EVALUATION OF LABORATORY TESTS FOR CONFIRMING THE DIAGNOSIS OF ENCEPHALITIC LISTERIOSIS IN RUMINANTS

Retrospective analysis of 93 bovine, ovine, and caprine Cases diagnose d as listerial encephalitis revealed positive bacterial isolations in only 63% of 59 cases in which bacterial culture was attempted. Only 42 % of 41 attempted bovine brain cultures were successful, compared with 67% from 6 sheep brains and 92% from 12 goat brains. Gram stains and Listeria-specific immunohistochemistry were evaluated as tools for ver ifying the presence of bacteria or listerial antigens in 38 animals. S ixteen of 17 animals in this group with positive bacterial isolations were immunochemically positive for listerial antigens (including 5/6 c attle), but Gram stains detected only 9/17 positive animals (including 1/6 cattle). Antigen was also detected in 15 of 21 animals (including 5/9 cattle) with unsuccessful or unattempted bacterial isolations. Of all 38 animals, the histologic diagnosis could be verified in 82% by immunohistochemistry, compared to 47% verified by Gram stains. Immunoh istochemical testing was especially beneficial in locating antigen in lesions with few bacteria or bacterial antigens and is a rapid method of confirming the diagnosis of encephalitic listeriosis where inapprop riate material is submitted for bacterial isolation or in culture-nega tive cases.