Equine tetanus is a highly infectious neurological disease which is more commonly known as “lockjaw”. This name is a result of the clinical signs that follow infection.
Equine tetanus is caused by the bacteria Clostridium tetani. The disease is generally fatal and usually enters the horse via access to the bloodstream. For example if the horse has an open wound exposed to the bacteria, the pathogen replicates rapidly in the open wound, enters the bloodstream and then attacks the central nervous system (CNS) by producing a toxin called tetanospasmin. Horses are often affected more severely by this toxin than other animals and they also appear to be more susceptible to acquiring the disease following an injury. In addition, it has been known for horses to become infected with tetanus after an operation.
Equine tetanus is usually a result of infection from the bacteria which is found in soil. Symptoms include extreme sensitivity to the surrounding environment, stiffness, and spasms. The bacteria Clostridium tetani affect humans as well as horses and so is known as a zoonotic disease. Prevention via vaccination is highly encouraged and recommended for healthy horses. Vaccination is further encouraged if the horse injures itself in a manner which results in an open wound or puncture.
Soil contaminated with infected faeces is the most common method of transmission. This contamination can be found in the majority of areas, including where most horses are kept. The bacteria gains access the horse’s system via open wounds on the skin or puncture wounds, usually from nails, in the sole of the foot. The bacteria may also be ingested and so even horses with no external wounds may be at risk.
These anaerobic bacteria are able to survive for large periods of time, as long as a few years, in most soil conditions. Unfortunately, most disinfectants or high temperatures do not destroy the bacteria and this allows the bacteria to remain in the soil for a very long time, generally leaving the unvaccinated horse constantly at risk.
The symptoms are initially difficult to spot and so may result in the diagnosis being too late for a possible recovery. The horse experiences extreme sensitivity to noise, light and even light contact which can be very stressful for both horse and owner. As a result the horse becomes and nervous and may respond by an unwillingness to be handled or with aggression.
The symptoms progress as the toxin begins to take effect. The term “lockjaw” arises as the horse’s jaw muscles contract so the mouth cannot be opened. The animal will have trouble eating and the horse will be reluctant to move as spasms occur in other muscles. The neck will be extended and the front and hind legs become increasingly stiff. A constant expression of anxiety results from facial muscle spasms, as wells as the ears being permanently pricked.
In the later stages, the horse will also sweat more than it would normally and show signs of colic. The severity of the symptoms greatly increases with time and there will be even more violent muscle spasms which generally involve the whole body. Protrusion of the third eyelid is commonly seen. In some cases the horse may actually collapse or die as a result of an inability to respire. This is often due to paralysis.
Treatment and Prevention
The tetanus toxoid is used with the tetanus antitoxin as part of the treatment plan. A course of antibiotics, such as penicillin, is administered to destroy the bacteria, thus preventing further release of the harmful toxin. With the aim of calming the horse and reducing stress, sedatives are given. The horse needs to be kept in a darkened room, again to reduce stress, and placed in a warm area where there is little noise. Due to stiffness of the neck, food should be placed in an accessible area
As is the rule of medicine; “prevention is better than cure”. As early as four months of age, foals can be vaccinated to protect them against equine tetanus. Therefore, most responsible owners have their horses vaccinated every two years to prevent equine tetanus. The initial vaccine to start the course is administered with the second given between four to six weeks following the first. Horses with open wounds, either following an injury or operation, should be given the vaccine if not already vaccinated.
Diagnosis and Prognosis
Protrusion of the third eye is usually confirmed as a positive diagnosis of equine tetanus. If there are any signs of injury, where there may have had an open wound, then this will also be taken into account when diagnosing the horse.
The prognosis for unvaccinated horses diagnosed too late is poor. Often, these horses are euthanized to ease the severe suffering caused. Vaccinated animals have a much better survival rate and so it is argued that this proves that horses and ponies should be vaccinated against this often fatal condition.