Manual of Dermatologic Therapeutics
7th Edition

Spiders. The spiders that cause serious reactions in humans in the United States most commonly are the black widow (Latrodectus mactans) and the brown recluse spider (Loxosceles reclusa). The black widow spider is found throughout the United States. Systemic symptoms resulting from its bite include chills, nausea, tremors, muscle spasms, pain in the abdomen and legs, sweating, and cramps. Symptoms typically begin in 15 to 60 minutes and subside within hours. The brown recluse spider inhabits dark warm areas such as attics, closets, and woodsheds. This spider is endemic to the Midwest but can be found in eastern United States. Reactions to its bite are trivial approximately 90% of the time. Severe local pain and swelling may occur between 4 and 8 hours after a bite. Severe systemic symptoms include respiratory failure with pulmonary edema, anemia, renal failure, neurotoxicity, and rhabdomyolysis. In contrast to the bite of the black widow, there are no neurologic symptoms. Viscerocutaneous loxoscelism, with severe chills, vomiting, arthralgias, and severe intravascular hemolysis, is rare.

Snakes. Of approximately 45,000 snakebites in the United States each year, only approximately 20% are by poisonous snakes. The Viperidae and Elapidae families of snakes are poisonous snakes of medical importance in the United States. The Viperidae family or pit viper snakes include the rattlesnake, cottonmouth, and copperhead varieties. The Elapidae family includes the coral snake. Increased interest in snakes as pets has brought the problem of snakebites to urban areas, and injuries are often associated with alcohol consumption. Bites from the diamondback rattlesnake account for 95% of fatalities. Local reactions to venomous snake bites include pain, swelling, ecchymosis, and lymphadenopathy, which may be accompanied by a tingling sensation around the lips, vertigo, muscular twitching, or bleeding (hematuria, hematemesis).

Insects. By far the most important venomous insects are those belonging to the Hymenoptera family including bees, wasps, and ants. Venom from Hymenoptera contains serotonin, kinins, acetylcholine, lecithinase, hyaluronidase, phospholipase,
and melittin; exposure to this venom has been shown to release histamine from leukocytes of patients allergic to Hymenoptera. Most stings result in instantaneous pain followed by a localized wheal and flare reaction with pruritus and variable edema. The harvester ant and fire ant cause most ant-sting reactions in humans. Both are associated with “fire” because of the intense burning and pain associated with their stings. Some patients may develop immediate systemic allergic reactions.

The immediate allergic reaction to the injected salivary fluids of mosquitoes is pruritus; the delayed reaction, occurring several hours later, is a more severe, intense, burning itch. Flies do not actually bite but pierce through the skin, thereby allowing salivary gland fluids to enter and cause toxic and allergic reactions. The black fly is renowned for inducing an extremely painful and long-lasting reaction. Fleabites manifest as scattered pruritic papules.

Caterpillars. Injury following contact from caterpillars usually involves contact with urticating hairs or venomous spines. The largest outbreaks have been associated with spines detached from live or dead caterpillars or cocoons. Direct contact with caterpillars with hollow spines containing venom glands can cause instantaneous pain, erythema, and swelling. Although nausea, vomiting, and fever may occur, systemic symptoms are rare. Caterpillar hairs may cause an erythematous, papular, or urticarial rash persisting for several days to 1 week. Conjunctivitis, upper respiratory tract irritation, and asthma-like symptoms may also occur.

Animal bites. Approximately 2 million animal bites occur yearly (mostly to children), with 300,000 emergency room visits, 10,000 hospitalizations, and 20 deaths per year. Dogs are responsible for 80% of the bites, although cat bites are more infectious. Dog and cat bites can become infected with a complex group of pathogens usually including the Pasteurella species (50% of dog bites and 75% of cat bites). Pasteurella canis is the most common dog isolate and Pasteurella multocida and septica in cat bites. Other aerobic isolates include streptococci, staphylococci, moraxellae, and neisseriae. Common anaerobes include fusobacteria, Bacteroides, Porphyromonas, and Prevotella. Human bites are usually deep puncture wounds and often result in a polymicrobial infection. The usual case scenario is a high force hand injury that is a result of a fistfight with a punch to the mouth. A clenched fist injury can lead to soft tissue infection and tendon or bone injury.

Spiders. The black widow spider can be identified by a distinct red to orange hourglass marking on its abdomen. Its bite leaves an urticarial papule with a white halo surrounding. In patients who develop systemic symptoms, neuromuscular symptoms can become quite severe with involuntary spasm and rigidity affecting large muscles predominantly in the abdomen and also in the extremities and lower back. Patient presentation may mimic that of an acute abdomen. Severely ill patients may also develop diaphoresis, ptosis, vomiting, pulmonary edema, rhabdomyolysis, hypertension, and a characteristic pattern of facial swelling known as Lactrodectus facies.

