Comparison of fluorescent antibody test, immunohistochemistry, and PCR testing for diagnostic confirmation of neurolisteriosis in 25 goats.

Neurolisteriosis, a common disease of small ruminants, is most often caused by Listeria monocytogenes. Here we describe 25 cases of caprine neurolisteriosis diagnosed in our laboratory over a 5-y period and compare our fluorescent antibody test (FAT) results with immunohistochemistry (IHC) and polymerase chain reaction (PCR) testing for diagnostic confirmation. Neurohistologic changes consistent with neurolisteriosis affected the pons in all cases, extending rostrally to the mesencephalon in 6 cases, caudally to the medulla oblongata in 6 cases, and/or dorsally to the cerebellum in 4 cases. Acute inflammatory changes were observed in 17 cases, and included neuroparenchymal microabscesses, neuronal necrosis and neuronophagia, axonal swelling, microgliosis and astrogliosis, and perivascular neutrophils with macrophages, lymphocytes, and plasma cells that occasionally extended to the leptomeninges. Subacute-to-chronic changes (8 cases) consisted of neuroparenchymal and perivascular clusters of macrophages with rare neutrophils, lymphocytes, and plasma cells admixed with glial nodules. Bacterial bacilli were observed within neutrophils or macrophages in H&E-stained tissue sections in 4 cases. Gram stain highlighted gram-positive bacilli in 13 cases. Neurolisteriosis was confirmed by FAT in 2 cases, by IHC in 19 cases, and by PCR in 20 cases.