Bites and Toxic Envenomation
From WiserWiki
[edit] Bites and Toxic Envenomation
Ann Gateley
Patrick McKinney
Human encounters with the animal world, both in the domestic setting and in the wild, provide ample opportunities for bites and envenomations. The primary care physician is often called on to treat or triage these wounds.
[edit] ANIMAL AND HUMAN BITES
[edit] Dog Bites
Dog bites are the most frequently reported bite, averaging over half a million cases reported per year in the United States. The human victim is usually a 7-to 9-year-old boy, who is often teasing or playing with a dog. The dog is most often a working dog, such as a boxer, collie, German shepherd, Great Dane, or a sporting dog, such as a pointer, setter, or retriever.Occasionally, dogs inflict extensive wounds resulting in death by trauma.
[edit] Cat Bites
Cat bites are less frequently reported. Because of their size and the sharpness of their teeth, domestic cats deliver puncture wounds, mainly in the hand. It is estimated that over 50% of cat bites become infected. Serious complications include infectious tenosynovitis, closed space infection of the hand, and inoculation of the periosteum, leading to osteomyelitis.
[edit] Management of Dog and Cat Bites.
Evaluation and treatment of bite wounds depends on the immune status of the victim, site of the bite, and extent of the wound. Most wounds should be irrigated and left open. Deep wounds can be closed by delayed primary closure after 3 days if there is no apparent infection. Facial wounds are usually referred to a surgeon and can be closed after careful irrigation, exploration, and cautious debridement. Hand wounds should be followed closely for closed space infection. Splenectomized patients or other immunocompromised patients should be treated with prophylactic antibiotics. Tetanus immune status should be evaluated, and rabies immunization considered in certain cases.
A prospective study of infected wounds from dog and cat bites found that infection was due to aerobes and anaerobes together or singly in over 90% of the cases. Pasteurella species were the most common isolates in both cat bites (75%) and dog bites (50%). Other common aerobic isolates included streptococci, staphylococci, Moraxella, and Neisseria organisms. Therefore, if wounds become infected or prophylaxis is indicated, a β-lactam and β-lactamase inhibitor (e.g., amoxicillin/clavulanic acid) would be appropriate. Treatment recommendations are summarized in Box 94-1.
| Box 94-1 - Recommendations for Treatment of Dog and Cat Bites |
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[edit] Special Issues with Dog and Cat Encounters
[edit] Cat-scratch Disease.
Cat-scratch disease (CSD) is a worldwide bacterial infection of the Bartonella species. In the United States, CSD typically occurs in children or adolescents most often in the fall or winter. Over 95% have had a history of contact with cats, usually kittens. Cats act only as vectors; they do not become ill themselves. Fleas appear to transmit the bacteria among cats, but data do not support flea-to-human transmission.
The typical history includes a scratch, perhaps a bite as well, 3 to 10 days before developing a round, reddish, nontender papule at the site (Fig. 94-1). Proximal lymphadenopathy develops, often the epitrochlear, axillary, or cervical nodes, within a week to 2 months after appearance of the papule. These nodes may be tender or nontender and may suppurate and drain late in the course. Systemic symptoms may include fever, headache, or malaise. Rare complications include encephalopathy, endocarditis, stellate retinitis, or oculoglandular disease (Parinaud's syndrome, which is preauricular lymphadenopathy with conjunctival granulomas), and systemic dissemination with hepatosplenomegaly. The diagnosis is suggested by a history of regional lymphadenopathy developing slowly over weeks after a cat scratch. The history of a prior papule is highly supportive of the diagnosis. Rarely, bacteria can be recovered from blood or lymph nodes. Positive serology for Bartonella henselae is confirmatory.
In the immunocompetent host, the disease is granulomatous, suppurative, and usually self-limited. In the immunocompromised patient, the disease is vasculoproliferative and can be progressive and fatal if untreated. Antibiotics that appear to be the most effective include macrolides, tetracyclines, aminoglycosides, and quinolones.
[edit] Rabies.
Humans are at risk for acquiring various zoonoses from domestic and wild animal bites. However, in the case of the viral infection of rabies, no effective treatment exists for the full-blown clinical syndrome of encephalomyelitis. Therefore, preexposure and postexposure prophylaxis are critical considerations.
