From the Summer 2020 Newsletter:

The case for this issue is from an adult cat that mysteriously died at home. The owner performed the autopsy and brought selected tissues into the referring veterinarian, who submitted them to the VDL for additional testing.

On gross examination, the cat had dozens of 5- to 10-millimeter (mm) diameter raised, firm, tan nodules throughout the spleen (Figure A). Microscopically, the splenic nodules corresponded to necrosis and inflammation characterized by eosinophilic cellular and karyorrhectic debris, small to moderate amounts of fibrin, and moderate numbers of degenerate neutrophils with fewer macrophages and lymphocytes (Figure B). PCR was positive for Francisella tularensis, the causative agent of tularemia.

A) Spleen from a cat. Throughout the splenic parenchyma are variably sized white to tan nodules that correspond to regions of inflammation microscopically B). Gross image by L. Rice, NDSU. Photomicrographs by H. Pecoraro, NDSU.

Multifocal tan nodules in the spleen can denote neoplasia (e.g., lymphoma) or may be due to necrosis and inflammation. Two infectious causes of necrotizing splenitis are tularemia and plague (Yersinia pestis). Dogs, cats and humans can become infected with F. tularensis after being bitten by an infected tick. Dogs and cats also may become infected when they ingest infected rodents or rabbits. Infections in people also arise from inhalation of infected aerosols or through ingestion of contaminated food or water.

Cases of tularemia also have been reported in foals and sheep with heavy infestations of ticks. Zoo animals also have been infected with tularemia, especially in areas with heavy rodent or rabbit populations.

Heidi Pecoraro, DVM, PhD, DACVP

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