Tyzzer’s Disease (C. piliforme) in Foals: Transmission, Risk Factors & Prognosis

Tyzzer’s Disease
Symptoms
Risk Factors
Diagnosis
Treatment
Prognosis and Prevention

Tyzzer’s disease is a rare, highly fatal liver condition that can affect any foal, even those who are well fed and in good health. The disease is caused by infection with C. piliforme bacteria, which is passed to foals through the feces of infected horses.

The presence of bacteria in a contaminated environment can lead to outbreaks of multiple cases on the same farm. For example, foals may become infected by consuming their dam’s feces.

Affected foals tend not to show any prior symptoms, with most cases only being diagnosed after rapid and sudden death. When symptoms are observed, they include lethargy, reduced appetite, dehydration, fever, seizures, weakness, jaundice, abdominal pain, and diarrhea.

Unfortunately, there are currently no treatment options available and the vast majority of affected horses die suddenly or within a day and a half from the onset of symptoms.

Prevention is complex and no vaccine is available. General preventive strategies include maintaining a clean environment, making sure foals receive adequate colostrum within 24 hours of birth, and minimizing stress.

Tyzzer’s Disease in Foals

Tyzzer’s disease, caused by the bacterium Clostridium piliforme, is a severe and highly fatal liver condition that can affect any foal, even those who are otherwise healthy and well-nourished.

C. piliforme is an anaerobic gram-positive bacteria. Various species from the Clostridium genus are responsible for serious health conditions in both humans and animals, including botulism and tetanus. The majority of affected foals die suddenly without prior symptoms. ^[1]

This condition is named after the American parasitologist Ernest E. Tyzzer who first identified the disease and named the pathogen Bacillus piliformis in 1917. Tyzzer’s disease was described in the literature as infection with B. piliformis until 1994 when the bacteria was reclassified as Clostridium piliforme, due to its closer relation to the Clostridium genus than to the Bacillus genus. ^[2]

In horses, Tyzzer’s disease primarily affects foals between seven and 42 days of age. The condition can occur sporadically or can affect multiple foals on the same farm simultaneously. ^[3]^[4] Typically foals are exposed to the bacteria in the environment, primarily through fecal matter. ^[1]

Transmission and Pathogenesis

Not much is currently known about the mechanism of disease progression for C. piliforme infection in foals. To date, the prevailing theory suggests that transmission occurs through the fecal-oral route. Foals are believed to ingest bacterial spores present in contaminated feed, feces, water, or bedding. ^[4]

These spores enter the environment through the feces of infected animals, including: ^[4]

Rodents
Cats
Adult horses

Clostridium piliforme is highly resilient and can survive in harsh conditions for over a year. It is also resistant to most disinfectants and heat. ^[4]

Once ingested, the bacteria infect the horse’s gastrointestinal (GI) tract and, subsequently, the liver, where it causes hepatic necrosis – irreversible tissue death in the liver. Foals die rapidly as the result of acute liver failure. ^[4]

The incubation period of Tyzzer’s disease is between four to seven days following oral exposure to bacterial spores. Many adult horses are thought to be asymptomatic carriers of C. piliforme, and foals likely become infected by bacteria shed in the feces of carriers. ^[4]

Young nursing mares that are newly exposed to the bacteria may play a significant role in spreading the infection. This is because foals naturally practice coprophagy in the early weeks after their birth, and mares without a history of exposure may not pass relevant antibodies to their foals through colostrum. ^[4]

As foals grow, their GI tract matures and their immune system develops. Mature horses are presumed resistant to Clostridium piliforme bacteria. ^[4]

Effects of Liver Disease

It is unclear how C. pilliforme injures the liver, but the characteristic rapidly progressing fatal symptoms show severe liver tissue death in juvenile horses. The liver is one of the largest internal organs in horses, and is responsible for critical functions including: ^[5]

Detoxifying substances from the blood
Storing vitamins, minerals and glucose (stored in the form of glycogen)
Secreting bile, a digestive fluid involved in breaking down fats and proteins
Synthesizing amino acids and coagulation factors used in blood clotting
Metabolizing drugs
Influencing immune responses

Young foals do not have a fully developed immune system and are reliant on antibodies from their dam’s milk to protect them in the early weeks of life. ^[6]^[7]

Foals with C. piliforme infection do not have sufficient immune system defenses to fight off the bacteria, which allows them to infiltrate the liver.