The virus of rabies is introduced into the body through the bite of an infected animal. The virus travels centrally alongperipheral nerves, producing a focal encephalitis that mainly involves the cervical cord, the brainstem, and the temporal lobes (Fig. 94-2). The latent period between the bite and the clinical features of the disease may be as long as a year.
Clinically, early irritability and agitated delirium lead on to muscle hypertonia especially affecting the pharyngeal muscles, which go into spasm—thus the term hydrophobia. Convulsions and death usually occur within 10 days of the onset.
Fortunately, because of effective vaccination of domestic animals, the human disease is rare in the United States with fewer than five cases reported per year. Although dogs account for most cases of rabies worldwide, the sylvatic reservoir of skunks, raccoons, wolves, bats, woodchucks, and foxes account for 90% of rabid bites in North America. The infected animal has the rabies virus proliferating in the salivary glands (see Fig. 94-2). Any introduction of this saliva into skin or mucous membranes constitutes an exposure.
The decision to prophylactically treat for rabies is based on the history (species of animal, apparent state of health of the animal, and circumstances of the attack) and local public health data on the prevalence of rabies and examination of the wound. Significant risk of exposure is based on the extent and depth of the wound. If the decision to offer postexposure prophylaxis is made, the wound should be cleaned thoroughly and a virucidal agent used if available (e.g., povidine iodine). Both passive and active immune products should be used. The passive agent (rabies immune globulin) should be infiltrated around the wound at 20 IU/kg body weight. The active immune–response producing product should be given in the deltoid area on days 0, 3, 7, 14, and 28.
Preexposure prophylaxis is offered to individuals, such as veterinary personnel, laboratory workers, and spelunkers, who may be members of high-risk groups. The recommendations for preexposure prophylaxis are summarized in Box 94-2.
| Box 94-2 - Recommendations for Preexposure Rabies Prophylaxis✢ |
High Risk Group
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[edit] Human Bites
Human bites deserve special attention because a large percentage of them become infected with aerobic andanaerobic mouth organisms. A bite to the hand is at risk for a serious closed-space infection. The physical examination should be thorough with special attention to those wounds over a joint or deeply penetrating with possible periosteal contamination. The wound should be irrigated copiously and left open. The patient should be started on oral antibiotics and referred to a hand surgeon if there is a question of deep space or joint and bone infection. Additionally, referral should be made if a hand wound is sustained at high velocity (e.g., a punch to the mouth) since these wounds are deep and at high risk for infection.
[edit] Special Issues with Human Bites.
Human bites now include concern for inoculation of the human immunodeficiency virus (HIV) and hepatitis B virus (HBV). If the bite is from a high-risk individual, prophylaxis with antiviral agents or immunoglobulin may be indicated. Management recommendations for human bites are summarized in Box 94-3.
| Box 94-3 - Recommendations for the Treatment of Human Bites |
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[edit] ARTHROPOD ENVENOMATION
[edit] Spiders and Scorpions (Arachnida)
Over 20,000 species of spiders are found in the United States and almost all produce venom. About 50 of these species have fangs large enough to penetrate human skin. Bites from the majority of these 50 species produce only minor local pain or mild cutaneous reactions. Two spiders with medical significance to humans account for the two main envenomation syndromes, the black widow syndrome or Latrodectism, and a dermonecrotic syndrome, which may be produced by brown spider members of the genus Loxosceles, as well as several others.
[edit] Black Widow (Latrodectus).
Members of the Latrodectus genus are found throughout the continental United States. Typically, only the female is large enough to envenomate humans. The spider is easily recognizable with a shiny, round abdomen, small cephalothorax, and long, spindly legs. Although known as the “black” widow, the spider may be black, brown, tan, or even variegated, and the classic red hourglass on the ventral abdomen may be an indistinct yellow or orange spot. The web is coarse and irregular and is often found in brush piles, around stacks of firewood, and in garages and basements. The venom contains multiple fractions that activate cation channels, resulting in sympathetic and parasympathetic activation and muscular spasm.
Most bites occur on the lower extremity and may occur when the spider has crawled into clothing or bedsheets. The initial black widow bite is sharp and mildly painful. The bite site is often not remarkable. One or two small punctures may be seen 1 or 2 mm apart with a zone of erythema or a target lesion. Thirty minutes to 12 hours after the bite, muscular cramping begins, usually in the large muscle groups of the back, thighs, and stomach. Hypertension and diaphoresis may occur. Severe envenomations may cause a maculopapular rash and periorbital edema, salivation, lacrimation, tachypnea, tachycardia, convulsions, and respiratory failure. Deaths are extremely rare. Untreated, the symptom complex may last several days, although weakness and spasm may recur for weeks to months.
