Key takeaways
Anthrax in horses is a rare disease caused by infection with the spore forming bacteria Bacillus anthracis.
- The disease results following spread of the bacteria throughout the body, and subsequent production of a deadly toxin
- The bacterial spores are most commonly found in contaminated soil
- Horses become infected from grazing, biting insects, or through contamination of open skin wounds
- Symptoms commonly include severe colic, bloody diarrhea, and sudden death
- Anthrax is diagnosed based on history, physical exam, and blood tests
- If diagnosed early in disease progression, it can be treated with antibiotics and supportive care
- More commonly, horses die from the rapidly progressive disease
- Prevention with vaccination is key in endemic areas as the prognosis is poor once symptoms are apparent
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A closer look: Anthrax in Horses
Although anthrax in horses is extremely rare, it is a life-threatening, and typically fatal disease. Anthrax is an emergency as it is a rapidly progressive and fatal disease, and requires immediate treatment for the best prognosis.
The disease can also be spread to other animals and humans. Due to the risk of disease in both animals and humans, suspected cases must be reported to local and federal authorities.
Risk factors
Bacillus anthracis is most commonly found in Africa and central/southern Asia. It is rarely found in North America.
Horses usually contract anthrax by eating contaminated forage or other material. After consumption, it can take up to a week for the bacteria to proliferate and spread throughout the body. The toxin produced by the bacteria leads to widespread tissue death, resulting in the severe symptoms and often death associated with this disease.
Anthrax is most commonly seen in endemic areas after heavy rainfalls, preceded by a period of drought. Overgrazing of pasture may increase the risk of exposure due to horses ingesting more soil during grazing.
Possible causes
Anthrax is caused by infection with the spore-forming bacteria Bacillus anthracis. Spores are primarily found in the soil, or on contaminated objects. The spores are extremely resistant to extreme temperatures, disinfection, and dehydration.
Horses become infected with the bacterial spores after ingesting them while grazing, through contamination of an open wound, or occasionally from a biting insect.
Main symptoms
Symptoms can vary depending on the method of infection. Horses often develop gastrointestinal symptoms after ingesting the bacterial spores.
In some cases, horses develop swelling of the head and neck due to anthrax.
Testing and diagnosis
Anthrax can be difficult to diagnose as it is extremely rare in horses, and has several clinical signs that overlap with more common diseases. To rule out other common diseases, tests such as a physical examination and blood work may be conducted.
A definitive diagnosis of anthrax can be made using a blood test specific to the bacteria or through examining blood under the microscope.
Steps to Recovery
Anthrax is treatable with antibiotics if recognized early and treated aggressively. Other supportive care may be instituted, including intravenous fluids and anti-inflammatories. Due to the severity of the disease, most horses are euthanized. Treating other, potentially exposed horses with antibiotics is recommended to prevent further spread of the disease.
Most horses develop symptoms late into the progression of disease, when treatment is unlikely to be effective. In most cases, horses die within 4 days to 2 weeks of developing symptoms. Horses who are diagnosed quickly and aggressively treated still have guarded prognosis due to the severity and rapid progression of the disease.
Prevention
Vaccinating horses in anthrax-endemic areas is key in prevention.
Further preventative measures aim to minimize the spread of the bacteria to other animals and humans and include:
- Quarantining infected horses and reporting cases to relevant authorities
- Proper disposal of horses that die (or are euthanized) from anthrax, such as burning or burying the carcass
- Using extreme caution and appropriate personal protective equipment if in contact with infected individuals
- Disinfecting areas with possible anthrax contamination
- Not physically moving or opening horse carcasses suspected of dying from anthrax
- Prompt disposal and decontamination of dead animals
- Using insect repellents to prevent spread through biting insects
Humans can also become infected with the bacteria, and it can likewise be a fatal disease.
Is Anthrax in Horses common?
Anthrax is extremely rare in horses.
Typical Treatment
- Antibiotics
- Supportive care (intravenous fluids, anti-inflammatories)
