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What is Infectious Necrotic Hepatitis (Black Disease)?

Infectious necrotic hepatitis is typically found in sheep throughout the world, however it has also been found in horses. This disease is communicable and is known as an acute toxemia which means the toxins are found in a horse’s bloodstream and is severe in nature. This disease does tend to be fatal to the carrier animal.

The symptoms have a sudden onset and there is not often a lot of time between the appearance of symptoms and your horse’s condition worsening. Fever, lack of appetite, and abdominal pain can evolve to panting and a high heart rate. Lesions on the liver are usually found at post mortem examination.

Infectious necrotic hepatitis (black disease) is a condition caused by the toxin Clostridium novyi and impacts your horse’s liver. This disease is relatively rare in horses, however there have been cases. The symptoms vary but are specific to black disease.

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Symptoms of Infectious Necrotic Hepatitis (Black Disease) in Horses

The symptoms of this disease are sudden and severe in nature. Some of the symptoms are fever, depression, decreased appetite, separation from the herd, reluctance to walk and more.

  • Fever – Your horse may have a sudden onset of a high fever with no obvious cause
  • Depression – Your horse may present with a depressed mood such as being listless or dull
  • Decreased appetite – He may not be eating or have developed a sudden decrease in his appetite 
  • Separation from the herd – You may notice your horse lagging behind the rest of his herd mates and separating himself from the rest 
  • Reluctance to walk – This may present as straining or leaning to one side of his body against things 
  • Pain in abdomen – This is typical upon physical examination of his body 
  • High heart rate – You may notice that your horse has developed a rapid heart rate that is much higher than it should be at rest 
  • Rapid breathing – He may be panting or breathing heavy with no explanation

Causes of Infectious Necrotic Hepatitis (Black Disease) in Horses

The cause of black disease in your horse is the toxin Clostridium novyi. This toxin is found in the environment, in the carcass, and fecal matter of infected animals and within the soil and water supplies. 

  • Age - Young sheep and horses aged 2 to 4 years are at a high risk of contracting the disease
  • Seasonal occurrence – Liver fluke infestation at certain times of the year can cause an increase in infection
  • Snails – They are a host of the toxin and can spread it during the dry times of the year 
  • Infected animals – if your horse came into contact with another horse who was infected, a carcass of an infected animal, or fecal matter he runs a risk of developing the infection as well

Diagnosis of Infectious Necrotic Hepatitis (Black Disease) in Horses

Unfortunately, due to the acute onset of symptoms and the sudden time frame of the progression of the disease, there is no need for a diagnosis. Most diagnoses are done post mortem and are done through biopsy of the liver. The liver is cultured for the toxin which will most likely be present. The liver will show lesions displaying the migratory path of the liver fluke. Death in a recumbent animal will occur within a few hours of the onset of symptoms.

Treatment of Infectious Necrotic Hepatitis (Black Disease) in Horses

Due to the nature of the severity of infectious necrotic hepatitis, treatment is not an option. Documentation is limited for black disease in horses, though in sheep, evidence points to acute death. However, there is some indication that vaccinations are beneficial prior to an outbreak. These vaccinations can also be utilized once an outbreak has begun on sheep and horses that are not already infected with the disease. Once a horse is infected, even with treatment, the prognosis is poor.

Recovery of Infectious Necrotic Hepatitis (Black Disease) in Horses

This is a disease where prevention is the best method for management. The suggestion is to keep the snail population low as they are natural carriers of the toxin. If the snails can not be controlled, then controlling the fluke infestation is another option for minimizing the risk of black disease. The last option to mention is vaccinating your horse against the disease to begin with, if this is done only newly introduced horses need the vaccination after that.