Tetanus Toxin
Dr. Mamta Meena1* and Dr. Om Prakash Meena2
1Assistant Professor Veterinary Pharmacology and Toxicology, Apollo college of Veterinary Medicine, Jaipur
2Assistant Professor Veterinary Medicine, Apollo college of Veterinary Medicine, Jaipur
Corresponding author: drmamtameena04@gmail.com
INTRODUCTION
Tetanus is a non-transmissible disease (often fatal) of humans and other animals with a worldwide occurrence. Tetanus toxin is highly potent neurotoxin. It is produced by Clostridium tetani, an environmental soilborne, 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 are round and terminal, giving a characteristic shape usually termed “drumstick.” Spore formation is variable according to the strain. 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.
Clostridiun tetani live and survive for many years in soil and manure. This means that grazing animals such as sheep and cattle are at risk of tetanus, especially following wounds resulting from standard management practices such as castration and dehorning, calving, nail punctures, stake wounds and wounds inflicted at shearing are also potential risks as is the use of rubber ligatures for tail-docking, which can provide suitable sites for the growth of the organism. The disease is seen in stock of all ages. 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 an outbreak 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.
TOXICITY
- tetani produces two main toxins, neurotoxin (tetanospasmin) and hemolysin (tetanolysin). The others are tetanolepsin and nonspasmogenic toxins. The role of tetanolepsin in the pathogenesis of tetanus is not clinically significant. The toxins are absorbed by the motor nerves and transport to the CNS occurs retrograde within nerves and viathe bloodstream. The toxins bind to gangliosides in the brain stem or spinal cord. It blocks inhibitory synaptic input, especially at glycine mediated sites, by binding to the presynaptic membrane and blocking the release of glycine , resulting in spastic paralysis. It may also inhibit release of GABA and other amino acid neurotransmitters. Tetanus toxin may also cause paralysis by inhibiting the release of acetylcholine at neuromuscular junctions. Constant muscular spasticity may be produced and normally innocuous stimuli cause exaggerated responses. Death occurs as a result of rigidity of the muscles of respiration and associated asphyxia.
https://www.pashudhanpraharee.com/tetanus-in-livestock-prevention-treatment/
Susceptible species
Although all species of domestic animals are susceptible to tetanus, most cases appear to occur in the horse. Horses are the domestic species most sensitive to tetanus toxin. Pigs, cattle and sheep are less sensitive and dogs and cats are fairly resistant but are sometimes affected. Young animals like piglets and lambs are more susceptible to toxin than adult animals. Humans are also susceptible to tetanus toxin.
Poultry are relatively resistant to the toxin. Generally, tetanus occurs in individual animals although outbreaks have been described in cattle, young pigs and lambs.
CLINICAL SIGNS
Tetany, the predominant clinical sign of tetanus, is characterized by sustained tonic contractions of muscle without twitching. Other signs include hyperesthesia and convulsions with eventual rigidity of the muscles of respiration, asphyxia, and death. Clinical signs may include a sawhorse stance, protrusion of the third eyelid, opisthotonus, stiff gait, hyperextension of all four limbs, rigidity of the generalized musculature, ‘sardonic grin’ and secondary postural effects which diminish defecation and urination. Rigidity with extension of the tail has been described for cats ‘pump-handle tail’.
In horses, spasms of the masseter muscles occur early in the disease and it results ‘lock jaw’ condition. If paralysis of laryngeal and pharyngeal musculature occurs, aspiration pneumonia may develop. Excitation or loud noises may elicit convulsions in hyperesthetic animals. Excess stimulation of sympathetic nervous system can occur with excess sweating, tachycardia, arrhythmias, vasoconstriction and colic. Complications occur due to continuous recumbency. As the dose of toxin is increased, paralysis can result. Localized tetanus involving only the muscle groups closest to the site of injury is relatively uncommon. Characteristic ‘saw horse’ stance of a dog with generalized tetanus showing stiff, outstretched tail and contracted facial musculature.
TREATMENT AND MANAGEMENT
- Tetanus antitoxin: Animals given appropriate preventative measures (toxoid and antitoxin) are at low risk of developing tetanus. Administration of tetanus antitoxin will not reverse the clinical signs. Tetanus toxoid is administered concurrently. So all susceptible animals should be immunized with tetanus toxoid, an alum precipitated, formalin treated toxin. Horses should receive 300,000 units 12 hourly for three injections. Pregnant mares should be vaccinated during the last 6 weeks of pregnancy.
- The wound should be located and meticulously debrided. IV antitoxin will reduce uptake of toxin by nerves. Local infiltration of wounds with antitoxin has been recommended.
- Parentral antibiotics Penicillin G and metronidazole are the antimicrobials of choice to treat infection but are ineffective against existing disease. Nonspecific treatment includes sedation and muscle relaxation, and supportive nursing care (feeding, maintaining hydration, and preventing soiling). A combination of chlorpromazine and phenobarbitone sodium may be used to control convulsions and hyperaesthetic reactions.
- Wound debridement and cleaning, antibiotic use, and injection of tetanus toxin immunoglobulin are recommended when a risk of tetanus is suspected. Injection of 10% magnesium sulphate solution was found to be effective. Tranquilizers and sedatives may be required.
- In neonates, good hygienic practices, notably disinfection of the umbilicus, are important in the prevention of tetanus. Surgical interventions (tail docking and castration) must be performed with sterilized materials and in appropriate conditions of hygiene.
- Keep the affected animals in dark and at quiet place. Provide adequate bedding to animals to avoid injury from convulsions.
- https://www.cdc.gov/tetanus/index.html
