VPT 421: Veterinary Toxicology (2+0)

TETANUS

• Tetanus toxin is produced by Clostridium tetani, a gram-positive, spore-forming bacillus under anaerobic conditions.
• C. tetani spores are also commonly present in the faeces of domestic animals, especially those of horses, and in soil contaminated by faeces.
• C. tetani spores may persist in soil for many years and are resistant to many standard disinfection processes, including steam heat (100º C for 15 minutes).
• Poisoning is known to result from clostridial growth in contaminated wounds in which anaerobic conditions predominate.
• The usual incubation period is 1 - 3 weeks.
• It is possible for the original point of entry to heal without any evidence of infection and for subsequent trauma, even months later to set up the necessary environment for clostridial growth and toxin production.
• Animals given appropriate preventative measures (toxoid and antitoxin) are at low risk of developing tetanus.
• The usual portal of entry in horses is deep puncture wounds.
• Clinical toxicosis is most likely when there is sufficient accompanying tissue damage to result in an anaerobic environment favorable for clostridial growth.
• Umbilical infections also occur in foals that receive no maternal immunity.
• The usual portal of entry in cattle is via the reproductive tract at parturition.
• Outbreaks of tetanus in cattle have suggested that the toxin may have been produced in the gut or ingested preformed in the feed.
• Grazing of rough, fibrous feeds before such outbreaks is a common factor in the history, and it is possible that infection may have begun via wounds in the oral cavity.
• Castrating and dehorning with elastic bands can also result in clostridial infection.
• In pigs, castration wounds are the most common point of infection.
• In lambs and adult sheep, infection is most often associated with castration, docking or shearing.
• Docking with elastic bands is one of the most common causes of tetanus in lambs