Exam 1 - Equine Neurology: Bacterial & Toxic Diseases Flashcards
what is a common name for tetanus?
lock jaw
what is tetanus?
bacterial neurologic disease characterized by extensor muscle rigidity & death
what species is most susceptible to tetanus?
horses
what organism causes tetanus?
clostridium tetani
what is the etiology of tetanus?
common soil inhabitant & strict anaerobe
how does c. tetani commonly gain access to the horse’s body?
puncture wound
what is the pathogenesis of the tetanolysin toxin of tetanus?
damages tissues & creates an environment favorable for anaerobes & facilitates infection
what 2 toxins are produced/released by clostridium tetani?
tetanolysin & tetanospasm
what is the pathogenesis of the tetanospasm toxin in tetanus?
diffuses locally & via the bloodstream to peripheral nerve terminals throughout the body
travels retrograde up neurons
into CNS after 1-14 days
how does tetanospasm work?
binds irreversibly to pre-synaptic neurons blocking release of inhibitory transmitters causing spastic paralysis
when do clinical signs typically develop in tetanus infections?
usually 7-10 days after the wound but can be as short as 1 day or as long as 60 days
what are the main clinical signs of tetanus in the horse?
prolapsed 3rd eyelid, generalized whole body rigidity, saw horse stance, elevated tail, hypersensitivity
if an animal presents with a prolapsed eyelid, what 2 differentials immediately come to mind?
tetanus & HYPP
what is the saw horse stance characterized by?
ears held pricked up
paralysis of breathing muscles
stiff legged gait
tail held out & stiff
what are the advanced clinical signs associated with tetanus?
clonic-tonic spasms
severe muscle contractions - rhabdomyolysis
autonomic signs - tachycardia, sweating
recumbency & death
how is tetanus diagnosed?
clinical signs, history, & ruling out other diseases
in tetanus, when may you see a patient with a prolapsing nictitating membrane upon stimulation?
early in the course of the disease process
what are some differentials for tetanus?
myopathy
meningitis
rabies
HYPP
trauma
laminitis
colic
what are the 4 principles of treating tetanus?
- provide a safe, quiet environment
- eliminate organism & unbound toxin
- sedation & muscle relaxation
- general support
what should the environment be like for a tetanus patient?
large, well-bedded stall, padded if possible
minimize light, noise, & other stimuli
cotton in the ears
hang water & feed
how is tetanus eliminated from the body?
clean/debride wound
tetanus antitoxin into wound
penicillin
how are the exotoxins eliminated or inactivated in tetanus treatment?
use the antitoxin which bounds any residual unbound toxin
T/F: tetanus antitoxin can rarely cause acute hepatic necrosis (theiler’s disease)
true
what should be included in general support for a tetanus patient?
iv fluids, parenteral or enteral nutrition, & pain control
what is the prognosis for tetanus?
usually poor, fatality >75%
what are poor prognostic markers of a tetanus patient?
rapid onset/progression of clinical signs & absence of vaccination
how is tetanus prevented in the horse?
annual vaccine - tetanus toxoid
tetanus antitoxin for non-vaccinated horse with wound or foal from non-vaccinated mare & give toxoid concurrently
botulism affects what horses?
adults & foals
what is botulism called in foals?
shaker foal syndrome
what age of foals are typically affected by shaker foal syndrome?
foals 1-3 months old - can occur in outbreaks
what is the etiology of botulism?
clostridium botulinum
what is the mechanism of infection of botulism?
toxins are absorbed into circulation & neuroparalytic botulinum toxins reach presynaptic nerve terminals which blocks exocytosis of acetylcholine at the presynaptic membrane of the neuromuscular junction
how do horses get clostridium botulinum?
they ingest it or have wound contamination
how do horses get botulism from forage toxicity?
toxin is in the contaminated feed (decaying vegetable matter, decomposing animal, bird carcass)
hay/silage - anaerobic conditions, pH remains above 4.5
T/F: the presence of animal & bird carcasses in processed food materials is incriminating evidence for diagnosing botulism
true
how do foals get botulism?
toxicoinfectious form - associated with type b forms in inflammatory lesions such
-intestinal ingesta
-wounds
-gi ulcers
-liver abscesses
what are the common toxic forms of botulism in horses?
a, b, c, & d
T/F: clinical signs of botulism are acute in onset
true
what are common clinical signs of botulism in horses?
muscle tremors, slow eating, mydriasis (dilated pupil), poor muscle tone, depressed reflexes, weak tongue/eyelid tone, & urine & fecal retention
what are the clinical signs of shaker foal syndrome?
suckling foals tend to show repeated episodes of trembling just before becoming recumbent - rapidly progressive
what are the advanced clinical signs of botulism?
recumbency, dyspnea, cyanosis, & death
how is botulism diagnosed?
typically presumptive based on multiple cases of recumbency/tetra-paresis with evidence of appetence but oral/pharyngeal dysplasia
isolation from feed, patient feces, or wounds
what tests detect botulinum toxins?
ELISA, PCR, & mouse inoculation assays
what is paramount for success in botulism treatment?
nursing care!!!
hydration, nutrition, & metabolic support/status
what does the prognosis of botulism depend on?
amount of toxin affecting the animal & ability of specific antitoxin
what are poor prognostic markers of botulism?
inability to stand
lower survival rates for adult horses
T/F: survival rates for severely affected foals treated with polyvalent antiserum/intensive support can be as high as 50-90%
true
why is botulism a public safety risk?
humans are susceptible - especially infants
don’t take infants to site of outbreak
how is botulism prevented in foals?
vaccination of mares with clostridium botulinum type b toxoid twice in the last trimester of pregnancy
especially in areas where shaker foal syndrome is common
what is the best treatment for botulism for the toxins?
IV polyvalent botulism antitoxin
expensive & needs to be administered in the early stages of disease
why should tetracyclines & aminoglycosides be avoided when treating botulism?
potential exacerbation of neuromuscular blockade
what antibiotics should be given IV for a patient with botulism?
penicillin or metronidazole
when should oxygen be supplemented in a patient with botulism?
if PaO2 is low
T/F: some foals with shaker foal syndrome require mechanical ventilation
true
T/F: the survival rate for adult horses with botulism is higher than foals with botulism
false - adults have lower survival rates
what happens to your botulism patient’s prognosis if you don’t have the specific antitoxin on hand?
prognosis is POOR
