Tetanus is a highly fatal disease that affects the nervous system of all animals. It is caused by the neurotoxin Clostridium tetani, a bacteria found in the soil and in the intestinal tracts of animals and people. Wound contamination is the most common way that people and animals become afflicted with tetanus.

Tetanus is very rare in dogs, and dogs have been shown to be quite resistant to the toxin. Rare cases usually affect dogs with injuries around the mouth or pups that are teething. Horses and people are much more sensitive to the tetanus toxin, so for these species, vaccinations are recommended. However, the potential risks inherent in the vaccine, such as allergic reaction, along with their normal resistance to the toxin, make this vaccine rarely given in dogs and cats.

Clinical signs include limb stiffness and difficulty walking. Spasms of the facial muscles cause abnormally erect ears and retraction of the lips that resembles "risus sardonicus" seen in humans with tetanus. Dogs can't eat or swallow, and as a result, often develop pneumonia.

Thorough cleaning of wounds and appropriate use of antibiotics is generally effective in allowing a dog's wound to heal.