Toxicological effects of Toads

Toxicological effects of toads

Introduction

Toads (order: Anural; family: Bufonidae; genus: Bufo) are distributed throughout the world, but are found mainly in areas of tropical and humid temperate climates . Each region is characterized by the presence of some species of these amphibians. The most commonly found species are Bufo marinus, B. typhonius, B. crucifer, B. ictericus, B. granulosus, B. ocellatus, B. rufus and B. paracnemis (5). However, not all of these species cause death to envenomed dogs .

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Although toads do not have a venom inoculation system, they are considered venomous animals, as the glands covering the whole surface of their skin secrete a highly toxic venom .

Some of these glands are the bilateral glands located in post-orbital position. These glands, which are somewhat diamond-shaped and can be seen by the naked eye , are known as parotid glands.

The parotid glands are composed of a large concentration of granular glands responsible for the production and storage of a thick and creamy secretion. There are also the mucous glands that produce a less viscous secretion.

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These secretions help protect against predators, and thus, are considered a kind of defensive mechanism of these animals that lack spines, nails, or sharp teeth.

History

Knowledge about the toxicity of toad venom comes from the past when the venom was used by different people for various purposes. Roman women used toad secretion to poison their husbands. South American Indians, especially from the Amazon region, used venoms of anurans from the Dendrobatidae family and species of B. blombergi on the tip of their arrows for hunting and fighting.

In Japan, under the called of "Senso", and in China, under the name of "Ch’an’Su", dried toad venom was used as an expectorant, anti-hemorrhagic, diuretic, and cardiac stimulant. In Hawaii, a child died after having eaten a toad killed by his father in a sugarcane field. This report shows that toad envenoming is also a problem in humans.

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Toxic components of toad venom

Toad venom contains a mixture of different classes of toxic chemicals .the concentration of each of the different chemicals in toad venom vary from species to species

The first class of chemicals in toad venom includes the cardiac glycosides called bufodienolides.the bufodienolides comrises of 2 subgroups -bufogenins and their derivative bufotoxins.the cardiac glycosides in the venome are known for their effects on the cardiovascular system ,including the heart and blood vessels.

The second class of chemicals in toad venom includes phenethylamines and their derivatives . These include catecholamines such as dopamine , noradrenaline ,and adrenaline. This class of chemicals are not as prominent as bufodienolides in producing the quick adverse effects in animals ,but it is thought that they probably contribute to vasoconstriction.

The third class of chemicals consists of tryptamines and their derivatives . These include serotonin [5-hydroxytryptamine ] and 5-hydroxy dimethyltryptamine (5-hydroxy DMT,bufotenine).these class of chemicals in toad toxin is thought to have ototoxic action and frequently a marked pressor effect . The 5-meO-DMT (5-methoxy-N,N-methyltryptamine), a tryptaminergic derivative present only in the venom of bufo alvarius, has significant hallucinogenic and /or psychoactive effect .

the fourth class of chemicals in toad venom includes non-cardiac sterols. These contain cholesterol, provitamin D , ergosterol, and gamma sitosteral. Their exact role in toxic effects is not clear.

the venom is produced by all toads , but its potency varies with species . Bufo vulgaris is least toxic and bufo marinus is most toxic to animals

most toad poisonings occure in dogs , cats ,and children . In dogs severity of poisoning depends on the size of dog and the amount of toxin abosorbed into blood stream . Puppies and small breed dogs such as Dachshunds, Mini-pins, Jack Russell terriers and miniature schnauzers are more seriously affected because they get more poison per kg body weight than a large breed dog

bufo toads are most active in the spring and summer months when the environment is warm and moist . A dog can die following one exposure to B.marinus toxin

Toxicity OF toad venom

MOA of this venom[bufodienolides] is almost similar to that of digitalis

When dog mouths or bites a bufo toad the toxin is released and rapidly abosorbed across the mucous membrane of the mouth

After the absorption of the venom ,the bufodienolides bind to a specific receptor site on the cardiac cell membrane and inhibit the Na+/K+ ATPase pump.

Mechanism of action

When this pump inhibited , the cell relies on the Na/Ca2+ pump to maintain its sodium gradient ,which pumps sodium out and calcium in ,this results in increased intra cellular calcium concentration in cardiac cells and hence excessive cardiac stimulation and ventricular fibrillation.

