Chapter 211: Bites and Stings

The phylum Arthropoda is the largest division of the animal kingdom. The phylum includes insects (bees, wasps, hornets, flies, mosquitoes, bedbugs, fire ants, caterpillars, fleas), arachnids (spiders, scorpions, chiggers, ticks), and crustaceans (shrimp, lobsters, crabs). Venomous bites and stings from arthropods are a significant worldwide problem.¹ In the United States, the American Association of Poison Control Centers reported almost 50,000 cases of exposures to arthropods in 2012.² Some of these were listed as resulting in major or severe reactions, including severe pain, neurotoxicity, or other signs and symptoms. Fatalities among these exposures are rarely reported to poison centers and usually result from allergic reactions to Hymenoptera stings. Toxic reactions to multiple stings by members of the order Hymenoptera and severe systemic allergic reactions to one or more stings or bites of other insects, such as deerflies, blackflies, horseflies, and kissing bugs, can all present as emergency, life-threatening situations.³ Other arthropod bites and envenomations merit review either because they cause specific organ system toxicity or because they can result in transmission of infectious disease. This chapter discusses the most common and serious arthropod bites and envenomations. Tick bites are discussed in the "Tickborne Zoonotic Infections" section of chapter 160, "Zoonotic Infections: Tickborne Zoonotic Infections."

More fatalities result from stings by these insects than by stings or bites by any other arthropod. There are three major subgroups or superfamilies of medical importance: (1) Apidae, which includes the honeybee and bumblebee; (2) Vespidae, which includes yellow jackets, hornets, and wasps; and (3) Formicidae, or ants.

BEES AND WASPS (APIDAE AND VESPIDAE)

Apids, such as honeybees and bumblebees, are usually docile, stinging only when provoked. A female honeybee is capable of stinging only once (male bees have no stinger), because its stinger has multiple barbs that cause the sting apparatus to detach from the bee's body, which leads to evisceration and eventual death.

Africanized honeybees, or so-called killer bees, are now found in most of the southern and warmer regions of the United States extending from coast to coast. These bees are hybrids of African bees that escaped from laboratories in Brazil during the 1950s and have successfully spread northward along the coasts and temperate regions of the continent. Their venom is no more toxic than that of their American counterpart, but Africanized hybrid honeybees are more aggressive, and a hive can respond to a perceived threat with >10 times the number of bees that respond from a hive of typical North American bees. An attack from Africanized bees can lead to massive stinging, resulting in multisystem damage and death from severe venom toxicity.^4,5

Most of the allergic reactions reported each year due to Hymenoptera occur from vespid (wasp, hornet, and yellow jacket) stings. These arthropods nest in the ground, in trees, or in walls; have volatile tempers; and may be disturbed by work taking place around the nest. As with bees, only the females have adapted a stinger from the ovipositor on the posterior aspect of the abdomen. Although vespids also possess barbed stingers, they have the ability to withdraw their stingers from the victim, which permits multiple stings.

Venom

Hymenoptera venom contains several components.⁶ Although histamine is one of those components, other substances are now recognized as more important. Melittin, a known membrane-active polypeptide that can cause degranulation of basophils and mast cells, constitutes >50% of the dry weight of bee venom. Protein enzymes such as phospholipase and hyaluronidase may account for most systemic reactions.^7,8 Because all Hymenoptera share many of these components, cross-sensitization may occur in individuals allergic to one species. Yellow jacket venom is perhaps the most potent sensitizer.

Clinical Features

The most common response to Hymenoptera venom is a local reaction: pain, slight erythema, edema or urticaria, and pruritus at the sting site. A severe local reaction may involve one or more neighboring joints. A local reaction occurring in the mouth or throat can produce airway obstruction. Stings around the eye or on the lid may result in the development of an anterior capsule cataract, atrophy of the iris, lens abscess, perforation of the globe, glaucoma, or refractive changes. When local reactions become increasingly severe, the likelihood of future systemic reactions appears to increase, and if skin test results are positive, immunotherapy may be warranted.

Anaphylaxis Symptoms range on a continuum. Criteria for anaphylaxis are presented in Table 211–1, and detailed discussion of anaphylaxis is provided in chapter 14, "Anaphylaxis, Allergies, and Angioedema." Most reactions develop within the first 15 minutes, and nearly all occur within 6 hours. Initial mild symptoms may progress swiftly to shock. There is no correlation between systemic reaction and the number of stings. Symptoms include nausea, vomiting, and diarrhea; light-headedness and syncope; involuntary muscle spasms; edema without urticaria; and, rarely, seizures. Respiratory distress and cardiac arrest can result. Urticaria and bronchospasm do not need to be present. In general, the shorter the interval between the sting and the onset of symptoms, the more severe is the reaction. Fatalities that occur within the first hour after the sting usually result from airway obstruction or hypotension.

Renal and hepatic failure and disseminated intravascular coagulation can result from massive bee stings. Creatine phosphokinase concentrations can reach 100,000 IU/L or more in cases in which rhabdomyolysis occurs from direct venom toxicity.⁵ Toxic reactions are believed to occur due to a direct multisystem effect of the venom. Symptoms usually subside within 48 hours but may last for several days in severe cases, and some effects, such as rhabdomyolysis, can be delayed. We recommend hospital admission or observation for victims with >100 stings, for those with substantial comorbidities, and for those at extremes of age.