Once the bacteria has taken hold, the young foal’s underdeveloped liver is susceptible to catastrophic, irreversible damage. Since the liver is involved in so many vital functions and the foal’s entire physiology is under-developed, symptoms progress rapidly as the liver stops functioning.

Coprophagia in Foals

Coprophagia, commonly known as eating feces or manure, is normal behavior in foals and not a sign of malnutrition. On the contrary, there is some evidence young horses may benefit from eating feces.

The theory is coprophagia may provide essential nutrients and help establish robust bacterial flora in the foal’s gut, thereby strengthening their immune system and digestive health. ^[8]^[9]

Coprophagy is commonly observed in foals from one week of age up to one and a half months old. Foals tend to prefer the manure of their mothers, which may suggest the presence of a maternal pheromone. ^[8]^[9]

Symptoms

Clostridium piliforme causes inflammation of the liver, resulting in symptoms that are common to other hepatic diseases. Affected foals are frequently found dead with no prior symptoms. When symptoms are observed, they appear suddenly and progress rapidly. ^[2]^[4]^[10]

Possible signs may include: ^[2]^[4]^[10]

Lack of appetite
Lethargy
Dehydration
Coma
Fever
Seizures
Weakness
Jaundice (yellowing of the skin and mucous membranes)
Colic
Diarrhea

Risk Factors

While the pathophysiology of Tyzzer’s disease is not fully understood, several environmental and nutritional factors are thought to increase the risk of infection, including: ^[2]^[4]

High protein/carbohydrate diet: when fed to breeding mares is considered a potential predisposing factor; such feed regimens can alter the mare’s intestinal microbiome and potentially allow overgrowth of C. piliforme
Nurse mares: equine surrogate nurse mares used for orphan foals may play a role in the occurrence of Tyzzer’s disease in new farms
Hygiene: foals living in unclean environments are more likely to ingest material infested with spores of C. piliforme
Mare maturity: foals born to young mares, under the age of six, appear to be more likely to develop the disease
Seasonal spore activity: foals born in March and April are at higher risk of developing the disease, which is more prevalent during spring. This season exposes nursing mares to lush, high-protein pastures, increasing nutrient availability from forages. This may promote the proliferation of C. piliforme bacteria in the mare’s gastrointestinal tract.

Diagnosis

Diagnosing Tyzzer’s disease before death is unusual and complex. In the rare case of investigation in a living foal, veterinarians may use a combination of the following diagnostic tests to confirm Tyzzer’s disease: ^[4]

Physical examination
Analysis of fecal samples
Bloodwork
Diagnostic imaging
Liver biopsy

Differential Diagnosis

If presented with a suspected case of Tyzzer’s disease, the attending veterinarian will rule out other conditions with similar symptoms, particularly other forms of liver disease.

Some similar conditions to rule out include:

Sepsis
Meningitis
Iron hepatotoxicity
Equine herpesvirus-1 infection
Portosystemic shunt
Biliary disease such as cholangitis

Post Mortem Examination

Tyzzer’s disease is a highly lethal disease, with a mortality rate close to 100% and symptoms which develop rapidly. This means most foals die prior to diagnosis.

In these cases, owners may opt to conduct a post-mortem examination (necropsy) to confirm the cause of death.

Common post-mortem findings in cases of Tyzzer’s disease include: ^[10]

Swollen liver
1 to 5 mm white spots scattered throughout liver tissue
Icteric tissues (yellowish discoloration of tissues)
Multiple, small hemorrhages in multiple tissues
Presence of C. piliforme in tissues on bacterial testing

Treatment

Unfortunately, to date, no specific medication or established treatment protocols are available. Documented cases of successful treatment following a definitive diagnosis are extremely rare.

