Introduction
The kidney is an important organ which performs a number of crucial functions in the body including filtering the blood; remove the waste materials from food and toxic substances; control the fluid balance in the body [6,12]. Renal failure is the end stage of chronic kidney disease characterized by severe decline in renal functions [2].
Muskrat (Ondatra zibethicus) is the only semi-aquatic rodent that belongs to the tribe Ondatrini and it is found in different parts of the world [16,17]. Muskrats inhabit lakes, ponds, streams, rivers and marshes. Their population is estimated to be 40 animals per hectare [5]. They have body characteristics that enable them to survive in aquatic environments such as lips that close behind incisors, hind feet that are partially webbed, besides their ability to stay under water up to 20 minutes. They feed on aquatic vegetation (cattails and horsetails) and occasionally mussels, turtles, mice, birds, frogs and fish [4,10]. They are skilled architects that they use vegetations to build their houses above water level, while the entrance via underwater tunnels [5]. However, renal failure syndrome rarely reported in muskrat. Here, we describe the histopathological observations of major body organs in muskrat.
Materials and Methods
Female muskrat died at the age of 6 months was brought to our laboratory at department of Pathology, College of Veterinary Medicine, Kyungpook National University for necropsy. Animal was died suddenly without prior clinical signs. Muskrat was fed on Alfalfa, hay and commercial rabbit diet. Animal was housed in appropriate conditions with water temperature of 15~16℃ and a shade temperature of 20℃. For microscopic examination, the tissue specimens were fixed in 10% neutral buffered formalin and embedded in paraffin. The tissue samples were sections at 5-µm slices and then sections were routinely processed with a graded ethanol series and toluene. Finally, the sections stained with hematoxylin and eosin (H&E) [8,11].
Results and Discussion
At necropsy, muskrat showed sand like Urolithiasis in the ureter, and kidneys; hydronephrosis was also evident (Fig. 1, Fig. 2). Systemic hemorrhage and calcification of all organs were observed.
Detailed histopathology of female muskrat showed severe congestion and hemorrhage of the lung accompanied with edema that occupying alveoli. Focal infiltration of neutrophils and diffuse infiltration of mononuclear cells were observed in interstitial tissue and inside alveoli (Fig. 3A). Severe hemorrhage and depletion of lymphoid follicles were evident in the spleen. Diffuse infiltration of plasma cells was also observed especially in sub-capsular region in the spleen (Fig. 3B). Both kidneys showed diffuse microcalcification in the cortex and medulla with tubular degeneration and in-flammation remarkably, Calcification was mostly evident in proximal convoluted tubules and collecting ducts. Peri-glomerular and inter-tubular hyalinization were remarkable and it was suggestive for chronic nephritis (Fig. 3C). The left ureter revealed desquamation of the lining epithelium with calcium salts that were detected in the lumen (Fig. 3D).
In the current case we are describing the pathology of renal failure in a muskrat for the first time, to the author’s best knowledge. Various nephrotoxic drugs are identified including cancer therapeutics, drugs of abuse, antibiotics, and radiocontrast agents [13]. Several Pollutants also found in environment and affect the kidney such as cadmium, mercury, arsenic, lead, trichloroethylene, bromate, brominatedflame retardants, diglycolic acid, and ethylene glycol [18]. Aristolochic acid and mycotoxins such as ochratoxin, fumonisin B1 and citrinin are natural toxins that target kidneys [1,9].
Fig. 1. Gross pictures representing pathological changes in various body organs. (A) Picture of a female musk rat. (B) Severe hemorrhage in all lobes of the lung. (C) Diffuse hemorrhage and a little edema of the heart. (D) Serosal hemorrhage in the small intestine. They were also filled with brown to black contents with mucosal ulceration. (E) Severe hemorrhage and congestion of the meninges.
Fig. 2. Gross pictures representing pathological changes in kidneys, ureter and urinary bladder. (A) Moderate congestion of both kidneys. The left kidney also showed hydronephrosis and renal calculi on cut section. (B) The ureter contained sand-like green to yellowish lithiasis. (C) Hemorrhage on the serosal and mucosal membrane of urinary bladder with round and yellowish urolithiasis 2-2.5 cm in a diameter. RT, Right Kidney. LT, Left Kidney.
In our case, the histopathological observations were supportive of a chronic toxicity and mainly on convoluted tubules in kidney. Moreover, the calculi, the systemic hemorrhages and calcification in several organs were compatible with uremia. The cause of renal failure in our case did not seem to be toxification by aflatoxins and fumonisin, since specific lesions in liver that are caused by theses toxins were not detected [3, 7, 14, 15]. Therefore, there is a high possibility that the renal failure in this case may have been produced by other nephrotoxins in the foodstuffs. However, we couldn’t determine the exact toxins and fungi for this case. This report presents evidences that support the mycotoxic hypothesis of diet-induced nephropathy [8]. Here, we have described a rare case report of renal failure with calcification in a muskrat displaying nephrotoxicity most likely by foodstuffs.
Fig. 3. Histopathological findings of lung, spleen, kidney and ureter in died muskrat. (A) Severe hemorrhage and congestion with interstitial pneumoniae accompanying inflammatory cells infiltrates in the lung. Focal infiltrate of neutrophils (arrow), infiltration of mononuclear cells in interstitial tissue (arrow heads). (B) Severe hemorrhage and depletion of lymphocytes in the white pulp with infiltration of a large number of plasma cells (arrow heads). (C) Both kidneys showed diffuse microcalcification (arrows) in the cortex and medulla with tubular degeneration. Hyalinization of glomeruli (black arrow head) and interstitial tissue (red arrow heads) were suggestive for chronic inflammation. (D) The left ureter revealed desquamation of the lining epithelium with necrosis and microcalcification. Hematoxylin and eosin (H&E) staining. All scale bar = 100 μm.
Acknowledgement
This research was funded by the Republic of Korea government (Ministry of Science and ICT); grant number (NRF-2017R1E1A1A01072781).
The Conflict of Interest Statement
The authors declare that they have no conflicts of interest with the contents of this article.
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