Only 11% of Southern Africa's 173 snake species are considered dangerous, according to the African Snake Bite Institute. It adds that there are 3 500 to 4 000 snakebite cases every year in South Africa, and only around 800 of these are hospitalised, with as many as 40% showing no symptoms or very minor symptoms. The effect of a snake's venom largely depends on the size of the victim bitten and the volume of venom injected.
The most common type of snake venom is neurotoxin, which either overor understimulates the nervous system.
Ken Winkel, toxinologist and senior research fellow at the University of Melbourne's Australian Venom Research Unit, says: "This is rarely a good thing, [but] the most dangerous of these [neurotoxins] are [those] that block nerve signalling, causing the paralysis of the muscles reauired for breathing."
This can happen over a few minutes or a few hours and, in some cases, it may even take days for the victim to become paralysed.
"Snake venoms […] start their paralysing effects on the muscles around the eyes and typically manifest as fixed and dilated pupils, reduced eye movement, and droopy eyelids. If not treated with antivenom, these early signs will eventually be followed by increasing difficulty in talking, swallowing and, ultimately, breathing," he adds.
TOXINS
Snake venom may include one or more of the following types of toxins:
• Neurotoxins. These exist in various forms, and their effects on a victim vary, depending on the form they take.
These will be described in greater detail as they apply to the species of snakes discussed later in this article.
• These include phospholipases, which cause the rupturing of cell membranes, as seen with the Okinawan habu pit viper of Japan; cardiotoxins, which prevent the muscle contraction of the heart, as with mamba species; and hemotoxins, which cause the destruction of red blood cells or induce clotting, as seen in most viper and cobra species. Cytotoxic venom has a localised action at the site of the bite.