Delayed Reaction A delayed reaction, appearing 5 to 14 days after a sting, consists of serum sickness–like signs and symptoms of fever, malaise, headache, urticaria, lymphadenopathy, and polyarthritis.⁹ Frequently, the patient has forgotten about the encounter and is puzzled by the sudden appearance of symptoms. This reaction is believed to be immune complex mediated.

Unusual Reactions Infrequently, a reaction to Hymenoptera venom produces neurologic, cardiovascular, and urologic symptoms, with signs of encephalopathy, neuritis, vasculitis, and nephrosis. Guillain-Barré syndrome has been reported as a possible consequence of a Hymenoptera sting. Identification of the offending insect can be difficult, except for the honeybee, which predictably leaves its stinger with venom sac attached in the lesion. In general, definitive insect identification is unnecessary, because signs and symptoms of envenomation are similar for all species of Hymenoptera. If edema persists at the sting site, then consider secondary cellulitis. Severe local reactions on the foot or ankle can be misdiagnosed as gout if the insect sting is not visible.

General Treatment

If the bee stinger is present in the wound, remove it. Although conventional teaching suggested scraping the stinger out to avoid squeezing remaining venom from the retained venom gland into the tissues, involuntary muscle contraction of the gland continues after evisceration, and the venom contents are quickly exhausted. Immediate removal is the important principle, and the method of removal is irrelevant. Wash the sting site thoroughly with soap and water to minimize infection. For local reactions, intermittent application of ice packs at the site diminishes swelling and delays the absorption of venom while limiting edema. Oral antihistamines and analgesics may limit discomfort and pruritus. Nonsteroidal anti-inflammatory drugs can be effective in relieving pain. Standard doses of opioid analgesics also can be administered. If edema is significant, elevation and rest of the affected limb should limit swelling unless secondary infection develops, in which case antibiotics are necessary. In local tissue reactions, there is often significant inflammatory erythema and swelling, which make it difficult to distinguish from infection. As a general rule, infection is uncommon. We recommend hospital admission or observation for victims with >100 stings, for those with substantial comorbidities, and for those at extremes of age.

Anaphylaxis Treatment

Although the initial signs and symptoms of a systemic reaction may be mild, the victim's condition can deteriorate rapidly in a matter of minutes. Administer IM epinephrine, 0.3 to 0.5 milligram (0.3 to 0.5 mL of 1:1000 concentration) in adults and 0.01 milligram/kg in children (up to 0.3 milligram). Massage the injection site to hasten absorption. To avoid mishaps in dosing, many EDs now stock adult and pediatric EpiPens, which provide a standard adult or pediatric dose (EpiPen, 0.3 milligram epinephrine; EpiPen-Jr, 0.15 milligram epinephrine for children <30 kg). Provide aggressive fluid resuscitation with crystalloids. Antihistamines, histamine-2 receptor antagonists, and steroids are also commonly given. See chapter 14 for detailed discussion. Antivenoms have been studied for the treatment of mass bee attacks but are not yet commercially available.¹⁰

Long-Term Management and Preventive Care

Results of skin tests and radioallergosorbent tests are not fully reliable for determining which patients are at risk for systemic reaction during future encounters with Hymenoptera (Table 211–2) but should be coupled with information from the clinical history.^8,11 Patients with negative test results may have been sensitized by the skin tests themselves. Every patient who has had a systemic reaction should be provided with an insect sting kit containing premeasured epinephrine and should be carefully instructed in its use. The physician should stress that the patient must inject the epinephrine at the first sign of a systemic reaction. Physicians should also advise their patients who are allergic to insects to wear identification (e.g., medical alert tags) describing their severe allergy. They should also be advised to follow up with an allergist.

ANTS

There are five known species of fire ants (Solenopsis) in the United States: the native species Solenopsis aurea, Solenopsis geminata, and Solenopsis xyloni, and at least two imported species, Solenopsis invicta and Solenopsis richteri. These two imported species entered the United States through Mobile, Alabama, in the 1930s, have now become well established throughout the Gulf Coast states, and are spreading throughout the southwest.¹² Fire ants inhabit loose dirt and breed 9 to 10 months of the year. One mature nest can produce 200,000 ants during a 3-year period, which accounts for rapid spread. The venom of the fire ant is almost entirely an insoluble alkaloid. There is possible cross-reactivity between the venoms of fire ants and those of other Hymenoptera, and individual stings may produce systemic toxicity in sensitized individuals.