Failure of Na+/K+ - ATPase pump also results in an increased extra cellular potassium concentration , resulting in hyperkalemia . Death occurs rapidly from heart failure

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Signs of toad poisoning are variable and range from local effects to systemic effects . Local effects in dog are immediate and include profuse and sometimes frowthy salivation , vigorous head shaking ,pawing t mouth and retching . These are due to extremely irritant nature of venom

with more severe intoxication cardiac arrhythmias, dyspnoea , diarrhoea , incoordination of stiff gait , cyanosis ,apparent blindness , convulsions , prostration and collapse are characteristic .

Ventricular fibrillation preceedes death from heart failure. In general, morbidity rates are high.

Clinical signs

Distinctive lesions are not present in toad poisoning

Post-mortem findings

diagnosis of toad poisoning is usually based on seeing a dog or cat mouthing a toad , or finding a toad or toad pieces in vomitus ,if symptoms have already occurred.

Circumstantial evidences and clinical signs may also help in the diagnosis

Haematological and clinical chemistry changes in toad poisoning include increase in packed cell volume (PCV), blood glucose , blood urea nitrogen , potassiuum and calcium levels.

Diagnosis

There is no specific antidote for bufo-toxin and treatment consists of mainly of supportive care

a) The mouth of the dog should be immediately and thoroughly flushed with water from a slow moving stream from a garden pipe / house . The toxin is very is sticky ,so it may need to be gently rubbed off of the mucus membranes of mouth.

b)detoxification with activated charcoal and an osmotic cathartic is recomended.

Treatment and management

Cont... c) A large dose of propranolol (upto to 2 mg/kg ) may

used to control cardiac arrhythmia and potential fibrillation . Any other beta-1 adrenoceptor blocker may also be used.

d) Atropine may help to control salivation and

potential bronchoconstriction.

e)CNS excitation , if present , should be controlled by pentobarbitone or diazepam , or a a combination of the two.

prognosis of toad poisoning is good to guarded , if prompt intervention and detoxification are followed by appropriate supportive therapy .

Prognosis

Toxicological effects of Lizards

The only poisonous lizard known is the Gila Monster or Beaded Lizard [Helodrema suspectum and Heloderma horridum] found in the desert regions of south-western regions of united states and northern Mixico.

Gila monsers are identified by their beaded skin [as opposed to scales ], distinct colour banding of black and red or black and yellow / orange and big size [upto 2 feet long].

These animals are heavy, slow moving lizard, which spend about 80% of their life underground but become more active at surface during spring season.

Introduction

The Gila monster bites with its teeth rather than fangs and the venom enters the bite wound by dripping down grooves in the teeth.

Unlike venomous snakes , these lizards tend to hang on to their victims , making them hard to remove once they have bitten.

The jaws of Gila monster are strong ,so their bite can cause a crushing or compression injury. These injuries can cause severe swelling and may damage underlying tissues , blood vessels , nerves ,joints ,or bones.

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the venom of Gila monster is mainly neurotoxic also called as Gilatoxin.

Venom is composed of complex mixture of proteins and enzyme , many of which similar to those found in snake venoms including hyalurinidase [spreading factor]

Toxic components of lizard venom

Hyalurinidase catalyzes the cleavage of internal glycoside bonds of acid mucoglycosides , resulting in decreased viscosity of hyaluronic acid which in turn increases tissue permeability and allows deeper penetration of venom into tissue.

Phospholipase A2 uncouples oxidative phosharylation , inhibits cellular respiration , causes cell membrane destruction and inhibit platelet aggregation .

Various proteolytic enzymes result in local tissue

damage as well as aid in spread of venom through the tissue.

Mechanism of action

The toxicity of heloderma venom is dependent on the amount of venom delivered to tissues which inturn is dependent on the duration and severity of the bite .due to their inquisitive nature and tendency to harass wild life that they encounter.

Dogs are the species most likely to have a significant encounter with heloderma species.

Toxicity

Intense local pain ,edema and hemorrhage at the site of the wound

Regional lymphangitis and local ecchymosis may occure although tissue necrosis is not common

Systemic signs include weakness , dizziness ,tachypnea ,vomiting, polyuria, salivation, and lacrymation

Clinical signs

The 1st cource of action is often disengaging a lizard that is still attached to the victim .removal should be attempted as quickly as possible because the amount of venom delivered is propotional to the duration of the bite.

The bite site should be irrigated with any local aneshetic or sedation through intramuscularly ,may be helpfull in sedating agitated or highly painfull animals

Treatment

Broad spectrum antibiotics should administered to prevent infection from the myriad of potentially pathogenic bacteria that have been reported frequent in the mouth of reptiles

General wound care should be instituted....

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