What are venoms?

So, before we try to understand venoms and their effects, we need to know exactly what they are! – Venoms are a substance that contain toxic chemicals (usually protein/ peptide based but can be non-biological compounds) that are injected into a biological system via fangs, spines, claws etc.

There is a wide misconception of the differences between venoms and poisons! Venoms differ from poisons as they must be injected into a model system, whereas a posion must be ingested or absorbed into the body – However, in some cases, certain toxins can  be used  for both purposes e.g. tetrodotxoin – a poison in Pufferfish and venom in Blue-ringed octopus.

Venoms are used by an array of organisms as both predatory and defensive mechanisms. Venoms are composed of a high percentage (approximately 90% dry-weight, depending on the species) of proteins and peptides – with a small proportion consisting of amino acids, salts and neurotransmitters. Some of the proteins and peptides making up the ‘active’ compounds that cause the toxic effects, whilst other proteins, such as hydrolytics enzymes are used to digest the prey from the inside for easy digestion.

There are 3 ‘main’ classes/ types of venoms   – although amongst them there are many other types, sub-classes and mixtures which are aptly named by how they affect/ intereact with biological systems or by the organism that produces it, e.g. myotoxins, cardiotoxins etc. (The names and terms used to describe and characterise venoms and toxins can be very complex and confusing as there is to date, no universal nomenclature).

Neurotoxins

These are considered the most potent of the venom classes and as the word ‘neuro’ suggests, it affects the nervous system. These venoms disrupt the enzymatic receptor activity of synapses and ion channels which in turn ‘shutdown’ the central and peripheral nervous system. They do this via a number of different mechanisms by which they inhibit neuron cellular processes, from depolarisation of the neurones to inter-neuron communicion breakdown; causing little bodily control and even paralysis.

A synaptic junction by where the toxic proteins effect and cause damage (image: Wikipedia)

A synaptic junction by where the toxic proteins effect and cause damage (image: Wikipedia)

Different neurotoxins can affect the nervous system in different ways through alternate means of inhibition. Na+, K+, Cl+, Ca2+, acetylcholine/ acetylcholinesterase inhibitors are just amongst some of the effects in which these toxins exhibit.

By altering the natural ability of neurons to pass signals between cells and organs, brings about many autonomic bodily functions to cease working. Once the central and peripheral nervous systems shutsdown, signals are no longer being passed between the brain and vital organs/ muscles. Death can occur from cardiac failure to cerebral hypoxia (lack of oxygen to the brain); and if these effects don’t kill you, it can cause strokes, comas and even full body paralysis can occur.

Cone snail or ‘cigarette snail’ (image: scinenceblogs)

Cone snail or ‘cigarette snail’ (image: scinenceblogs)

The time for these toxins to kill varies from organism to organism and the potency of the venom. Some of these venom however are so potent that they can kill a fully grown human in a matter of minutes – an example of this would be members of the marine snail genus; Conus spp (cone snails). They are eloquently nicknamed the ‘cigarette snails’, as it takes the venom around the same amount of time you have to smoke a cigarette to kill you.

There are a range of characterised neurotoxic peptides; and below a short list has been devised to name some of the dangerous culprits: α– toxins, β-toxins, Kappa-toxins, Dendrotoxins, Chlorotoxins, Conotoxins, Botulinum toxin, Bunarotoxin, Tetrodotoxin. All these toxins have unique effects but all similarly affect the central and peripheral nervous system.

Tetrodotoxin (TTX) is possibly the most unique toxin from the short list, as it derives from a small group of marine bacterium. The two genera of Pseudomonas and Vibrio seem to be the main producers of the toxin, utilising their symbiotic relationship with marine organisms. TTX is very potent neurotoxin that has no known receptor antagonist to dampen its effects (it has no anti-venom). TTX binds to voltage-gated Na+ channels and in turn degrades the action potentials across that nerve cell membrane; similarly to the other neurotoxins. It is its symbiotic relationship that allows other organisms such as Blue ringed octopus (Haplochlaena spp.) to be considered as one of the world’s most venomous organisms.

Haemotoxins

Haemotoxic venom affects blood cells and their properties to clot. Depending on the species utilising the venom, there can be two different effects of the venom. 1) It can act as a pro-coagulant, by where the blood simply clots within the body; leading to blood clots, thrombosis, strokes etc. blocking up arteries causes blood flow to be restricted and vital organs are deprived of vital oxygen. 2) The toxins can act as a anti-coagulant, thus causing the blood to lose its clotting properties. Haemolysis (destruction of red blood cells) can occur and the destruction of fibrinogen (the bloods natural coagulant protein). This leads to internal bleeding, brain hemorrhaging and multiple organ failure. These types of venoms are slow acting and death can occur from 24-72 hours if left untreated, without the admission of an antivenom.

Here is a short video clip of just how effective haemotoxic venoms are at clotting blood; •http://www.youtube.com/watch?v=4CQKLiwQCIs

Haemotoxic venoms seem to be the rarest form of venom throughout the animal kingdom. Some examples of named toxins include; Haemorragines, mucrotoxin A and convluxin. The most notorious organisms to utilse these venoms are the Gaboon viper (Bitis gabonica) and the Boomslang (Dispholidus typus).

Boomslang snake (image: Google images)

Boomslang snake – Dispholidus typus (image: Google images)

The gaboon viper (image: Dreamstime)

The gaboon viper – Bitis gabonica (image: Dreamstime)

 Cytotoxins

Cytotoxin could be considered as the least life threatening of the venoms. Cytotoxins cause necrosis of cells and tissues; they destroy the phospholipd bilayer of the cell mambrane by which causes the cell wall to rupture and its organelles to leak out. The cell essentailly dies once this happens, it is known as cell lysis. Other cytotoxic affects include the process of apoptosis, by where the cells DNA is altered and it causes the cell to terminate itself.

The effects of cytotoxic venom (image:

The effects of cytotoxic venom (image: Cutenaturals)

Through these effects, the toxin can leave deep scarring, the damaged tissues can become gangrenous and eventually rot away. The victims of an unsuspected bite may feel no pain and not know they were bitten – untill 12-36 hours later when their skin cells begin to form blisters, ulcers and deep scarring.

The Brown recluse spider - Loxosceles reclusa (image: Richard S. Vetter)

The Brown recluse spider – Loxosceles reclusa (image: Richard S. Vetter)

Like other venoms there are also multiple sub-classes, one which is myotoxin. This effects muscle cells and can cause paralysis and muscle degredation. Worse case scenarios of cytotoxic bites are limb amputation – but still there have been cases of death. There are alot of snake species that use these chemical compounds but the brown reculse spider (Loxosceles reclusa)  is possibly the most notorious of cytotoxic venom distributors.

(Last updated 18/11/13)

References

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McCleskey, E. W. (1987) Omega-conotoxin: Direct and Persistent Blockade of Specific Types of Calcium Channels in Neurons but Not Muscle. Proceedings of the National Academy of Sciences, 84 (12): 4327–331.
Simidu, U., Kita-Tsukamoto, K., Yasumoto, T. & Yotsu, M. (1990). Taxonomy of four marine bacterial strains that produce tetrodotoxin. Intern. Jour. of System. Bacteriology. 40 (4), 331-336.
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