Animal: Captive young wild boar (Sus scrofa)
Organ: Lungs (tracheal bifurcation)
History: Sudden death, keepers did not notice any previous symptoms
Macroscopic findings: The primary bronchi and trachea up to the larynx were obstructed by a plug of innumerable threadlike approximately 40 mm long nematodes. The parenchyma of the lung was markedly distended with alveolar emphysema disrupted by multiple atelectatic foci
Histologic findings: Within bronchial lumina there were large numbers of adult nematodes, often containing embryonated and larvated eggs. The pulmonary parenchyma contained areas of alveolar emphysema disrupted by multiple atelectatic foci. These consisted of nematode larvae surrounded by large numbers of macrophages, fewer neutrophils and some Langhans-type giant cells.
Morphological diagnosis: Lung: Airway obstruction by adult nematodes and severe acute diffuse alveolar emphysema, moderate chronic multifocal pyogranulomatous pneumonia with intralesional nematode larvae
Etiology: Metastrongylus sp.
Comment: Metastrongylus salmi, M. apri and M. pudendotectus are the most common species of lungworms found in wild boars. Adults lay larvated eggs in bronchi and bronchioles. After excretion via host feces the first larval stage hatches and is ingested by the intermediate host (earthworm) where it develops into the infective third larval stage. Ingestion of the earthworm by the end host and larval migration to the lung completes the cycle.
In the presented case the alveolar emphysema is most likely due to overinflation following airway obstruction caused by the nematode plug.
Contributors: Angelika Weyrich, Dipl. ECVP; Anne Nesseler, Department of Pathology and Parasitology, Landeslabor Hessen, Giessen, GERMANY
Bibliography:
Barutzki D, Schoierer R, Gothe R. Helmintheninfektionen von Wildschweinen bei Gatterhaltung in Sueddeutschland: Artenspektrum und Befallshaeufigkeit [Helminth infections in wild boars in enclosures in southern Germany: species spectrum and infection frequency]. Tierarztl Prax. 1990 Oct;18(5):529-34. German. PMID: 2264058.
Oliveira, W.J., Perin, P.P., Arias Pacheco, C.A. et al. Integrative taxonomy of Metastrongylus spp. in wild boars from Brazil. Parasites Vectors 16, 449 (2023). https://doi.org/10.1186/s13071-023-06047-x