Endotoxins are large molecules that make up the outer wall of certain gram negative bacteria. When released into the blood stream, they can cause systemic disease including diarrhea and founder, shock, and death. Endotoxemia is a serious complication of inflammatory bowel disorders, retained placenta, and septicemia. This article discusses what endotoxins are, how they affect horses, and treatment for endotoxemia.

Endotoxins are a normal part of the lipo-polysaccaride outer membrane of the cell wall of Gram-negative bacteria. The diseases most often associated with horses are caused by E. coli, Salmonella, and Pseudomonas, though there are others. Gram negative bacteria in the bowel release small amounts of endotoxin while growing but the gut wall acts as a barrier and the small amount that gets through is generally removed by the liver before causing harm. Disease is most commonly associated when the organism has infected the tissues of the horse and then the cell wall is disrupted by our immune system and antibiotics causing a release of larger amounts of endotoxin. As the released endotoxins enter the blood disease from endotoxemia results.

The effects of endotoxin in the blood stream are mediated by the chemical called Lipid A. In white blood cells three types of events are triggered during their interaction with Lipid A:

• Production of cytokines. Cytokines are hormone-like, low molecular weight proteins, that regulate the intensity and duration of immune response and mediate cell-cell communication. These are powerful mediators of inflammation, hypotension, and septic shock.
• Activation of the complement cascade. Complement is a substance, normally present in serum, that is destructive to certain bacteria and other cells sensitized by a specific complement-fixing antibody.
• Activation of the coagulation cascade. This results in wasting the components that help regulate proper coagulation and as a result hemorrhage occurs.

The result of this overactivation of the immune system is: inflammation, intravascular coagulation, hemorrhage, and shock. Endotoxemia is not so much an infection as it is a poisoning. The poisoning results in overactivation of the immune system and from this disease results. A wide spectrum of physiological events occurs and generally divided into the following sequence:

• The latent period during which there are some physiological events
  • changes in white blood cell counts
  • disseminated intravascular coagulation
  • hypotension
• Physical disease period
  • diarrhea, fever, laminitis
  • shock
• And if the dose is large enough, death

The course of the disease depends on the amount of endotoxin, how it gets into the system and the length of time of exposure. Currently the exact cause for founder in horses is not known but the decreased profusion of the capillaries of the laminae by blood is hypothesized to be one of the causes. For More Information....