Listeriosis in an Arabian foal with combined immunodeficiency.

A 1-month-old Arabian foal with signs of central nervous system disease was found to have combined (B- and T-lymphocyte) immunodeficiency. The foal died in spite of intensive antibiotic therapy. At necropsy, generalized lymphoid hypoplasia and acute necrotizing and granulomatous inflammation of the brain, heart, and adrenal glands were found. In addition, there were spinal meningitis and focal hepatic necrosis. Listeria monocytogenes was isolated on primary culture from the brain.