Tetanus in Domestic Species

Question 1

what is the causative agent of tetanus

Answer 1

clostridium tetani

Question 2

what type of bacteria is clostridial tetani

Answer 2

anaerobic bacterium

Question 3

how does clostridial tetani survive in the environment

Answer 3

spores in the soil

found in human and horse feces

Question 4

how does clostridium tetani infection come about

Answer 4

Organism invades wounds, changing from vegetative to replicative state in anaerobic environment

Question 5

what exotoxins are produced from clostridium tetani

Answer 5

Tetanolysin

Tetanospasmin

Question 6

what does tetanolysin do

Answer 6

Damages viable tissue, promoting anaerobic environment for bacterial growth

Question 7

what does tetanospasm do

Answer 7

Enters circulation, binds to receptors on motor nerve endings

Spastic paralysis

Question 8

what is the pathogenesis of tetanus

Answer 8

deep puncture wounds most important

toxin produced and onset of clinical signs may occur several days after deep wound or entry point

Question 9

what are entry points of clostridium tetani

Answer 9

Umbilical artery

Foot abscess

Injection site abscess

Wound

Post surgical entry and multiplication

Question 10

what is the pathogenesis of tetanospasmin

Answer 10

Transmission from infection site

Diffuses to muscles from infection

Spreads via lymphatics to blood

Binds receptors on motor end plates

Fragment of toxin internalized and moved along neutron by retrograde axonal transport to CNS

Pre-synaptic endocytosis

TeNT is 2,000 times more toxic at central inhibitory nerves than at peripheral synapses

Question 11

what is the mechanism of action of tetanospasmin

Answer 11

Binds pre-synaptic receptor

Entire toxin endocytosed in CNS

Damage to synaptobrevin protein

Inhibition of release of GABA at synaptic cleft as synaptic vesicle fusion inhibited

Spinal cord, brain stem, peripheral nerves, neuromuscular junctions, muscles all affected

• Constant excitation of motor neurones
• Hyperreflexia, hypertonia, sympathetic excitability

Question 12

what is the half life of the toxins produced

Answer 12

5-6 days

Question 13

is the condition reversible

Answer 13

Neuronal binding of toxin is irreversible

Recovery requires growth of new nerve terminals

Prolonged disease course (6-8 weeks)

Antitoxin should be given as soon as possible for management

Question 14

what are the target species of clostridium tetani

Answer 14

Ubiquitous organism but requires skin to break for entry

Horses, goats, sheep, monkeys and cattle are more sensitive

Dogs are relatively resistant and cats are more resistant

Greatest susceptibility in equids?

Question 15

when is tetanus commonly seen in cattle

Answer 15

commonly seen after castration (open + closed)

increased risk with ringing techniques

hoof injuries, umbilical or puerperal infection

Question 16

what is the fatality rate of tetanus in cattle

Answer 16

~80% in young calves

higher in adult

Question 17

what are the clinical signs of tetanus in cattle

Answer 17

Generalized muscular rigidity and spasms

Hyperaesthesia

Third eyelid prolapse

Trismus (lockjaw)

Convulsions

Respiratory arrest and death

Opisthotonus

Bloated abdomen

No ruminal contractions

Fixed expression

Muscles of head are affected because cranial nerves are short, particularly CN V (trigeminal nerve)

Question 18

how is tetanus diagnosed

Answer 18

clinical signs

history

anxious expression, rigid ears

salivation due to lockjaw

may become unable to swallow

Question 19

what are the clinical signs of tetanus in dogs

Answer 19

Stiff gait

Facial muscles are contracted

Raised brows; anxious expression

Trismus

Ptyalism

May be concurrent wound

Question 20

how is tetanus diagnosed in dogs

Answer 20

Clinical signs

History

Question 21

what are the early clinical signs of tetanus in equids

Answer 21

May be unilateral/spastic gait in limb with pre-exisiting injury or foot abscess

Nictitating third eyelid *

• Characteristic

Muscle hypertonia

• Slapping of legs as horse walks forward
• Hindlimb spastic paresis

Inability to lower head fully

Slow mastication and swallowing

Pyrexia

Hyperaesthesia

• Not many other conditions
• Sensitive to bright light, loud noises

Question 22

what are the progression of clinical signs in tetnaus in horses

Answer 22

Fixed dilated nostrils and permeant protrusion of the third eyelid

• Rigidly uptight ears
• Increasingly shuffling gait in all limbs

Wide based stance

Complete trismus and ptyalism

Inability to raise relax anal sphincter results in impactions and colic

May fall over spontaneously; respiratory muscles compromise

Variable hyperaesthesia

Question 23

what are the principle ddx for tetnus in equids

Answer 23

rhabdomyolysis

myotonia (QHs)