Fire ants are characterized by their tendency to swarm when provoked, and they may attack in great numbers. Fire ants in a swarm most often position themselves on their victim and sting simultaneously in response to an alarm pheromone released by one or several individuals. Immobilized or elderly patients can become rapidly covered by swarms, with multiple severe stings or death.¹³ Each sting usually results in a papule that becomes a sterile pustule in 6 to 24 hours. Localized necrosis, scarring, and secondary infection can result. Rarely, a systemic reaction manifested by urticaria and angioedema can occur. Fatalities and other severe reactions have been reported to occur rapidly following single stings from ants, but most occur in patients with a history of prior venom allergy and prior cardiopulmonary disease, and injectable epinephrine was not given.^14,15 Rhabdomyolysis and renal failure have also been reported after massive fire ant stings.¹⁶

Estimated hypersensitivity to fire ant venom occurs in 16% of the general population, with some crossover with those sensitized to the stings of other Hymenoptera. Treatment of fire ant stings consists of local wound care.¹³ In systemic reactions, treat for anaphylaxis. Desensitization may be necessary in patients exhibiting potentially life-threatening reactions to these arthropods. The wearing of socks or cotton tights seems to provide more protection from fire ant stings than the use of insect repellants.¹⁷

Although nearly 40,000 species of spiders have been described worldwide, medically significant envenomations have been described in only a few dozen (Table 211–3). Spiders are carnivores, and venom probably evolved for paralyzing prey. The vast majority of spiders pose little harm to humans because their venom-injecting fangs are too small to penetrate human skin, the amount of venom injected is too little to produce toxicity, or the venom itself has little effect on mammalian cells. Even if a reaction is elicited, it is often local, and systemic toxicity is confined to a few specific species (Table 211–3 and Figure 211–1).

SPIDERS CAUSING NECROTIC ARACHNIDISM (LOXOSCELES)

Loxosceles are brown spiders that have a worldwide distribution. Native species exist in the United States (Figure 211–1), and of these, Loxosceles reclusa (the brown recluse spider) occupies the largest geographic area and accounts for the majority of significant envenomations. In South America, particularly Brazil, Loxosceles laeta and Loxosceles intermedia account for most significant envenomations. Envenomation outside of endemic areas is unusual.¹⁸ Loxosceles spiders are nocturnal; are shy; are found both indoors and outdoors in dark, dry areas such as basements, closets, and woodpiles; and may bite when threatened. A pigmented, violin-shaped pattern on the cephalothorax of the brown recluse is often present (Figure 211–2). However, this characteristic is considered unreliable and often misinterpreted. Loxosceles species are most accurately identified by their eye pattern, which consists of six paired eyes (one anterior pair and two lateral pairs).¹⁸ Most other U.S. spiders have eight eyes arranged in two rows of four. The venom of the brown recluse contains multiple enzymes, including hyaluronidase and sphingomyelinase D, which is the major enzyme responsible for necrosis. Significant necrotic wounds are rare but possible through neutrophil activation, platelet aggregation, and thrombosis. Although both local and systemic complications of Loxosceles envenomation have been well described, the perceived threat of the brown recluse far exceeds its actual danger. For more information about recluse spiders see http://spiders.ucr.edu.

Clinical Features

Bites by Loxosceles spiders are described as initially painless, which often prohibits possible identification of the spider. The most common manifestation of a bite is a mild erythematous lesion that may become firm and heal with little or no scar within several days or weeks. Occasionally, a more severe local reaction occurs, beginning with mild to severe pain several hours after the bite, accompanied by localized erythema, pruritus, and swelling. A hemorrhagic blister then forms, surrounded by vasoconstriction-induced blanched skin (Figure 211–3). By day 3 or 4, the hemorrhagic area may become ecchymotic, which leads to the "red, white, and blue" (erythema, blanching, and ecchymosis) sign. The ecchymotic area may become necrotic, with eschar formation by the end of the first week. The necrotic, slowly healing ulcers may not reach maximum size for many weeks after envenomation and can occasionally result in a significant cosmetic defect requiring skin grafting.

Although significant systemic effects are not uncommon after bites of L. laeta, the predominant South American species, they rarely occur after bites of the brown recluse, the predominant U.S. species. Systemic effects, the hallmark of which is hemolysis, are seen more often in children and typically occur 24 to 72 hours after the bite. Other effects include nausea, vomiting, fever, chills, arthralgias, thrombocytopenia, rhabdomyolysis, hemoglobinuria, and renal failure. Disseminated intravascular coagulation and death are extremely rare.

Correct diagnosis of a brown recluse envenomation without definitive spider identification is difficult. Although the presence of a consistent clinical picture in an endemic area is suggestive, it is likely that a myriad of infectious and noninfectious conditions are misdiagnosed as brown recluse bites.¹⁸ In patients who are suspected of having been bitten and who exhibit signs and symptoms of envenomation, obtain a CBC, BUN and creatinine, and coagulation profile. Assays to detect envenomation have been used in research, but a commercial test is not currently available.

Treatment

Treatment of a possible necrotic spider bite should include the usual supportive measures, including pain medication. Antibiotics are indicated if signs of infection exist. However, secondary infections are uncommon. Arrange follow-up for serial wound evaluation. If ulceration develops, surgical debridement is delayed until clear margins are established, often 2 to 3 weeks after the bite.

Patients with systemic symptoms following a bite warrant hospitalization. Various treatments have been advocated for brown recluse spider bites, including antihistamines, antivenom, colchicine, dapsone, hyperbaric oxygen, surgical excision, steroids, and topical nitroglycerin. None of these therapies have clear benefit, and most wounds from the brown recluse are self-limiting and heal without any medical intervention. Administration of the leukocyte inhibitor dapsone continues to be advocated by some despite lack of supporting research and known adverse effects, including hemolysis and methemoglobinemia. Early antivenom administration after envenomation is efficacious in animal models.¹⁹ However, the delayed time in which patients typically present after envenomation, the current inability to definitively identify an envenomation, and the inability to prognosticate the development of dermatonecrosis, which in itself is rare, greatly limits its potential use.

