Mechanisms of Venom Toxicity

 

 

Although, as is obvious, there are many mechanisms of action for just one venom, it is convenient to classify venoms according to the composition and main modes of action. The venoms of different types of venomous snakes are different in composition. Elapidae and Hydrophidae venoms are rich in neurotoxic polypeptides. These venoms are typically fast acting on nerve tissue and neurotransmitters, often degrading neurotransmitters or depolarizing the axonal membrane for long periods of time, thereby preventing nervous impulses from being conducted. Cobra cardiotoxin acts similarly to depolarize cardiac cell membranes, which leads to systolic arrest. Cardiotoxic venoms have an affinity for cardiac tissue but appear to function by similar mechanisms as the neurotoxic elapid venoms. Crotalid neurotoxins are not membrane depolarizing, but rather are antagonistic to acetylcholine and act as a blocking agent at the neuro-muscular junction. Phospholipases, proteases and lytic factors contained in venom tend to cause hemolytic effects and are largely responsible for the necrosis that follows viperid and crotalid bites. Cell metabolism is interrupted by inhibition of oxidative phosphorilation, which leads to an insufficient supply of ATP for the cell. Mitochondrial electron transport is also interrupted as Q-Cytochrome C, an electron acceptor protein in the Electron Transport Chain, is denatured. For specific information of mechanisms of venom action, I must recommend consulting the references page. There are some fantastic books on the subject, but most require that the reader have a good comprehension of cell biology and bio/organic chemistry.

The Ach-Nicotinic receptor. This receptor, on the cell membrane of certain neurons, is the primary site of action for many neurotoxic venoms.

 

While snake venoms are potent and very complex, the mortality rate of snakebite patients is low because often there is only slight, and in some cases no envenomation. Approximately half of treated snakebites do not show any signs of envenomation at all. (Minton, 1971) localized effects of venom toxicity are difficult to treat as the venom usually disperses into the tissue surrounding the bite rapidly, however, antivenins are usually effective at treating and preventing systemic symptoms. Common symptoms of an envenomated bite are: local swelling (viperids and crotalids only), local pain, non-clotting of blood, and respiratory difficulty (elapids and hydrophids only).

 

The following images are cartoon depictions of some of the hemotoxic and myonecrotic effects of snake venoms. The top illustration depicts the rupture of an endothelial cell and the release of a red blood cell into the surrounding tissue. The lower illustration is a depiction of muscle degradation. The sarcomeres, or structural units of muscle, appear as a series of vertical lines and bands, and are obviously gone in image C.

Image taken from Rattlesnake Venoms, copyright 1982. Marcel Decker Inc.

 

The next two images are actually photographs of actual striated muscle tissue. The first one is an image of normal sarcomeres and the second one is an image of the same portion on muscle after exposure to venom. The muscle in the second image is totally destroyed and non-functional.

 

Image taken from Rattlesnake Venoms, copyright 1982. Marcel Decker Inc.

Image taken from Rattlesnake Venoms, copyright 1982. Marcel Decker Inc.

 

 

I have posted some clinical photographs of snake bite symptoms. They are very graphic and may be disturbing to some people. I recommend that, if you dislike blood and guts, you do not scroll down. These images are mostly of viper and pit viper bite, and were taken in cases where the individuals were not treated for days after the bite occurred. Not all snake bites will be as severe as the ones pictured here. Elapid and sea snake bites do not usually have any severe necrotic damage as is seen in these images.

 

 

 

 

 

 

 

 

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Image taken from Snake Venom Poisoning, copyright 1983. Scholium International, Inc.

 

 

Image taken from Snake Venom Poisoning, copyright 1983. Scholium International, Inc.

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