Pathology of complicated Babesia rossi-associated acute lung injury and respiratory distress syndrome in dogs

Abstract

A proportion of Babesia rossi infections in dogs are classified as complicated. One of the most lethal complications is the acute lung injury (ALI) and acute respiratory destress syndrome (ARDS). Patients affected by this complication usually succumb within 24 hours and there are similarities between this disease and malaria associated ALI and ARDS in humans, both rapidly fatal conditions. Both diseases are caused by haemoprotozoal parasites transmitted by insect vectors, namely ticks for babesiosis and mosquitoes for malaria. The pulmonary pathology of complicated babesiosis is poorly described and the aim of this study is to provide a thorough histomorphological analysis with immunohistochemical labelling of leukocytes to further define the immune cell population. The left caudal lung lobes from 11 Babesia rossi infected dogs and 4 healthy controls were examined with standard light microscopy and immunohistochemical markers applied. Markers included CD204 (resident tissue macrophages and dendritic cells), MAC387 (monocyte-macrophages of bone marrow origin), CD3 (mature T-lymphocytes), CD20 (mature B-lymphocytes and normal plasma cells), Mum-1 (plasma cells) and PAX-5 (immature and mature B-lymphocytes). Histopathology showed a severe increase in monocyte-macrophages within the alveolar walls and lumens. This was invariably accompanied by alveolar oedema as well as multifocal to coalescing areas of haemorrhage. Immunohistochemical labelling showed a significant increase in MAC387, CD204 and CD3 positive cells in the infected cases compared to healthy control dogs. This study provided novel insights into the pathology of and similarities between babesia and malaria associated ALI/ARDS in dogs and humans, respectively. Further fine ultrastructural examination of the pulmonary vascular endothelium is required in future studies.