Therapy is directed primarily toward relieving muscle pain and spasm. A combination of an opioid and a benzodiazepine is often successful. Parenteral administration of these drugs is often necessary. Calcium gluconate intravenous injection may be used; however, relief is inconsistent and often transient. Hypertension usually resolves when adequate analgesia is administered; however, calcium channel blockers and β-adrenergic blocking agents are two reasonable choices if therapy were needed. An equine-derived antivenin is available, but its use should be limited to severe envenomations because of the risk of anaphylaxis and serum sickness. Antivenin may be indicated for severe symptoms that are not responsive to conservative therapy and for higher risk patients including children, pregnant women, geriatric patients, and those with preexisting hypertension or vascular disease. Symptoms typically resolve almost immediately with 1 to 2 vials of antivenin. Most patients treated with antivenin improve within 24 to 48 hours.
[edit] Brown Spiders (Loxosceles).
The brown recluse spider, Loxosceles reclusa, is found primarily in the Midwestern United States, but other members of the genus Loxosceles are distributed across the United States. Loxosceles spiders are less distinct than black widows and can easily be mistaken for a variety of other spiders. They are brown-to-tan in color, with a hair-covered abdomen and a cephalothorax marked by a darker inverted violin or “fiddle” on the dorsal side. Loxosceles spiders are often found indoors, hiding in clothes and bedsheets. The spider is usually not seen at the time of the bite, making definitive diagnosis problematic. The venom contains various proteases, peptides, and sphingomyelinase D that result in local inflammation, polymorphonuclear cell attraction, local small vessel thrombosis, and tissue necrosis. The venom has hemotoxic constituents as well.
The initial Loxosceles bite is mildly painful and may not be noticed at all. An area of redness develops surrounded by pallor then ecchymosis within hours. Vesicle formation may occur within the first 2 hours. Mild systemic symptoms, such as malaise, chills, sweats, dizziness, gastrointestinal upset, and headache may occur. Within 24 to 48 hours, an area of central necrosis may be seen that may continue to enlarge for several days. In a minority of cases, large slow-healing ulcers are formed.
A systemic syndrome of toxicity may occur marked by fever, myalgias, chills, hemolysis, disseminated intravascular coagulation (DIC), and, rarely, renal dysfunction and death. The development of the systemic syndrome does not appear to be correlated to the appearance of the necrotic lesion.
Initial treatment should be directed toward local woundcare. In the case of suspected infection, an antibiotic with coverage of skin flora, such as cephalexin or erythromycin, is indicated. Early excision is to be avoided because appropriate wound margins are difficult to identify, and a large surgical wound with necrotic margins may result. Other therapies, such as dapsone, hyperbaric oxygen, and corticosteroids, are controversial and should not be routinely recommended pending more favorable data.
[edit] Hobo Spider (Tegenaria).
The hobo spider, Tegenaria agrestis, is found in the Pacific Northwest and is a common cause of necrotic bites in this area. Local necrosis resembling a brown spider bite may occur and similar systemic syndromes have been reported.
The great majority of patients who present with a presumed necrotic bite did not see the spider or insect and often were not aware of the bite at the time. Because of this, diagnosis must be presumptive and the differential diagnosis of cutaneous necrosis (diabetic ulcers, herpes simplex, pyoderma gangrenosum, Lyme disease, purpura fulminans, foreign body, factitious ulcer, fat necrosis, vasculitis, or heparin or warfarin necrosis) should be kept in mind. It is important not to diagnose beyond the limits of the history and examination to avoid undue patient anxiety and potential adverse effects of unnecessary therapy. In many cases, the diagnosis of “necrotic skin lesion” or “necrotic insect bite” may be as specific as the history and examination allow.Box 94-4 lists spiders that may produce a dermonecrotic lesion.
| Box 94-4 - Spiders That May Produce a Dermonecrotic Lesion |
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[edit] Scorpions (Centruroides).
Scorpions are large arachnids (2 to 8 cm) with pincers, a segmented body, and a tail equipped with a stinging apparatus (Fig. 94-3). Scorpion envenomation is a common occurrence in the southwestern United States, but the majority of bites produce only local pain. The only indigenous scorpion with a medically significant envenomation syndrome is Centruroides exilicauda, which is found in Arizona, Texas, Nevada, New Mexico, California, and Mexico. This scorpion is slender yellow or brown and is also known as the bark scorpion.
