Toxicity of Toads

Family: Bufonidae

Genus: Bufo

Species: B. marinus ( marine, giant toads )

1. alvarius ( river toads )
2. vulgaris ( common toads )

Sources:

Bufomarinus gained access to the United states from Puerto Rico via Hawaii. It now additionally resides in the southern tip of Florida and Texas. Bufoalvariusinhabits southern Arizona, south eastern New Mexico.

Toads have mucous and glandular glands that aid in defense against predators.Bufo toads have a pair of parotid glands, which begin caudal to the tympanum and continue over the shoulders. The parotid glands serve as the primary release site of a thick, creamy, poisonous secretion through pinhole orifice on the surface of the skin. Bufoalvarius, although considered less toxic than Bufomarinus, is equipped with an additional pair of poison glands on the forelimbs and several pair on the hind limbs.

Transmission:

• By biting of Bufo
• By accidentally ingestion of contaminated food with toad venom.
• By eating a toad.

Toxic components:

1. The 1^st class of chemicals in toad venom:

• Cardiac glycosides called bufodienolides.
• Bufodienolides subgroup into: bufogenins and bufotoxins.

1. The 2^nd class of chemicals in toad venom:

• Phenethylamines and their derivatives, these includes catecholamines such as dopamine, noradrenaline and adrenaline.

1. The 3^rd class of chemicals in toad venom:

• Tryptamines and their derivatives. These include serotonin ( 5-HT;5- hydroxytryptamine ) and 5-hydroxy dimethyl/ tryptamine ( 5-hydroxy DMT, bufotenine).

1. The 4^th class of chemicals in toad venom:

• Non- cardiac steroids. These contain cholesterol, pro-vitamin D, ergosterol and Y-sitosterol.

Toxicity:

→ potency varies with species:

Bufo vulgaris- least toxic.

Bufomarinus– most toxic.

Mechanism of action:

                                     Biting

                                            ↓

          Rapid absorption of toxin ( bufodienolides )

                                            ↓

        Bind to specific receptor site on the cardiac cell membrane

                                           ↓

     Inhibit Na +/ K+  ATPase pump

                                           ↓

          Na+/Ca++ pump open to maintain Na+ gradient

                                           ↓

                          Na+ efflux and Ca++ influx

                                           ↓

              Increase intracellular Ca++ concentration

                                           ↓

                       Excessive cardiac stimulation

                                                 ↓                   

                                Ventricular fibrillation

                                          ↓

                                      Death

Clinical Signs:  variable signs from local effects to systemic effects.

• Profuse and sometimes frothy salivation.
• Vigorous head shaking.
• Pawing at mouth and retching.
• cardiac arrhythmias.
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• Incoordination or stiff gait.
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• Apparent blindness.
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• Ventricular fibrillation.

Diagnosis:

• History of biting or eating a toad.
• Important because the clinical syndrome is not specific.
• Several diseases and intoxification with similar manifestations.
• Must consider this potential poison when examining a dog with these cardiac effects.
• Excessive salivation.
• Cardiac clinical signs.
• Toad / toad pieces in vomitus.
• Change in hematological and clinical condition:
• Increase PCV
• Increase glucose, K+ &Ca++ level.

Treatment:

• Decontamination:

Wash mouth with copious amounts of running water.

• Antidotal therapy:
• No specific antidote.
• Centered on preventing ventricular fibrillation.
• Propranolol 5.0mg/kg IV rapid bolus may be used to control cardiac arrhythmia& potential fibrillation. Repeat dose by same route in 20minutes, if necessary.
• Atropine = control salivation & potential Bronchoconstriction.
• Anesthetize:
• Administer pentobarbital.
• Wash oral mucosa membranes again.
• Provide supportive therapy with fluids.
• Use caution in using ꞵ-adrenergic blockers to treat older dogs with cardiac or respiratory disease.

Differential diagnosis:

Signs associated with Bufo toad exposure are similar to those associated with seizure disorders, ataxia conditions, heart stroke and trauma. Exposure to insecticides in organophosphorous, carbamates, pyrethroids, metaldehyde or chlorinated hydrocarbons can cause similar signs. Ingestion of outdoor plants such as rhododendron ( Rhododendron sp. ), oleander ( Nerium oleander ), and foxglove    (Digitalsispurpurea ) can result in development of signs seen inBufoexposures. Additionally exposure to caustic agents such as liquid potpourri and various cleaning agents, orally irritating agents such as topical flea and tick products and plant containing insoluble calcium oxalates such as Diffenbachia and Philodendron can cause copious salivation.