Naturally Occurring Tyzzer's Disease in a
Tyzzer's disease, an acute multifocal
bacterial hepatitis caused by Bacillus piliformis,
is a fatal disease of young animals that has been reported
in a number of domestic, wild and laboratory animals. This
article describes the finding of Tyzzer's disease in a foal.
Case Report: The reported history
was as follows: An 8 day old, male foal was born seven days
premature to a 5 year old maiden mare. A few days after birth,
the foal was sluggish and had a temperature of 96°
F. The foal was treated with intravenous dextrose, Lactated
Ringer's Solution® (LRS), Bana-mine®, and Gentocin®.
The foal appeared to respond well to treatment. The temperature
returned to 100ºF and the foal was up and nursing. The following
morning the foal became weak and died upon transport to the
The gross examination was performed by
the referring veterinarian. The only gross lesion observed
was severe icterus.
Multiple tissue samples including liver,
kidney, heart, spleen, and lung from this foal were submitted
to the Animal Disease Diagnostic Laboratory. Histologically,
the liver contained multiple coalescing foci of coagulative
hepatocellular necrosis scattered throughout the parenchyma.
The centers of these foci were composed of pyknotic nuclei,
karyorrhectic nuclei, pink fibrillar material, and rare erythrocytes.
The periphery of the necrotic foci was infiltrated by moderate
to large numbers of degenerate neutrophils. Hepa-tocytes bordering
these necrotic foci contained intracytoplasmic basophilic
filamentous bacterial rods, which stained faintly with hematoxylin
and eosin (H&E). Giemsa and Warthin Starry stains revealed
numerous filamentous bacilli arranged in parallel and interlacing
bundles within the cytoplasm of hepatocytes. In addition to
the hepatic lesions, moderate suppurative subendocardial inflam-mation
was observed. The lung and kidney were microscopically unremarkable.
Discussion: The microscopic lesions
and identification of filamentous bacilli (Bacillus piliformis)
with H&E, Giemsa and Warthin Starry stains were consistent
with a diagnosis of Tyzzer's disease.
Tyzzer's disease is not common in horses
but has been reported in foals between 7 and 40 days of age.
The pathogenesis is not well understood. The organisms are
most likely picked up by the foal from the environment. The
proposed pathogenesis involves an oral route of infection
resulting in a primary enteric infection and subsequent dissemination
via the portal circulation to other tissues, especially the
liver. Rodents, rabbits, cats, and non-clinically infected
horses may serve as reservoirs. Because the dam may act as
the source of the infection, subsequent foals should be monitored
carefully and treated appropriately. In conclusion, the disease
is sporadic, and as such, specific control and preventative
measures are not commonly indicated.
- by Lavun Anothayanontha, DVM
- edited by M. Randy White, DVM, PhD