Severe local pain and hyperesthesias, restlessness, hypertension, and autonomic dysfunction mark Centruroides syndrome. Roving eye movements, dysphagia, respiratory distress, salivation, slurred speech, and rarely, pancreatitis, rhabdomyolysis, metabolic acidosis, and pulmonary edema can be seen. The majority of severe envenomations occur in young children. Diagnosis is usually made in conjunction with the observations of a scorpion bite, but in cases where the bite was not witnessed, appropriate signs and symptoms may strongly suggest the diagnosis. Treatment is primarily supportive.
[edit] Wasps, Bees, and Ants
The order, Hymentoptera (Insecta), includes three families of medical importance: Vespidae (wasps, yellow jackets, hornets), Apidae (bees) (Fig. 94-4), and Formicidae (ants). Hymenoptera stings are responsible for more deaths than rattle snake bites every year in the United States. Most of these deaths are due to anaphylaxis, although massive envenomations may result in serious toxicity and even death. It is speculated that up to 50% of sudden deaths occurring outdoors may be due to Hymenoptera-induced anaphylaxis. Groups at risk include the elderly, those with preexisting cardiac disease, and those with multiple previous stings. Hymenoptera sting anaphylaxis is probably an IgE-mediatedhypersensitivity reaction. However, many cases of Hymenoptera anaphylaxis have no previous history of sting, which suggests a non-IgE-mediated mechanism may play a role. Hymenoptera venoms are antigenically similar, therefore there may be some cross reactivity among families.
[edit] Wasps, Yellow Jackets, and Hornets (Vespidae).
Yellow jackets are the most aggressive of the flying Hymenoptera and are responsible for the greatest number of stings (excluding bee stings incurred by beekeepers). Yellow jackets nest in the ground and are often found in areas of human activity. They are attracted to bright colors, floral patterns, sweet floral scents, and carrion. Hornets and wasps typically nest off the ground and are less likely to be found in areas where human contact is likely. The vespidae stinging apparatus is located at the distal end of the abdomen, and they may sting more than once. In contrast, honeybee stingers are barbed, and the stinger usually remains embedded in the victim, mortally wounding the bee. Potential venom allergens and toxins include phospholipase A, hyaluronidase, acid phosphatase, mellitin, kinins, serotonin, dopamine, apamin, and other polypeptides.
[edit] Africanized Honeybees (Apidae).
Most North American honeybees are descendants of European strains and are generally docile unless provoked. In the 1950s, African honeybees were imported to Brazil in hopes of producing a hybrid better suited to tropical climates. The resulting “Africanized honeybees” (sometimes referred to as “killer bees”) are much more aggressive than their European cousins and more cold tolerant than pure African strains. Thus hives composed of very aggressive bees have been migrating northward. The northernmost limit of their range is not known. Africanized honeybees swarm frequently and will attack at seemingly minimal provocation. They are capable of stinging in massive numbers and will recruit other hive members through pheromone signaling. Once agitated, the hive will remain active for many hours, endangering other people or animals that wander into its range. The primary danger of the Africanized bee is the potential for massive numbers of stings, numbering in the hundreds or even thousands. It is estimated that 2000 stings may be fatal to a healthy adult, although far fewer may be dangerous to children or older patients with cardiopulmonary disease. Massive stings may cause acute renal failure, rhabdomyolysis, and hemolysis independent of any immune mechanism.
If attacked by a swarm of bees, the most effective strategy is to run from the scene. Africanized bees reportedly will not pursue aggressors more than ¼ to ½ mile. Avoid smashing the bees as pheromones will be released that may agitate and recruit other hive members.
[edit] Fire Ants: Solenopsis (Formicidae).
Imported fire ants can be found across the southeastern United States. Fire ants are small black or red ants and appear similar to other native ant species. Their mounds are composed of loose dirt and may house hundreds of thousands of individuals. Mounds extend far underground, making eradication very difficult. Stings occur when the mound is disturbed; agitated ants stream out and hundreds of bites can occur in seconds. The ant grabs the skin with large mandibles and envenomates with the distal stinger (which it may swivel around its head), producing a circular series of stings. The venom has necrotic and hemolytic effects and produces painful, edematous lesions, which usually form pustules. Scarring can occur. Extensive local reaction with persistent pain and swelling may be seen. Although the pustules are sterile, cellulitis and superinfection can occur. Systemic symptoms including DIC, seizures, rhabdomyolysis, and mononeuritis may be seen in 1% to 2% of cases. In the Southeast, fire ant stings are now the leading cause of insect sting hypersensitivity.
