Encephalitic listeriosis in ruminants: immunohistochemistry as a diagnostic tool.

A retrospective analysis of 42 ruminants (sheep, goats and cattle) with suspected meningo-encephalitis was performed. The clinical findings and the post-mortem results of the animals have been specified. Bacteriological culture, Gram's stain and Listeria-specific immunohistochemistry were performed in order to confirm the diagnosis of these cases. The results of the different methods were evaluated for the detection of listerial antigens. Bacteriological culture was positive in 28.5% of the cases. In 47.6% of the cases, Gram-positive bacteria were found and 80.9% of the cases were immunohistochemically positive for the listerial antigen. The most important conclusion from this investigation is that the traditionally used Gram's stain and the bacteriological culture techniques are insufficient compared with immunohistochemistry for the confirmation of a Listeria monocytogenes infection.