LAUSR

Porcine pulmonary metastrongylosis is caused by 3 helminth species: Metastrongylus apri, M. pudendotectus, and M. salmi. Pigs are infected by ingestion of earthworms containing the infectious third-stage larvae, which molt in mesenteric lymph nodes and reach the lungs via lymphatics as fourth-stage larvae. Adult worms reside in bronchi and bronchioles (Image 1). Gray-pink pulmonary nodules of up to 3 mm in diameter indicate an eosinophilic and granulomatous inflammation in response to eggs and larvae in the alveoli. Later stages of infection may be associated with hyperplasia of bronchial epithelium, goblet cell hyperplasia, and exudation of mucus, eosinophils, neutrophils, and macrophages.