[edit] Management of Hymenoptera Stings.
Local sting reactions begin with immediate pain and swelling. Symptoms typically resolve within 24 to 48 hours. Cold packs and antihistamines are occasionally required. Severe local reactions, such as massive swelling of the stung extremity, may occur. Corticosteroids and H1 and H2 blockers may provide benefit. Stings in proximity to the airway may compromise respiratory status. Most serious envenomations are due to anaphylaxis. Following the sting, symptoms reflecting mast cell degranulation occur in sensitized individuals. Hoarseness, wheezing, and laryngotracheal swelling may occur, along with pruritus and urticaria. Anxiety and gastrointestinal symptoms, such as nausea and vomiting, may be seen. In more severe reactions, cardiovascular toxicity including hypotension and myocardial ischemia may develop. Deaths due to Hymenoptera stings that do not show evidence of airway obstruction may be due to direct cardiovascular causes.
Symptoms of anaphylaxis including hypotension, hoarseness, or other evidence of airway compromise should be treated aggressively. An IV line should be established, and the patient should be placed on a cardiac monitor. Epinephrine 0.3 to 0.5 mL 1:1000 should be given subcutaneously, if there are no contraindications. Antihistamines should be given (H1 and H2 blockers); diphenhydramine 25 to 50 mg IV and cimetidine 300 mg IV are reasonable choices. For cases with severe airway compromise or hypotension, epinephrine 1 mL 1:10,000 can be given intravenously. Orotracheal intubation or cricothyrotomy may be necessary.
Patients with moderate to severe allergic reactions to Hymenoptera stings should be monitored for a minimum of 8 to 12 hours to watch for recurrence or delayed manifestations of anaphylaxis. All patients with allergic reactions should be counseled about insect stings and be provided with an autoinjectable epinephrine device and oral antihistamines and instructed about their use. They should be told to seek emergency health care immediately if they are stung again. The purchase of a medical alert bracelet should be considered. These patients, like any with anaphylaxis, should also be referred to an allergist for consideration of immunotherapy. Venom immunotherapy has been associated with an overall desensitization rate of 98%.
If one is stung by a bee, the stingers should be promptly removed because the venom sac remains attached and may contract, injecting more venom. It is generally recommended to scrape the stingers out rather than grasping them with fingers or tweezers to avoid squeezing the venom sac.Box 94-5 summarizes the management of Hymenoptera stings.
| Box 94-5 - Recommendations for the Treatment of Hymenoptera Stings |
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[edit] REPTILIAN ENVENOMATION
About 8000 poisonous reptile bites (mostly snake bites) are reported each year. Usually less than three deaths per year result from these bites. The vast majority of envenomations occur in intoxicated young men and in children. Regionally,the largest number of reported bites are from the Southwest and the Gulf Coast area. Ninety percent of these reported bites occur from April through October. The majority of the bites are on extremities.
To avoid bites, it is important to understand reptiles. Because reptiles cannot regulate their body temperature, they are most active in the evening of hot summer days. They will inevitably seek relief from heat on hot days and seek warmth on cool days. Careful foot placement in wooded areas and the avoidance of casual hand placement in concealed areas are important. Wearing long loose pants with high top boots are helpful strategies to help prevent bites.
The two major families of poisonous snakes in North America are the Crotalidae (pit vipers) and Elapidae (coral snakes). One family of poisonous lizards, Heloderma (Gila monsters), is found in southern Arizona, New Mexico, and Nevada.
[edit] Pit Vipers (Crotalidae)
Crotalidae are represented by rattlesnakes, copperheads, and water moccasins (cottonmouths). These snakes have a triangular head and a heat-sensing maxillary pit located between each nostril and eye. They have vertical pupils and an obvious neck between the head and body (Fig. 94-5). Most of this country's venomous bites are from rattlers, which usually strike after a warning rattle. These snakes' venom is complex with variable enzymes and toxic proteins that serve to decrease the escape of the prey and to increase digestion. Crotalid proteolytic enzymes result in significant local necrosis, as well as increased capillary permeability leading to hypotension. The venom is delivered via dual fang hypodermic injection.