An equine-derived antivenom is commonly used in Brazil; however, its efficacy is unclear. In the United States, there is no commercially available Loxosceles antivenom.

HOBO SPIDER (ERATIGENA AGRESTIS; FORMERLY TEGENARIA AGRESTIS)

A native of Europe and central Asia, the hobo or northwestern brown spider is now found in the Pacific Northwest of the United States and southern British Columbia.  Hobo spiders are brown with gray markings and have a 7- to 14-mm body length and a 27- to 45-mm leg span. They live in moist, dark areas such as woodpiles and basements.

Little documentation supports the occurrence of necrosis from hobo spider bites.¹⁸ In its native European habitat, it is not considered poisonous to humans, and venom analysis comparing European to U.S. species has confirmed no unique differences. Confirmed bites have demonstrated localized erythema, itching, pain, and swelling.²⁰

There is no diagnostic test for hobo spider envenomation, and there is no proven treatment.

WIDOW SPIDERS (LATRODECTUS)

Latrodectus or "widow" spiders have a worldwide distribution. In the United States, the black widow is the most well known, although of the five Latrodectus species found commonly in the United States, only three (Latrodectus mactans, Latrodectus variolus, and Latrodectus hesperus) are actually black. Other varieties may be predominantly brown (Latrodectus geometricus) or red (Latrodectus bishopi). An orange-red hourglass-shaped marking characterizes many of the Latrodectus species (Figure 211–4). Female spiders are relatively large, with a body size ranging up to 1.5 cm in length and leg spans of 4 to 5 cm. The male spider is approximately one-third the size of the female and lighter in color, and his bite cannot penetrate human skin. Black widow spiders are found most often in woodpiles, basements, garages, and sheds. Latrodectus will aggressively defend her web, particularly when guarding her eggs. Most black widow bites occur between April and October and are usually seen on the hands and forearms.

The black widow spider injures its victim and its prey with highly potent venom. The most active component of the venom is α-latrotoxin, which acts through both calcium-dependent and calcium-independent pathways leading to receptor stimulation, pore formation, and ultimately massive release of neurotransmitters (predominantly acetylcholine and norepinephrine).²¹ Acetylcholine release accounts for neuromuscular manifestations, and norepinephrine release accounts for the cardiovascular manifestations.

Clinical Features

Most Latrodectus bites are felt immediately as a pinprick sensation at the bite site, followed by increasing local pain that may spread quickly to include the entire bitten extremity. Erythema appears approximately 20 to 60 minutes after the bite. In many bites, a small, <5-mm erythematous macule develops that may evolve into a larger target lesion with a blanched center and surrounding erythema (Figure 211–5). The clinical syndrome is called latrodectism. Victims frequently complain of muscle cramp–like spasms in large muscle groups, although physical examination of the "cramping" extremity rarely reveals rigidity. The pain often increases progressively, becomes generalized, and can involve the trunk, back, and abdomen. Localized diaphoresis near the site of envenomation can be seen. Severe abdominal wall musculature pain and cramping are well described. Hypertension and tachycardia are common, and systemic symptoms include headache, nausea, vomiting, diaphoresis, photophobia, and dyspnea. Rarely reported complications include atrial fibrillation, myocarditis, priapism, and death. The pain with envenomation can be severe and intermittent and, if untreated, often lasts for a day. Occasionally, symptoms may persist for several days.

Because an immediate pinprick sensation is usually reported with Latrodectus bites, it is common for the offending spider to be identified. In the absence of a witnessed bite, a clinical diagnosis can be made based on characteristic symptoms and signs. There is no confirmatory laboratory test.

Treatment

Cleansing of the bite site is reasonable. Pain and muscle spasms can generally be controlled with liberal doses of opioids and benzodiazepines.²² Although IV calcium has been advocated to relieve symptoms, a retrospective review of patients with Latrodectus envenomation indicated that this treatment is ineffective.²² For severe envenomations, admission may be required for continued analgesia. The most effective therapies for severe envenomation are parenteral opioids and Latrodectus antivenom.

Administration of Latrodectus antivenom often causes rapid resolution of symptoms and can significantly shorten the course of illness. Even in severely symptomatic cases of Latrodectus envenomation, patients can often be discharged from the ED after a short observation period when antivenom is administered. Successful treatment of latrodectism with antivenom has been described even with administration 90 hours after envenomation.²³ Antivenin Latrodectus mactans is not contraindicated in pregnancy.²⁴

Latrodectus antivenom is produced in at least three countries with specificity for indigenous species: Redback (Latrodectus hasselti) Spider Antivenom (CSL Ltd., Melbourne, Australia), Button Spider Antivenom (South African Vaccine Producers Institute, Edenvale, South Africa), and Antivenin Latrodectus mactans (Merck & Co., Inc., Whitehouse Station, NJ). It is likely that the antivenom to one species would be clinically effective in treating the bites of the others. Indications, amount, and route of administration vary according to product. Antivenin Latrodectus mactans and Button Spider Antivenom are administered IV, and Redback Spider Antivenom is typically administered by IM injection. An Australian-based study using Redback Spider Antivenom found minimal clinical difference between IV and IM routes.²⁵

