Case 4 - 180511-4

One-month-old, male Boer goat)

The patient was acquired from an auction with an unknown history. Immediately upon acquisition, the patient had ongoing seizures that the owners believe were exacerbated by bottle-feeding. In the two days prior to presentation, the seizures became more frequent and the patient never regained normal mentation. At the time he was presented to the clinic, the patient was obtunded, tremoring, and was unable to stand or support himself. The patient was euthanized due to quality of life concerns and poor prognosis.

The lateral ventricles and the fourth ventricle are moderately dilated.

One section of brain, including thalamus, hippocampus and cerebral cortex, is examined. The ependymal and subependymal parenchyma surrounding the lateral ventricle is densely infiltrated by lymphocytes, plasma cells and histiocytes that occasionally form pervascular cuffs. A similar inflammatory population extends to and expands the meninges, where is occasionally forms perivascular cuffs, and the choroid. The lateral ventricle is moderately dilated and contains aggregates of lymphocytes, plasma cells, neutrophils, histiocytes and necrotic debris. Histiocytes within the meningenes, choroid and ventricle frequently contain intracytoplasmic, short, bacterial rods.

A Gram stain reveals that histiocytes infiltrating the meninges frequently contain intracytoplasmic, gram-positive, short bacterial rods.

Brain: severe chronic, focally extensive histiocytic neutrophilic leptomeningitis, choroiditis and encephalitis with intracytoplasmic gram-positive short bacterial rods

The patients presentation and the presence of intrahistiocytic, gram-positive bacterial rods are suggestive of listeriosis. However, participants in the biopsy conference commented on the unusual distribution of lesions in this case. Encephalitis in ruminants typically occurs in older animals and is associated with the centripetal dissemination of bacteria along the trigeminal nerves to the brain, after invasion of the oral mucosa. Septicemia in younger animals is typically associated with multifocal hepatitis and, to a lesser extent, lesions in other organs. Hematogenous dissemination to the brain, in such cases, is very rare. In this case there was no evidence of infection except for that in the brain.

Listeria monocytogenes is a ubiquitous, intracellular, anaerobic bacillus that is resistant to harsh environmental conditions. The three common disease syndromes of listeriosis are abortion and, as previously mentioned, encephalitis and septicemia. Abortion occurs secondarily to hematogenous spread through the placenta to the fetal liver, leading to hepatic necrosis. Encephalitis is most common in adult ruminants in association with contaminated silage. The most common histologic findings in the central nervous system are microabscesses, glial nodules, acute vasculitis, mononuclear perivascular cuffs and mononuclear leptomeningitis. Septicemia, which is most common in neonates as a continuation of the fetal infection, results from bacterial infection of macrophages, which permits them to travel throughout the body. Liver is affected more severely and lesions in other parenchymal organs are variable.The brain was not cultured in this case, and there were no ancillary diagnostic assays to prove the identity of the bacteria. The morphology of the bacteria, the gram-positive staining, and the presence of numerous bacteria in macrophages, however, are all suggestive of Listeria monocytogenes infection. If so, the focally extensive distribution around the lateral ventricle, and the absence of other lesions consistent with Listeria septicemia, are atypical of ruminant listeriosis.

Cantile C., Youssef S. Nervous system. In: Maxie, MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals, Vol I. 6th ed. Philadelphia, PA: Elsevier Ltd; 2016:362-363.

Miller AD and Zachary JF: Nervous system. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Mosby, Inc.; 2016:881-882.

Case contributor: Drs. Rose and Woolard

Conference presenter: Drs. Rose