Immunohistochemical evaluation of natural cases of encephalitic listeriosis in sheep.

Listeriosis is an important public health problem in the world. It can cause abortion, encephalitis, septicemia, conjunctivitis and mastitis in ruminants. The development of central nervous system lesions is not fully understood in encephalitic listeriosis. We performed a retrospective analysis of 15 sheep with encephalitic listeriosis. Hyperemia and opacification of the meninges were common necropsy findings. Lesions generally were localized in the caudal part of the brain including the pons, medulla oblongata, thalamus and cerebellum. Microabscesses usually were found in the caudal brain and cerebellum, while perivascular infiltrates were found most often in other parts of the brain. Evidence of Listeria monocytogenes was detected immunohistochemically in the medulla oblongata, pons, thalamus and cerebellum. Prominent reactions for glial fibrillary acidic protein (GFAP), S100 protein, N-methyl-D-aspartate receptor-1 (NMDAR1) and inducible co-stimulatory protein (ICOS) were detected in the caudal brain, which indicates that these proteins may play roles in the pathogenesis of encephalitic listeriosis.