[edit] Clinical Syndrome and Management.
The degree of toxicity of envenomation depends on the type and size of pit viper. Copperhead venom and water moccasin venom, although similar to rattlesnake venom, are less potent. The larger the snake, the more potentially serious the envenomation. Up to 30% of pit viper bites deliver little or no venom.
Most envenomations are marked by instant pain, followed by swelling and ecchymosis within the first 15 minutes. Usually one or two puncture sites or a scratch can be located. Initial first aid includes calming the victim, immobilizing the limb below the level of the heart and rapidly transporting the patient to a health care facility. There is no clear documented benefit of electric shock administration, cryotherapy, or tourniquet placement. Only the Sawyer Extractor, a powerful suction device applied within 3 minutes and left on for 30 minutes has been demonstrated in animal studies to be helpful in extracting venom.
After transportation to the emergency room, priorities include establishing a physiologic baseline and IV access. The next step is to assess the degree of envenomation and the need for antivenin by noting the advancing borders and the increasing circumferential swelling, as well as laboratoryabnormalities. The examination and laboratory studies should be repeated every 6 hours until the patient is stable. Before administration of antivenin, the patient should be skin tested for hypersensitivity. Commercial antivenin is a pooled hyperimmune serum from a equine source and is suitable for all Crotalid envenomations but is highly allergenic.Table 94-1 summarizes IgG antivenin administration.
Table 94-1 Guide for IgG Crotalid Antivenin Administration
| Level of envenomation | Administration |
|---|---|
| No envenomation | No antivenin |
| Mild envenomation | 5-10 vials |
| Moderate envenomation | 10-20 vials |
| Severe envenomation | >20 vials |
A new product of sheep-derived, highly-purified polyspecific crotalid antivenin consisting of Fab fragments is now available at several locations in areas where snake bites are highly prevalent. The Fab fragment binds with the toxins as does the older IgG antivenin. However, the Fab toxin is smaller than the IgG toxin, has a larger volume of distribution, and can be more rapidly eliminated by renal clearance. Case studies have suggested immediate reversal of clinical deterioration, including neurotoxicity, with Fab-antivenin administration in mild-to-moderate cases of envenomation. Repeat doses over 36 hours may be necessary for local control of symptoms. This newer antivenin appears to have less allergic complications.
[edit] Coral Snakes (Elapidae)
Coral snakes are found primarily in the Southeastern United States (Eastern coral snake) and in the Western United States (Western or Sonoran coral snake). These snakes are typically small and colorful with black noses and round pupils. Because of their short, fixed fangs and small mouths, they rarely cause significant envenomation. Elapidid venom has significant neurotoxicity. The clinical envenomation syndrome may initially cause few local symptoms but may be followed after 15 minutes to an hour with extremity weakness, paresthesias, and fasciculations. Several hours later, systemic toxicity may become manifest. These symptoms may include tremors and paresthesias. Late (5 to 10 hours) symptoms may include cranial nerve palsies. Death is rare. Therapy includes antivenin for the Eastern coral snake envenomation and supportive care.
[edit] Gila Monster and Mexican Beaded Lizard (Helioderma)
The only species of venomous helioderma lizards found in the United States are found in southern Arizona, New Mexico, and Nevada. The Gila monster and the Mexican beaded lizard are large with flat heads and bulging mandibular areas. The envenomation occurs through capillary action after the lizard has grasped the victim and punctured the skin. Not all bites result in envenomation but both lizards, particularly the Gila monster, may hang on and require assistance in dislodging. The clinical syndrome usually involves intense, severe pain at the wound site, edema, and systemic symptoms of mild hypotension. Severe local or systemic complications are rare. Treatment involves cleaning the wound and providing analgesia.
[edit] MARINE TOXIC ENVENOMATION
Many sea creatures are capable of inflicting serious injury and toxic envenomation. Two common sources of marine envenomation in the United States are jellyfish and stingrays.
[edit] Jellyfish (Cnidaria)
The Cnidaria are represented along all three coasts in the United States. Toxic jellyfish possess venom discharging cells called nematocysts that are found in their tentacles. The sea nettle (Chyrsaora quinqecirrha) is one of the most common of the jellyfish found along the Atlantic and Gulf coasts (Fig. 94-6). Its close relative, the lined sea nettle, is commonly encountered along the Alaska and California coasts. Contact with a sea nettle usually produces a mild pruritic rash. Extensive contact may produce a systemic reaction, including severe cramps and respiratory difficulty.
