Tyzzer’s disease in a foal. Light- and electron-microscopic observations.

The research focuses on an instance of Tyzzer’s disease diagnosed in a 17-day-old foal. The disease, caused by the bacteria Bacillus piliformis, was identified from multiple regions of liver necrosis and the presence of the bacteria in the foal’s hepatic cells.

Diagnosis of Tyzzer’s Disease

• The occurrence of Tyzzer’s disease was determined in a 17-day-old foal. This disease is an infectious entity, typically infecting rodents but also seen in other domestic animals. It is caused by a bacterium known as Bacillus piliformis.
• The presence of the disease was confirmed through the identification of multiple regions with necrosis, or death of cells, in the liver of the foal. These necrotic areas indicated tissue damage, a common manifestation of Tyzzer’s disease.
• The researchers further found organisms within the dead hepatic (liver) cells that were morphologically similar to Bacillus piliformis, thus corroborating the diagnosis of Tyzzer’s disease.

Observations of Bacilli

• The identified bacilli, or bacteria, were between 300 and 500 nm in diameter. Some ‘giant’ bacilli were noted to be as large as 1000 nm.
• Many of these bacterial organisms were observed within the nuclei of cells. The process of penetration by these bacteria into the cell nuclei could be traced, further supporting their identification as Bacillus piliformis – a type of bacteria known to invade cell nuclei.

Additional Pathological Findings

• There was evidence of hemorrhaging in the foal’s heart, along with inflammatory changes noted in the mesenteric lymph node. These findings suggest that the infection by Bacillus piliformis may have spread systemically, or throughout the foal’s body.
• No signs of enteritis, or inflammation of the small intestine, were observed in the jejunum— the mid-section of the small intestine and the only portion available for examination. This might suggest the intestinal tract wasn’t severely affected by the disease, or simply reflect the localized nature of the sample examined.