Feline Emergency :: Snakebite Toxicity
(Updated 2005)
 

There are 5 groups of venomous snakes:

  • Colubrids (colubridae): rigid, rear-fanged snakes such as the boomslang and bird snake.
  • Elapids (elapidae): rigid front-fanged snakes such as the cobra, krait, mamba and coral snake.
  • Vipers (viperidae): true vipers, hinged, front-fanged snakes such as adders, asps, vipers, crotalines (pit vipers).
  • Solenoglyphs: rattlesnakes, copperheads, cottonmouths, and asian lanceheads.
  • Hydrophiidae: rigid front-fanged sea snakes.

Elapine snakes have short fangs and tend to hang on and "chew" venom into their victims. Their venom is neurotoxic and paralyzes the respiratory center. Animals that survive these bites seldom have any sequelae. Viperine snakes have long, hinged, hollow fangs; they strike, inject venom (a voluntary action), and withdraw. Many bites by vipers reportedly do not result in injection of substantial quantities of venom. Viperine venom is typicaly hemotoxic, necrotizing, and anticoagulant, although a neurotoxic component is present in the venom of some species, e.g., the Mojave rattlesnake (Crotalus scutulatus).

The elapids, colubrids and hydrophiids (rigid front or rear fangs) hold their prey after striking. For example, the coral snake (elapid) hunts other snakes and its powerful neurotoxic venom is used to immobilize its prey. Rattlesnakes and other viperids (hinged, moveable, front fangs) strike and release the prey and then search for the dying animal after it has ceased moving; their toxins are primarily proteolytic and hemotoxic.

Snake venom is an extremely complex mixture of enzymes, proteins, and peptides. To date, at least 26 enzymes have been characterized. Ten of these enzymes appear to be common to all the venoms studied. Different families of snakes generally contain higher concentrations of some fractions of enzymes than other fractions of enzymes; for example, the venoms of elapidae are rich in acetylcholinesterase, wheras those of crotalinae have not demonstrated any acetylcholinesterase but are rich in endopeptidase. Proteolytic enzymes are found in higher concentrations in the venomn of crotalines than in viperids, while elapid and hydrophiid (sea snakes) venoms contain small amounts of proteolytic enzymes or none at all.

All venoms are not created equal. There is variation in toxicity amoung species; geographic and seasonal variation of venom toxicity within species; and seasonal and age-related differences amoung individuals within a species. Also, the amount of venom injected can vary with each biting incident.

Fatal snakebites are more common in dogs than in any other domestic animal. Due to the relatively small size of some dogs in proportion to the amount of venom injected, the bite of even a small snake may be fatal. Because of their size, horses and cattle seldom die as a result of a snakebite, but death may follow bites on the muzzle, head, or neck when dyspnea results from excessive swelling. Serious secondary damage sometimes occurs; livestock bitten near the coronary band may slough a hoof.

Snakebite, with envenomation, is a true emergency. Rapid examination and appropriate treatment are paramount. Owners should not spend time in efforts at first aid other than to keep the animal quiet and limit its activity.

    For Example: Owners should NOT apply of the following: tourniquets, cut or suck venom out of the wound, wash or cleanse the wound with antiseptics, apply ice packs, give pain relievers or any other medication, or use electrical shock devices...it is crucial the pet is taken to an emergency veterinary facility immediately for identification of the bite, symptoms, emergency treatment.

Diagnosis: In many instances, the bite has been witnessed, and diagnosis is not a problem. However, many conditions thought by the owner to be snakebites are actually fractures, abcesses, spider envenomations, or allergic reactions to insect bites or stings. When possible, owners should be instructed to bring the dead snake along with the bitten animal; they should be warned not to mutilate the snake's head because identification may depend on the morphology of the head. Many bites do not result in envenomation, or are made by nonpoisonous snakes.

Typical pit viper bites are characterized by severe local tissue damage that spreads from the bite site. The tissue becomes markedly discolored within a few minutes, and dark, bloody fluid may ooze from the fang wounds if not prevented by swelling. Frequently, the epidermis shoughs when the overlying hair is clipped or merely parted. Hair may hide the typical fang marks. Sometimes, only one fang mark or multiple punctures are present. In elapine snakebites, pain and swelling are minimal; systemic neurologic signs predominate.

Signs and symptoms of a potential snake bite:

  • Rapid swelling primarily from edema
  • Pain, nausea, vomting, mental confusion, hypotension, respiratory distress, bleeding disorders, weakness, tachycardia, increased thirst, perioral numbness, fever, arrythmia, nystagmus
  • Salivation, convulsions, paralysis, respiratory paralysis, sloughing of skin/tissue, sudden death
  • Effects, and prolonged effects: Cardiovascular system, systemic hemmhorage, hemolytic, thrombocytopenic activity, nervous and central nervous system, muscular system, urinary system, renal system, respiratory system

Crucial Note: Even if local signs indicate mild signs or symptoms of a snake bite, it is important to note that some envenomizations may worsen in a matter of minutes, hours. Progression of symptoms can act extremely rapidly, necessitating immediate veterinary attention. Never waste time, immediate emergency veterinary treatment is critical for survival.

