Gross and histopathological characterization of cardiac lesions associated with stress by active stranding in a bryde’s whale (Balaenoptera edeni)

Abstract

Active stranding in cetaceans constitutes an anomalous and extreme situation for such organisms that are not adapted anatomically neither physiologically to the environmental conditions different from those of the aquatic environment. It is a pathological entity “per se” in which acute stress is the central axis of its etiopathogenesis. It presents clinical-lesional findings that can cause the death of the animal or seriously aggravate a previous disease situation, being able to influence the subsequent rehabilitation and recovery of the affected animals. These findings coexist and are comparable to lesions of the “Capture Myopathy Syndrome” (CM), as it has been previously described in terrestrial mammals and wild birds. In cetaceans, the CM has been previously reported in different species, although the descriptions in the Mysticeti suborder are still very scarce. In this work, we describe, by gross, histological, histochemical and immunohistochemical studies, the cardiac lesions related to the extreme response to stress of active stranding in an Bryde’s whale (Balaenoptera edeni). The specimen, a neonate male, with a total length of 393 cm and a poor body condition, stranded alive on the coast of Fuerteventura (Canary Islands, Spain) in 2016. It presented an optimal conservation code at the time of the necropsy. Endocardial and epicardial haemorrhages were the cardiac lesions observed macroscopically. Furthermore, with observation under the optical microscope, it was possible to detect other acute or subacute degenerative-necrotic changes consisting of contraction band necrosis, loss of transverse striations, perinuclear vacuolization, interstitial edema, cytoplasmic hypereosinophilia, vascular congestion and infiltration of inflammatory cells. Moreover, skeletal muscle and kidney were studied in examination of possible lesions characteristic of CM. Immunohistochemically, different markers were studied, such as myoglobin, fibrinogen and troponin, which suggested a hypoxic and/or oxidative, acute, antemortem muscular damage.