Venomous Snake Bites

Rhea V. Morgan, DVM, DACVIM (Small Animal), DACVO

BASIC INFORMATION diagnostic tests are available to confirm the presence of venom Description in the body; rather, laboratory tests are used to assess damage to Snake envenomation occurs when poisonous material is injected into blood cells and other body organs. the victim during a bite. Of the 120 species of snakes that live in the United States, only 25 are venomous. Alaska, Maine, and Hawaii TREATMENT AND FOLLOW-UP are the only states without venomous snakes. With the exception of the coral snake, all venomous snakes in the United States are pit vipers. Treatment Options Pit vipers include rattlesnakes, cottonmouths, and copperheads. No effective measures exist to prevent spread of the venom from the Causes bite site, so cutting and sucking on the wounds, applying a tourni- The composition of snake venom varies by species and age of the quet, and applying ice are not recommended. If a snake bite is sus- snake, season of the year, geographic location, and time since the pected, transport your pet to a veterinary hospital immediately! snake’s last bite. Venom is not injected with every bite. In up to 25% of Treatment of pit viper bites involves intravenous (IV) fluid pit viper bites and 50% of coral snake bites, venom is not released. therapy and other medications for shock, administration of pain Pit viper venom kills cells at the site of the bite, and may cause medications, and local cleansing of the wound. If the animal is in hypovolemic shock, destruction of red blood cells, and abnormal respiratory failure, a mechanical ventilator may be used and oxygen bleeding. Neurotoxins in the venom may produce muscle weak- therapy started. Antivenin (antivenom) is available from two dif- ness and respiratory paralysis. ferent manufacturers. Cottonmouth and copperhead bites are less Coral snake venom causes less local tissue damage, but it con- likely to require antivenom than bites from the Eastern diamond- tains a neurotoxin that causes progressive weakness and respira- back, Western diamondback, or Mojave rattlesnake. Antivenin is tory failure. Destruction of red blood cells can also occur. added to the IV fluids and may be repeated as needed, depending on the response induced. Severe tissue death at the wound site may Clinical Signs require surgery at a later date. Signs usually develop within 30 minutes after a pit viper bite. Following a coral snake bite, most animals are hospitalized for Puncture wounds that ooze bloody liquid and pain and swelling at at least 48 hours, because clinical signs can be delayed for 10-18 the bite site are common. Evidence of shock may be present, with hours. Treatment is primarily supportive, with IV fluids, oxygen high heart and respiratory rates, weak pulses, pale gums, weakness, therapy, and mechanical ventilation as needed. No commercial and mental dullness. Widespread microscopic blood clot forma- coral snake antivenin is currently available in the United States. tion within the body may consume all available circulating clotting Antivenin produced for Australian tiger snake and Mexican coral proteins, with subsequent serious bleeding from many body sites. snake bites may be helpful and can be considered for suspected Abnormal effects on red blood cells may occur within 24 hours, and coral snake bites. platelet numbers may decrease within 2 weeks. Progressive muscle weakness and respiratory paralysis may develop. Severe tissue Follow-up Care death around the bite wound may occur within 6-24 hours. Muscle Frequent monitoring is needed for 24-48 hours. During initial destruction, with secondary kidney failure, may also occur. therapy, blood pressure, pulse quality, gum color, heart rate and Fang wounds are not as obvious with coral snake bites, and less rhythm, breathing rate, blood oxygen levels (pulse oximetry), neu- local tissue damage occurs. Generalized muscle weakness or trem- rologic reflexes, body temperature, and urine output may be moni- ors, drowsiness, disorientation, drooling, and trouble swallowing tored. In the following days, laboratory tests and chest x-rays may may occur within 3 hours. Difficulty breathing and aspiration be performed to detect problems that may arise in other organs pneumonia may develop. Death from respiratory failure can occur from the effects of the venom. within 4 hours. Sometimes the onset of weakness and paralysis is Prognosis delayed for up to 48 hours. Prognosis depends on the location of the bite on the animal (legs are best; head and face are the worst sites), amount of venom Diagnostic Tests injected, and availability of antivenin. Many dogs survive with Diagnosis is often made by observation of the bite, discovery of appropriate, intensive therapy; however, signs of neurotoxicity bite wounds, and the presence of compatible clinical signs. No may not be reversible.