Tetanus in Dogs : Causes, Treatment, and Prevention

August 21, 2023

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Tetanus in Dogs : Causes, Treatment, and Prevention

Tetanus is a very serious disease caused by a neurotoxin called tetanospasmin that is secreted by a bacterium known as Clostridium tetani. The neurotoxin affects the nervous system of dogs, which can lead to painful stiffening and paralysis of the dog’s jaw, neck, and other muscles. The toxin binds to local nerves and moves up into the central nervous system where it interferes with the release of glycine, an amino acid that also acts as an inhibitory neurotransmitter. The result: painful muscle over-activity, spasms, and rigidity in the dog’s muscles. In severe cases of tetanus, a dog cannot breathe because the respiratory muscles become paralyzed. In these cases, a mechanical ventilator is needed.

Tetanus bacteria are anaerobic, meaning they grow in conditions where there is no oxygen, such as a deep bite wound or puncture. Clostridia are soil bacteria and they live in dirt, so it is easy to see how a puncture on a dog contaminated with dirt would be a classic tetanus-yielding wound. Such wounds are particularly common on farms where there might be nails on the ground, ready to pierce a dog in the foot. A fight involving a bite wound and rolling around in dirt might also lead to tetanus in dogs.

What causes tetanus in dogs?

As we have already mentioned, tetanus is caused by the bacterium Clostridium tetani, namely by the two neurotoxic toxins released by this bacterium:

Tetanospasmin: is a toxin that prevents the release of inhibitory neurotransmitters (glycine and GABA) in the spinal cord and brain. The absence of these neurotransmitters leads to predominant neuronal excitation, which causes the characteristic clinical signs of this disease.
Tetanolisin: is a toxin that has a necrotizing effect on tissues. The tissue necrosis favors the creation of an anaerobic environment in the wound, which in turn favors the growth of bacteria. It can therefore be said that this toxin favors the spread of infection.

But how do these bacteria come into contact with the dog’s body in the first place? The bacterium usually enters the body through a wound.

As mentioned earlier, Clostridium tetani is widely distributed in the environment. Therefore, the bacterium, which is found in soil, dust, feces, or contaminated objects, can easily enter the body through any type of open wound (large or small, deep or superficial). There they find an anaerobic environment (without oxygen) where they can transform into a vegetative form and produce neurotoxins.

Symptoms Of Tetanus In Dogs

The symptoms of tetanus often appear within two weeks. For many dogs, the initial signs of tetanus are subtle eye changes which can easily be mistaken for eye disease.

Inability to blink
Constricted pupils
Sunken eyes
Sensitivity to light
Risus sardonicus (a sardonic grinning)
Erect ears
Inability to open jaw
Rigid tail
Sawhorse stance
Difficulty swallowing
Seizures
Muscle spasms
Walking rigidly or inability to walk

In the early stages, a dog affected by tetanus loses the ability to blink and will solely use their third eyelid to moisten their eyes. The dog may become sensitive to light because the pupil has constricted. In localized tetanus, dogs will see stiffness near the muscles closest to the initial wound, but in generalized tetanus, a dog’s muscles across their body may become more rigid and tense, leading to spasms and seizures. Some of signs may be attributed to other toxins, such as snail bait or moldy toxins, resulting in a misdiagnosis.

As the disease progresses, dogs with ears that hang down may develop ears that stand up straight, and the facial muscles may pull back, creating risus sardonicus (a.k.a., a sardonic grin). In more advanced stages, dogs can no longer walk and will stand stiffly in what is called a sawhorse stance.

What are the types of tetanus in dogs?

There are two types of tetanus your dog can develop, localised tetanus and generalised tetanus.

Localised

This is the most common form of tetanus that our pets encounter. It is characterised by stiff muscles and sometimes muscle tremors that only affect the limb and muscles closest to the initial wound. Sometimes, localised tetanus can progress into generalised tetanus, but this isn’t always the case.

Generalised

Generalised tetanus is where symptoms arise throughout the dog’s entire body, or at least widespread areas, rather than just the location of the initial wound. This type of tetanus is definitely more severe in both appearance and the impact it has on your pup, meaning that the signs are easier to spot early on.

