o The Frog Blog: Biology Prize Entries 2011 - The Black Mamba & Neurotoxic Venom

Wednesday, 16 March 2011

Biology Prize Entries 2011 - The Black Mamba & Neurotoxic Venom

In Africa the word Black Mamba is synonymous with fear and rightly so. This snake, Dendroaspis polylepis, is also known as the ‘Shadow of Death’ in some parts of the continent.

The Black Mamba is found throughout Southern and Eastern Africa but can be spotted in isolated areas in other parts of the continent. It is the fastest snake in the world, slithering up to speeds of 20kph in short bursts but usually travelling around 12kph. The females and males generally look the same and large specimens can grow to nearly 4 metres, average being around 2.5m. The Black Mamba is slender, long and rather scrawny, not at all muscularly built. Its body however is not really black, but a sort of dark brown, so in fact the snake draws its name from the very much black interior of its mouth. The Black Mamba is able to lift a third of its body into the air, and open a small hood like a cobra, to make itself look more formidable when encountered. It hunts for rodents, lizards and other snakes on the ground, as well as being equally capable of hunting in the trees for birds. Mambas are diurnal and only hunt during the day, taking refuge in cracks and crevices during the hours of darkness.

The Black Mamba likes to spend its time in scrublands, often leading to it ending up in the vast sugarcane plantations of South Africa. The Mamba’s venom consists mainly of a powerful neurotoxin. And a bite, colloquially called the ‘kiss of death’ delivers about 120mg of venom, which will kill nearly 100 per cent of victims if not treated with anti venom very promptly. The neurotoxins that the Black Mamba uses are called dendrotoxins, it is these toxins that attack and disable neuronal tissues. Dendrotoxins do this by blocking potassium channels of the nervous system. A human can be killed by the Black Mamba’s venom sometimes in as quick as twenty minutes, but usually will die after around 45 minutes if not treated. The rapidness of fatality also depends on the health, size and age of the victim, as well as the location of the bite on the body and the amount of venom injected. And almost all people will survive a bite if the anti venom arrives in time.

Symptoms of the venom are immediate dizziness, coughing, difficulty breathing and very irregular heartbeat. The neurotoxic venom is also known to paralyse victims. Neurotoxins attack the brain and the nervous system, which stops the heart from beating, and the victim will then die of respiratory failure or cardiac arrest. Before anti venom was discovered less than 1 per cent of victims survived.

All that said the Black Mamba is a surprisingly timid snake and prefers to avoid any confrontation with humans. Fortunately making a bite a rare occurrence compared to other snakes such as the very common Puff Adder which kills the most people in Africa than any other snake. The Puff Adder uses exceedingly painful tissue – destroying cytotoxic venom. There also haemotoxic venom which attacks cells, inhibiting the blood from clotting, haemotoxic venom is found in snakes such as the tree dwelling Boomslang and Russell’s Viper.

Rab Sheeran, Form V

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