30 – Venomous and Poisonous Animals

Question 1

Black widow spider

Answer 1

• Australian counterpart: red-black
• ONLY female can envenomate
• In US but not in Alaska
• Do NOT bite unless provoked
• **TOXICITY: single bite can be FATAL
  o CATS, HORSES=very sensitive
• Mechanism: massive release followed by depletion of acetylcholine, NE, DA, others

Question 2

Black widow spider: clinical features

Answer 2

• Bite painful, but NO local tissue damage
• Progressive onset of EXTREME PAIN
  o Local vocalization, howling in cats
  o Hypersalivation, restlessness
  o Muscle cramping, abdominal rigidity
• Systemic signs: hypertension, hyperesthesia, tachycardia
• *MUSCLE TREMORS AND RIGIDITY TO FLACCID PARALYSIS over several hours
• Death due to respiratory or CV collapse
• Long term: weakness, lethargy, muscle pain

Question 3

Black widow: management

Answer 3

• ANTIVENIN (if available)
• Symptomatic and supportive care
• Secondary issues: hypothermia, myoglobinuria and renal issues

Question 4

Black widow: diagnosis

Answer 4

• Clinical signs, ID of spider in vomitus (small animals)
• NO confirmatory test available
• Bites can be difficult to locate
• No specific PM or histo lesions

Question 5

Black widow: prognosis

Answer 5

• Poor for cats
• Fair for dogs
• *recovery can take several weeks

Question 6

Brown recluse spider

Answer 6

• ID: ‘vioin’ shape on dorsal cephalothorax
• Non-aggressive
• Toxicity: single bite
• TARGET: SKIN, RBCs
• Venom components: complex mixture
  o One eats away at skin: massive ulcers

Question 7

Brown recluse spider: clinical features

Answer 7

• NON-PAINFUL BITE
• Within 3-8hrs: TARGET LESION, pruritus, pain, swelling +/-central vesicle that blackens over time
• Tissue can slough within 2-5 weeks: massive indolent ulcer
• Systemic signs within 72hrs: fever, vomiting, tachycardia, renal failure
• Hemolytic anemia with hemoglobinuria

Question 8

Brown recluse spider: management

Answer 8

• NO specific antivenin
• Symptomatic and supportive care
• *OPEN WOUND MANAGEMENT: DO NOT SURGICALLY REMOVE
• Can take up to weeks to heal

Question 9

Brown recluse spider: diagnosis and DDx

Answer 9

• Challenge, no confirmatory test
• DDx: chemical or thermal burns

Question 10

Brown recluse spider: prognosis

Answer 10

• Good if only localized skin lesions
• Guarded if systemic manifestations

Question 11

Tick bite paralysis

Answer 11

• Most common in DOGS
• Dermaentor (ornate scutum)
• Seasonality: any time of year
• Ixobotoxin (female tick’s saliva)
• Target: CNS
• Mechanism of action: flaccid paralysis
  o Inhibit ACh release at NMJ and autonomic ganglia (NM blockade)

Question 12

Tick bite paralysis: clinical features

Answer 12

• Onset: 72hrs to 1 week after tick attachment
• Rapidly progressive neurologic signs
• Early: loss of appetite, loss of back/change, ataxia
• ASCENDING SYMMETRICAL LMN PARALYSIS
  o Pelvic limb to thoracic limbs
  o Decreased to absent spinal reflexes
  o CN signs
  o Tetraplegia, respiratory paralysis, death

Question 13

Tick bite paralysis: management

Answer 13

• REMOVE THE TICK
  o Clip hair and look for other ticks
  o Rapid improvement post-removal
• Symptomatic and supportive care: mechanical ventilation
  o 50-52% survival to discharge when had respiratory decreased
• **PREVENTION OF TICK BITES

Question 14

Tick bite paralysis: DDx

Answer 14

• Botulism
• Coonhound paralysis
• Acute/fulminant myasthenia gravis
• Coral snake envenomation

Question 15

Crotalid snakes/pit vipers

Answer 15

• Rattlesnakes, copperheads
• Triangular head, elliptical pupils, heat sensing pit, retractable front fangs
• **VAST MAJORITY OF BITES IN NA
• Venom components: multiple
  o Don’t strangle their prey, trying to break down their prey so they can eat it
  o Anticoagulants, hemotoxic, necrotic
• Different types of bites: offensive vs defensive vs. agonal
  o ~25% are ‘dry bites’

