Biotoxins_-_Zootoxins-1__2_

Zootoxins Overview

  • Zootoxins are chemical means of defense and/or food acquisition found in various animals.

  • Present in all phyla of the animal kingdom; species produce poisons or venoms.

  • Poisons: Compounds in nonspecialized tissues, requiring usually oral contact for toxicity.

  • Venoms: Produced in specialized tissues or glands, delivered through mechanisms like stingers or fangs.

Types of Zootoxins

Poisons

  • Characteristics:

    • Produced as secondary metabolites without active delivery systems.

    • Exposure typically requires direct contact (oral or rarely dermal).

Venoms

  • Characteristics:

    • Produced in specialized organs; involves mechanisms like envenomation.

    • Venomous animals have apparatuses to inject venom into prey.

    • Mixtures of chemical compounds that can synergistically enhance toxicity.

Clinical Considerations

  • Envenoming or poisoning events are rare in domestic animals due to responsible ownership.

Snakes: Venomous Species

  • Approximately 400 species of venomous snakes globally, absent in Hawaii, Ireland, and New Zealand.

  • Crotalidae and Elapidae are prevalent in the Western Hemisphere.

Crotalids (Pit Vipers)

Characteristics

  • Heat-sensing pits between nostrils and eyes.

  • Features include elliptical pupils, triangular-shaped heads, retractable fangs.

  • Rattlesnakes possess keratin rattles on their tails.

North American Crotalids

  • Rattlesnakes: Includes genera Crotalus and Sistrurus (29 subspecies).

  • Cottonmouths (Agkistrodon piscivorus) and Copperheads (Agkistrodon contortrix) are also present.

Clinical Impact

  • Copperheads are responsible for most snakebites in the U.S.

  • Rattlesnakes are linked to most human deaths due to more potent venom.

  • Annually, 150,000 to 300,000 animals bitten by pit vipers in the U.S.

Venom Composition of Crotalids

  • Complex mixtures of:

    • Enzymes

    • Cytotoxins

    • Neurotoxins

    • Cardiotoxins

    • Hemolysins

    • Coagulants/anticoagulants

    • Other components (e.g., lipids, nucleotides).

Types of Rattlesnake Venom

  • Classic Diamondback Venom: Severe tissue destruction.

  • Mojave A Venom: Severe neurotoxic effects, little tissue damage.

  • Mixed Venom: Contains elements of both classic neurotoxic venoms.

Impact of Venom Components

  • Hyaluronidase: Increases venom spread through tissue breakdown.

  • Myotoxins: Cause muscle damage and necrosis.

  • Cardiotoxic Agents: Lead to hypotension unresponsive to treatment.

Clinical Signs of Crotalid Bite

  • Local pain, swelling, discoloration.

  • Systemic signs can include shock, tachycardia, nausea, and lethargy.

  • Neurological signs in neurotoxic bites (e.g., ataxia, paralysis).

Treatment Protocols

First Aid

  • Keep the animal calm, keep bite location below heart level.

  • Monitor swelling and mark bite site.

Medical Interventions

  • Intravenous therapy: Address hypotension.

  • Blood transfusions: Manage coagulopathy.

  • Antivenom: Main treatment for moderate to severe envenomation.

Antivenoms

  • Polyvalent Crotalid Antivenom: Effective for multiple pit viper species.

  • Fab antivenoms: Newer options with higher potency but higher costs.

Vaccination

  • Rattlesnake vaccine protects against major rattlesnake venoms in dogs and horses.

  • Does not protect against Mojave rattlesnake venom.

Elapid Snakes

  • Two venomous species in North America: Sonoran Coral Snake and various subspecies of Eastern Coral Snake.

  • Coral Snake Characteristics: Non-aggressive, nocturnal, bright-colored.

Venom and Effects

  • Coral snake venom causes neuromuscular blockade and local tissue necrosis.

  • Clinical signs develop slowly; CNS effects like quadriplegia may follow.

Widow Spiders (Latrodectus spp.)

  • Worldwide distribution with distinctive markings.

  • Widows are shy and typically bite only when threatened.

Widow Venom

  • Contains neuroactive proteins, primarily α-latrotoxin.

  • Clinical signs include severe muscle pain, hypertension, tachycardia.

Treatment Options for Widow Spider Bites

  • Symptomatic treatment: Opioids, muscle relaxants, and specific antivenom for cats.

Recluse Spiders (Loxosceles spp.)

  • Medical importance primarily from Brown Recluse distribution in the U.S.

  • Produces necrotizing enzymes leading to severe tissue damage.

Clinical Signs & Treatment

  • Characterized by a “bull’s-eye” lesion around the bite site.

  • Treatment includes wound care, pain management, and possible antibiotics.

Scorpions

  • Mainly Bark Scorpions in North America (e.g., Arizona bark scorpion).

  • Venom consists of polypeptides, causing pain and neurotoxic symptoms.

Treatment

  • Focuses on symptom control and managing systemic reactions after envenomation.

Tick Paralysis

  • Common in livestock and dogs from specific ticks; presents as paralysis similar to botulinum.

  • Supportive care and tick removal are crucial for treatment.

Blister Beetles

  • Toxic principle: Cantharidin, found in hemolymph and excretions.

  • Potentially lethal if ingested in hay contaminated by crushed beetles.

Clinical Signs and Treatment

  • Causes severe gastrointestinal and urinary tract signs.

  • Diagnosis confirmed through cantharidin detection; treatment is primarily supportive.