Tetanus

Tetanus is caused by a toxin produced by an anaeobic bacteria (which develops without oxygen) : Clostridium tetani.

This bacteria forms very resistant spores which are :

• Resistant to heat : over 2 hours at 90°C, it takes 15 minutes at 100°C to destroy them. The sporulated form resists for 6 hours at 80°C, and 15 minutes at 140°C;
• Resistant to numerous disinfectants and antibiotics;
• Able to survive for up over 32 years in the outside environment away from light (especially in the soil).

Clostridium tetani is also a part of herbivores’ normal intestinal flora : the animals excrete large quantities of spores every day which contaminate the outside environment  (grss, hay, straw…)

Hot humid climates are favorable to the bacteria and to the development of the disease : tetanus is considered enzootic (permanently present) in tropical climates.

• Accidental tetanus following a puncture wound or a prick by a foreign object;
• Post surgery tetanus ;
• Post obstetrical tetanus, following foaling;
• Umbilical tetanus in the foal.

When the spores enter a deep wound (accidental or following surgery), they are in the right conditions to germinate and multiply (dark, heat, low oxygen environment…).

The bacteria then starts to produce neurotoxins which will reach the nervous system and migrate along the nerves.

Effects of the toxin

One of the toxins involved blocks the secretion of substances inhibiting nervous influx. This leads to generalised muscle spasms and convulsions, combined with an exacerbated response to stimuli (comparable to the effects of strychnine).

Another toxin causes necrosis of local tissues.

Yet a third toxin causes paralysis of the peripheral nerves.

Incubation

The incubation period is typically between 8 to 10 days, but can reach several months if the spores remain in a latent state in the organism.

First symptoms

The first symptoms include : stiffness of gait, reluctance to turn or move backwards, the horse appears to move as a block as if on crutches, and profuse sweating.

The symptoms will rapidly worsen with generalised muscle spasms which in turn lead to :

• Difficulties in feeding : the horse grasps food but seems unable to chew or swallow, food hanging from the mouth is often noted, hence the name « lock-jaw » (it looks as though the horse is « smoking a pipe »);
• Characteristic signs : head extended, eyes sunken with protrusion of the third eyelid which covers the eye, ears pricked and touching one another over the head ;
• No remission periods ; on the contrary, when the horse is stimulated, it triggers a crisis and exacerbates the muscle contractions;
• When the rib cage muscles become affected, the horse will have trouble breathing and death ensues.

Other complications can also be the cause of death : fractures due to falls, pneumonia due to swallowing the wrong way.

Death will occur in 1 to 3 weeks (subacute form), sometimes even in 1 to 2 days (acute form).

As soon as signs of stiffness after a recent injury are observed, tetanus should be considered.

An apparently insignificant wound can cause tetanus if it is deep and dirty, e.g. a prick from a hay fork.

Prognosis is extremely reserved : the rate of survival varies from 25 to 60 % when treated in a clinic.

Treatment is based on :

• Neutralizing the toxin through repeated administration of antitoxin serums ;
• Halting the production of toxins around the wound (cleaning and trimming…) ;
• Destroying the multiplying bacteria by repeatedly injecting antibiotics, usually penicillin ;
• Alleviating the symptoms (and therefore the effects of the toxin) by placing the horse in a calm, dark environment, away from any stimuli, and administering sedatives, analgesics, and muscle relaxing drugs.

Supportive treatment via a drip and/or via gastro-nasal tubing enables to provide fluids and nutrients.

Prevention is based on thorough cleaning and disinfecting of any wounds, and vaccination.

Hygiene

Throughly clean and disinfect any wounds (oxidant antisceptics), remove any foreign objects.

Vaccination

Tetanus is not one of the diseases subject to regulations and vaccination is not compulsary. However, due to the severity of the disease and the fact that the vaccine is effective and innocuous, vaccinating all horses from 3 months old onwards is strongly recommended. A lot of the vaccines available associate tetanus and equine influenza valencies.

Vaccination protocol

• First time vaccination
  • 2 injections one month apart;
  • Booster jab 12 months later.

The horse is protected as from 10 days after the second injection of the first time vaccination protocol.

• Booster jabs
  • Every one to three years depending on the vaccine used ;
  • An additional booster jab may be recommended following a wound ;
  • For brood mares, a booster during the last month of gestation will ensure that the foal receives antibodies in the colostrum ;
  • When the horses has any surgery, make sure the last booster was administered less than two years prior to the operation.

Anti toxin injections

Protection after an antitoxin injection is immediate, but only lasts a short time (around 3 weeks). Antitoxin injections should be administered in the following cases

• When a horse who is not up to date with the vaccination protocol is wounded ;
• For foals born to an unvaccinated mare, or to a mare who was not given a booster jab one month prior to foaling (the specific quantity of antibodies in the colostrum is uncertain in this case), an antitoxin administered at birth will prevent tetanus from being passed on to the foal from the umbilical cord.

Tetanus is not subject to any regulations regarding contagious diseases and no compulsary declaration needs to be established.