The brown recluse spider has a characteristic violin-like marking on its dorsal thorax. Local reactions to its bite range from mild skin irritation to severe local necrosis. Severe reactions generally begin as localized edema with an erythematous halo surrounding an irregularly shaped center of necrosis. If the edema is severe, serous or hemorrhagic bullae may arise over the underlying eschar. Multiple toxins released, including sphingomyelinase D, result in progressive necrosis resembling necrotizing fasciitis or pyoderma gangrenosum. Healing can take 3 weeks or more. Severe systemic symptoms include hemoglobinuria, anemia, fever, chills, a morbilliform rash, arthralgias, nausea, and vomiting. Death may result from renal failure or intravascular hemolysis.

Snakes. The pit viper family of snakes can be recognized by a triangular head, elliptical “cat’s eye” pupils, and a single row of ventral scales. All have a depression, or heat-sensing facial pit, in the maxillary bone near the nostril on both sides of the head. The venom is anticoagulative and bites typically result in local pain immediately after the bite with fang puncta, weakness, swelling, paresthesias, nausea, and vomiting. Ecchymoses, hypotension, and damage to the vascular
endothelium may ensue. The most dreaded complications are respiratory arrest, disseminated intravascular coagulation (DIC), acute renal failure, neurotoxicity, and/or rhabdomyolysis. Studies are in progress to develop a rapid enzyme-linked immunosorbent assay (ELISA) to determine the snake species to provide specific antivenom.

The Elapidae family of coral snakes can be identified by round eyes with red and yellow or white bands. Nonvenomous mimics tend to have red and black bands in the United States; however, this rule does not hold true south of Mexico City and in other foreign countries. Bites usually have little or no pain, local edema, or necrosis. The venom is primarily neurotoxic, causing a weak or numb feeling in the bitten extremity. Systemic symptoms may appear within hours including tremors, marked salivation, muscle fasciculations, bulbar paralysis manifested as dysphagia and dyspnea, and total flaccid paralysis. Paralysis of the diaphragm leads to respiratory paralysis and death.

Caterpillars. Pain, erythema, and urtication are the most common reactions to bites of the caterpillar species. Atypical reactions include muscle spasms, paresthesias, and radiating pain. The most important urticating caterpillars in the United States are the Automeris io characterized by red and white lateral stripes, the Megalopyge opercularis or puss caterpillar resembling a tuft of cotton, and the Sibine stimulea or saddleback caterpillar resembling a brown or purple saddle on a green blanket.

Animal bites. Animal bites range from small scratches to severe bites which may involve muscle, tendons, or fractured bone. Cat bites have a high likelihood of infection due to puncture inoculation from their longer, pointed teeth.

Spiders. Mild local reactions to black widow spider bites should be treated by application of a cold pack and/or a topical corticosteroid. When there is a severe reaction, immediate treatment should include application of a proximal band to occlude venous return, administration of opiates for pain, muscle relaxants, calcium gluconate, and antivenom effective against bites of all spiders of the genus Latrodectus (Lyovac). Mild local reactions to brown recluse spider bites heal well with no specific therapy. Brown recluse bites have a more favorable prognosis if (i) the bites are treated with ice bags and elevation, (ii) strenuous exercise is avoided, (iii) localized heat, surgery, and intralesional steroids are avoided, and (iv) antibiotics (erythromycin or cephalosporins) and aspirin are given. Test for anemia and thrombocytopenia. Administer dapsone if the patient is not glucose 6-phosphate dehydrogenase deficient and the lesions are progressive. High-dose systemic corticosteroids are indicated in the treatment of severe bites and when hemolysis occurs. Dialysis may be required in patients with acute renal failure, anuria, and azotemia. Tetanus prophylaxis must be considered. Brown recluse spider antivenom is being developed, and there is early evidence that hyperbaric oxygen might help speed healing of the skin.

Dr Michael L. Smith, an entomologist and pediatric dermatologist, has a spider bite hot line for physicians that can be reached at 615-322-BITE.

Snakes. The best firstaid measures for snakebites are as follows: (i) Immobilize the injured part by splinting as if for a fracture. A constricting band may be applied proximal to the bite tightly enough to occlude veins and lymphatics but loosely enough to preserve a distal pulse. (ii) Incision and suction with a negative pressure device can remove a significant amount of venom; however, it must be applied within 3 to 5 minutes of the bite and left in place for 30 minutes. Ice is generally not recommended as vasoconstriction of already compromised tissue may contribute to necrosis. (iii) Get the victim to a physician or hospital as soon as possible. At that time, start an IV in the contralateral arm; type and cross match blood early, before venom action makes this impossible; and check for the presence of coagulopathy. (iv) In severely envenomized patients, administer horse-based antiserum. Two types of antivenom are commercially available, one for bites by rattlesnakes and other pit vipers and the other for coral snake bites. Antivenom reactions are common. Pit viper envenomation causes local platelet consumption, which can be ameliorated
somewhat by antivenom but is worsened by steroids. Platelet and clotting factors should be restored by blood component therapy as indicated. Tissue necrosis and injury should be limited by debridement and mechanical removal of venom and local necrotic tissue. Locations of antivenom for rare species of poisonous snakes and the names and phone numbers of experts on venomous bites can be obtained 24 hours a day from the Arizona Poison Control Center (602-626-6016).