laminitis

electrolyte disturbances

• Hypomagnesemia
• Hypocalcemia
• HYPP (QHs)
• Hypernatremia

Seizures

Meningitis

Strychnine toxicity

Question 24

how is a tetanus diagnosis confirmed

Answer 24

Diagnosis by exclusion of other ddx

Clinical signs

Poor vaccination history

Elimination of metabolic causes

Attempt to localize lesions

Perform specific tests for hypertonia and nictation

Question 25

what is the prognosis for tetanus

Answer 25

Rate of onset/deterioration in clinical signs is correlated to prognosis

Inability to support weight and balance at rest = poorer prognosis

Unable to stand once fallen

Complete inability to eat or drink requires more intensive nursing, greater costs and also poorer prognosis

5-6 weeks for new vesicles to generate

Question 26

what is the decision tree for tetanus treatment

Answer 26

Mild clinical signs:

• Nictitans membrane flashing, ears pulled caudally, slightly stiff gait but still walking and eating

​Moderate clinical signs:

• Nictitans membrane flashing, ears pulled caudally, limbs stiff and walking with difficulty, trismus and generalized muscle spasm

Severe clinical signs:

• Capable of standing, but incapable of walking, severe trismus
• Difficulty with prehension, chewing and swallowing

Terminal clinical signs:

• Animal recumbant
• Incapable of standing
• Incapable of eating

Question 27

what are the treatment goals of tetanus

Answer 27

Debride and lavage any pre-existing wound to remove anaerobic environment and bacteria

• Includes searching for foot abscesses

Stop further absorption of tetanospasmin

Provision of dark, quite stable —> decrease stimuli

Sedation

Antibiotic therapy to eliminate bacterial challenge if not historical

Maintenance rate IV fluid therapy may be required if unable to swallow (50 ml/kg/day)

Enteral nutrition if unable to swallow

Monitor urinary and fecal output

Indwelling catheter may be needed and manual fecal removal

Sling to partially support body mass

Smaller patients easier to manage if recumbent

Question 28

how would you sedate a horse being treated for tetanus

Answer 28

Acepromazine 0.05 mg/kg IM QID

Diazepam 0.1 mg/kg IM q4-6h

Question 29

what antibiotic therapy would you use to treat a horse with tetanus

Answer 29

Metronidazole 15 mg/lg IV perffered

Or penicillin G at 20,000 IU/kg QID

Question 30

how is tetanus prevented

Answer 30

Tetanus toxoid vaccination extremely effective

Dose 1 at ~4 months with dose 2 after 4 weeks

Booster dose at 1 year

good antibody levels after 3 years

Antitoxin 1500 IU might be indicated before high risk procedures if not vaccinated — provides 10-14 day protection

Boost pregnant mare at 6-12 weeks before parturition date so as to increase colostral antibody levels to tetanus

Question 31

what should you do if there is a wound on an unvaccinated horse

Answer 31

Lavage wound thoroughly to remove all organic material

Drain foot abscess with hoof knife then soak

Administer tetanus anti-toxin SC locally

Start course of tetanus toxoid IM at same time

Remember to give second part of primary course after 4 weeks

Record in passport

Boost after 12 months

Immunopurified tetanus toxoid absorbed to aluminium phosphate

Question 32

what is the equine tetanus vaccination schedule

Answer 32

Primary course:

• Single IM dose from 3 months of age with second dose after 4-6 weeks and third 1 year after that

Foals born to highly vaccinated mares should not be vaccinated until 6 months of age due to interference from maternally derived antibodies

Thereafter bi-annual vaccination

Foal born to unvaccinated dam

Tetanus anti-toxin

Umbilical care

Tetanus toxoid start at 3 months