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Also Known As

Quick killer, Infection (anthrax)


Anthrax is an acute, rapidly-developing, fever-producing, infectious disease that requires the immediate attention of an equine veterinarian.

In horses, anthrax may take either a pulmonary form with fever, muscle pain, respiratory distress, sweating, and shock-like symptoms, or it may take a gastrointestinal form with fever, colic, and bloody diarrhea. Common symptoms include septicemia, enteritis, and colic.

Stricken animals may die within one to three days. Failure to achieve rigor mortis after death is common.

Characterized by a high fever, anthrax progresses rapidly. In addition to a high fever, horses are obviously sick and often have ventral edema. If the horse dies, the carcass will likely have dark blood oozing from the mouth, nostrils, and anus. .

Because anthrax is known as "the quick killer," diagnosis may be based on the clinical signs, but it is routine to confirm the presence of Bacillus anthracis from a blood sample or culture sent to a laboratory.

In their vegetative stage, cells of the anthrax agent multiply in the lymph nodes of animals. When cells of the Bacillus anthracis escape the body, they form spores when exposed to oxygen. Environments friendly to the anthrax organism include areas with high levels of soil nitrogen, alkaline soil, and temperatures higher than 60 degrees F.


  • High fever and sweating
  • Respiratory distress
  • Muscle pain
  • Colic
  • Septicemia
  • Enteritis
  • Bloody diarrhea
  • Shock-like state


Animals are usually infected by ingesting soil-borne spores through grazing close to the ground. Spores may also be present in bone meal, protein concentrates, and excreta.

Bites from flies and other insects that harbor vegetative anthrax are also vehicles for transmission. In the case of insect bites, localized, hot, painful swellings at the bite location may be seen. These subcutaneous swellings then spread to the throat, neck, abdomen, and mammary glands.


Since no specific horse vaccine has been developed, the Sterne's strain, nonencapsulated, live spore vaccine licensed for use in cattle has been used to vaccinate horses. Initial doses of the vaccine should be administered two to three weeks apart, then followed by an annual revaccination. Horses that contract anthrax should be vaccinated seven days after the last antibiotic treatment.

Vaccination is recommended only in endemic areas of the country, including South Dakota, Louisiana, Texas, Missouri, California, and Arkansas. In case of an outbreak, only horses not running a temperature or exhibiting clinical signs should be vaccinated to ensure that they don't contract the disease.


Horses respond quickly to long-acting antibiotic treatments. Temperatures of all horses in the herd should be taken, and any animal that has a temperature in excess of two degrees above 99.5 F should be treated with penicillin or a penicillin derivative. .

The incubation period is three to seven days and temperatures should be taken and recorded for at least ten days to ensure that horses have been cured of the disease and no longer show symptoms.

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.