Tetanus (Lockjaw) in Animals

Tetanus (Lockjaw) in animals is a non contagious, non-febrile, infectious disease of mammals affected by toxins released by Clostridium tetani. It is characterized by spasmodic contractions of skeletal muscles.

Etiology

Clostridium tetani is a gram positive, a long, slender, rod shaped anaerobe with rounded ends. The organism develops terminal spores and has a drumstic appearance. It lives in the intestine of herbivores as a normal inhabitant.

The organism grows mainly under strict anaerobic condition. Spores are resistant and persists in soil for many years.

The organism releases three types of toxins under anaerobic condition:

• Tetanospasmin
• Tetanolysin
• Fibrinolysin

Epidemiology

Prevalence of infection

• The disease is more common in tropical countries than in temperate.
• It is a sporadic disease in India.
• Case fatality rate in young cattle may be over 80%.
• Mortality rate may be 50% in animals die of acute infection.

Predisposing factors

• Infected nature of soil, climatic conditions and environment influences the infection.
• Wound or break in the skin, and accidental injury.
• Shearing, docking, parturition period, favors the infection.
• Sources of infection
• Infected soil, discharges and environment.

Transmission

• The organism present in soil gain access into animals during parturition, shearing, docking, castration, spaying and any other unprotected surgical and accidental injury.
• Spread can also occurs through ingestion.
• Host affected Farm animals are probably most affected.
• Horses and mules are highly susceptible.
• Cattle are relatively less susceptible than man and horses.
• Sheep, goats and  pigs are more susceptible compared to cattle.

Pathogenesis

The organism enter through any broken skin or injury does not cause tetanus. For the tetanus to develops need some favourable conditions such as; Access of spores in to body tissues.

Tissue damage caues localized impairment in blood supply oxygen creates anaerobic condition.

Anaerobiosis leads to germination of spores. Following germination of spores vegetative growth occurs rapidly and releases toxins; tenospasmin, (neurotoxin), tetanolysin (haemolysin), and fibrinolysin (muscle and tissue cell lysis).

All these toxins are released by cellular autolysis and get absorbed from site of production and spread into blood stream, exert neuro-toxic effect in peripheral nervous system by retrograde intra axonal transport, via motor nerves to central nervous system via brain and spinal cord, along the nerve route. Among these toxins tetanospasmin is considered very important and potent toxin.

Through axonal terminal and intra axonal transport mechanism the toxin gain the central nervous system. From the CNS toxins reaches dendrites and transferred to neurons that synops with cells. Generally, toxin can not cross the blood brain barrier. The released toxin bind with a “protogon”, which is made of cerebrocide and oligosaccharides like N-Acetyl galactosamine and galactose. The toxin acting on the inhibitory synapses interfere with action of the inhibitory transmitter thus cause hyperirritability and there by leads to spasm. As the toxins enter the blood stream causes spastic paralysis, and invasion into nerve endings develops flaccid paralysis.

Death usually occurs due to asphyxiation as a result of fixation of respiratory muscles. Mortality in horse is 50% and cattle 80%.

Clinical Signs

Horses

• Initially affected animals are very hypersensitive to the external stimuli.
• Inability to open the mouth.
• Animals continue to be with spasm for several days with mild muscle spasm.
• Saw horse stance, prolapse of the third eye lid, erection of ears, immobility of the ears seen as predominant signs.
• Head, neck, and leg are in extended position.
• Spasm of facial muscle, masseter muscle leads to trismus.
• Mastication impairment, drooling of saliva because of spasm and swallowing difficulty.
• Very sensitive to light and noise.
• Trembling and profuse sweating.
• At the end, affected animals unable to stand and die due to asphyxia in 3-10 days.

Cattle and Buffaloes

• Affected animals exhibits mild problems and identified at the initial level recover from the infection.
• Affected animals restrict its movement, exhibits muscle stiffness, difficulty in walking and decrease milk yield.
• Lock Jaw, hyper irritability, prolapse of the 3rd eyelid, pump handled position of the tail are more common and unique sign of tetanus in these cattle.
• Lateral recumbency, extend rigidity and opisthotonus.
• Suspension of rumination, drum like appearance of the rumen and left abomasal displacement Animal dies due to asphyxiation. Sheep and goats
• Dullness, head is drawn on one side or backward, opisthotonus, hypersensitivity to noise and bending of neck.
• Kids and lambs fail to suck milk due to tonic contraction of masseter muscle.
• Death occurs by asphyxiation.

Dogs

• Localised Rigidity of one leg, hypersensitivity, erection of ears, wrinkling of forehead, hypertonicity, opisthotonus, masseter muscle spasm, caudal retraction of the lips.
• Generalized Clinical signs may be prominent in 10 days of infection.
• Dyspnoea, laryngeal spasms, mitosis and stiff gait.
• Out stretched tail, difficulty in rising or lying is the most common.
• Constipation, retention of urine due to spasm of the sphincter.
• Affected animals die of respiratory muscle failure, muscle spasm, laryngeal dysphagia, decrease secretion from respiratory tract and death occurs in 5 days.

Human

• Rigidity of muscles, painful paroxysmal spasms of voluntary muscles, (masseter), the facial muscle paralysis and the muscles of back.

Necropsy Findings

• Rigor mortis develop very quickly.
• Congestion of spinal cord, medulla.
• Hyperaemia of lungs due to asphyxia.
• Skeletal muscles reveal haemorrhages, loss of cross striation and atrophy of the myofibrils.

Diagnosis

• Based on clinical signs and necropsy findings.
• Biological Inoculation: Challenging of mice, rabbit and guinea pig with cultured C. tetani.
• Demonstration of toxin.
• In acute case elevation of serum creatinine Phosphokinase (CRK).

Differential Diagnosis

• Strychnine poisoning
• Grass tetany
• Milk fever
• Rabies
• Epilepsy

Differential Diagnosis

• Tetanus toxoid is used to inducing active immunity.
• Vaccination with tetanus toxoid is recommended for healthy domestic animals and human being as preventive measures.
• Pregnant animals can be vaccinated at the advance stage of pregnancy (cattle at seventh and eigth month, sheep and goats third and fourth month of pregnancy).
• Tetanus toxoid is adviced before all surgical operations like docking, shearing and castration.
• Dose: Tetanus toxoid – 0.5ml s/c.

Control

• All surgical operations should be carried out aseptically in a hygienic area.
• Spores are resistant to many disinfectants but can be destroyed by 115◦C for 20-60 minutes.
• Vegetative form can be destroyed by heat and disinfectants but spores are not.