Treatment: Each case of envenomization is unique. There is no one treatment protocol recommended; instead, treatment is directed toward the clinical signs with the understanding that vigilant patient monitoring is a crucial component of successful treatment.

Intensive therapy should be instituted as soon as possible because irreversible effects of venom begin immediately after envenomation. Animals bitten by an elapine snake may be treated with antivenin (which may be available on an as-needed basis through larger human hospital emergency rooms) and supportive care, including anticonvulsants if necessary. A polyvalent antivenin (horse-serum origin) against North American pit vipers is readily available and should be used in all cases of substantial pit viper envenomation. The progression of events after pit viper envenomation can be divided into three phases: the first 2 hours, the ensuing 24 hours, and a variable period (usually ~ 10 days) afterward. The first 2 hours is the acute stage in which untreated, severely envenomized animals usually die. If death does no occur during this period, and the untreated animal is not in shock or depressed, the prognosis usually is favorable. The acute phase can be prolonged for several hours by use of corticosteroids and, if they are administered, prognostication should be witheld. If the animal is active and alert after 24 hours, death due to the direct effects of the venom is unlikely. The third phase is a convalescent period in which infection (possibly anaerobic) may be of concern. If necrosis has been extensive, sloughing occurs and may be so severe as to involve an entire limb. It is important to estimate the severity of envenomation. Although not infallible, it is prudent to consider both the size of the snake as an indicator of the quantity of venom injected, and the size of the snake relative to that of the victim. In dogs and cats, mortality is generally higher from bites to the thorax or abdomen than from bites to the head or extremities. However, this may relate to the size and vulnerability of the victim because smaller animals are more likely to be bitten on the body. Domestic animals vary in their sensitivity to the venom of pit vipers. In decreasing order, sensitivity is reportedly horse, sheep, goat, dog, rabbit, pig, and cat. If there has been a previous bite, the victim may have developed some degree of active humoral immunity and be less vulnerable to the toxic effects of the venom.

Treatment for pit viper envenomation should be directed toward preventing or controlling shock, neutralizing venom, preventing or controlling disseminated intravascular coagulation (DIC), minimizing necrosis, and preventing secondary infection. Any dog or cat presented within 24 hours of a snakebite showing signs of pit viper envenomation requires intensive treatment, starting with IV fluids to combat hypotension. The use of corticosteroids has been questioned, principally because they alone do not alter the ultimate outcome. They do, however, prolong the clinical course and therefore allow more time in which to institute curative measures. Rapidly acting corticosteroids may help to control shock, protect against tissue damage, and minimize the liklihood of allergic reactions to antivenin. Antivenin is highly beneficial because its action is the only direct and specific mechanism for neutralizing snake venom. Smaller animals probably receive a larger dose (per unit body weight) of venom than more massive animals and, accordingly, require proportionally larger doses of antivenin. Up to 100 ml of antivenin may be necessary for small dogs bitten by a large snake; 5-10 ml may be injected into the tissues around the bite, and the remainder given IV. The efficacy of antivenin is diminished if the bite occured over 24 hours previously. In the event of anaphylactoid reaction tot he heterologous (horse) serum components in antivenin, 0.5-1 ml of 1:1,000 epinephrine should be administered SC. If DIC occurs, appropriate treatment, including blood products and heparin sodium (in mini dose at 5-10 u/kg/hr or low dose at 50-100 u/kg, t.i.d.) should be administered SC. Broad-spectrum antibiotics should be given to prevent wound infection and other secondary infections. Several potential pathogens, including Pseudomonous aeruginosa, Clostridium spp, Corynebacterium spp, and staphylocci have been isolated from rattlenakes' mouths. Antibiotics should be continued until all superficial lesions have healed.

Tetanus antitoxin also should be administered; other supportive treatment (e.g., blood transfusion in the case of hemolytic or anticoagulant venoms) is administered as needed. In most cases, surgical excision is impractical or unwarranted. Antihistamines have been reported to be contraindicated, but diphenhydramine hydrochloride is frequently given along with antivenin to treat snakebite in man. Other procedures to neutralize venom (high-voltage, low amperage electric shock and trypsin) have not proved effective in controlled studies.

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Sources:
Emergency Practice in Small Animal Medicine- Compendium - Stormy Hudelson, DVM and Paul Hudelson, MA
Merck Veterinary Manual, Eighth Edition Copyright 1998 by Merck & Co, Inc.

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If you feel your kitty may have been bitten by a snake, do not waste time, get your kitty to an emergency veterinary hospital immediately, time may be of the essence. Remember, smaller animals are more susceptible to snake bite envenomation due to their size and typical route of exposure; in cats, particularly the head and neck areas or front limbs and thorax, where excessive and quick swelling can ensue, causing respiratory distress, along with quick action of skin and tissue necrosis. DO NOT DELAY in seeking immediate emergency veterinary treatment!

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National Animal Poison Control Center: (888) 426-4435
$50 Fee (V, MC, DC, AmEx) : 24 hrs / 7 days a week

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