are quite unremarkable.

Evaluation of antimicrobial compounds for the control of bacterial kidney disease in rainbow trout, Salmo gairdneri Richardson

Abstract From a comparison of over 70 antimicrobial compounds by in vitro and in vivo methods, it was found that clindamycin, erythromycin, kitasamycin, penicillin G and spiramycin could be used successfully for combating early clinical cases of bacterial kidney disease (BKD) in rainbow trout, Salmo gairdneri Richardson. In addition, cephradine, lincomycin and rifampicn were effective for chemoprophylaxis of BKD, although they were of no use for therapeutic purposes.

Experimental transmission of proliferative kidney disease in rainbow trout, Salmo gairdneri Richardson

Experimental transmission of proliferative kidney disease in rainbow trout, <i>Salmo gairdneri</i> Richardson

The effects of water temperature on the development of proliferative kidney disease in rainbow trout, Salmo gairdneri Richardson

The effects of water temperature on the development of proliferative kidney disease in rainbow trout, <i>Salmo gairdneri</i> Richardson

Ultrastructure of a Haplosporean‐like organism: the possible causative agent of proliferative kidney disease in rainbow trout

The protozoan parasite which has been suggested as the causative agent of proliferative kidney disease in rainbow trout has previously been described as an‘amoeba’. However, this ultra‐structural study of the organism (named‘PKX’) has demonstrated many similarities to a group of invertebrate parasites, the genus Marleilia (currently classified in the Haplosporea). The suggested affinity of PKX‘ to Marteilia is based on the presence of internal cleavage,‘haplosporosomes’, and an amorphous cell wall. Other cytoplasmic inclusions also show characteristics of the genus. Since a spore stage has not been recognised in ‘PKX’, a definitive taxonomic statement cannot yet be made.

Proliferative kidney disease in rainbow trout Salmo gairdneri Richardson

Abstract. Two entirely separate outbreaks of PKD are described in an attempt to properly define the condition and enable it to be differentiated from other diseases of a similar nature. Losses of up to 75% of fingerling rainbow trout were recorded in one outbreak, illustrating the potentially serious nature of the disease. Although the kidneys showed the most obvious pathological changes, other organs were also affected. The host response was granulomatous in type, the foci of each cellular reaction being 5‐20 μm eosinophilic cells considered to be parasitic. The cytoplasm of these cells contained numerous electron dense bodies some with a tail, but each with an electron lucent bar always orientated at right angles to the plasmalemma whenever they were near it. The most obvious cytoplasmic inclusion of these ‘parasites’ were other cells numbering up to five or six, each with its own nucleus and nucleolus, but devoid of any of the small electron dense bodies. The significance of either of these inclusions is unknown.A limited differential diagnosis is given, and the argument presented that the condition PKD is the result of infection by a parasite, possibly an amoeba, in combination with poor quality water.

Protozoa associated with proliferative kidney disease in rainbow trout (Salmo gairdneri).

Protozoa associated with proliferative kidney disease in rainbow trout (Salmo gairdneri).