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By Lin Chen, MD
At the eighth conference of the International Society of Travel Medicine (CISTM8) held in New York City, May 7-11, 2003, one symposium addressed envenomations, land and sea. Dr. Robert Norris discussed poisonous animals. The American Association of Poison Control Centers reported 93,821 calls for bites and stings in 2001, which comprised 4% of all calls to poison centers. There were only 3 recorded deaths from snake bites, all due to pit viper. Greatest threats for stings were the Hymenoptera (bees, wasps, ants). Anaphylaxis can occur in 0.5-5% of the population, resulting in 40-150 deaths per year. Yellow jackets rank first in the killer bee category.
Envenomation with spiders and scorpions occurs in the United States and includes widow spiders (Latrodectus spp.), brown spiders (Loxosceles spp.), hobo spiders (Tegenaria agrestis), and bark scorpion (Centruroides exilicanda). The widow spiders and bark scorpion are neurotoxic, whereas brown spiders and hobo spiders cause necrotic arachnoidism. Children are more severely affected. Tarantulas will bite when handled, but do not cause significant systemic toxicity. The hairs can cause urticarial dermatitis when aerosolized. The management for tarantula bite is primarily ice. Management of widow spider bite includes ice, tetanus-diphtheria booster, analgesics, and only rarely antivenom.
Snakebite rates were last assessed in the 1950-1960s, according to Dr. Norris, with an incidence of 8000 bites and 6 deaths per year. Most common causes in the United States are Mojavi rattlesnake, cottonmouth pit viper, copperhead, which is the least toxic of pit vipers, coral snakes, and Western diamondback rattlesnake. Risks associated with venomous snakebites are young age of the person bitten, male gender, and prior alcohol use. Pressure and immobilization are indicated in acute management. Antivenom, CroFab (sheep or ovine), binds to venom, and has a broad spectrum of activity. CroFab is manufactured by immunizing a host animal, harvesting the IgG, converting IgG to Fab, and purifying the product. It is an improved product when compared to previous antibody preparations. No skin testing is needed, it is safer, requires no pretreatment, and has a shorter duration of action. Acute reactions occur in 17%, but they are considered mild to moderate; serum sickness occurs in 3% of recipients. Each vial of CroFab costs $800, and 4-6 vials are needed to treat mild-to-moderate symptoms of snakebites.
Dr. David Warrell discussed current global issues concerning snakes, scorpions, and spiders. Community based studies on the risk to indigenous populations showed 14/100,000 bites per year in Senegal and 7.7/100,000 per year in Nigeria. Travelers also get bitten, as illustrated by 4 cases that Dr. Warrell presented:
Case 1. A 36-year-old male German tourist in central Bangkok heard some rustling in grass, and was bitten by a Cobra;
Case 2. A 45-year-old male visited Mazamari waterfall in Chanchamayo, Peru, grabbed a "rope," which turned out to be a bushmaster, Lachesis muta;
Case 3. A 38-year-old American herpetologist in Rat Baw, Burma, mistook a krait, Bungarus spp., as a benign Dinodon septentrondis. He succumbed to the neurotoxicity after prolonged resuscitation efforts;
Case 4. A 27-year-old male Dutch tourist was in Malacca, Malaysia, and uncovered a spitting cobra, Naja sumatrama, in his hotel bed.
High-risk areas for terrestrial snakebites are West Africa, Southeast Asia, Amazon, and New Guinea. Habitats include rain forest, savanna, and plantations. Rainy season and nighttime pose high risk. Risk is also related to activity, with zoologists, botanists, and explorers experiencing high risk.
First aid should emphasize immobilization, especially the bitten limb. Pressure-immobilization should be used for neurotoxic Elapid bites only and not for viper bites. The victim should be transported to medical care immediately to prevent death from shock or respiratory paralysis. Long bandage and splint are appropriate, but avoid harmful treatment.
