Xishan Biology

Introduction to Pathogens

Taizé Pathogen

Tyzzer’s organism is a hair-like Bacillus species—*Clostridium piliforme* (formerly known as *Bacillus piliformis*)—that can cause hepatic and intestinal necrosis along with diarrhea in laboratory animals. First discovered by Ernest Tyzzer in mice, the disease it induces was subsequently named "Tyzzer’s disease" after him. While Tyzzer’s organism is well-known as a pathogen explicitly required to be eliminated under national standards, in practice, it often seems surprisingly distant from everyday concerns—after all, infections caused by this organism are rarely observed in animals. But what could explain this curious phenomenon? Let’s find out in this article.

Pathology

 

The Theileria pathogen is a Gram-negative bacterium, filamentous or slender rod-shaped, and capable of forming spores. It can only be cultured using specific cell lines or chicken embryos. Physicochemical properties of the pathogen are highly unstable—exposure to room temperature for 2 hours or to 45°C for 15 minutes will inactivate it. However, under spore-forming conditions, it exhibits greater resistance. Formalin, phenol, and povidone-iodine are effective at eliminating the pathogen.

The morphology of the Taiga pathogen under an electron microscope (Image source: Reference 5)

Epidemiology

 

The Theileria pathogen typically causes asymptomatic or subclinical infections. Mice, rats, hamsters, rabbits, and other animals are all susceptible hosts. Currently, only one case has been reported involving a human immunodeficiency virus (HIV)-infected patient harboring the Theileria pathogen; however, approximately 58% of the population tests positive for Theileria antibodies. Theileria infection can lead to acute clinical illness and even death in laboratory animals, while also affecting the gastrointestinal tract and liver of infected animals. Therefore, experimental studies should avoid using animals that have been exposed to this bacterium. In the past three years, several domestic institutions have detected Theileria-positive samples among their animals or biological products.

Since this bacterium easily loses its activity under external conditions, infections are typically transmitted via the fecal-oral route from animals with asymptomatic infections to others. Generally, only immunocompromised or young animals develop symptoms, while adult animals usually remain asymptomatic carriers. Additionally, *Tyzzer's bacillus* can also be transmitted vertically.

Data source: Suzhou Xishan Biotechnology Co., Ltd.

Clinical symptoms and pathological changes

 

Infection with this bacterium typically leads to rapid death in animals after symptoms appear. Before death, affected animals often exhibit characteristic signs such as diarrhea, arching of the back, and disheveled fur. Autopsies of deceased animals usually reveal intestinal and liver lesions, including noticeable liver enlargement and the presence of white, pinpoint necrotic foci. Additionally, the cecum, small intestine, and intestinal lymph nodes may show symptoms like congestion and swelling.

Diagnosis and Prevention

 

Currently, Theileria species cannot yet be isolated on artificial culture media, making it impossible to identify them through isolation and cultivation. According to national standards, injecting immunosuppressive agents (such as cortisone) is used to induce pathological changes in animals that may harbor the infection, with microscopic examination serving as the primary diagnostic method. However, this approach is time-consuming and relatively complex in practice. In real-world applications, serological methods (such as enzyme-linked immunosorbent assay and immunofluorescence assays) and molecular biology techniques are predominantly employed as laboratory-based diagnostic tools.

After infection with *Tyzzer's disease* bacteria, antibacterial drugs such as tetracycline can provide partial relief, but they cannot completely cure the disease. Currently, there is no vaccine available against *Tyzzer's disease* bacteria, and animals infected typically succumb to the illness very quickly after showing symptoms. Therefore, preventing the emergence and spread of this pathogen among animals is of paramount importance. For laboratory animals, it is essential to regularly disinfect their feed, bedding, cages, and other equipment using chlorine- or iodine-based sanitizers. Additionally, animal facility managers must establish strict disinfection protocols to minimize the risk of bacterial transmission. If a positive case is detected in the animal facility, immediate action must be taken to sanitize all affected animals promptly, thereby preventing an outbreak within the colony and reducing potential losses for the facility.

References

 

1. Chinese Pharmacopoeia 2020 Edition

2. Natural Pathogens of Laboratory Mice, Rats, and Rabbits and Their Effects on Research. Clin Microbiol Rev. Apr 1998

3. Tao Junhao, Yan Huiqiong, Xie Hun, Ying Huazhong, Dai Fangwei. Research Progress on *Tyzzer's Organism* in Quality Control of Laboratory Animals. Laboratory Animals and Comparative Medicine, 2022, 42(4)

4. Charles River Technical Sheet: Helicobacter spp.

5. SHERRI L. MOTZEL* AND LELA K. RILEY. Bacillus piliformis Flagellar Antigens for Serodiagnosis of Tyzzer's Disease. JOURNAL OF CLINICAL MICROBIOLOGY, Nov. 1991, p. 2566-2570

 

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