Abstract

In the southwestern Atlantic Ocean, humpback whales (Megaptera novaeangliae) migrate annually from the feeding areas in Antarctic waters to the Brazilian coast to breed and nurse their calves in the first months of their lives. Strandings have been recorded along the whole Brazilian coast and efforts to gather information on pathological conditions and cause of death through postmortem examination have increased in the last decade. The aims of this study are to describe pathological changes of a humpback whale stranded in São Mateus, Espirito Santo State, Brazil. On September 9th, 2008, a four-meter long female calf stranded alive presenting good body condition. After unsuccessful rescue attempts with the several restrandings, the animal was euthanized using a lethal dosage of thiopental sodium. Necropsy was carried out using a standardized protocol. Selected tissues were collected during necropsy, fixed in 10% buffered formalin and processed for routine histopathologic analyses. Hematological analysis of cardiac blood showed low hemoglobin values (9.5 g/dL), hematocrit (29%) and total leukocytes (1,700/µl). The most significant pathological findings were suppurative bronchopneumonia, pulmonary edema, atelectasis, type II pneumocyte hyperplasia, occasional intra-alveolar squames, acute tubular necrosis, hemorrhagic enteritis and gastritis, lymphoid depletion, acute hepatocellular necrosis and hemorrhage. Gram-negative bacterial colonies were observed in the lung, heart, intestines and blood vessels. Pure culture of Escherichia coli was isolated from blowhole and abundant cultures of E. coli and Aeromonas hydrophila were isolated from lung. Septicemia due to gram-negative bacteria occurs commonly in bovine calves, and sporadically in young animals of other domestic species. Reduced transfer or absorption of maternal colostral immunoglobulin, or intercurrent disease or debilitation is usually prerequisite for E. coli septicemia. Most likely portal of entry in neonates includes navel, upper respiratory tract and possibly tonsils and intestines. In our case, the microscopic findings such as bronchopneumonia, hepatocellular necrosis, clumps of small bacilli in vessels through the body and serosal hemorrhages, are suggestive of an endotoxemic process. The animal also presented anemia and lymphopenia, which may be expected in a debilitated animal with acute septicemia. Determination of the cause of death is difficult in free-ranging wild animals, particularly cetaceans. In the present case, an acute septic process associated with E. coli and A. hydrophila infection was the most plausible cause of stranding. To the best of our knowledge, E. coli septicemia has not been previously reported in humpback whales. Complementary studies on the characterization of the E. coli strain may give further insights on its pathogenesis in cetaceans. We believe these findings may contribute to the understanding of pathological processes in humpback whales and add valuable information for comparative pathology.

Acknowledgments

We thank Sr. Ariosvaldo Pinto dos Santos and volunteers for the invaluable support in the fieldwork; Projeto TAMAR, Parque Estadual de Itaúnas and Instituto Orca for the logistical support in many stranding events. The support of Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), processes 2010/50094-3, 2011/08357-0 and 2012/00021-5, is greatly appreciated. Projeto Baleia Jubarte is sponsored by Petróleo Brasileiro (Petrobras). J.L.C.D. is a recipient of a professorship by the Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq (301517/2006-1). This study was conducted by K.R.G. as partial fulfillment of the requirements for the doctoral degree at the Departamento de Patologia, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo.

* Presenting author