Latrodectus antivenom is derived from horse serum, and hypersensitivity reactions are possible. Redback antivenom is the most frequently used antivenom in Australia, and adverse reactions are rare. Until recently one death from anaphylaxis had been reported after administration of Antivenin Latrodectus mactans in the United States. Analysis attributed this to the antivenom being administered undiluted via IV push to an asthmatic patient with known allergies to multiple medications. Slow administration of diluted Antivenin Latrodectus mactans has generally been considered safe.²⁶ However, two additional cases of anaphylaxis to Antivenin Latrodectus mactans have been described despite dilution and slow administration.^27,28 In one of these cases, the anaphylaxis resulted in cardiac arrest, and despite successful resuscitation, the patient later died.²⁷ Such cases should be kept in mind, particularly because latrodectism itself is rarely life-threatening. A F(ab)2 antivenom [Antivenin Latrodectus Equine Immune F(ab)2 (Analatro)], expected to be less immunogenic and safer than whole-antibody products, is currently commercially available in Mexico. At the time of writing, it is not approved in the United States.²⁹

ARMED SPIDERS (PHONEUTRIA)

The armed spiders are found throughout South America and Costa Rica. The majority of clinically important bites have been described in Brazil. The spiders are solitary, nocturnal, do not construct a web, and possess potent neurotoxic venom. They have been reported to hide in banana bunches during shipping and can bite workers handling these bananas at their destination. When threatened, they assume a characteristic aggressive position by raising their four front legs, displaying their fangs, bristling their leg spines, and moving position to continually face their threat. The best-known armed spider, Phoneutria nigriventer (banana spider), is large, with a body size up to 3.5 cm and leg length up to 6 cm. P. nigriventer venom contains a mixture of potent neurotoxins that produce CNS, spinal cord, and autonomic effects.

Most P. nigriventer bites produce no significant symptoms. Significant envenomation produces local symptoms (severe pain) followed by sympathetic stimulation (tachycardia, hypertension), parasympathetic hyperactivity (nausea, vomiting, diaphoresis, salivation), spinal cord impairment (priapism), and CNS effects (vertigo, visual changes). Children and the elderly are at highest risk for serious envenomation. Pulmonary edema, shock, and death are rare.³⁰ Most healthy adults recover in 1 to 2 days.

In most cases, supportive care is adequate. Local anesthetic infiltration at the bite site can control pain. A polyvalent antivenom (Instituto Butantan, São Paulo, Brazil) is available for cases of severe envenomation from P. nigriventer.

FUNNEL-WEB SPIDERS (ATRAX/HADRONYCHE)

Funnel-web spiders are arguably the most deadly spiders in the world. Fortunately, they exist in a localized geographical location in eastern Australia, and no fatalities have been reported since the introduction of antivenom in 1981.³¹ The spiders are so named because they construct a cylindrical web that extends into a recess, such as a burrow in the ground or a hole in a tree.

Funnel-web spiders have a shiny black body and long fangs, and females can grow up to 4 cm in body length. Females stay close to their webs, but the smaller and more aggressive males tend to wander, especially during the summer following a rain. Atrax venom contains a potent mixture of neurotoxins with neuromotor and autonomic effects.

Clinical Features

Atrax bites may result in local reaction with immediate pain, followed by wheal formation and surrounding erythema. Later, localized sweating and piloerection may be observed. The vast majority of Atrax bites do not result in significant envenomation or systemic toxicity. The onset of severe envenomation is rapid and unlikely to begin after 2 hours.³¹ Symptoms and signs of systemic toxicity include perioral paresthesias, parasympathetic hyperactivity (nausea, vomiting, diaphoresis, salivation, lacrimation, bronchorrhea), neuromuscular stimulation (muscle fasciculation, tremors, spasms, weakness), and CNS toxicity (altered level of consciousness). Death after Atrax robustus envenomation has been reported as a result of cardiac arrest, hypotension, or pulmonary failure occurring between 15 minutes and 3 days after a bite.

Treatment

To reduce venom absorption and systemic toxicity from a bite on an extremity, apply a compressive elastic bandage to the entire length of the limb, and splint the extremity to prevent movement.³² Immobilize the victim and transport promptly to the hospital.

The specific treatment for systemic toxicity is Funnel-Web Spider Antivenom (CSL Ltd., Melbourne, Australia). If the patient has signs of systemic toxicity upon arrival or develops them after the compressive elastic bandage is carefully removed, antivenom should be administered until symptoms improve. Supportive therapy for hypotension (IV fluid), bronchorrhea (atropine), tremors and agitation (benzodiazepines), and hypertension and tachycardia (β-blockers) may be necessary, but antivenom is the only therapy known to consistently improve survival.

