Tetanus in Domestic Species Flashcards
what is the causative agent of tetanus
clostridium tetani
what type of bacteria is clostridial tetani
anaerobic bacterium
how does clostridial tetani survive in the environment
spores in the soil
found in human and horse feces
how does clostridium tetani infection come about
Organism invades wounds, changing from vegetative to replicative state in anaerobic environment
what exotoxins are produced from clostridium tetani
Tetanolysin
Tetanospasmin
what does tetanolysin do
Damages viable tissue, promoting anaerobic environment for bacterial growth
what does tetanospasm do
Enters circulation, binds to receptors on motor nerve endings
Spastic paralysis
what is the pathogenesis of tetanus
deep puncture wounds most important
toxin produced and onset of clinical signs may occur several days after deep wound or entry point
what are entry points of clostridium tetani
Umbilical artery
Foot abscess
Injection site abscess
Wound
Post surgical entry and multiplication
what is the pathogenesis of tetanospasmin
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
what is the mechanism of action of tetanospasmin
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
what is the half life of the toxins produced
5-6 days
is the condition reversible
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
what are the target species of clostridium tetani
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?
when is tetanus commonly seen in cattle
commonly seen after castration (open + closed)
increased risk with ringing techniques
hoof injuries, umbilical or puerperal infection
what is the fatality rate of tetanus in cattle
~80% in young calves
higher in adult
what are the clinical signs of tetanus in cattle
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)
how is tetanus diagnosed
clinical signs
history
anxious expression, rigid ears
salivation due to lockjaw
may become unable to swallow
what are the clinical signs of tetanus in dogs
Stiff gait
Facial muscles are contracted
Raised brows; anxious expression
Trismus
Ptyalism
May be concurrent wound
how is tetanus diagnosed in dogs
Clinical signs
History
what are the early clinical signs of tetanus in equids
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
what are the progression of clinical signs in tetnaus in horses
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
what are the principle ddx for tetnus in equids
rhabdomyolysis
myotonia (QHs)
laminitis
electrolyte disturbances
- Hypomagnesemia
- Hypocalcemia
- HYPP (QHs)
- Hypernatremia
Seizures
Meningitis
Strychnine toxicity
how is a tetanus diagnosis confirmed
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
what is the prognosis for tetanus
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
what is the decision tree for tetanus treatment
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
what are the treatment goals of tetanus
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
how would you sedate a horse being treated for tetanus
Acepromazine 0.05 mg/kg IM QID
Diazepam 0.1 mg/kg IM q4-6h
what antibiotic therapy would you use to treat a horse with tetanus
Metronidazole 15 mg/lg IV perffered
Or penicillin G at 20,000 IU/kg QID
how is tetanus prevented
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
what should you do if there is a wound on an unvaccinated horse
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
what is the equine tetanus vaccination schedule
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
