After a deep, penetrating wound such as a hoof puncture the disease usually occurs and is typically caused by a nail or sharp object.
This disease can also occur after a castration or umbilical infection in foals when there is necrotic tissue present. Horses are more susceptible to the causative bacterium than any other mammals.
Clostridium tetani causes tetanus which is a bacterium with spores capable of surviving within the soil for many years.
The organism is also considered to be a normal inhabitant of the gastrointestinal tract of the horse. This means that horses are frequently exposed to the organism both in the barnyard and pasture.
The organism needs an anaerobic or without oxygen environment for survival once the spores are deposited deep in the tissue and this typically occurs when there is dead or devitalized tissue.
The bacterium releases a potent toxin when these anaerobic conditions are met and it is transported in the blood to the central nervous system where it creates problems that can eventually lead to paralysis and death.
Anywhere from several days to a month or more can be the incubation period for tetanus and it all depends on the wound environment and the proximity of the wound to the central nervous system. It is frequently difficult for owners to pinpoint the injury or wound that initially started the condition due to the long incubation period. Tetanus is common in horses of all age but especially with those who have no vaccination history.
The owner may first notice some increased muscle stiffness which is then followed by muscle tremors. When the horse is walking or trotting this stiffness will be noticed or the tail may be held out stiffly. Soon restricted jaw movement will follow which is where the term lockjaw comes from and there may also be a protrusion of the third eyelid.
The horse will appear anxious after the classic tetanus signs, during this time the ears will be pricked forward and the nostrils flared. Chewing will become more difficult as the disease progresses and drooling will be evident. The horse will assume a saw-horse posture when walking becomes extremely difficult and there will be a progressive stiffness of the limbs and neck. Some horses may even fall and then have their legs remain rigid and extended.
Asphyxiation is the most common cause of death in the horse which occurs from the paralysis of the respiratory muscles. Five to ten days is the typical course of the disease from the onset of clinical signs although signs may persist for weeks in horses who appear only mildly affected. There is always a guarded prognosis for horses with tetanus and the prognosis is grave if the condition is left untreated.
Supportive care for these horses is usually very labor intensive and required a veterinary referral center. Most of the veterinary work is aimed specifically at eliminating the toxin from the horse through aggressive wound treatment, neutralizing the existing toxin with an antitoxin and controlling muscle spasms.
The key to tetanus control is prevention. The most effective and inexpensive equine vaccine available is the tetanus vaccine and owners are always encouraged to vaccinate all their horses.
For mares they should get a tetanus toxoid booster at least a month prior to foaling in order for them to have good quality colostrum to pass on to the newborn foal. At two months, the foal should be vaccinated and then again at three months and six months of age. To maintain active immunity annual tetanus toxoid boosters are sufficient.
Proper Care of Puncture Wounds:
A mild dishwashing soap should be used to wash puncture wounds to remove the dirt and congealed blood. You can use an antiseptic solution but it should be used carefully since they can cause additional tissue damage if the concentration is too high. Gently explore puncture wounds to check the extent of the injury.
X-rays may be necessary. Never suture puncture wounds and in some cases they may need to be enlarged in order to be let open to the air. The foot is the most common site for puncture wounds on horses. A hoof knife can be used to open them and they should be kept
open in order to allow drainage and healing. Especially in the hoof many small puncture wounds will go unnoticed which means it is imperative to have a tetanus vaccination. Call your veterinarian right away if a puncture wound enters a joint.
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