Interstitial lung disease in small ruminants

Interstitial lung diseases of sheep and goats, which are caused by a range of infectious, parasitic, and toxic agents, have substantial negative health and welfare impacts globally. Within this category of pulmonary disease, entities such as peste des petits ruminants (PPR) can undermine the livelihood of farming communities in sub-Saharan Africa and Southeast Asia; enzootic pneumonia, maedi, and ovine pulmonary adenocarcinoma compromise the productivity of farm enterprises where sheep are housed for prolonged periods. I detail the pathogenesis and lesions caused by a range of viral, bacterial, parasitic, and toxic agents that target the pulmonary interstitium in small ruminants, ultimately resulting in parenchymal damage and clinical disease. These lesions range from the progressive distortion of alveolar walls by infiltrating lymphocytes and macrophages following small ruminant lentiviral infection, to the acute impact of alveolar septal thromboembolism in Bibersteinia trehalosi infection, and eosinophil-mediated necrosis of alveolar walls triggered during the migratory larval stages of parasitism by Dictyocaulus filaria. In addition, I review the pathologic impact of neoplastic type II pneumocytes extending over the interstitial scaffold in cases of sheep pulmonary adenocarcinoma (jaagsiekte) and the toxic injury induced by plants (Trema and Crotalaria sp.) and other toxins (carbolic dips, 3-methyl indole) on the pulmonary interstitium.