Lockjaw, or tetanus, is an uncommon condition in dogs and cats.
In my 27 years in practice, I have only seen 1 confirmed case in a dog, and 1 suspected case — which turned out to be something different. Unlike people, cats and dogs are relatively resistant to the toxin responsible for causing the symptoms.
Lockjaw is caused by a toxin produced by a bacterium called Clostridium tetani. Animals usually become infected when a wound is contaminated by clostridial bacteria. The signs develop about 1 week later (but it can be up to 3 weeks afterward), by which time the original injury has healed.
Dogs and cats with tetanus have a typical “sardonic grin” on their faces because of the contraction of muscle groups around the head. Animals with lockjaw are unable to feed, and paralysis of their respiratory muscles can lead to death.
The most obvious symptom is the characteristic tetanus “grin.” The facial muscles go into spasm, drawing the lips back and deeply furrowing the brow.
Also, the ears of drop-eared breeds stand erect because the muscles pull them upward. Typically, the affected pet cannot open his mouth — hence the name “lockjaw.”
As the disease progresses, the animal walks stiffly with a rocking-horse gait, and as he becomes more ill, he is unable to stand, lying with his legs stiffly extended. Eventually, paralysis of the respiratory muscles means the animal is unable to breathe and may die unless given aggressive supportive care.
Clostridium tetani enters wounds and uses the nerves as a highway to the rest of the body. The clostridium releases a toxin that inhibits motor nerve function.
Once stimulated, the nerves cannot “defuse” and remain on constant alert. The muscles are stuck with a permanent message telling them to contract, and so muscles remain permanently rigid.
The “sardonic grin” and erect ears are highly suggestive of tetanus, especially if the pet’s caretaker recalls a cut to the pet a few days before the symptoms developed.
In most cases, a diagnosis is reached by eliminating other possible causes of neurological symptoms such as poisoning, meningitis, myositis (muscle inflammation) and rabies.
Pets with lockjaw are hypersensitive to noises and stimulation. This sends them into more muscular contractions and should be avoided by placing pets in a quiet, dark room.
Penicillin antibiotic can kill the clostridial infection and prevent further toxin release, but it cannot do anything to reverse the effects of toxin already bound to nerves.
Unfortunately, bound toxin has to run its course, which means giving the animal intensive supportive care to get him through this period. If the respiratory muscles are affected, this means putting the patient on a ventilator and feeding him through a tube.
Antitoxin is available but rarely used because there is a high risk of an anaphylactic (shock)-type reaction that is potentially life-threatening in its own right.
An anti-tetanus is available, but again, it is rarely used because both dogs and cats are much more resistant to the effects of the tetanus toxin when compared to humans or horses.
- “Thirteen cases of tetanus in dogs.” Adamantos & Boag. Vet Rec, 161: 298–303.
- “Feline tetanus.” Illingsworth, Chiapella, Veralli & Lahunta. JAAHA, 13: 209–215.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.