The aim of this section of the website is to give some clarity as to how the terms used surrounding Australian reptiles and their potential danger. While historically the terms venom and poison were interchangeable, now used for different types of toxin classified by its delivery mechanism. 

 

There is no doubt about it, Australia is home to some dangerous snakes. But what is the most dangerous Australian Snake?

To begin we need to define a few terms:
Venom –  a specialised type of toxin that can  cause a physiological injury that is injected via a bite or sting.

Poison - a toxin that can cause a physiological injury that may enter the body via swallowing or inhaling.
Toxungen – a toxin that is released from one animal and on contact the toxin can cause a physiological injury.
Venom yield - the amount of venom that is injected in a typical snake bite.
Ld50 -  this is the lethal dose, that kills 50% of the animals in laboratory testing. Most Ld50 experiments use laboratory raised mice. Snake venom is very specific, you can NOT extrapolate the Ld50 from mice to predict the effect on human beings.
 

Occasionally an animal can be both venomous and poisonous. In snakes, a classic example is the Tiger Keelback Rhabdophis tigrinus. This species has a nuchal gland that stores toxins sequestered from their prey (toads) and is used as an anti-predator system.
Spitting Cobras Naja sp. and Rinkhals Hemachatus hemachatus are both venomous and toxungenous. While they can still bite making them venomous, they can also spit and when the toxin comes into contact with the eye it can cause significant injury.
Many factors can influence the toxicity of the venom of a snake- they can include the species location, the age of the snake, the health of the snake and even the injection site. The injection site for most elapids in subcutaneous due to the relatively short fangs. – Vipers and pit vipers can inject intramuscularly or subcutaneously. While possible, it is very unusual for bite 
 

What makes a snake dangerous?
There are generally five factors used to determine how dangerous a snake is:
1) The toxicity of the venom.

2) The venom yield – amount of venom injected.

3) The efficacy of the venom delivery system- the position and length of the fangs.

4) The disposition of the snake.

5) The likelihood that the snake would come into contact with a person.
 

While an Inland Taipan Oxyuranus microlepidotus – is the most toxic snake in the world to mice,  has a moderate venom yield, its generally fairly even natured and in the wild almost never comes into contact with people. It close relative the Coastal Taipan Oxyuranus scutellatus is less toxic but has a much higher yield, is nervous and found in close proximity to people. Therefore they are much more dangerous to people.
 

All Australian elapids are venomous. The venom is used by snakes for two reasons first and foremost as a means to subdue its prey and start the digestion process and secondly as a means of defence. Australia doesn't have any poisonous snakes. 

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The potential lethality of the bite from a snake relates to more than a single factor. Relevant considerations include the toxicity of the species involved, the venom yield, the length of the fang and the temperament of the snake. These factors combine to influence the severity of any given snake bite.

 

Toxicity of snake venom is often represented by a term called the LD50. This stands for lethal dose, 50%. This LD50 result is determined from injecting test subjects (usually mice) with an estimated sub lethal dose and a larger lethal dose of venom. From these points the dosage is adjusted until a dosage is reached that kills 50% of the test subjects. This number along with the amount of venom usually injected in a bite (the venom yield) can give scientists a comparable prediction on how lethal in people the bite from a particular species could be. What should be remembered is that many snakes have evolved to prey on rodents. This may mean that a species that is not that toxic to rodents may still cause a serious illness in people.

 

Therefore, if you are bitten by any venomous snake, regardless of the species or size medical assistance should be sought.

 

The term medically significant venomous snake can be somewhat of a misnomer for people who keep venomous snakes. While the bite of a usually harmless species may not affect the normal person, reptile keepers may have a heightened sensitivity to snake venom from either past bites or even the dust that can be caused from urates or dried venom that could be inhaled in minute quantities while cleaning. In addition, if a member of the general public is bitten by any snake they will almost always seek appropriate first aid measures and in turn go to the hospital where the bite is managed by staff trained to do so. In the case of some snake keepers, they may have the misguided belief that they know better than the medical staff and as a consequence may not apply appropriate first aid measures and or seek out medical assistance.

 

Hypersensitivity to snake venom can also be problem for some keepers. This can be as serious as having an anaphylactic reaction to a protein within the snake venom. In such cases it will be necessary to manage both the allergic reaction to the snake venom and the effects of the snake venom itself. Some keepers have anti-histamine tablets or a nasal spray for fast absorption and an EpiPen as well as their bandages in their snake bite first aid kit. If you think you may have an allergic reaction to venom you should immediately consult your doctor.

 

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There are four main types of components to Australian Snake venom that cause significant effects in humans. These are:

 

Neurotoxins

Within neurotoxins there are two main groups.

The first are the ‘presynaptic’ neurotoxins that bind to the nerve ending and destroy the nerve cells. The second are the ‘postsynaptic’ neurotoxins that reversibly bind and block the receptors on the muscle cells thereby preventing the chemical messengers from getting to the receptors. Note that this process does not damage the muscles themselves.  It is the neurotoxins that cause symptoms such as ptosis [droopy eyelids], blurred vision and interruption to the smell and taste senses as well as the most serious effect of paralysis of the breathing muscles.

 

Myotoxins

These toxins destroy muscle fibres. This process can take a long time to recover from. The muscle proteins that leak from the damaged cells can also start to interfere with kidney function and may eventually cause to them to fail [requiring dialysis]. Potassium released from damaged muscle can also cause the heart to stop.

 

Coagulants

These toxins can disturb blood clotting leading to the risk of fatal bleeding into the brain. Most dangerous are the so-called procoagulants, such as that found in brown snake venom. The toxins can strip the blood of clotting factors leaving the blood unable to clot properly. True anticoagulants, such as that found in Mulga Snake venom, are less common in Australian snakes and are much less dangerous.

 

 

Haemotoxins

These cause the destruction of the red blood cells that reduces the capability for the blood to carry oxygen. The broken down cells can then leak into the surrounding tissue and cause extensive swelling and pain. Also the broken down cells can also impair kidney function. This is relatively rare with Australian snake bite.

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Recent research has suggested that all Australian Colubrids are also venomous, however only one species may be capable of a potentially serious envenomation. Previously it was thought that the solid toothed Colubrids of the genera Dendrelaphis, Stegonotus and Tropidonophis were completely harmless. It appears that species from these genera venom that is delivered via an unsophisticated apparatus. It is thought the venom enters the victim from the chewing action of the snake. The toxicity of this venom and whether it can have significant effects on humans is largely unknown.

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Lastly, in Australia we have some very large constrictors, while they might not be venomous species they can still be dangerous and have been implicated in at least one death locally.

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