If a foal is diagnosed with Tyzzer’s disease, treatment mainly focuses on supportive and symptomatic care to stabilize the condition and alleviate pain and other symptoms.

Supportive treatment options include: ^[12]^[13]

IV fluids to address dehydration and maintain cardiovascular function
Glucose supplementation to provide energy during recovery
Sodium bicarbonate supplementation to counteract acidosis if the foal is not eating normally during recovery
Vasopressor medications to improve blood pressure
Broad-spectrum antimicrobial therapy
Feeding milk or a milk substitute
Anti-inflammatory drugs
Seizure medication

There is some evidence that aggressive treatment for septic shock can increase the chances of survival. Septic shock treatment may include: ^[14]^[15]

Antibiotic therapy to eradicate the bacteria in the bloodstream
Plasma transfusion
Administration of glucose solution to counteract low blood sugar
Supplemental oxygen therapy
Mechanical ventilation
Administration of anti-prostaglandin drugs

Despite the high mortality rate of Tyzzer’s disease, a successful outcome is possible with the prompt initiation of intensive care. Early detection and prompt and aggressive treatment provide a highly guarded chance of survival.

Prognosis and Prevention

The prognosis for foals infected with Tyzzer’s disease is extremely poor. Even with aggressive and prompt treatment, virtually all affected foals die as the result of the infection within 35 hours of the onset of symptoms. ^[12]^[17]

Unfortunately, to date, no vaccine or other medical prevention is available. Current preventive measures aim to reduce the risk of exposure to Clostridium piliforme bacteria, enhance immunity, and screen foals for early treatment.

Prevention measures include: ^[4]^[16]

Ensuring adequate colostrum intake: Colostrum (the first milk produced by the mare after birth) is rich in antibodies that help protect the foal from infections. Ensuring the foal receives adequate colostrum shortly after birth is crucial to properly develop its immune system.
Minimizing stress: Stress can impede a foal’s immune system. As such, providing a safe and calm environment for both the foal and the mare is essential.
Maintaining environmental hygiene: Good sanitation is fundamental to horse health and safety, and reduces the risk of many infections, including C. piliforme.
Housing foals in a designated area: Keeping foals in well-grassed paddocks has been suggested as a preventive measure as this helps reduce their exposure to contaminated soil.
Close monitoring of foals: Detecting early signs of disease can increase the scarce chances of survival.

Manure Management and Biosecurity

Manure management is fundamental to overall health and safety at any farm, and helps promote robust biosecurity for all animals sharing space, pastures, and equipment.

Depending on your operation’s size and layout, management strategies to ensure manure doesn’t pose a biohazard may include:

Mucking out stalls, pastures, paddocks, and arenas regularly, especially those where lactating mares are stabled and turned out
Providing a clean environment for dams to give birth and nurse in
Quarantining new horses, such as surrogate nurse-mares, for an appropriate amount of time before exposing them to vulnerable foals
Ensuring runoff from manure piles does not drain into pastures where horses are grazing
Soil testing to ensure pastures are not biohazardous

Summary

Tyzzer’s disease is a highly fatal liver disease caused by bacterial Clostridium piliforme infection. This bacterium is typically contracted through exposure to fecal matter.

Tyzzer’s disease only affects foals, and adult horses are presumed resistant to C. piliforme infection
Affected foals usually show no prior symptoms and often die suddenly
Tyzzer’s disease is rarely diagnosed prior to death. Most cases are confirmed on post-mortem examination (necropsy)
No specific treatment options are currently available; in cases presented for veterinary intervention, care is supportive and symptomatic
Young mares may be more likely to transmit the disease to their foals. Other risk factors include high-protein and carbohydrate diets for breeding mares, and poor hygiene
Preventive measures include ensuring adequate colostrum intake, minimizing stress, and maintaining good farm hygiene
The prognosis is extremely poor, with almost all affected foals dying within 35 hours of symptom onset