Venom is a toxic poison that animals inject by biting or stinging.
In the tropics, there is a wide and varied range of poisonous snakes! Stingers, biters or spitters, most snakes are venomous and to be feared: from the green mamba of Central Africa to the Gaboon viper, the cobra of the Far East and the spearhead of Martinique. Marine snakes are amongst the most venomous snakes. Furthermore, in Africa and elsewhere, spiders and of course, insects are also venomous...as well as fish: stings from weevers (Trachinus spp.), lionfish or scorpion fish (Scorpena spp.), are relatively common along the coasts of the Mediterranean.
Fish commonly sting when a bather walks on their dorsal, pelvic or anal spines, or even when they are caught by professional fishermen. Pain is immediate, intense and irradiates through the limb. It may cause sweating, nausea, vomiting and lipothymia...
Diagram of a viper's head with venomous fangs. © DR
Living species mainly use poison to:
- defend themselves against micro-organisms or predators;
- defend their territory and food sources from competition;
- attack with more power and efficiency than brute physical force.
Necrosis of the hand after a snake bite. © DR
Proteins constitute 90 to 95% of the dry weight of venom and are responsible for nearly all of their biological effects.
The main toxic agents in venom
Venom contains many toxic agents, including:
- paralysing neurotoxins which produce effects similar to those of curare (curare antagonists, such as eserine, are not effective) ;
- haemorrhagine, viperids, which causes haemorrhaging;
- cytolysins, which destroy cells and sometimes cause major cutaneous nercosis;
- hydrophid myotoxin;
- hemolysins, which attack white blood cells and prevents phagocytosis, which can lead to frequent infections;
- histaminic substances, vasomotor reactions that cause shock after a snake bite;
- other substances that cause a wide range of enzymatic effects.
A bee sting, enlarged 700 times . In this case, the animal dies from the sting. © DR
Possible reactions after a sting
- a painful local reaction, redness, oedema, or a slight induration, itching. This reaction lasts for a few hours. A wasp sting, for example in the mouth or the throat, can be fatal;
- a toxic reaction with global reactions, fever, vomiting, diarrhoea, headaches, drops in blood pressure, convulsion and loss of consciousness;
- an allergic reaction, called anaphylactic shock, which does not depend on the amount of venom injected.
A bee sting can cause
anaphylactic shock. © DR
Symptoms and causes of anaphylactic shock
Before anaphylactic shock occurs, a first sensitising sting must occur: lgE antibodies are produced. These antibodies settle into the mastocytes present in the skin, the intestines and respiratory tract.
When the second sting occurs: the combination of the antigen (venom) with the antibody (lgE - mastocytes) produces a violent and major release of histamine and other substances present in the mastocytes. This reaction takes place within 5 to 10 minutes. It is very serious but rare, and is similar to other types of anaphylactic shock: general urticaria, major swelling, oedema of the tongue, oedema of the epiglottis and the larynx, thoracic oppression, anxiety and cyanosis. In addition, a loss of consciousness, nausea, vomiting, diarrhoea and coma may occur. This syndrome may be fatal.