Listeria monocytogenes septicemia in foals: A case series (1986 to 2024)

Listeriosis is caused by Listeria monocytogenes, a Gram-positive, facultative anaerobic, intracellular rod bacterium that can infect a wide variety of species. Listeriosis occurs in a diverse range of domestic and wild animals but is most commonly a disease of ruminants. Clinical signs include meningoencephalitis, typhlocolitis, septic arthritis, and abortions. Listeriosis in horses has been reported in several countries but is an uncommon diagnosis. This report describes clinical, bacteriological, histopathological, and immunohistochemical findings in 6 foals with neonatal septicemia from which L. monocytogenes was isolated. Key clinical message: Listeriosis is considered rare in neonatal foals but should be considered in neonatal foals exhibiting septicemia and neurological signs. Cerebrospinal fluid cytology and blood culture testing are crucial in establishing the diagnosis, though L. monocytogenes is difficult to isolate. Cases in foals have a high risk of non-survival.