Severe Idiopathic Eosinophilic Pneumonia and Vasculitis in 11 Horses

Introduction: Various eosinophilic lesions have been described in horses. Multisystemic eosinophilic epitheliotropic disease (MEED) characterized by eosinophilic granulomas in various organs represents the most diffuse manifestation. In the present study we describe the gross and microscopical lesions of idiopathic eosinophilic pneumonia and vasculitis in 11 horses without systemic involvement. Materials and Methods: During a 2-year period (2010–2011), lungs from 88 horses with gross signs of pulmonary disease were collected at a slaughterhouse. Lung sections were stained with haematoxylin and eosin, Giemsa and periodic acid–Schiff. Results: In 11 horses, lungs were enlarged, pale pink and collapsed, with multifocal to coalescing, white–red, 0.4–4.0 cm diameter nodules distributed throughout the parenchyma. Histologically, the lesions ranged from severe eosinophilic bronchointerstitial pneumonia to severe eosinophilic lobular bronchopneumonia associated with eosinophilic necrotizing vasculitis affecting small to medium sized vessels. Mild interstitial fibrosis was also present. The other part of the parenchyma appeared emphysematous. There was no histological evidence of parasites within these lesions. Conclusions: Eosinophilic pneumonia and vasculitis without intralesional parasites are rarely described in horses. Histological findings do not resemble the typical eosinophilic granulomas observed in lungs of horses with MEED, but are similar to the findings in idiopathic chronic eosinophilic pneumonia of man and of Churg–Strauss syndrome of man.