TARANTULAS (THERAPHOSIDAE)

Tarantulas are large, hairy spiders belonging to the family Theraphosidae that are popular as pets. The hairs found on the abdomen of most species of tarantulas in North and South America resemble a velvety covering and are used defensively. When threatened, tarantulas may flick these hairs a short distance with their two back legs. Although North American tarantula hairs rarely penetrate human skin, the hairs can imbed deeply into the conjunctiva and cornea and can cause inflammation in all levels of the eye, from conjunctiva to retina. Patients who manifest a red eye and pain after handling a tarantula should be examined to determine if offending barbed hairs are present in the cornea or conjunctiva. Although hairs are sometimes easily seen on slit-lamp examination, they may at times be very difficult to detect. Therapy includes surgical removal of the hairs and topical application of steroids to control inflammation. Ophthalmia nodosa is a granulomatous, nodular reaction that can occur in cases of ocular exposure to tarantula hairs.³³ Patients may also develop a diffuse contact dermatitis from indirect exposure to hair while cleaning a tarantula cage. Bites from tarantulas are typically painful, with local erythema and edema, and some patients describe local joint stiffness following bites on nearby areas. Systemic symptoms other than fever are unusual.

OTHER SPIDERS

Yellow sac spiders (Cheiracanthium) are medium-sized, typically yellow spiders that have a worldwide distribution. A few species are commonly found in homes. The most common symptoms of a bite are local sharp pain. Minor erythema, swelling, and pruritus may occur at the bite site. Dermatonecrotic lesions are rare.³⁴

Wolf spiders (Lycosa) are small- to medium-sized (3- to 5-mm body length) ground-dwelling spiders with a worldwide distribution. The venom produces local pain and occasionally induration and erythema, but no systemic symptoms and no skin necrosis.

Jumping spiders (family Salticidae) are typically small (<15 mm), brightly colored, and very active spiders with a worldwide distribution. A bite may produce pain, swelling, pruritus, and erythema with resolution in 2 days.

Daddy long-legs spiders (family Pholcidae) are common cellar and outbuilding dwellers along the Pacific coast and in southwestern deserts. There are no case reports of human envenomation.

Scorpions have a worldwide distribution, and highly toxic species are found in Africa, India, Mexico, North Africa, South America, the Middle East, and the Caribbean island of Trinidad. The toxins of the Centruroides and Parabuthus scorpions exhibit primarily neuromuscular effects, but toxins of the Androctonus, Buthus, and Mesobuthus scorpions exhibit cardiovascular effects.³⁵ Several species of scorpions are found in the warmer parts of the southern United States, but most species cause little more than localized pain. In the United States, only Centruroides sculpturatus (bark scorpion), found throughout Arizona, New Mexico, and parts of Texas and California, possesses venom potent enough to cause systemic toxicity.

CLINICAL FEATURES

Most stings cause localized pain at the bite site, and systemic toxicity occurs in <10% of stings. Scorpion venom contains many toxins, but the toxins with the most serious medical effects can open neuronal sodium channels and cause prolonged and excessive depolarization. Somatic and autonomic (parasympathetic and sympathetic) systems are affected (Table 211–4).³⁵ Infants and young children are at highest risk for severe systemic symptoms, which can be life threatening. Motor hyperactivity is nearly universal when symptoms are systemic and may present as restlessness or uncontrollable jerking of the extremities that appears to be seizure-like activity. Peripheral nervous system toxicity includes abnormal oculomotor function, loss of pharyngeal muscle control, uncoordinated neuromuscular activity with respiratory compromise, and tongue fasciculations. Hypersalivation is common and, combined with cranial nerve dysfunction, can threaten airway integrity. Cardiovascular toxicity from systemic envenomation includes tachycardia, hypertension, pulmonary edema, and cardiogenic shock.

DIAGNOSIS

Diagnosis is clinical. Laboratory studies are needed in severe envenomation to identify organ system involvement.

TREATMENT

Treatment is described in Table 211–4. Administer opioids for pain control and short-acting benzodiazepines for sedation as needed. In Latin America and India, the vasodilator prazosin is used to counteract the adrenergic surge that can lead to hypertension and resultant pulmonary edema. Envenomations in North Africa, on the other hand, are thought to develop pulmonary edema from systolic dysfunction, and the use of dobutamine may be helpful.³⁶ Scorpion antivenom directed against different species has been produced for research or clinical use in many other countries. Recommendations for use and dosing of these products vary widely. Like all animal-derived antivenom, both immediate and delayed allergic reactions, including serum sickness, are possible. A randomized, double-blind study from Arizona in children suffering from significant neurotoxic effects of Centruroides stings demonstrated that an intravenous scorpion-specific antibody resolved the clinical syndrome within 4 hours and significantly reduced the need for concomitant sedation.³⁷ The antivenom Anascorp® is a F(ab) equine preparation that is approved by the Food and Drug Administration in the United States but currently is quite expensive and should be restricted to patients with severe systemic symptoms.

Chigger infestations result from mite larvae feeding on host skin cells. Mites are found in almost every habitat and are 0.3 to 1.0 mm in length, and the larvae attach themselves to host skin with mandibular structures. They tend to attach in areas where an obstacle like tight-fitting clothing is met, such as at the tops of socks, the leg bands of underwear, the waistband, or the edges of a bra. Once attached, the larvae release digestive enzymes to liquefy epidermal cells. The combination of digestive enzymes secreted by the mite and subsequent host immune response produces the "chigger bite."

