by Janet Spencer
If you swallow it, inhale it, or absorb it and it kills you, it’s poisonous. But if it is delivered to you via fangs, spines, stingers, stinging cells (jellyfish), squirting (cobras, cane toads) or spurs (platypus), then it’s venomous. Come along with Tidbits as we avoid venom!
THE DANGER
• The potency of venoms is measured using a method called “Median Lethal Dosage” in which researchers calculate how much of a substance it takes to kill half of a group of test subjects, where the substance is measured in milligrams of toxin per kilogram of body weight, notated as mg/kg. Water, for instance, has a toxicity rating of 90,000 mg/kg, meaning a typical person can consume an amount of water equal to around 6 liters of water before dying. On the other hand, the venom of a box jellyfish has a median lethal dose of about 0.05 mg/kg.
• Pufferfish and the blue ringed octopus use a venom called tetrodotoxin which is one of the deadliest compounds known to man, being more potent than arsenic, cyanide, or anthrax. It targets the nervous system and shuts down communication between nerve cells. The result is the inability to breathe combined with the stopping of the heart.
VENOM
• Out of the 5,416 known species of mammals, 12 are venomous, including four species of shrews, three vampire bats, two kinds of rodents, one mole, the slow loris, and the platypus. Of those, eleven of them deliver venom through a bite. Only the platypus has a venomous sting, delivered through spurs on the ankle, usually in a fight over a female.
• In the phyla Cnidaria, which includes jellyfish, anemones, and corals, there are over 9,000 venomous species.
• The toxin located in the venom of box jellyfish is called “porin.” It punches holes in cell membranes. When red blood cells are punctured, they burst and release potassium and hemoglobin. When too much potassium is released into the blood stream, it triggers a heart attack within minutes.
SNAKE VENOM
• The king cobra can deliver enough venom to kill 20 people in every bite. About half of all bites from the king cobra are fatal, compared to about 2% of other venomous snakebites.
• The krait is a venomous snake found in India. Its bite is not very painful, and people can even be bitten while they sleep without knowing it. Often, they refuse medical treatment because it doesn’t seem serious, even though antivenom for the bite exists. But the venom is a neurotoxin that takes several hours to begin working. By the time the victim has trouble breathing, it’s too late. Over 70% of people bitten by a krait die.
• The method of delivery matters a lot. The taipan is one of the deadliest snakes. When the venom is injected into the bloodstream, as it would be by a snake bite, the venom is far more deadly than it is if the venom is delivered subcutaneously, injected under the skin but not into the veins.
ANTIVENOM
• Alber Calmette, who studied under Louis Pasteur, invented the first antivenom in 1896, spurred by a flood in Viet Nam where he was living at the time. Hordes of cobras invaded the town where he was staying, resulting in many deaths, and propelling him towards experimenting with cures. His solution was to inject horses with cobra venom and then use the horse’s blood serum to treat the victim. The serum would bind with the toxins in the venom, leaving them harmless.
• When the body is under attack by bacteria and viruses, the immune system kicks into high gear, manufacturing antibodies to kill the intruders. The body remembers how to fight the invaders, making the person immune. This is how vaccines work.
• The same thing happens when the body is under attack by venom, but the problem is that venom often acts so quickly that the body doesn’t have enough time to react. Antivenom is so effective because it acts like a vaccine. When snake venom is injected into a horse, the horse is so large that it’s only slightly affected. It develops antibodies to combat the venom, which can then be harvested from the horse’s blood and delivered to a human. The horse only retains these antibodies for several months, requiring repeated injections of venom, and the antivenom has a limited shelf life.
• Other animals can also be used, including sheep, goats, and cats. The antibodies only work against the specific species they reacted to, so antivenom for rattlesnakes won’t work against a cobra bite. And many venomous creatures such as spiders and jellyfish produce venom in such tiny amounts that it can’t be harvested in order to develop an antivenom. These circumstances make antivenom an expensive antidote.
RESISTANCE
• There are 48 known species of animals that have the ability to withstand snake bites, including opossum, skunk, weasel, cats, hedgehog, honey badger, mongoose, and the snake eagle. All of these animals eat snakes. One type of opossum can withstand 40 times the dose that would kill a human.
• Similarly, one species of mouse that regularly eats scorpions can withstand up to 20 times the dose of scorpion venom that would kill a laboratory mouse.
• The fan-fingered gecko can withstand up to 4,000 times the dose of venom from the yellow scorpion that would kill a mouse. This is equal to being stung by a scorpion 100 times with no ill effect.
• The Texas horned lizard eats harvester ants, one of the more venomous species of ant. They can withstand 1,500 times the dose that would kill a mouse.
• The opossum is resistant to certain types of snake venom, but not others. The mongoose, however, seems to be resistant to all types of snake venom. When researchers tried to develop an antivenom based on the blood of the mongoose, they completely failed. The mongoose is innately resistant to venom, but that resistance cannot be shared. However, serums developed from opossum blood can be transferred to other animals.
• On the other hand, Guinea pigs are ten times more sensitive to the venom of a black widow spider than mice are, and 2,000 times more sensitive than frogs.
• Researchers were trying to maintain a captive population of rattlesnakes for study. They offered the snakes wood rats to eat, but the rats often killed the snakes. Research showed that the rats were naturally immune to the rattlers’ venom.