Highly toxic reactions may result from contact with two common, large jellyfish. The first, the Portuguese man-of-war (Physalia physalis), is a jellyfish that floats on the surface by means of a gas-filled float that changes shape to catch the prevailing wind. Its tentacles contain an extremely toxicpoison that can produce severe burns and blisters even when the jellyfish is dead and has washed up on the beach.
The lion's mane (Cyanea capillata) is the other highly toxic jellyfish. It is prevalent along the Pacific, Atlantic, and Gulf coasts. This jellyfish has a bell-like saucer shape and develops a reddish-brown color as it grows larger. It has 16 marginal lobes and shaggy clusters of more than 150 tentacles below. Lion's mane is the largest jellyfish in the world, sometimes attaining a diameter of 8 feet. Its tentacles produce severe burning and blistering, and exposure may cause muscle cramps and respiratory difficulty.
[edit] Management.
A swimmer who sustains major contact with any poisonous jellyfish should be brought aboard a boat or assisted to the beach because swimmers can panic and drown when stung. Ocean water should be poured over the wound; sand should not be rubbed on the wound because this will fire the nematocysts that have not discharged. Alcohol or acetic acid (vinegar) inactivates the penetrating nematocysts. An attempt should be made to remove the tentacles with protective gloves. A paste of talc or shaving cream may be used with subsequent skin scraping. A traditional but unproved treatment is to cover affected areas of skin with meat tenderizer. The papain present in most of the preparations supposedly digests the nematocysts and tentacles and alleviates the discomfort. Hot water should not be used on coelenterate stings; it may also cause firing of the nematocysts. No systemic drugs have shown to be helpful except for analgesia.
[edit] Stingray (Rajiformes)
On the North American coasts, several spiny groups of fish contain poison. This group includes the stingray, which is responsible for most human envenomations by fish.
Stingrays abound off the coast of southern California, the south Atlantic states, and the Gulf coast. The stingray body is flattened, and the pectoral fins broadened laterally so that they present a flat disk. The tail is long and equipped with barbs (Fig. 94-7). The barb often penetrates a foot of a wader, releases venom, and lacerates tissue on coming out. The pain is sharp and immediate. The jagged wound bleeds and may contain torn integumentary sheath. The leg becomes edematous, and if a large amount of venom is inoculated, systemic symptoms may also occur.
[edit] Management.
Treatment starts with immediate and thorough irrigation of the wound with a cold diluent (e.g., salt water) to remove the venom and act as a vasoconstrictor. The wound is then immersed in hot water to tolerance for at least ½ to 1 hour. The heat will neutralize the toxin. Finally, remaining pieces of sheath should be searched for. In general, wounds are to be left open. Tetanus toxoid should be given if the last booster was more than 5 years before, and antibiotics should be prescribed to cover marine organisms such as the vibrio species.
[edit] ADDITIONAL READINGS
- JW Bass, JM Vincent, DA Person: The expanding spectrum of Bartonella infections. II. Cat-scratch disease. Pediatr Infect Dis J 1997; 16:163 - 179.
- RA Berg,et al.: Envenomation by the scorpion Centruroides exilicauda (C. sculpturatus): severe and unusual manifestations. Pediatrics 1991; 87:930 - 933.
- RC Dart,et al.: Affinity-purified, mixed monospecific crotalid antivenom ovine Fab for the treatment of crotalid venom poisoning. Ann Emerg Med 1997; 30 (1):33 - 39.
- TM Davidson,et al.: North American pit vipers. J Wildern Med 1992; 3:397 - 421.
- R DeShazo, BR Butcher, WA Banks: Reactions to the stings of the imported fire ant. N Engl J Med 1990; 303:462 - 465.
- Human Rabies Prevention. Recommendations of the advisory committee on immunization practice (ACIP). MMWR 1999; 48:RR-1.
- DA Jerrard: ED management of insect stings. AJEM 1996; 14 (4):429 - 433.
- C Stewart: Emergency management of arachnid envenomations: spider bites and scorpion stings. Emerg Med Rep 1993; 14:75 - 82.
- D Talan,et al.: Bacteriologic analysis of infected dog and cat bites. N Engl J Med 1999; 340:85 - 92.
- DC Wilson, King LJr: Spiders and spider bites. Dermatol Clinics 1990; 8:277 - 286.