CLINICAL FEATURES

Although diseases such as rickettsialpox and scruff typhus have been spread by mite vectors, the major clinical manifestation of chigger infestation is most often intense pruritus. The attached chigger may be seen initially as a bright red fleck on the skin, and it, along with the larvae, may be easily scratched off. Lesions are intensely pruritic and often appear as grouped papules or papulovesicles. The localized allergic response may last for weeks, and significant excoriation may occur at the site from intense scratching.

The diagnosis of chigger infestation may be difficult, because many other arthropods cause similar clinical manifestations. The history of outdoor exposure combined with the presence of signs and symptoms localized to areas of snug-fitting clothing may be helpful.

TREATMENT

Treatment is primarily symptomatic to control the itching and consists of oral antihistamines and topical steroids. Oral steroids may be helpful in severe cases. Chiggers themselves may be killed with permethrin and other topical scabicides. If secondary infection occurs, antibiotics are indicated.

MOSQUITOES

Mosquitoes penetrate skin with the piercing motion of a bayonetlike proboscis. The actual puncturing of the skin surface causes minimal trauma and frequently is not felt by the host. A local anesthetic is injected into the wound that causes local tissue damage and local hypersensitivity. Bites can lead to both immediate and delayed reactions. An immediate skin reaction includes redness, a wheal, and itching. A delayed reaction can occur and usually consists of edema and pruritus. The immediate reaction tends to be of short duration, whereas a delayed reaction may persist for hours, days, and even weeks. Severe local reactions with skin necrosis are possible. Patients can acquire allergy to mosquito saliva constituents and develop symptoms consisting of an escalating reaction to seasonal exposures with increasingly pronounced edematous and pruritic lesions, sometimes accompanied by fever, malaise, generalized edema, severe nausea and vomiting, and necrosis with resulting scarring. Treatment is symptomatic with antihistamines and nonsteroidal anti-inflammatory drugs.

The greatest danger from mosquitoes is the transmission of disease. Even with extensive pest control programs, arbovirus infections and malaria are epidemic in many parts of the world. Chikungunya virus, dengue, Japanese B encephalitis, yellow fever, and various types of equine encephalitis are among the many viruses transmitted by mosquitoes. In addition, West Nile virus has recently spread west across North America. Malaria is also encountered frequently in patients in the United States after travel and in immigrant populations from areas where malaria is endemic. Insect repellents offer some protection from mosquito bites.

FLIES

Bloodsucking flies range in size from the tiny sand fly, approximately 1 to 3 mm in length, to horseflies, which can be >2 cm. All flies stab and pierce the skin, causing some degree of pain and pruritus. Several species, such as deerflies, blackflies, horseflies, and sand flies, can produce allergic reactions, although these are rarely as severe as those produced by Hymenoptera venom. There is also the possibility of myiasis (infestation of tissue with fly larvae, i.e., botfly) from fly bites, but this condition is rare in the United States.

The diagnosis of fly bite depends chiefly on the patient's history and a knowledge of the arthropods that frequent the area of encounter. Treatment for most local reactions to Diptera bites is symptomatic, and treatment of systemic reactions is the same as for reactions to Hymenoptera venom. Application of cold compresses may alleviate localized edema. Secondary infection of Diptera bites can occur, and antibiotics may be necessary in some cases. Oral antihistamines may be helpful in relieving pruritus from fly bites, but topical steroids can be used when local reactions are severe, and oral steroids are indicated when systemic hypersensitivity symptoms are present.

FLEAS (SIPHONAPTERA)

Bites of fleas, lice, and scabies mites produce lesions so similar that diagnosis is often difficult. Flea bites are frequently found in zigzag lines, especially on the legs and in the waist area. The lesions most often have a hemorrhagic-appearing center surrounded by erythematous and urticarial patches. Flea bites are usually quite pruritic, and red spots can persist at bite sites for some time.

The main concern in the treatment of these bites is the possibility of secondary infection. Children may develop impetigo as a complication. The lesions should be washed thoroughly with soap and water. Children with flea bites should have their fingernails cut short to prevent scratching. To relieve discomfort and itching, local application of calamine, cool soaks, and oral or topical antihistamines may be helpful. For severe discomfort, application of a topical steroid cream or spray may be necessary. If secondary infection develops, topical or oral antibiotics may be needed.

KISSING BUGS AND BED BUGS (HEMIPTERA)

The order Hemiptera includes two blood-sucking families of arthropods with medical importance. These are Reduviidae (reduviids, or "kissing" bugs) and Cimicidae ("bed bugs" and their relatives). Various species of kissing bugs are found predominantly in the southern United States and Central and South America. The common name "kissing bugs" derives from their habit of feeding at night on any exposed surface of a sleeping victim, commonly the face. Bed bugs are also nocturnal feeders, and their distribution is worldwide. Recently, there has been a worldwide major resurgence in bed bug infestations, particularly in developed countries. This has been attributed to immigration, international travel, and insecticide resistance.³⁸ Both bugs are attracted to warm bodies and hide near beds. Bed bugs are found in nearby cracks and crevices. Kissing bugs of Central and South America are vectors of Chagas' disease (trypanosomiasis). Although transmission of many diseases to humans has been attributed to bed bugs, there is little evidence to support it. The transmission of hepatitis B does appear at least theoretically possible.³⁸

Clinical Features

Bites from both bugs are typically painless. Erythematous papules, bullae, and wheals may develop. A linear bite pattern on the skin is well described with bed bugs, and telltale brown or black patterns of excrement may be found on bed linen. A thorough search of bedding and nearby cracks and crevices will often reveal the bugs. Bed bugs are notoriously difficult to eradicate. One study demonstrated the potential for ivermectin (oral antiparasitic drug) administration to help eradicate those bed bugs that are feeding on the patient.³⁹

Treatment

Treatment of both types of bite is symptomatic. Cool compresses, topical steroids, and antihistamines can be used to relieve associated pruritus. Some individuals become highly sensitive to kissing bugs and react with systemic allergic symptoms following a bite. They should be treated as previously outlined for Hymenoptera envenomation.

