In March, a goat in New York began exhibiting nonspecific signs including anorexia and depression, which progressed to opisthotonus and ultimately death. The animal showed no evidence of bloat and had been maintained on a standard diet of hay and corn. A field necropsy performed by the attending veterinarian was largely unremarkable. Diagnostic samples were subsequently submitted to the Animal Health Diagnostic Center at Cornell for further evaluation. Histopathologic examination revealed necrosuppurative meningoencephalitis characterized by vasculitis and microabcess formation in the brainstem. In addition, culture of brainstem tissue yielded Listeria monocytogenes, confirming a diagnosis of listeriosis.

Listeriosis is an infectious disease caused by Listeria monocytogenes, a Gram-positive, non-spore-forming bacterium notable for its ability to survive across a wide range of temperatures, making it particularly resilient in diverse environments¹. The disease affects a broad spectrum of domestic and wild mammals, most commonly ruminants such as sheep, goats, and cattle. It is also found in wildlife, including white-tailed deer and moose, as well as domestic species such as pigs, dogs, and cats¹. In ruminants, transmission most commonly occurs through ingestion of contaminated feed, particularly poor-quality silage². The disease typically presents in three forms: encephalitic, abortive, and septicemic. The encephalitic form is the most prevalent and is characterized by clinical signs such as circling, incoordination, head tilt, and facial paralysis². The abortive form generally occurs in late gestation and results in abortion, producing weak, moribund, or macerated fetuses². The septicemic form develops rapidly within two days of silage ingestion resulting in fever, inappetence, depression, and death².

Listeriosis is often suspected based on clinical presentation, but a definitive diagnosis requires bacterial culture. For the encephalitic form, the most reliable diagnostic method is culture of the brainstem. In cases of the abortive form, diagnosis is best achieved through aerobic bacterial culture of fresh tissues, particularly the fetus or placenta. In the case of septicemia, aerobic culture of lungs, kidney, spleen and lymph nodes would yield Listeria bacteria.

When necropsy is performed, histopathologic lesions across all forms of the disease can provide additional support for the diagnosis, although they are not consistently observed. In encephalitic cases, gross lesions of the brain may include congestion, malacia, and hemorrhages³. In ruminants, microscopic findings often consist of brainstem microabscesses, gliosis, perivascular lymphocytic cuffing, and meningitis³. In the abortive form, necrotic foci may be present in the fetal spleen and liver, along with endometritis in the placenta and, in some cases, encephalitis in the fetal brain³.

References

1. Constable, P. D. (2024). Listeriosis in animals. In Merck Veterinary Manual.
2. Fentahun, T., & Fresebehat, A. (2012). Listeriosis in small ruminants: A review. Advances in Biological Research, 6(6), 202–209.
3. López-Almela, I., Sheth, C. C., Gomis, J., Gómez-Martín, Á., Lecuit, M., & Quereda, J. J. (2024). Epidemiology, clinical and pathological features and outcomes of listeriosis in ruminants: A systematic review and meta-analysis. Frontiers in Veterinary Science.