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Australian snakes - very venomous but so few deaths


 
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Professor Graham Nicholson from the Faculty of Science at UTS looks at Australian snakes, many of which are venomous but which only cause an average of two deaths a year.     
Australia snakes are widely distributed throughout the continent, but they are not really a venomous menace here.
Part of the reason for this is that there are not many places where human and snake environments overlap. Bushwalkers and farmers would see snakes on a reasonably regular basis, although the advent of farm machinery means those contacts are fewer.

 
The low death rate in Australia from snake bites is not indicative of low bite rates. Australia’s antivenoms, developed in Australia, largely by the Commonwealth Serums laboratory, are the most effective in the world and associated with very few side effects.
Left: Copperhead. Photo supplied by Graham Nicholson

 
Our snakes, all of which are from the same family of snakes, also play a part. Australian snake bites – like those from overseas – inject venom quite shallowly into our tissues and the venom then travels through the lymphatic system (which ordinarily dispatches by-products from different areas of our bodies) in order to reach the circulation and then be widely distributed to organs and tissues.

This means that our muscles must push the venom around, giving us time to thwart the slow process of the venom finally entering our bloodstream. This is the major reason for a tourniquet around a snake bite and upwards on the limb. The pressure bandage restricts the venom from moving, as does keeping a bite victim motionless. With the muscles not working to create movement, the venom is further inhibited, allowing even more time for proper medical care to reach the victim.

This approach was developed in Australia and is only effective because our snakes’ venoms need to reach distant tissues (for example, nerve or cardiovascular tissues). This is not the case for many overseas snakes such as the rattlesnake, whose venoms contain substances that cause horrendous local tissue destruction and therefore rapid poisoning.

Snake venoms are always a complex mix of toxins and different toxins have different effects, such as paralysis, bleeding or digestion of tissues. Snakes need to rapidly digest prey as they eat relatively large meals and need to avoid undigested food going rancid in their stomachs. The cocktail of toxins produced in even the same species of snake may change according to their diet. Death adders, widely distributed across Australia, vary in their venom profiles depending on their prey.

Why are so many of our snakes so venomous? In part it reflects the harsh Australian environment. Snakes living in arid areas, for example, tend to be smaller since this requires less energy to move. However, this means they lack the power to crush their prey and so rely on venoms to capture and kill their prey. Further, since it requires considerable of energy for an animal to make venoms, it is a definite advantage to have a very potent venom since only small volumes will be needed. Finally, having a very efficient delivery system for their venoms also reduces the amount needed to be injected.
As a result many Australian snakes, including as the taipan and brown snake, do not inject much venom when they bite, but what is injected is very potent and delivered by highly efficient fangs.

Professor Graham Nicholson was interviewed for A Question of Balance by Ruby Vincent. Images were supplied by Professor Nicholson. Summary text was prepared by Victor Barry,  November 2008.

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