Insects. Insects should be flicked or brushed (not squeezed) off the skin. This action should also remove the venom sac. Forceps are not recommended to remove the stinger as it may squeeze the attached venom sac and worsen envenomation. Cold packs, systemic antihistamines, and a topical steroid may be useful for the pruritus and inflammation of local reactions.

The treatment of systemic allergic reactions and anaphylaxis to insect bites should follow conventional guidelines: (i) Inject 0.3 to 0.5 mg epinephrine HCl (0.3 to 0.5 mL of a 1:1,000 dilution) IM and repeat q15 to 30 min as needed. Lower doses should be used in the elderly and in patients with cardiovascular problems. Only in profound anaphylaxis with hypotension and poor peripheral circulation should intravenous administration be necessary. In such cases, use epinephrine in a 1:10,000 dilution (1 mg = 10 mL) and give 0.1-mg boluses until symptoms improve. (ii) Begin an intravenous line as soon as possible with a saline drip. If patients are not responsive to initial measures, critical care with fluids, oxygen, and pressors may become necessary. Cases of severe laryngeal edema may require intubation or tracheostomy. (iii) Persistent bronchospasm should be treated with intravenous aminophylline and inhaled bronchodilators such as albuterol, isoetharine, or isoproterenol. The recommended dose of aminophylline is a loading dose of 3 to 5 mg/kg followed by a drip of 0.5 to 0.9 mg/kg/hr. The dose should be lowered in elderly patients and in those with congestive heart failure or liver disease. Smokers may require higher doses. (iv) Antihistamines should be administered as an adjunct to epinephrine because their effect is not immediate. Use diphenhydramine 50 mg PO or IM, depending on the severity of the reaction. Treatment should continue as long as symptoms persist. (v) Steroids have a delayed onset of action and are not first-line drugs for treating a severe systemic reaction. However, unless medically contraindicated, they should be used to prevent continued reaction in all but the mildest allergic reactions. Begin with hydrocortisone 100 mg IV q6h and discharge on prednisone 30 mg/day, tapering over 3 to 7 days as symptoms dictate.

Sensitive patients should carry medications such as an epinephrine inhalation spray, ephedrine, and antihistamine tablets with them at all times. Commercial kits containing a syringe loaded with epinephrine (EpiPen) and antihistamine tablets (Ana-Kit) are available. Patients should also always carry an aerosol insecticide spray and avoid walking without shoes. They should dress in protective clothing and avoid wearing items that attract flying insects such as perfumes and other scented preparations; brightly colored clothing or jewelry; and wool, suede, or leather apparel. Insect venom immunotherapy is effective and should be considered mandatory for patients who have had an immediate systemic reaction to an insect sting. Commercial venoms and fire ant extract can be used for diagnosis (skin testing) and desensitization. Adults with a previous systemic reaction to a sting and a positive venom test will have a similar reaction in approximately 50% of instances if stung again. After immunotherapy, a resting will elicit a systemic reaction in <5% of patients.

Insect repellents containing diethyltoluamide (DEET) are the agents of choice for protection against mosquitoes, flies, fleas, mites, and ticks. These include Mosquitone lotion, OFF products, and Cutter insect repellent. Ethyl hexanediol, dimethyl phthalate, and dimethyl carbate butopyronoxyl are also effective but do not cover the wide spectrum that DEET does. A combination of two or more of these repellents is more effective than one alone. No product will protect against spiders, wasps, or bees. Factors that attract mosquitoes to skin include warmth, sweat, moisture, carbon dioxide, and other body emanations found in the convective air currents above or downwind of humans. Repellents do not mask these attractive stimuli but form a barrier against penetration that extends to <4 cm away from
the skin. DEET blocks the ability of the mosquito to track the human’s carbon dioxide vapor trail. At room temperature, protection time may last 10 to 12 hours. Approximately 10% of applied DEET evaporates from the skin in the first hour after application. There are many factors that will decrease the protection time, including heat, wind, friction against clothing, water, or sweat. Repellent-treated nets and clothing not only prevent mosquitoes from biting through clothes but also from biting adjacent areas. Repellents may remain effective for several days on fabric.

Caterpillars. Any spines or hairs from the caterpillar should be removed from the skin with adhesive tape, a commercial face peel, or a thin layer of rubber cement. Oral antihistamines and topical steroids should be administered to decrease urticaria and localized reactions. Severe dermatitis may benefit from oral prednisone 30 to 60 mg for adults and 1 mg/kg for children, tapered over 10 days.

Dog and Cat Bites. Wounds should be washed immediately with a non-tissue toxic soap. Pulsatile forced irrigation can be administered if available. Infected or necrotic tissue should be manually debrided. Primary closure of the wound should be avoided in high-risk wounds (the hand, deep penetrating wounds, immunocompromised patients, any wound showing signs of infection or devitalized tissue, and ferret and cat wounds). A delayed primary closure can be undertaken at 4 to 5 days if there is uncertainty about infection. Prophylactic antibiotics have not been shown to prevent infection although they are frequently used in dog and cat bites. Tetanus status should be updated and postexposure rabies prophylaxis should be considered. Human bites should be treated in a manner similar to dog and cat bites. They should never be sutured closed because of the high risk of soft tissue infection, especially on the hand.