The ‘sawhorse stance’, where all legs are held rigidly, and their tail is extended behind them is one of easiest things to spot if your dog is suffering with this disease.

Due to the persistent muscle contractions caused by generalised tetanus, many dogs actually develop a fever. This isn’t actually caused by the disease, this is the secondary aftermath of the heat produced by the muscles constantly contracting.

Take a look at your dog’s mouth, as this is also a big indicator of generalised tetanus. In some cases, it may look like your dog is flashing you a grin, but this is actually a symptom referred to as risus sardonicus, which originates from Latin, meaning ‘sinister smile’. This smiling effect is caused due to the muscle spasms that tetanus creates in the lips.

On the other hand, your dog’s mouth could be held tightly shut, hence why this condition is often labelled as lockjaw. The jaw will be rigid and essentially locked, which can result in big puddles of drool being left all over your floor. Eating will become difficult, and it can even result in spasms happening within the throat and diaphragm, which is the muscle that oversees breathing.

Consequently, breathing will become a huge struggle for your poor pooch, potentially having fatal outcomes.

Diagnosis of Tetanus in Dogs

Unfortunately, there is no easy diagnostic test that can confirm tetanus in dogs. The diagnosis is generally made based on the visual appearance of the dog and history of the wound. Typically, there is a history of a wound in a tetanus case (usually in the preceding one to two weeks) but sometimes the wound may have gone unnoticed by the human and this important clue is not available.

It’s possible to measure antibody levels against the tetanus toxin, but this has not been widely used in clinical settings. Attempting to culture Clostridium tetani from the wound, as a way to support a diagnosis, usually doesn’t work.

Treatment of Tetanus in Dogs

The first step in treatment is antibiotics to kill the Clostridia toxin. The good news is, exotic antibiotics are not needed — good ol’ fashioned penicillin does the trick. In addition to the antibiotics, sedation and anti-seizure medications may be necessary to control the muscle spasms and/or seizures.

Nursing care may also be needed and requires a darkened room with minimal stimulation and soft bedding to prevent bedsores. The clenched jaws caused by tetanus can be problematic for feeding so a liquid diet or slurry is often necessary. Improvement is generally noted within the first week of therapy but complete recovery can take a month.

A controversial treatment called Tetanus Antitoxin may be an option, if the tetanus is diagnosed early. Antitoxin is an antibody solution (a blood product) generated by either a horse or human blood which works by binding and destroying the tetanus toxin, preventing it from attaching to the dog’s cells. Unfortunately, if the toxin has already attached to the cells, the antitoxin will not work; in fact, the tetanus antitoxin can actually cause significant side effects in dogs, so your veterinarian will weigh the risks versus the benefits.

TREATMENT OPTIONS FOR TETANUS IN DOGS

Penicillin and Metronidazole are antibiotics used to treat tetanus in dogs. They’ve no effect on the neurotoxin but can stop C. tetani from spreading.
Intravenous (IV) fluids are used to halt dehydration while oxygen is used to prevent respiratory failure. If your dog’s throat and diaphragm are paralyzed, he needs an endotracheal tube or a mechanical ventilator.
Dead tissue is removed from around your dog’s wound to decrease tetanus bacteria. Then it’s cleaned with mild soap and water or iodine.
Acepromazine and chlorpromazine are recommended to control your dog’s sensitivity to light, sound, or touch. He may also be injected with phenobarbital, diazepam, or midazolam to control muscle stiffness.
Equine antitoxin.A controversial treatment, equine antitoxin may be an option if tetanus is caught early. Made from the blood of horses, it can be given by IV or injected under the skin or into the muscle. It can take up to three days to destroy the tetanus toxin. Skin tests are recommended because equine antitoxin can cause potentially life-threatening allergic reactions.
Nursing care.Your dog may require around-the-clock care in a dark and quiet room for seven to 30 days. He needs soft bedding, frequent rotation to avoid bedsores, hand feeding or feeding by a G-tube, and help expressing his bladder.