Reptiles Flashcards
what is envenomation?
injection of poisonous material by sting, spine, bite or other means
venomous reptiles come from what order?
squamata - includes lizards and snakes
where are venemous lizards found? what genus do they belong to?
north and central america, belong to Heloderma genus
what members of the venomous reptiles are represented in the western hemisphere?
members of the Crotalidae and Elapidae
H. suspectum and H. cinctum
Gila moneters, members of Heloderma
H. horridum
mexican beaded lizard
snakebites in companion animals
150k dogs and cats in north america annually
99% of snakebites come from what animals?
Crotalidae - pit vipers
why are dogs more likely to get a snake bite?
because of their inquisitive nature- come more in contact with them
Elipidae
Coral snakes
coral snakes
Elipidae
red touching black
safe for jack
the 2 genera of coral snakes are indigenous to where?
U.S
red touching yellow
kill a fellow
what 2 genera of coral snakes Elipidae are indigenous to the US?
Sonoran coral snake: Micururoides euryxanthus
Texas coral snake/eastern coral snake/south florida coral snake: Micurus fluvius
why are interactions between coral snakes and domestic animals less common than with pit vipers?
North American coral snakes tend to be shy, non-aggressive and nocturnal
Micuroroides Euryxanthus
Arizona coral snake/Sonoran coral snake
Micrurus Tener
Texas coral snake
Micrurus Fulvius
Eastern Coral snake
venom delivery of coral snakes
not very efficient- length of bite will determine deliverance
- short, fixed front fangs that are partially membrane covered
- 60% don’t result in venom deliver!
what amount of coral snake venom is lethal to a large dog?
1-2mg (4-5mg) is lethal in humans
how much venom does a large coral snake contain?
20mg of venom: but size of snake correlates to the amount of venom
PK/TK of coral snake venom
- uptake delayed by hours
- onset of neuro signs is delayed- 12+ hrs
- binds irreversibly
- can take 14 days to clear body!
coral venom PK in cats
in envenomated cats, clinical improvement began at 36 hours, recovery of limb motion after 48 hours
MOA of coral snake venom
neurotoxic! with not much swelling
- several neurotoxins involved, nondepolarizing neuro-muscular blockers. net effect is a “curare-like” syndrome (Flaccid paralysis)
clinical signs of coral snake venom
neurotoxic with little tissue reaction or pain at bite site
CNS depression, muscle paralysis, vasomotor instability, emesis, salivation, decreased spinal reflexes
maybe: intravascular hemolysis, anemia, hemoglobinuria, altered RBC
coral snake venom in dogs
hemolysis with severe anemia has been reported
clinical signs of coral snake venom in cats
acute ascending flaccid quadriplegia, CNS depression, reduced nociperception
- aniscoria, absent spinal reflexes, hypothermia have all been reported
you see a dog for a presumed snake bite. the dog presents with excessive salivation, quadriplegia and CNS depression. there is little swelling at the bite site. what is your suspicion?
coral snake bite
what was the only definitive treatment for coral snake bites?
Antivenin (Wyeth labs)- has been discontinued
how do you treat coral snake toxicity?
- adequate supportive care!!
- compression bandage around and over bite site
- clinical signs may be delayed by 12 hrs! patient should be hospitalized for min of 24 hrs
- be prepared to respond to respiratory collapse, dysphagia, aspiration pneumonia: ventilatory support!!
- broad spectrum abx are generally recommended
why should coral snake bite pts be hospitalized for a minimum of 24 hours?
because clinical signs may not happen until 12 hrs after
what meds can you give a coral snake bite patient?
broad-spectrum abx
may need respiratory/ventilatory support
what is a possible anivenin treatment for coral snake
Coralmyn: new, made in Mexico, lyophilized antivenom of polyclonal abs from horses immunized with black banded coral snake venom. available for vetmed with USDA import permit
coral snake envenomation
- rare: 1% of all snake bites
- venom delivery is only 40%
- dogs most likely recipients
- neuro effects and “curare-like” paralysis
- onset of effects are delayed and long-lasting
- supportive txt, prognosis fairly good
- major complication is aspiration pneumonia :(
Crotalidae
pit vipers
what genera do pit vipers (Crotalidae) belong to?
- Crotalus: rattlesnakes
- Sisturus: pygmy rattlesnakes and massasauga
- Agkistrodon: water moccasins/cottonmouths/copperheads
where are pit vipers found?
every state in the US except for Hawaii, Maine and Alaska
most pit viper bites are inflicted by what snakes?
copperheads- Agkistrodon- live thruout Southeastern US
99% of snakebites to animals in North America are by what species
pit vipers
pit viper envenomation
- very efficient- strike super fast
- venom given by rotating front fangs downward and stabbing forward
- muscle contraction of venom glands delivers venom thru fangs
what is a “dry” bite?
no venom delivered: 25% of time. defensive bites are more often dry, offensive bites deliver a controlled amount of venom
what are agonal bites?
pit viper bite that delivers the entire venom load- most dangerous!
severity of a pit viper bite is related to
volume and toxicity of venom, as well as location
toxicity of venom is most severe in what pit vipers? (descending order)
rattlesnake > water moccasin > copperhead
toxicity of rattlesnake venom varies widely
____________ will dictate uptake of poison into systemic circulation
location of the bite- also based on perfusion of that tissue region
PK/TK of pit viper venom
- may take weeks for venom to be cleared
- response depends on snake, volume of venom, species of recipient
MOA of pit viper venom
- NOT to kill but to immobilize and pre-digest tissues
- mixture of enzymatic and nonenzymatic proteins
- minimum of 10 enzymes in a specific venom
- 3-12 nonenzymatic protein/peptides in a specific venom: nonenzymatic fractions are the killing fraction and are 50x more potent
what comprises pit viper venom?
complete mixture of enzymatic and nonenzymatic proteins
- minimum of 10 enzymes in a specific venom
- 3-12 nonenzymatic protein or peptides in a specific venom
- nonenzymatic fractions are the killing ones! 50x more potent
what are the 3 types of rattlesnake venom in North American snakes?
