Envenomation

Question 1

What are the toxins of Elapid snake

Answer 1

• Neurotoxins (presynaptic = phospholipase A2 preventing release of Ach / post-synaptic = antagonists of Act receptor)
• Hemolytic toxins
• Hemostasis toxins
• Cytotoxins

Question 2

What tick species are involved in tick paralysis

Answer 2

• Dermacentor variabilis / Dermacentor andersoni in the US
• Ixodes holocylus in Australia

Question 3

What is the action of the toxin responsible for tick paralysis

Answer 3

• Inhibits depolarization in the distal segments of motor neurons
• Blocks the release of Ach at the neuromuscular junction

Question 4

Name some enzymes contained in crotalinae snake venom

Answer 4

• Hyaluronidase ->connective tissue breakdown
• Phospholipase A2 -> cytotoxicity (RBC) + anti-Xa activity
• Thromboxane -> thrombocytopenia
• Snake venom metalloproteinases -> platelet dysfunction

Question 5

What are the effects of crotalinae snake venom on coagulation factors / proteins

Answer 5

Pro-coagulant:
- Activators of factors II, V, X
- Thrombin-like enzymes

Anti-coagulant:
- Inhibitors of factors II, IX, X
- Activators of protein C
- Plasminogen activators
- Fibrinolytic enzymes

Question 6

Name one rattlesnake causing severe neurological signs

Answer 6

Mojave rattlesnake

Question 7

What RBC morphology abnormalities are expected in a patient with crotalinae snake envenomation

Answer 7

Echinocytosis, spherocytosis

Question 8

What are the Crotalinae antivenoms made of? What are the different types?

Answer 8

Immunoglobulin G against the different antigens

• Whole IgG antivenom: ACP = Antivenin (Crotalidae) Polyvalent, Rattler Antivenin
  -> also contains contaminants (albumin, globulins, IgM), higher risk of reaction
• Fab antivenom: CroFab (Fab1 ; monomer), Antivipmyn & VenomVet (F(ab’)2 ; dimer)
  -> less antigenic but faster clearance, formulation as a dimer increases half life + allows 2 antigen binding sites

Question 9

How to differentiate the venomous Eastern coral snake from the non-venomous Scarlet king snake

Answer 9

For the Eastern coral snake the red and yellow rings are adjacent (yellow - black - yellow - red - yellow - etc) vs. red and yellow are separated by black in Scarlet king snake

“Red on yellow kill a fellow, red on black, venom lack”

Question 10

What are the different toxins of Elapid venoms

Answer 10

• Neurotoxins -> presynaptic (phospholipase A2), post-synaptic (Ach receptor antagonists)
• Procoagulant toxins -> group C prothrombin activators (= analog of XaVa) or group D prothrombin activators (= analog of Xa, requires patient’s Va)
• Anticoagulant toxins -> phospholipase A2
• Myotoxins -> phospholipase A2
• Hemolytic toxins -> phospholipase
• Local acting cytotoxins (rare in North America / Australia)

(North American Coral snakes mainly cause severe paralysis and occasional hemolysis)

Question 11

When could FFP transfusion be indicated following snake envenomation

Answer 11

Not for Crotalinae snakes (mechanism of coagulopathy is not a factor deficiency and FFP can worsen thrombosis) ->should resolve with antivenoms

For Elapid snakes, only if coagulopathy is persistent after antivenom administration and causes life-threatening hemorrhage (more cases of coagulopathy can be due to factor consumption)

Question 12

Name some examples of Crotalinae snakes / Elapid snakes. Which ones are the most common in the US?

Answer 12

1. Crotalinae snakes
   - Rattlesnakes (Crotalus spp)
   - Copperheads and Water moccasins (Agkistrodon spp)
   - Pygmy rattlesnakes and Massasaugas (Sistrurus spp)
2. Elapid snakes
   - Coral snakes (Micruroides, Micrurus)
   - Brown snakes (Pseudonaja)
   - Black snakes (Pseudechis)
   - Copperheads (Austrelaps)
   - Death adders (Acanthophis)
   - Taipan (Oxyuranus)
   - Tiger snake (Notechis)

Mostly Crotalinae snakes in North America with some Coral snakes (in the south)

Question 13

What is the possible toxicity of Loxosceles spiders (= loxoscelism syndrome)

Answer 13

• Local necrosis of tissues around the bite (potentially leading to extensive wounds) = cutaneous loxoscelism
• Rarely intravascular hemolysis = systemic loxoscelism

Question 14

What are the main signs associated with lactrodectism (= widow spider envenomation)? What species is more sensitive?

Answer 14

• Mostly severe diffuse pain
• Muscle rigidity progressing to paresis
• Possible arrhythmias, bronchoconstriction, GI signs

Cats are more sensitive

Question 15

What toxins are present in scorpion venom

Answer 15

• Histamine
• Serotonin
• Acetylcholinesterases
• Phospholipase
• Hyaluronidase
• Neurotoxins
• Protease inhibitors

Question 16

What species of scorpion can cause envenomation in North America

Answer 16

Centruroides (Bark scorpion)

Question 17

What are clinical signs of scorpion envenomation

Answer 17

Mostly secondary to binding to voltage-gated sodium channels on neurons -> hyper excitability

• Pain
• Numbness
• Seizures
• Sympathetic stimulation: tachycardia, hypertension, mydriasis
• Parasympathetic stimulation less common: bradycardia, salivation, lacrimation, vomiting

Question 18

What treatment is recommended in case of hypertension secondary to scorpion envenomation

Answer 18

Alpha1-antagonists (prazosin, phenoxybenzamine)

Question 19

What are clinical signs of Bufo toad toxicosis

Answer 19

• Hypersalivation
• Hyperemic mucous membranes
• Seizures
• Arrhythmias (Digitalis effect)

Question 20

What is the primary allergen of bee / wasp venom

Answer 20

Bee venom: Phospholipase A2

Wasp venom: Antigen 5 (also contains phospholipase A)

Question 21

What is the number of bee / wasp stings that can be lethal in mammals

Answer 21

20 stings/kg

Question 22

Beyond causing anaphylaxis, what systemic effects can bee and wasp venoms cause

Answer 22

• Neuro: ataxia, facial paresis, seizures
• Rhabdomyolysis
• Hypotension
• ARDS
• Secondary IMHA / ITP