Case 2 - 170623

The subject was a 12-year-old, male, castrated, Labrador retriever

This dog presented to the emergency service for evaluation of a possible obstructive intestinal foreign body. On pre-operative ultrasound, a small intestinal obstruction, with fluid dilation of the duodenum and stomach, was identified. The liver had generalized enlargement with ultrasonographic changes indicative of an infiltrative process such as neoplasia. His small intestinal submucosal layer was also diffusely thickened. Both small intestine and liver were sampled during the enterotomy procedure. A walnut, the presumed cause of the obstruction, was removed from the small intestine.

N/A

This slide has one section of jejunum and two sections of liver. Numerous, 50- to 75-micrometer-diameter, round to misshapen, and frequently mineralized trematode eggs, with a simple lightly pigmented shell, are scattered in portal regions of the liver and the lamina propria of the jejunum. A few eggs are also present in the submucosa of the jejunum. The lamina propria of the jejunum has a moderate infiltrate of lymphocytes, plasma cells and neutrophils. Small segments of the villi are denuded of epithelium and covered by mats of fibrin, erythrocytes and fragmented cellular debris. Where intact, villi have moderately congested vessels and are lined by plump endothelial cells and often have increased numbers of luminal neutrophils. The eggs have a very thin shell and are often collapsed are torn. Many or most are completely mineralized, and nearly all are degenerate.

The liver numerous nodular aggregates of inflammatory cells which are typically periportal and variably contain the previously described eggs. These nodules contain lymphocytes, plasma cells, epithelioid macrophages, histiocytic syncitia and variable numbers of neutrophils, often intermixed with scattered pigment-laden macrophages. As in the jejunum the majority of the trematode eggs are degenerate. However, one section contained a clearly identifiable developing miracidium, consisting of an aggregate of poorly differentiated cells. surrounded by a thin wrinkled shell. Even where the eggs were difficult to see, remnants of the lightly pigmented shells often persisted in the center of granulomas. A significant number of the eggs were not surrounded by inflammatory cells, although they were dead and mineralized. The remaining hepatic parenchyma has moderate, midzonal hepatocyte cytoplasmic vacuolation characterized by wispy, delicate vacuoles. There is generalized, mild to moderate, brown globular hepatocellular cytoplasmic pigment.

No special stains.

Jejunum: moderate, chronic, diffuse, lymphoplasmacytic, neutrophilic enteritis with mild segmental superficial villous ulceration, and intralesional trematode eggs Liver: moderate, chronic, multifocal, granulomatous, portal hepatitis with intralesional trematode eggs

The lesions and trematode eggs in this case are consistent with infestation by Heterobilharzia americana. These are intravascular flukes in the family Schistosomatidae. The intermediate hosts are aquatic snails and raccoons are typically the natural definitive host, although patent infections are reported in other mammals. This parasite is found primarily in the southeastern United States and it is not known to occur in California. Anecdotal evidence suggests that raccoons in the region are not parasitized, though incidental infestations are common in the southeastern United States. The source of this dog’s infection is unclear, as there is no report of this patient traveling outside of California

Free-swimming cercaria emerge from affected snails (Lymnaea sp.) and infect dogs by penetrating intact skin. The cercaria then ultimately migrate to the liver where they mature. The adults migrate to mesenteric veins where they reproduce and release eggs in the distal branches of the veins. The eggs may migrate through the lamina propria to the lumen, thus completing the life cycle. However, eggs can also embolize to the liver and other organs such as the lungs. Clinical signs of affected dogs typically include lethargy, hyporexia, vomiting, and diarrhea. Affected dogs may also be hypercalcemic due to the described granulomatous inflammation.One comment that came up in the conference discussion was regarding the minor eosinophilic component to the inflammation despite this being a parasitic disease. It was not readily apparent in the literature why the dog granulomas were lacking in eosinophils. However, this trematode is also reported to cause granulomas in horses and camels, in which a much more prominent eosinophilic infiltrate is described.

References