- Classic diamondback venom
- Mojave A rattlesnake venom
- Intergrade - multiple species
classic diamondback rattlesnake venom
causes markred tissue destruction, coagulopathy, hypotension
mojave A rattlesnake venom
no tissue destruction or coagulation but induces severe neurotoxicosis: more potent
intergrade venom in multiple species
contains both neurotoxins and classic venom components
clinical signs of pit viper toxicity
- initially see marked regional swelling: ecchymosis/petechiation
- swelling and heavy haircoat could obscure wounds!
- local tissue response doesn’t always = severity
- delayed onset of clinical signs
- marked hypotension develops early
- progressive swelling up to 36 hrs
what clinical sign of pit viper envenomation develops early?
marked hypotension
additional clinical signs of pit viper envenomation
tachycardia, shallow respirations, lethargy, nausea, obtundation, muscle fasciculations, increased salivation, painful lymph nodes
where are dogs typically bitten? what kind of bite?
head or front legs
- usually a defensive strike
- seek humans right after, thus bite presents early
where are cats typically bitten? what kind of bite?
- cats often bitten in torso
- usually an offensive strike in response to “playing”
- presents later due to hiding
where are horses usually bitten?
nose, marked tissue necrosis is possible
clinical pathology of pit viper venom
- baseline blood counts and serum chemistries: repeat at 6, 12, 24 hrs
- early high levels of Creatine Phosphokinase can indicate severe envenomation: marker of tissue/muscle damage
- coagualation parameters should be monitored
- urinalysis: hematuria or rhabdomyolysis
where are cattle often bitten?
muzzle or tongue
tissue necrosis and secondary infection can be an issue due to later ID of envenomation
what diagnostic test is often indicative of pit viper envenomation?
evidence of echinocytosis on a non-EDTA blood smear or one drop of blood mixed with a drop of saline
- caused by phospholipases in venom that alter membrane structure of RBCs
treatment of pit viper envenomation
- keep calm, bitten area should be below heart level if possible
- circumferential measurements above, below and at bite site monitored at least 6 hours
- severity score to monitor severity
- IV crystalloid fluid therapy started
- broad-spectrum abx in species susceptible to clostridial infx
- diphenhydramine to calm animals and allergic reactions
what medical txts can be used for pit viper envenomation?
- antivenin! CroFab single vial
- IV crystalloid therapy: combats hypovolemic crisis
- broad-spectrum abx
- diphenhydramine to calm and forllergic rxns
what is the primary cause of death from pit viper envenomation? what txt helps combat this?
cardiovascular collapse from hypovolemic shock: IV crystalloid therapy helps combat!
severity score of pit viper envenomations
- pulmonary system
- cardio system
- local wound
- GI system
- hematologic system
- CNS
total possible score: 0-20
what is the only proven treatment for pit viper venom?
IV antivenin! CroFab: Equine origin. typical dose is a single vial, epi should be ready to treat anaphylactic events, diphenhydramine can also be used
antivenin is approved for treatment of what snake envenomation?
pit viper! stops swelling, reverses coagulopathy, thrombocytopenia, improves muscle strength
vaccine for venom?
rattlesnake one is being developed- western diamondback rattlesnake, but is not preventive. does enhance recovery tho! not recommended tho
prognosis of pit viper envenomation
with early medical intervention, most survive
large animals often survive initial effect, but are at risk of death from tissue damage and infection because of delayed recognition
venemous lizards?
only ones in north and central america are members of genus Heloderma
mexican beaded lizard
Heloderma horridum
gila monster
Heloderma suspectum
lizard envenomation?
- do not inject- released from venom glands on lower jaw, flows up teeth thru capillary action
- degree of envenomation is related to duration of bite
- lizard sometimes still hangs on to patient!
venom is for defensive purposes only
MOA of lizard venom
mix of biologically active proteins- no neurotoxins and don’t affect coagulation
clinical signs of lizard venom
- extreme pain at bite site- ouchhh
- significant bleeding from teeth that break off into wound
- edema around wound
- hypotension/tachycardia w resultant weakness
- regional muscle fasciculations
what does lizard venom NOT cause?
tissue necrosis! but secondary infection can be a sequela esp if tooth fragments are embedded
feline lizard victims clinical signs
tachypnea, tachycardia, vomiting- likely as result of pain
treatment of lizard venom
- pry lizard off!
- hospitalize and monitor
- no specific antivenin available
- txt is supportive; IVF, narcotics/fentanyl for pain, lidocaine for wound and check for lizard teeth
- broad spectrum abx for secondary infx
prognosis of lizard envenomation
good, single largest predictor is duration of bite. longer bite = more venom delivered
- patients w cardiac or pulmonary conditions are at greater risk
- federally protected- don’t let pets bother them!
