Envenomation in the context of Viperidae

Cnidaria (/nɪˈdɛəriə, naɪ-/ nih-DAIR-ee-ə, ny-) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in freshwater and marine environments (predominantly the latter), including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are an uncentralized nervous system distributed throughout a gelatinous body and the presence of cnidocytes or cnidoblasts, specialized cells with ejectable organelles used mainly for envenomation and capturing prey. Their bodies consist of mesoglea, a non-living, jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Many cnidarian species can reproduce both sexually and asexually.

Cnidarians mostly have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes, which are specialized stinging cells used to capture prey. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both (hence they are trimorphic). Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Cnidarians also have rhopalia, which are involved in gravity sensing and sometimes chemoreception. Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, and some have simple eyes. Not all cnidarians reproduce sexually, but many species have complex life cycles of asexual polyp stages and sexual medusae stages. Some, however, omit either the polyp or the medusa stage, and the parasitic classes evolved to have neither form.

Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved venom apparatus, such as fangs or a stinger, in a process called envenomation. Venom is often distinguished from poison, which is a toxin that is passively delivered by being ingested, inhaled, or absorbed through the skin, and toxungen, which is actively transferred to the external surface of another animal via a physical delivery mechanism.

Venom has evolved in terrestrial and marine environments and in a wide variety of animals: both predators and prey, and both vertebrates and invertebrates. Venoms kill through the action of at least four major classes of toxin, namely necrotoxins and cytotoxins, which kill cells; neurotoxins, which affect nervous systems; myotoxins, which damage muscles; and haemotoxins, which disrupt blood clotting. Venomous animals cause tens of thousands of human deaths per year.

Biting is an action involving a set of teeth closing down on an object. It is a common zoological behavior, being found in toothed animals such as mammals, reptiles, amphibians, fishes, and arthropods. Biting is also an action humans participate in, most commonly when chewing food. Myocytic contraction of the muscles of mastication is responsible for generating the force that initiates the preparatory jaw abduction (opening), then rapidly adducts (closes) the jaw and moves the top and bottom teeth towards each other, resulting in the forceful action of a bite. Biting is one of the main functions in the lives of larger organisms, providing them the ability to forage, hunt, eat, build, play, fight, protect, and much more. Biting may be a form of physical aggression due to predatory or territorial intentions. In animals, biting can also be a normal activity, being used for eating, scratching, carrying objects, preparing food for young, removing ectoparasites or irritating foreign objects, and social grooming. Humans can have the tendency to bite each other whether they are children or adults.

Bites often result in serious puncture wounds, avulsion injuries, fractures, hemorrhages, infections, envenomation, and death. In modern human societies, dog bites are the most common type of bite, with children being the most common victims and faces being the most common target. Some other species that may bite humans include urban animals such as feral cats, spiders, and snakes. Other common bites to humans are inflicted by hematophagous insects and arthropods, such as mosquitoes, fleas, lice, bedbugs, and ticks (whose "bites" are actually a form of stinging rather than true biting).

In immunology, antiserum is a blood serum containing antibodies (either monoclonal or polyclonal) that is used to spread passive immunity to many diseases via blood donation (plasmapheresis). For example, convalescent serum, or passive antibody transfusion from a previous human survivor, was the only known effective treatment for Ebola infection with a high success rate of 7 out of 8 patients surviving.

Antisera are widely used in diagnostic virology laboratories. The most common use of antiserum in humans is as antitoxin or antivenom to treat envenomation.

Many species of arthropods (insects, arachnids, millipedes and centipedes) can bite or sting human beings. These bites and stings generally occur as a defense mechanism or during normal arthropod feeding. While most cases cause self-limited irritation, medically relevant complications include envenomation, allergic reactions, and transmission of vector-borne diseases.

A scorpion sting is an injury caused by the stinger of a scorpion resulting in the medical condition known as scorpionism, which may vary in severity. The anatomical part of the scorpion that delivers the sting is called a "telson". In typical cases, scorpion stings usually result in pain, paresthesia, and variable swelling. In serious cases, scorpion stings may involve the envenomation of humans by toxic scorpions, which may result in extreme pain, serious illness, or even death depending on the toxicity of the venom.

Most scorpion stings range in severity from minor swelling to medically significant lesions, with only a few able to cause severe allergic, neurotic or necrotic reactions. However, scorpion stings account for approximately 3,000 deaths a year worldwide. The Brazilian yellow scorpion (Tityus serrulatus) is one species known for being especially dangerous, being responsible for most scorpion sting fatalities in South America.

A snakebite is an injury caused by the bite of a snake, especially a venomous snake. A common sign of a bite from a venomous snake is the presence of two puncture wounds from the animal's fangs. Sometimes venom injection from the bite may occur. This may result in redness, swelling, and severe pain at the area, which may take up to an hour to appear. Vomiting, blurred vision, tingling of the limbs, and sweating may result. Most bites are on the hands, arms, or legs. Fear following a bite is common with symptoms of a racing heart and feeling faint. The venom may cause bleeding, kidney failure, a severe allergic reaction, tissue death around the bite, or breathing problems. Bites may result in the loss of a limb or other chronic problems or even death.

The outcome depends on the type of snake, the area of the body bitten, the amount of snake venom injected, the general health of the person bitten, and whether or not anti-venom serum has been administered by a doctor in a timely manner. Problems are often more severe in children than adults, due to their smaller size. Allergic reactions to snake venom can further complicate outcomes and can include anaphylaxis, requiring additional treatment and in some cases resulting in death.