High-mortality outbreak of Yersinia pseudotuberculosis infection in a guinea pig herd

Yersinia pseudotuberculosis caused a fulminant outbreak in a Croatian breeding colony of 84 guinea pigs, in which 80 animals (95%) died within 72 hours after abrupt food refusal and marked lethargy, without diarrhoea. Seven freshly dead animals were examined. At necropsy, 2–5 mm, white-yellow nodules were found distributed in the liver, spleen, lungs, mesenteric lymph nodes and partly also in the small intestine. Aerobic culture of these organs on Columbia blood agar (28°C, 24–48 h) revealed pure growth of Y. pseudotuberculosis. Histology showed well demarcated necro-pyogranulomatous lesions with central bacterial colonies, margins of neutrophils and a peripheral coat of macrophages and few lymphocytes. Immunohistochemistry confirmed abundant lysozyme-positive macrophages and few CD3-positive T and CD79α-positive B cells, indicating a predominantly innate response. This case report emphasises the extreme lethality and rapid progression of guinea pig yersiniosis and highlights its zoonotic potential.