Snakes use venom to subdue prey and ward off predators. Medical researchers have developed antivenoms, which help save the lives of people bitten by snakes.
Venoms consist of complex mixtures of peptides, proteins and lipids. Snake toxins vary in function and are grouped into two broad classes – neurotoxins and hemotoxins.
Snake venom is a complicated brew of dozens of compounds. It comes in two basic types: neurotoxins that disable the central nervous system, causing their prey’s muscles to stop working and the victim to suffocate; and haemotoxins that disrupt the circulatory system, triggering uncontrolled bleeding.
Snakes rely on their venom to kill their predators and prey. But they can also use it to save lives with antivenoms — antibodies that mimic the body’s own immune system to fight the venom and restore proper blood flow and clotting.
Antivenoms can be delivered via a vein or orally. Injection of the latter is difficult, however, because most venom components are peptides and proteins that must cross cell membranes to reach their targets. To overcome this challenge, Clevers and his team are using organoids derived from snake glands to produce unlimited quantities of snake antivenom.
The researchers screened 18 viperid venoms for procoagulant activity in vitro, using the modified MCD-P assay16. The venoms were also tested for the ability to cleave fibrinogen chains, which promote stable clot formation. They found that most of the venoms promoted fibrinogen cleavage, but some degraded both the a and b chains of the protein. Immunoblots showed that the CSL polyvalent antivenom neutralised the in vitro procoagulant effects of most venoms except for those of the krait (Bungarus) and mamba (Dendroaspis) venoms.
The symptoms of snakebite vary, depending on the type of snake and the venom involved. The venom of vipers contains toxic protein components that cause tissue damage and inflammation in the area of the bite. It also causes abnormal blood clotting, which can lead to bleeding and hemorrhage. The venom of other snakes, such as coral snakes and cobras, contains neurotoxins that damage the nerves. These toxins cause weakness, dizziness and blurred vision, as well as difficulty breathing.
The first reaction to a snakebite is pain in the area of the bite, followed by swelling and discoloration of the affected body part. Within about three hours, great prostration, accompanied by vomiting and diarrhea, begins, and the pulse becomes faint and clammy. In some cases, the bitten area becomes cold and clammy.
Getting prompt medical attention can save lives. With modern treatment, deaths from venomous snakebite are rare. Nevertheless, the consequences of not seeking treatment can be severe, including the loss of a limb and permanent disabilities from nerve damage or other organ involvement. The first step in treatment is resting the bitten area. Avoid strenuous activity, and don’t touch the bitten area. Restrict movement, if possible, and splint or sling the bitten area to help limit swelling. Do not use a tourniquet. Remove any rings and other constricting items of clothing. If a venomous snakebite is suspected, a 20-minute whole blood clotting profile should be performed.
Snakes voluntarily discharge their venom when they bite, and 50 to 70% of venomous snakebites result in serious injury or death. A venomous snake bite should be considered a medical emergency and is best treated with antivenoms administered by injection or subcutaneously as soon as possible to minimize irreversible damage.
Venom peptides can be grouped into different families, according to their biological function and structural features. The most extensively studied and therapeutically promising venom components are neurotoxins (three-finger proteins) and haemotoxins.
Three-finger proteins have a conserved structure with two or more disulfide bonds, which stabilize their three-dimensional structure. These peptides bind to channels of the plasma membrane and cause neurotoxic, haemotoxic and myotoxic effects. Bungarotoxin, a member of this family, has been used as a tool for understanding underlying mechanisms in diseases such as Parkinson’s disease. Other venom toxins have also been used in the treatment of human diseases. For example, a serine protease inhibitor derived from the Indian Russell’s viper venom, tirofiban and its pharmacologically active derivative eptifibatide are in clinical use as antithrombotic agents.
Haemotoxins act by binding to and blocking ion channels in the cell membrane, leading to an imbalance of calcium, potassium and other ions. Several drugs are based on venom haemotoxins, including the blood clotting inhibitors heparins and ticlopidine. Other haemotoxins have been used in the treatment of cardiovascular diseases such as coronary artery disease, stroke, hypertension and heart attacks.
As summer approaches, snakes are active around houses and in their natural habitats. Many people fear them, but a majority of snakebites are harmless and those that aren’t are rarely fatal when proper medical treatment is available.
Maureen Frank, a Texas A&M AgriLife Extension Service wildlife specialist in Uvalde, said venomous reptiles usually want to avoid humans. They often rattle or hiss to warn people that they are nearby, but they also may hide in crevices or other places people don’t look. She advises people to watch where they walk in the yard and keep outdoor areas free of debris like wood piles, rocks and deep grass. She recommends wearing boots and long pants when walking in areas where snakes may be found and to never pick up a snake, even one that appears dead. Even dead snakes can bite in defense of themselves or to protect their young from predators.
Antivenom is available to treat a variety of snakebites, including the pit vipers that include rattlesnakes and water moccasins. It is created by immunizing horses or sheep with the venom from a particular type of snake, and there are antivenoms that treat bites from multiple types of snakes (polyspecific antivenoms) and those that treat bites from a specific group of snakes (monospecific antivenoms). Veterinarians also are trained to use tourniquets, ice and immerse wounds in water to slow venom absorption and prevent shock.