Tetanus:

Syn: Locked Jaw, Saw-horse stance

• It is an acute, non-febrile, infectious disease of mammals caused by bacterial toxins.
• It is characterized by spasmodic contraction of skeletal muscles, death due to respiratory arrest or convulsion.

Etiology:

• Clostridium tetani
• Organism is long, slender, rod shaped anaerobe with rounded ends
• Size; 2×0.5 µm
• Organism develops terminal spores which gives it drumstick appearance.
• Gram+ve, motile, spore forming bacteria
• Spores are resistant to heat, drying and remain in soil for years.
• Spores can be destroyed by boiling at 115°C for 30-60 minutes.

Epidemiology:

• Organism is more common in tropics than in temperate zones.
• It is sporadic disease in Nepal, India
• Organism produce three types of toxin; tetanospasmin (neurotoxin), tetanolysin (haemolysin) and fibrinolysin.
• Horses and mules are most susceptible to tetanus followed by sheep, goat, pigs. Cattle are less susceptible.
• Birds are resistant to tetanus due to their high body temperature, high metabolic rate.
• Morbidity is very low 1-2% while mortality is high; 80% if left untreated in affected animals.

Transmission:

• Through contaminated soil, animal manure
• Organism gains entry through deep punctured wound
• During parturition, manual handling of genitalia with contaminated hand
• Through ROP and prolapse if exposed to contaminated soil
• Through castration by open methods, shearing, docking
• Through contaminated umbilicus in case of neonates

Pathogenesis:

Clinical Signs:

Horse:

• Stiff gait and apathy to feed is initial sign of the disease.
• Characteristic “saw-horse stance” develops.
• Prolapse of third eyelid
• Erection of ears, immobility of ears
• Horse stands with its feet widely apart and its head and neck in an extension position.
• Rigidity of facial muscles gives an anxious appearance.
• Spasm of masseter muscle leads to trismus (lock jaw).
• Mouth is held tightly closed and separation of jaw is hardly possible.
• There is restriction of mastication and dribbling of saliva from mouth.
• Animal remains hypersensitive. Light noise, air current, aggravate the spasm of muscles.
• Violent trembling may occur sometimes due to hypersensitivity.
• Profuse sweating all over the body
• In acute case, temperature and pulse rate may be elevated but sub-acute case will show normal level.
• Finally, horse is unable to stand and dies due to asphyxia within 3-10 days.

Cattle and Buffalo:

• Initial signs include restricted movement, muscular stiffness and difficulty in walk.
• Fall in milk yield
• Lock jaw and hypersensitivity on little stimuli
• Prolapse of third eyelid
• Pump handle position of tail
• Finally, lateral recumbency supervenes along with extensor rigidity and opisthotonus
• Rumen may appear like drum.
• Cow dies due to asphyxiation.

Sheep and goat:

• Dullness
• Head drawn on one side or backward
• Opisthotonus
• Hypersensitivity to noise
• Tonic contraction of masseter muscle.
• Death occurs due to asphyxiation.

PM Findings:

• Lesion is not characteristic.
• There is setting up of early rigor mortis.
• Congestion in spinal cord, medulla and nerves.
• Lungs remain hyperemic.
• Hemorrhages in skeletal muscles, loss of cross striations and atrophy of myofibrils.

Diagnosis:

• Clinical signs are so suggestive, it is hardly difficult to diagnose.
• Identification of bacteria through gram staining.
• Inoculation of mice with cultured materials from wounds and produce signs of tetanus in unprotected mice.
• In lab, organism may can be cultivated by anaerobic method in meat broth or blood agar.
• Serum antitoxin antibody levels can be measured.
• Elevation of CPK levels in serum in acute cases.
• Thoracic radiography in small animal reveal aspiration pneumonia.

Differential Diagnosis:

1. Strychnine poisoning:

• History of access to drug or malicious act
• Absence of wound
• Tetany is not marked

2. Grass tetany:

• History of grazing pasture
• Absence of tetany
• Tetany and convulsion are more severe than tetanus
• Absence of prolapse of third eyelid
• Respond to magnesium therapy

3. Milk fever:

• History of parturition
• Sternal or lateral recumbency
• Low calcium level
• Absence of wound
• Response to calcium therapy

4. Rabies:

• History of dog bite
• Changed behavior, salivation, biting tendency
• Ascending paralysis

5. Seizure:

• Signs of constant seizure
• No signs of wound
• Response to anticonvulsant therapy

Treatment:

Principle of treatment lies in:

1. Neutralization of toxin
2. Destruction of organism
3. Relaxation of muscles
4. Supportive care

a. Neutralization of toxin:

• Antitoxin therapy is indicated to neutralize toxin. Antitoxin ranging from 3000-7000 IU may be used at 12-hour interval.
• The TAT dose may be mixed with saline and administered through IV drip method slowly over a period of 30 minutes or so.
• There is no specific dose for domestic animals. Suggestive dosage ranges from 1000-5000 IU/500kg animal to 1000-5000 IU/kg as single SC dosage.

b. Destruction of organism:

• Antibiotic therapy is indicated to eliminate vegetative form of tetanus and further elaboration of toxin.
• Penicillin G is drug of choice.
• It is given @ 22,000 IU/kg, b.wt. TID-QID through IV or IM.
• Procaine penicillin in similar dose may be given IM, BID.
• Debridement of necrotic tissues surgically is to be made. Penicillin G may be infiltrated at sites following debridement.
• Topical hydrogen peroxide may be infiltrated to prevent bacterial growth.
• In order to increase tissue oxygen level and to inactivate bacterium, hyperbaric oxygen therapy has been suggested.

c. Relaxation of muscles:

• Affected animal should be placed in dark place and sedated.
• Chlorpromazine@ 0.4 mg/kg, b.wt. or promazine @0.03mg/lb, b.wt.
• 5% sodium pentobarbital @ 2-4ml/50kg IV may be administered.
• Diazepam @0.01-0.4mg/kg, b.wt. through IV route has been suggested.
• Affected animals may be immunized with TT at time of treatment and second dose may be given at 1-2 months apart to establish active antitoxic immunity.

d. Supportive care:

• Bloat should be relieved through rumenotomy.
• Enema and catheter passing may be required for passing of feces and urine.
• Temperature, pulse and respiration should be monitored daily.
• Animals should be provided with good bedding. They should be made to stand through supported sling.

Control Measures:

• Proper care should be taken to handle the ROP and prolapsed case.
• Sterile surgical instruments are to be used at time of operation.
• Wound should be drained with deep incision. Animal should be kept away from metallic and sharp objects.
• Animal should not be allowed to graze near barbed wire fencing.
• All out precautions should be taken during castration.
• Open method of castration should be discouraged in the village level through motivation.
• Vaccines may be used. Injection of anti-toxin @ 1500-3000 IU for horse.
• For active immunization toxoid (anatoxin) can be used. Two doses are given at 6-8 weeks apart through IM route. Dose-10 ml for horse and 1-2 ml for cattle.