Lepidopterism refers to the adverse effects resulting from contact with butterflies, moths, or their caterpillars. Caterpillars, the larval stage of moths and butterflies, are responsible for the vast majority of symptomatic exposures. For protection, they may have either hairs or spines that can be attached to venom glands. The spines and hairs may cause mechanical irritation, whereas the venom can produce additional symptoms. Although isolated exposures are most common, particularly in children who may be attracted to the colored or "furry" appearance of caterpillars, there are multiple species that under the right conditions can cause "epidemics" of cutaneous or systemic exposures. A couple of moth species, most notably the Hylesia genus in Venezuela (responsible for the "Caripito itch"), can cause local irritant or allergic reactions.

CLINICAL FEATURES

Most reactions to Lepidoptera are mild and self-limited. The vast majority of caterpillars are harmless to humans. Pruritus from localized "caterpillar dermatitis" and occasional diffuse urticaria are the predominant symptoms of exposures to the hairs and venom. The puss caterpillar (Megalopyge opercularis) is found in the southeastern United States and accounts for most of the serious envenomations in that country. After initial contact, intense local burning pain, rather than pruritus, is typical. A gridlike pattern of hemorrhagic papules may be seen within 2 to 3 hours of these exposures and may last for several days. Regional lymphadenopathy is common, and the affected limb can swell considerably. Other potential symptoms include headaches, fever, hypotension, and convulsions. No deaths have been reported. Ingestions of the hickory tussock caterpillar (Lophocampa caryae), found in the eastern United States, have been reported, with symptoms ranging from drooling to diffuse urticaria. Spines have been visualized in the oropharynx and even the esophagus in some of these patients, requiring endoscopy to aid in removal.⁴⁰ Two species of Lonomia caterpillars, found primarily in Brazil and Venezuela, are capable of causing potentially fatal coagulation defects.

TREATMENT

Treatment is symptomatic and supportive. Spines can be removed using adhesive tape. Antipruritic or topical anesthetic preparations, topical steroids, and oral antihistamines are typically used. For symptomatic ocular and oral exposures, removal of hairs may be necessary, and endoscopy has been described. Anaphylaxis is rare but would be treated in the typical manner. An antivenom specifically for Lonomia obliqua is available in Brazil to reverse coagulopathy.⁴¹

Although the order Coleoptera includes a large number and variety of beetles, clinically significant envenomation occurs only from those that contain a vesicant (blister beetles). Blister beetles are found worldwide, including the United States. The most well-known blister beetle is the "Spanish fly" (Cantharis vesicatoria), found in Spain.

CLINICAL FEATURES

Blister beetles contain a highly potent vesicant (either cantharidin or pederin) that can be exuded or released if the beetle is brushed against, pressed, or crushed on the skin. For this reason, a blister beetle should be removed from the skin by blowing or flicking. Cantharidin–containing preparations are used medicinally in wart removal. Application of these substances in low concentration is without adverse effect.⁴² However, higher concentrations or contact with the beetle's venom may cause local inflammation, leading to bullae formation. Severe conjunctivitis may also occur if cantharidin or pederin contacts the eyes from contaminated hands. The majority of described cases of blister beetle dermatosis are from seasonal outbreaks due to pederin-containing beetles.⁴³ At least one outbreak has been described in the United States. Topical exposure to blister beetles can cause a vesiculobullous eruption typical of a vesicant. Pederin-containing dermal exposures result in a more delayed (up to 36 to 72 hours) but more painful and symptomatic eruption than those from cantharidin-containing beetles. Due to the delay in onset of symptoms and signs, misdiagnosis is common. High concentrations of cantharidin preparations may result in dermal absorption and systemic toxicity. Systemic toxicity is well described following the ingestion, either of the whole beetle or of cantharidin-containing preparations. Severe vomiting, hematemesis, abdominal pain, and diarrhea may occur, followed by dysuria, hematuria, oliguria, and renal failure. Although the exact mechanism by which cantharidin produces systemic toxicity is unknown, the vesicant action likely explains most of the findings. Direct cardiac toxicity with large ingestions of cantharidin is possible, and deaths have been reported. Fortunately, most preparations sold as "Spanish fly" for their purported aphrodisiac properties have very low concentrations of cantharidin. The local vascular congestion and urethral inflammation that occur following ingestion may be interpreted by some as enhanced sexuality.

TREATMENT

Treatment is supportive. The skin should be irrigated thoroughly after topical exposure to remove any persistent vesicant, followed by local wound care. Patients who are symptomatic after ingestion should be admitted and treated supportively.