The Case of the Downer Horses

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Tetanus and botulism ...a detective story.

The Navajo who owned the horse offered the mare a handful of alfalfa and she ate readily, despite her recumbency. Her tongue, as it moved in and out, seemed unusually lethargic. Dr. Sandigo pulled on the tongue and noticed a delay in the horse's natural response to pull it back. It appeared this mare was doomed, too.

CLOSTRIDIUM BACTERIA

As the doctor left the stricken horse he thought of an earlier visit where he'd examined a lamb that was trembling and appeared to be having uncontrolled muscle spasms, jumping reflexively when the doctor put his hand on its back. Also, the site of a recent tail docking appeared infected. The symptoms of tetanus in the sheep were different from those of the downer horses, but there was an important connection.

Tetanus is what is known as a clostridial disease because it is caused by a toxic protein produced by the bacteria Clostridium tetani. There are a host of other clostridial diseases aside from tetanus (which is the most common) including the dreaded Clostridium botulinum, better known as botulism.

While the Clostridium tetani bacteria is normally found in the feces of most species of farm animals, Clostridium botulinum thrives on dead and dying plant and animal tissue. Both bacteria can live in the environment for years. When a clostridium bacteria finds its way into a wound, the pus and dying tissue provide an ideal environment for growth. As the bacteria thrives and multiplies, toxins are released that travel through the peripheral nerves, eventually reaching the spinal cord. There the toxin interferes with normal activity at nerve junctions and, in the case of tetanus, causes a generalized muscular rigidity. Botulism results in a neuromuscular paralysis.

That said, tetanus has become less common in the United States because of a good annual vaccination program and timely boosters. Nevertheless, the disease, which is more common in the warmer southern states, has a poor prognosis. Indeed, 80% of affected animals die, even with treatment. Typically an affected animal will adopt a "sawhorse" stance, with all limbs extended rigidly out at an angle. Small ruminants like sheep will lay on their side with all of their limbs stiff. Eventually the toxin moves far enough up the spinal cord to cause respiratory paralysis and death.