Causalidad de muertes y caracterización de hallazgos anatomopatológicos en Ajolotes de Xochimilco (Ambystoma mexicanum)

Abstract

The axolotls of Xochimilco (Ambystoma mexicanum) are amphibians belonging to the order: Caudata, Family: Ambystomatidae, is the most common aquatic neotenic species in captivity and has been used for many years in biomedical research for its characteristics of body regeneration. The axolotl is an endemic species of the lagoon system of the Valley of Mexico and currently only lives in free life in the canals of Xochimilco in Mexico City. This amphibian is in danger of extinction and although there are multiple investigations around it, these focus on its regeneration capacity, which could support human health, there are also several advances in the description of some of its physiological processes. Studies related to their diseases are scarce and have generally been extrapolated from the information generated in other amphibian species; Today the idea of using amphibian descriptions as a "standard" model continues where no particularities are determined by species. With respect to the anatomopathological descriptions these are scarce, mainly generated from isolated cases. This study was carried out in the period between 2019 and 2022, from 50 corpses of Ambystoma mexicanum (21 males, 27 females and 2 of indeterminate sex) of different ages, all belonging to the collection of the Center for Biological and Aquaculture Research of Cuemanco (CIBAC), Mexico. The necropsies of these specimens were carried out in order to determine the causality of death of this species and describe macroscopically and microscopically the lesions found, in addition to identifying the etiological agents involved in the deaths and describing the antimicrobial resistance of the isolated strains. The main cause of death corresponded to septicemia with 45 cases that represented 90% of the deaths, from which bacteria of the genus Aeromonas spp., E.coli, Enterobacter aerogenes and Salmonella arizonae were isolated, 3 parasitosis processes that represented 6% and 2 starvation processes that represented 4%, in addition to identifying 37 microscopic lesions in the following systems; in the Granulomatous endocarditis, pulmonary congestion, phlebectasia, hyperinflation, and necrotic, purulent and granulomatous pneumonias were identified in the cardiorespiratory system. In the digestive system, lymphocytic gastritis and enteritis, necrotic enteritis, mucosal catarrhal enteritis and enteritis with melanomacrófagos were diagnosed, in addition to liver lesions such as vacuolar degeneration, telangiectasia, acute necrotic hepatitis, granulomatous hepatitis, chronic interstitial hepatitis, granulomatous hepatitis with predominance of melanomacrófagos and chronic fibrosing hepatitis. Splenic congestion, lymphoid depletion, red pulp hyperplasia, purulent splenitis, and granulomatous splenitis with melanomacróphagos were observed in the lymphoreticular system. At the level of the urinary system, lesions such as renal congestion, tubular necrosis associated with calcium deposits, lymphocytic interstitial nephritis, chronic glomerulonephritis associated with melanomacrófagos and mesangioproliferative glomerulonephritis were determined. Regarding the integumentary system, lesions such as epithelial vacuolar degeneration, erosive necrotic dermatitis, ulcerative necrotic dermatitis, mucus gland adenoma with carcinomatous area and melanoma were observed. The main antimicrobial resistances generated by Aeromonas spp. were developed against quinolones, nitrofurans and cephalosporins. The main antimicrobial resistances generated by Salmonella arizonae were developed against cephalosporins, nitrofurans and quinolones. The isolation of Enterobacter aerogenes showed resistance to cephalosporins and the isolation of E.coli. resistance to quinolones, aminoglycosides and nitrofurans. To our knowledge, this is the first catalog of specific lesions of Ambystoma mexicanum that aims to establish bases for the description of pathogenesis and the diagnosis of diseases that afflict this amphibian of global importance for biodiversity, in addition to supporting programs aimed at its conservation.