- Unable to get up by himself
- Normal temperature
- Startled easily
- Walked with head and neck extended
- Eyes "rolled back"
- Rapid breathing
Tetanus toxemia is caused by a specific neurotoxin produced by Clostridium tetani in necrotic tissue. Horses are the most sensitive of all species, with the possible exception of humans.
The incubation period varies from one to several weeks but usually averages 10-14 days. Localized stiffness, often involving the masseter muscles and muscles of the neck, the hindlimbs, and the region of the infected wound, is seen first; general stiffness becomes pronounced ~1 day later, and tonic spasms and hyperesthesia become evident.
The reflexes increase in intensity, and the animal is easily excited into more violent, general spasms by sudden movement or noise. Spasms of head muscles cause difficulty in prehension and mastication of food, hence the common name, lockjaw . In horses, the ears are erect, the tail stiff and extended, the anterior nares dilated, and the third eyelid prolapsed. Walking, turning, and backing are difficult. Spasms of the neck and back muscles cause extension of the head and neck, while stiffness of the leg muscles causes the animal to assume a “sawhorse” stance. Sweating is common. General spasms disturb circulation and respiration, which results in increased heart rate, rapid breathing, and congestion of mucous membranes.
Usually, the temperature remains slightly above normal, but it may rise to 108-110°F (42-43°C) toward the end of a fatal attack. In mild attacks, the pulse and temperature remain nearly normal. Mortality averages ~80%. In animals that recover, there is a convalescent period of 2-6 wk; protective immunity usually does not develop after recovery.