The venom of the tiger snake is highly neurotoxic, and affects mainly the nervous system, although it is also myotoxic and haemotoxic. The venom of a rattlesnake, on the other hand, is primarily haemotoxic, and causes the blood to coagulate, which inhibits circulation of oxygen around the body. As with the tiger snake, the venom of a rattlesnake also contains myotoxic and neurotoxic elements.
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| The result of adding one drop of haemotoxic venom to a blood sample. It took only a few minutes for the blood to coagulate into a thick jelly. |
The fact that venom consists of these four different types of toxin is what makes it so effective as a weapon. Each constituent plays its part in killing the prey item. The neurotoxic element cripples the nervous system, and in most cases paralyses the victim, while the haemotoxin prevents the supply of oxygen to vital organs (most importantly the brain). At the same time, the myotoxin attacks the muscles, causing spasms and destruction of the muscle tissue while the cytotoxin affects the tissue around the bite, which, in time, becomes a gruesome mess of swelling, blisters and dying tissue. If you are a prey item such as a field mouse, however, it is unlikely you would be worrying about long-term damage to the bite site. Having less than two minutes to live changes perspective, even for a mouse.
Unlike the unfortunate field mouse, humans often have access to medical treatment, and antivenin for almost all venomous animals to combat the effect of envenomation. If you are stung by the stonefish, however, it may not be so simple. The pain alone of the stonefish's sting can be enough to cause the body to go into shock, and it is possible to die simply from the pain. It is not unheard of for patients to request the amputation of the affected extremity just to be rid of the pain.
There is no doubt that the toxicity of venom produced by a venomous animal is an elegant and lethal weapon, however without the means of delivering it, the organism can do no harm, just as a bullet can do no harm without the appropriate firearm. Dropping venom onto skin will not help kill the prey. It must be injected into the organism, allowing direct access to the blood and lymphatic system, which helps the spread of venom throughout the body. The animal kingdom has evolved many creative means of injecting venom into prey. The next post on this blog will investigate the different structures that organisms have developed, and how they could have evolved.
Sources:
http://en.wikipedia.org/wiki/Snake_venom - Accessed 15MAR14
http://scribol.com/environment/the-worlds-5-most-venomous-species/2 -Accessed 15MAR14
http://www.venomdoc.com/venomdoc/Reptiles.html -Accessed 16MAR14
Image:
http://img.thesun.co.uk/aidemitlum/archive/01546/Blood-thickens-frm_1546499a.jpg
-Accessed 16MAR14
Interesting. The different types of toxins are quite fascinating. Are these different toxins proteins or are they some other type of macromolecule?
ReplyDeleteVenom consists mainly of proteins, with a smaller percentage of polypeptides. In a neurotoxic venom, for example, the proteins are able to bind to receptor sites in muscle tissue. This prevents chemical signals reaching the muscles from the brain, and causes paralysis.
DeleteVery interesting! Just wondering, how effective are antivenins? Also, are there any ways animals have evolved either their own version of an antivenin or way of lessening the impact of the venom on their body?
ReplyDeleteAntivenins are the most effective tool we have to combat envenomation. They are not a miracle cure, but they do save lives.
DeleteAntivenin consists of the required antibodies to neutralise a certain type of venom, and is probably most akin to a vaccine. That is, when an organism is infected by a virus, the body will develop antibodies in order to neutralise it. A vaccine is a weakened dose of the virus, which encourages the body to produce the required antibodies. Antivenin is produced in a similar way. However, as is the traditional human fashion, another mammal is injected with a non-lethal dose of venom. The unfortunate subject will then produce antibodies to combat the venom. These are harvested from the blood of the subject, and refined into antivenin. Each antivenin is specific to a species of venomous animal. That is, treating a bite from a tiger snake with cobra antivenin would not be effective.
In answer to your second question, yes, some animals have developed a resistance to venom. The Indian Mongoose has developed a very effective resistance to cobra venom. As mentioned in a previous comment, the neurotoxic proteins that make up cobra venom bind to a receptor site in the muscle tissue, which blocks incoming signals from the brain. While most mammals would succumb to the venom, the indian mongoose has a different receptor in it's muscle tissue which the cobra venom is unable to bind to. To simplify it, cobra venom doesn't fit. This doesn't make the mongoose completely immune, but it does give it high resistance.
The honeybadger possesses a similar trait to the mongoose, and it has long been thought that the secretary bird was also resistant to venom, however there is no evidence to support this.