Search

The Guiana dolphin (Sotalia guianensis) is a common species along Central and South American coastal waters. Although much effort has been made to understand its behavioral ecology and evolution, very little is known about its brain. The use of ultra-high field MRI in anatomical descriptions of cetacean brains is a very promising approach that is still uncommon. In this study, we present for the first time a full anatomical description of the Guiana dolphin's brain based on high-resolution ultra-high-field magnetic resonance imaging, providing an exceptional level of brain anatomical details, and enriching our understanding of the species. Brain structures were labeled and volumetric measurements were delineated for many distinguishable structures, including the gray matter and white matter of the cerebral cortex, amygdala, hippocampus, superior and inferior colliculi, thalamus, corpus callosum, ventricles, brainstem and cerebellum. Additionally, we provide the surface anatomy of the Guiana dolphin brain, including the labeling of main sulci and gyri as well as the calculation of its gyrification index. These neuroanatomical data, absent from the literature to date, will help disentangle the history behind cetacean brain evolution and consequently, mammalian evolution, representing a significant new source for future comparative studies., (© 2024. The Author(s).)

Objective: To describe morphological features of Megaptera novaeangliae eyes using ultrasonography and histology., Animal Studied: A total of 21 globes from 19 M. novaeangliae were used for the study, including two animals with bilateral assessment. Nine stranded animals were found alive, 10 dead., Procedures: Carcasses were classified according to decomposition state. Globes were assessed ultrasonographically, biometric measurements were taken and then the tissues were sectioned for histological analysis., Results: Seventeen carcasses were classified as decomposition code 2 and two as code 3. Fifteen animals were calves, three juveniles and one adult, twelve males, and five females. The cornea was thinner in the center of the eye and thicker at the periphery. The lens had an oval shape. Fourteen animals showed a structure in the vitreous body which looked triangular and filamentous by ultrasonography and, histologically, originated in the central part of the optic nerve and extended to the posterior region of the lens, composed of connective tissue. The most common abnormalities found by ultrasonograph were retinal detachment (n = 13) and displacement of the lens into the vitreous (n = 4), along with alterations suggestive of hemorrhage, fibrin deposits, and increased echogenicity in the optic nerve (n = 2)., Conclusions: An intraocular structure not previously described in cetaceans was found in this investigation; its function remains unknown. Circulatory changes that were evident in the histopathological analysis may be due to the stranding process and raise the need to consider ophthalmic examinations before reintroducing stranded mysticetes., (© 2024 American College of Veterinary Ophthalmologists.)

Mycoplasma spp. are wall-less bacteria able to infect mammals and are classified as hemotropic (hemoplasma) and nonhemotropic. In aquatic mammals, hemoplasma have been reported in California sea lions (Zalophus californianus) and river dolphins (Inia spp.). We investigated Mycoplasma spp. in blood samples of West Indian manatees (Trichechus manatus), pinnipeds (5 species), and marine cetaceans (18 species) that stranded or were undergoing rehabilitation in Brazil during 2002-2022. We detected Mycoplasma in blood of 18/130 (14.8%) cetaceans and 3/18 (16.6%) pinnipeds. All tested manatees were PCR-negative for Mycoplasma. Our findings indicate that >2 different hemoplasma species are circulating in cetaceans. The sequences from pinnipeds were similar to previously described sequences. We also detected a nonhemotropic Mycoplasma in 2 Franciscana dolphins (Pontoporia blainvillei) that might be associated with microscopic lesions. Because certain hemoplasmas can cause disease and death in immunosuppressed mammals, the bacteria could have conservation implications for already endangered aquatic mammals.

Cetacean morbillivirus (CeMV; Paramyxoviridae ) is the most significant pathogen of cetaceans worldwide. The novel "multi-host" Guiana dolphin ( Sotalia guianensis ; GD)-CeMV strain is reported in South American waters and infects Guiana dolphins and southern right whales ( Eubalaena australis ). This study aimed to describe the pathologic findings, GD-CeMV viral antigen distribution and detection by RT-PCR (reverse transcriptase polymerase chain reaction), and infectious comorbidities in 29 Guiana dolphins that succumbed during an unusual mass-mortality event in Rio de Janeiro state, Brazil, between November 2017 and March 2018. The main gross findings were lack of ingesta, pulmonary edema, ascites, icterus, hepatic lipidosis, multicentric lymphadenomegaly, as well as pneumonia, polyserositis, and multiorgan vasculitis caused by Halocercus brasiliensis . Microscopically, the primary lesions were bronchointerstitial pneumonia and multicentric lymphoid depletion. The severity and extent of the lesions paralleled the distribution and intensity of morbilliviral antigen. For the first time in cetaceans, morbilliviral antigen was detected in salivary gland, optic nerve, heart, diaphragm, parietal and visceral epithelium of glomeruli, vulva, and thyroid gland. Viral antigen within circulating leukocytes suggested this as a mechanism of dissemination within the host. Comorbidities included disseminated toxoplasmosis, mycosis, ciliated protozoosis, and bacterial disease including brucellosis. These results provide strong evidence for GD-CeMV as the main cause of this unusual mass-mortality event.

During November-December 2017, a mass die-off of Guiana dolphins (Sotalia guianensis) began in Rio de Janeiro, Brazil. Molecular and pathologic investigations on 20 animals indicated that cetacean morbillivirus played a major role. Our findings increase the knowledge on health and disease aspects of this endangered species.