Medical treatment should focus on rapid assessment, species diagnosis, and resuscitation. At bedside, a 20-minute whole blood clotting test can be done to determine whether coagulopathy is present. Laboratory evaluation should be obtained. Determine whether antivenom is indicated. Close observation of the patient and support of failing systems should continue. Treat the bitten limb. Provision and use of antivenom (which, unfortunately, can cause angioedema) should be considered by expeditions at remote locations, especially when signs of envenoming appear. If medical care is within 2 hours, the most appropriate approach would be immobilization with or without pressure, and evacuation. If medical care is more than 2 hours away, antivenom should be considered as IV or IM in anterolateral thigh, provided necessary skills and equipment are available. Evacuate on a strecher. Prevention should include learning something about indigenous snakes, protecting feet, and avoiding undergrowth and deep sand. Use a flashlight at night, and avoid sleeping on the ground.
Scorpions have a chitinous exterior, which is illuminated by ultraviolet rays. Between 4000 and 5000 stings occur each year. Risks are highest in North Africa, Middle East, southern Africa, India, southern United States, Mexico, Latin America, and Trinidad. Clinical features include excruciating local pain, autonomic storm (tachycardia, hypertension, myocarditis), vomiting, diarrhea, and fasciculations. First aid following scorpion stings should include local anesthetic by digital or nerve block, analgesia (opiates), antivenom for systemic envenoming, and ancillary drugs such as vasodilators (a-blockers), and anticonvulsants. Avoid harmful measures such as local dehydroemetine, electric shock, and cardiac glycosides.
Hot spots for spider bites are Australia, United States, Latin America, Mediterranean Europe, and South Africa. Clinical features are differentiated into necrotic bites vs neurotoxic bites. Necrotic bites are associated with increased pain over 12-36 hours, a local skin lesion, the red-white-blue skin sign, eschar formation in 7 days, fever, rash, hemolysis, hemoglobinuria, and renal failure. Case fatality rates are 1.5-3.7%. Neurotoxic bites are associated with severe pain, redness, sweating, headaches, nausea, vomiting, fasciculations, and muscle cramps. Treatment is with antivenom. For necrotic bites, dapsone, which inhibits leukocyte migration, can be considered. Steroids should be avoided. For neurotoxic bites, calcium gluconate can be considered.
Dr. Dietrich Mebs discussed marine envenomation and poisoning. Although the horseshoe crab is benign when touched, it may be poisonous when eaten. The box jellyfish has nematocysts that inject a toxic venom, which causes reactions from local blebs to cardiac failure. The Portugese Man-of-War looks like a plastic bag under water. First aid following jellyfish sting includes application of vinegar (acetic acid), which inactivates undischarged nematocysts.
Hot water treatment is controversial for venomous fish such as the stingray. Pufferfish (Fugu), another venomous fish, contains high concentrations of tetrodotoxin. Another toxin, ciguatera, is associated with diarrhea, vomiting, neurologic symptoms such as hot and cold reversal, paresthesia, and pruritus. Following envenomation, the goal is to treat symptoms using i.v. mannitol in the first 1-2 hours. Prognosis is good.
Shellfish can be associated with paralytic shellfish poisoning, caused by toxins such as saxitoxin. Symptoms are paresthesis, numbness, and progressive paralysis. Amnesia can result with cerebral symptoms, coma, or irreversible short-term memory impairment. Diarrhea can also occur. Scombroid toxicity is another poisoning associated with seafood and produces symptoms resembling allergic reactions. Ingesting the meat of whales and polar bears, which have high vitamin A concentrations in their livers, has lead to vitamin A intoxication.
References and Additional Resources
1. Auerbach PS, ed. Wilderness Medicine. 4th Edition. St. Louis, Mo: Mosby, Inc; 2001.
2. Norris RL, et al. Chapter 13. Animal Poisons in the Tropics. In: Tropical Infectious Diseases. Guerrant RL, Walker DH, Weller PF, eds. Philadelphia, Pa: Churchill Livingstone; 1999.
3. Warrell DA. Chapter 32. Animal Toxins. In: Manson’s Tropical Diseases. 21st Edition. Cook G, Zumla A, eds. London: Saunders; 2002.
Dr. Chen is Clinical Instructor, Harvard Medical School, Director, Travel Resource Center, Mt. Auburn Hospital, Cambridge, Mass.