Question 16

Pit vipers: clinical features

Answer 16

• Onset: peracute
• SEVERE LOCAL TISSUE DAMAGE
  o Swelling, bleeding, ecchymosis, pain, eventually necrosis
• +- neurotoxicity: muscle fasciculation
• Myotoxicity: release of myoglobin=renal damage, myoglobinuria
• Effects on blood:
  o Hemolysis
  o Hyperfibrinogenemia
  o Vascular damage
  o Thrombosis
  o Risk of DIC/consumption coagulopathy
  o *hemolytic anemia, prolonged PT/PTT, echinocytes
• Hypotension, shock

Question 17

Pit viper bite: management

Answer 17

• Depends on location of bite
• ANTIVENOM: within first 6hrs most effective
  o Anaphylaxis is possible from the antivenom (possibility for a reaction)
• Symptomatic and supportive care

Question 18

Pit viper: diagnosis

Answer 18

• Snake bit witnessed or evidence of snake bit
• Supportive bloodwork findings
• NO confirmatory test

Question 19

Pit viper: prognosis

Answer 19

• Depends on severity of clinical signs
• RESPONSE TO ANTIVENOM
• Mortality rate 1-30%

Question 20

Pit vipers: side effects of antivenin

Answer 20

• Anaphylaxis OR delayed (serum sickness)
• Vomiting, ptyalism, urticaria, pruritus, tachypnea
• Serum sickness
  o 3-21d post administration=fever, lethargy, diarrhea, joint pain, vasculitis
• Cost: $600-1000/vial

Question 21

Elapid snake envenomation

Answer 21

• CORAL SNACKE: only one in NA
• *Target: CNS
• Toxins: most significant are alpha-neurotoxins
• Mechanism: nAChR antagonists
• “red touching yellow, can kill a fellow”

Question 22

Elapid snake bite: clinical features

Answer 22

• Scratch like bites with MINIMAL PAIN AND NO SWELLING
• Onset: variable (acute or delayed)
• Vomiting, hypersalivation
• SUDDEN ONSET OF LOWER MOTOR NEURON SIGNS
  o Ataxia
  o Hyporeflexia or absent of reflexes
  o Paresis progressing to quadriplegia
• Hypoventilation (death due to respiratory failure)
• +/- hemolysis in dogs
• +/- acute kidney injury

Question 23

Elapid snake envenomation: management

Answer 23

• ANTIVENIN: each vial $400-800 USD
  o NA: it is horse IgG
• Symptomatic and supportive care

Question 24

Elapid snake envenomation: prognosis

Answer 24

• Good to excellent with antivenin administration

Question 25

Blister beetle poisoning

Answer 25

- HORSES - Associated with ALFALFA - Toxin: cantharidin - 4-6g of beetles can kill a 1100lb horse - Mechanism: severe mucosal irritation

Question 26

Blister beetle: clinical features

Answer 26

- COLIC - Tachypnea, tachycardia, congested MM, prolonged CRT, sweating - Watery, bloody feces - Mucosal damage - Can develop endotoxemia and shock - Thumps (diaphragm flutter) - Oral and muzzle lesions - Myocardial damage - Polyuria and dysuria, hematuria - Clin path: low USG, hypocalcaemia, hypomagnesemia

Question 27

Blister beetle gross and histological lesions

Answer 27

- Erosion/ulceration with hyperemia of oral, GI and bladder mucosa - Mucosal region of GIT - +/- renal tubular necrosis - +/- region of myocardial pallor

Question 28

Blister beetle; management

Answer 28

- No specific antidote - Decontamination - Symptomatic and supportive care o IVFT with Ca and magnesium supplementation o Gastroprotectants, pain control o Management of shock

Question 29

Blister beetle: diagnosis

Answer 29

- History of alfalfa in diet in any form - Send-out test: cantharidin in urine and intestinal contents

Question 30

Blister beetle: prognosis

Answer 30

- Variable o Depends on progression of clinical signs and response to supportive care