Case 4 - 180720-4

Adult dog.

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This slide has a section of lung including bronchus along one margin and extending to the adjacent pleural surface, in which approximately 90% of the parenchyma is inflamed and consolidated with embedded trematodes. The affected parenchyma is characterized by either collapsed alveolae or variably-filled alveolae by numerous lymphocytes, plasma cells, foamy macrophages and regionally variable numbers of eosinophils. Alveolar inflammatory cells are admixed with edema and fibrin and occasional clusters of macrophages contain cytoplasmic brown, globular pigment (presumed hemosiderin).

Scattered throughout the section of lung are numerous trematode eggs, which are approximately 40 to 80 um in diameter with a one to three um thick, clear to yellow-tinged shell. In some regions, there are larger numbers of these eggs and are associated with severe fibrosis that effaces normal pulmonary parenchyma. There are also few adult trematodes which are approximately 5 x 3 mm with a 40 um thick spiny tegument and a spongy parenchyma containing numerous subtegumental vitellaria. Present in one cross section are profiles of excretory system, testis, uterus, ovary and ceca. Adult trematodes are surrounded by moderate hemorrhage, early fibroplasia, increased capillary profiles and marked inflammatory cells of the same populations listed above. Often associated with the trematode adults are regions of granular brown-yellow pigment (excrement). There are multifocal lymphoid follicles and occasional small amounts of hemorrhage. Bronchiolar epithelium is moderately to severely hyperplastic, occasionally forming papillary extensions into the airway lumen and moderate generalized mucus cell hyperplasia.

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Lung: severe, diffuse, chronic, histiocytic, lymphoplasmacytic and eosinophilic bronchointerstitial (what do we think of type of pneumonia?) pneumonia with multifocal fibrosis, hemorrhage and intralesional trematode adults and eggs

This case was a nice example of lung flukes in a dog. Based on species, tissue location and histomorphology of the parasite, this is presumed Paragonimus sp., such as P. kellicotti or P. westermani.

This particular genus of trematode, Paragonimus sp., has members that reside as adults in the lungs of mammals. These are often found in cysts in the lungs of mammals such as dogs, cats and other wild animals. Clinical signs are often mild, however, more severe cases can occur including pneumothorax due to cyst rupture. Metacercariae from the gastrointestinal tract migrate into the peritoneal cavity then enter the pleural cavity through the diaphragm and migrate into the lungs. The formed “cysts” communicate with the bronchial tree to facilitate expulsion of operculated eggs into the airways to be coughed up, swallowed and passed in the feces. They then require two intermediate hosts, first involving snails and later involving crayfish or crabs, which are then eaten by animals, such as a dog resulting in infection. Discussion was predominantly inquiring about the route of infection and how the parasite reaches the lungs. The term “cyst” in reference to the structures formed by these trematodes is somewhat confusing as they appear to create a granulomatous/inflamed and fibrotic capsule, which is not necessarily lined by epithelium aside from perhaps where it communicates with airway epithelium.

Broman MM, Miller MA. Pathology in practice. Journal of AVMA. 2016.248(11):1253-1255.

Harrus S Nyska A Colorni A, et al. Sudden death due to Paragonimus kellicoti infection in a dog. Vet Parasitol1997; 71:59–63. Bowman DD. Helminths. In: Georgis’ parasitology for veterinarians. 9th ed. St Louis: Elsevier, 2009;124–125.