Effect of ivermectin treatment on eosinophilic pneumonia and other extravascular leisons of late Strongylus vulgaris larval migration in foals. Veterinary Pathology

Abstract. Eighteen parasite-free pony foals were infected orally with 500 third stage larvae of Sfrongylus vulgaris. At 56 days after infection, six ponies were treated with intramuscular ivermectin (22,23-dihydroavermectin B 1); six were treated with oral ivermectin; and six were not treated. Necropsy was done 91 days after infection to study the pathologic effects of migrating S. vulgaris larvae and to determine the efficacy of ivermectin in attenuation of S. vulgaris-induced lesions. Larval migration induced eosinophilic inflammation of the liver, spleen, mesenteric, colic and cecal lymph nodes, and small and large intestine. Previously unreported parasitic lesions included eosinophilic pneumonia with eosinophilic granu-lomas and pulmonary lymphoid nodules. S. vulgaris larvae were observed in eosinophilic granulomas in the lung, epicardium, liver, and intestinal serosa. Injectable and oral ivermectin formulations were equally effective in reduction of these lesions, Parasitic infection is a major cause of human eosin-ophilic pneumonia, which is an inflammation of the pulmonary parenchyma dominated by eosinophils and histiocytes and frequently accompanied by eosino-philia. Parasites may induce eosinophilic pneumonia directly by larval migration through the lungs or indi-rectly through hypersensitivity reactions.I6 The patho