Lungworm infection in a sheep flock in Maryland.

First-stage larvae of Protostrongylus rufescens were detected in the feces of a ram with diarrhea, anorexia, weight loss, and mucopurulent nasal discharge. Subsequently, a survey was initiated in the experimental sheep flocks maintained at the Agricultural Research Service's Helminthic Diseases Laboratory in Beltsville, Md to determine the extent and effect of infection with the parasite. Five of 31 ewes and 4 of 16 rams were found to be infected with the lungworm. Clinical signs of infection, which ranged from mild to severe, included diarrhea, weight loss, and respiratory distress. Natural transmission of the parasite to parasite-naive lambs grazing on pasture occurred during the course of this study. Three lambs born to infected ewes during this study were not infected, suggesting that there is no vertical transmission. Additionally, cattle grazing the same pastures as infected sheep were not infected with the parasite. Results of this study indicated that Protostrongylus rufescens can cause serious disease in domestic sheep in the United States and should be considered as a differential diagnosis in sheep with nonspecific respiratory tract signs.