Deadly and toxic reptiles, amphibians and arachnids
Snakes, frogs or spiders cannot be our favorite animals for the unique reason that applies to all of us: they are poisonous, venomous, toxic cold and dreadful creatures. I have excluded herpetologists, snake lovers and animal lovers from 'all of us' application. Let's see how exactly representative species from the class reptilia, amphibia and arachnida of kingdom animalia are toxic animals.
Snakes: Venom is secreted from modified parotid salivary gland situated below head on each side of eye; it is conveyed by a duct to fangs of poisonous snake. Snake venom is a combination of different proteins and enzymes which have cytotoxic, neurotoxic or coagulant properties. Functional proteins and enzymes of venom include phophodiesterase (lower blood pressure), phospholipase (hemolytic), hyaluronidase (increase tissue permeability), ATPase (ATP hydrolysis), oxidase and protease (digestion) and peptides that inhibit mammalian cholinesterase leading to loss of muscular activity. Snake venom is functionally characterized as neurotoxin and cytotoxin. Cytotoxins are phospholipases (produced by Habu), cardiotoxins (King cobra) and hemotoxins (Viper and Naga). Hemotoxins destroy erythrocytes (hemolysis) and inhibit clotting process. Cardiotoxins bind to heart muscle cells, prevent muscular contractions and stop heart beats followed by cardiac arrest. Phospholipases have surfactant action; they dissolve cell membrane resulting in cell necrosis. Neurotoxins are fasciculins (Black mamba), dendrotoxins (Green mamba) and alpha-neurotoxins (Cobra and Krait). Fasciculins destroy acetylcholine esterase causing tetani and death. Dendrotoxins are inhibitory to neurotransmission, inhibit ion exchange across neural membrane and cause paralysis. Alpha- neurotoxins attack cholinergic neurons and block acetylcholine receptors resulting in numbness and paralysis. Relative toxicity of snake venom is determined from comparison with Cobra venom which is assigned by point 1 toxicity.
Frogs: Toxic frogs or poison dart frogs as we know them are found in rainforests of central and Latin America. American Indians used their toxins to poison the tips of blow darts/ arrows for hunting. These frogs are very small, aposematic and very brightly colored; brightness is associated with level of alkaloid toxins present in them. Principle poison species are Colostethus, Ameerega, Adelphobates, Oophaga, Ranitomeya, Hyloxalus, Phyllobates and Dendrobates. These species are very special as now they are endangered. Frog toxins are lipophilic alkaloids and secreted through skin to defend predation. Toxins such as allopumiliotoxin, batrachotoxin, epibatidine, histrionicotoxin and pumiliotoxin have been extracted from different species for studying their toxicology with respect to humans. Epibatidine was used as painkiller and it is 200 times potent than morphine. Potency of toxin of golden frog is such a great that it can kill 20 men and thousands of mice in a dose. Frog toxins have been used as heart stimulants, muscle relaxants, antiappetizers but often accompanied by gastrointestinal, reproductive and neurological disorders.
Toads: Toad toxin acts like digoxin, cardiac glycoside. Toxin is secreted by poison glands underneath skin of a toad. Toad Bufo marinus poisoning is responsible for high mortality and typical symptoms are seizures, weakness, limb swelling, hyperkalaemia, bradycardia, acidosis and cardiac arrhythmias which is life threatening condition.
Spiders: There are about 40000 known species of spiders and 200 are known to be dangerous for humans. Not all spiders contain venom but bite of non-venomous spiders transmits fatal infectious diseases. In case of venomous spiders, toxicity of venom is fatal to human beings. Spider venom work on two principles: neurotoxic and necrotic. Toxin is composed of many peptides which act synergistically to disturb cell membranes and activity. One of the peptide, hyaluronidase acts as spreading factor for toxin spread and access to target membrane. Widow, Brazilian wandering spiders, funnel web and mouse spiders from Australia and Asia produce neurotoxins. Venom of widow is called as latrotoxin which causes abdominal cramps, muscle contraction and respiratory failure. Wandering spider contain serotonin toxin which attack ion channels in tissues. Toxin of funnel web and mouse spiders can permanently impair sodium ion channels interfering normal body functions. Necrotic toxins are produced by sand, Hobo, sac and recluse spiders. Toxin is sphingomyelinase D protein. Its toxic effects include minor itching, nausea, vomiting, fever and rashes to severe dermonecrotic lesions, ulcer and gangrenous wounds. Wounds may take prolonged time for recovery and induce permanent scars. Extreme toxicity involves intravascular coagulation, loxoscelism, thrombocytopenia, hemolysis and renal failure. Well known venomous species of spider are: black widow, tarantula, harvestman, brown recluse, tangle web, red back, primitive burrowing, Japanese sac, Chinese bird, yellow sac, cupboard spider, white tailed and jumping spider.
Toxins are produced by snakes, spiders, toads or frogs for self defense; they are also characteristic active chemical compounds which are synthesized naturally. Studies on their unexplored toxicological potential would certainly be important for future medical applications.
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