Bites and Stings From Arthropods and Mosquitoes
Disorders
Brown (“Fiddleback” or “Recluse”) Spiders
Necrotic arachnidism, or loxoscelism, is caused by spiders of the genus Loxosceles and other spiders that deposit a venom characterized by its local dermonecrotic activity. The fiddleback spider (see Plate 14) carries the characteristic violin-shaped marking on the dorsum of its cephalothorax. The clinical spectrum of loxoscelism ranges from mild and transient skin irritation to severe local necrosis accompanied by hematologic and renal pathologic conditions.
Signs and Symptoms
1. Most common presentation is an isolated cutaneous lesion.
2. Local symptoms begin the moment of the bite, with a sharp stinging sensation, although some patients report no awareness of having been bitten.
3. Stinging subsides over 6 to 8 hours and is then replaced by aching and pruritus.
4. Site becomes edematous, with an erythematous halo surrounding an irregularly shaped violaceous center of incipient necrosis; white ring of vasospasm and ischemia may be discernible between the central lesion and the halo.
5. Often erythematous margin spreads irregularly, in a gravitationally influenced pattern that leaves the original center near the top of the lesion.
6. In more severe cases, serous or hemorrhagic bullae arise at the center within 24 to 72 hours, with an underlying eschar (see Plate 15).
7. Systemic reactions: hemoglobinuria within 24 hours of envenomation; fever, chills, maculopapular rash, weakness, leukocytosis, arthralgias, nausea, and vomiting within 24 hours of the bite
Treatment
1. Apply cold compresses intermittently for the first 4 days after the bite. Do not apply heat.
2. If the wound appears infected, apply a topical antiseptic (mupirocin, bacitracin) under a sterile dressing. Administer an oral antibiotic such as cephalexin, dicloxacillin, or erythromycin (see Appendix H).
3. Seek advanced medical care to consider adjunctive measures for the bite wound and to evaluate for hospitalization for coagulopathy or renal failure caused by hemolysis and hemoglobinuria.
4. Obtain appropriate tetanus prophylaxis (when available).
5. Reported therapies include dapsone, glucocorticoids, hyperbaric oxygen, electric shock, antivenom, metronidazole, diphenhydramine, phentolamine, and cyproheptadine, although there is scant evidence to support their efficacy.
Widow Spiders
Female spiders of the genus Latrodectus carry the characteristic hourglass marking on the ventral abdomen (see Plate 16).
Signs and Symptoms
1. Initial bite is sometimes sharply painful, but often nearly painless, with only a tiny papule or punctum visible; surrounding skin slightly reddened and sometimes indurated; in many cases, no further progression of symptoms occurs.
2. Neuromuscular symptoms: can become dramatic within 30 to 60 minutes as involuntary spasm and rigidity affect the large muscle groups of the abdomen, limbs, and lower back; worst pain usually occurs within the first 8 to 12 hours but may remain severe for several days.
3. Predominantly abdominal presentation may resemble an acute abdomen
4. Priapism, fasciculations, weakness, ptosis, thready pulse, fever, salivation, diaphoresis, vomiting, bronchorrhea, pulmonary edema, rhabdomyolysis, hypertension with or without seizures
5. Characteristic pattern of facial swelling, known as Latrodectus facies, may develop hours after the bite.
Treatment
1. Cleanse the bite site. Apply a cold pack (ice pack) to the bite site. Provide tetanus prophylaxis (if available).
2. For muscle spasm, administer a benzodiazepine (e.g., diazepam 5-10 mg IV/IM, or lorazepam 1-2 mg IV/IM) or narcotics (e.g., morphine 4-8 mg IV/IM/SC).
3. Administer pain medication (IV opiates preferable).
4. Monitor the patient for hypertension.
a. Administer a centrally acting or vasodilating antihypertensive if the patient develops urgent hypertension and such a drug is available (e.g., nifedipine 30-60 mg ER PO daily, nicardipine 20-40 mg PO q8hr, or nicardipine IV drip started at 5 mg/h IV and increased 2.5 mg/h q5-15 min prn to a maximum of 15 mg/h).
b. Be alert for a seizure associated with rapid elevation in blood pressure.
5. Antivenom is available in the United States from Merck and Co.; in Australia from Commonwealth Serum Laboratories; and in South Africa from the National Health Laboratory Service. In general, antivenom is recommended for respiratory arrest, seizures, uncontrolled hypertension, or pregnancy. The usual dose is one to three vials or ampules intravenously.
6. All symptomatic children, pregnant women, and patients with a history of hypertension with suspected or confirmed envenomations should be admitted to a hospital for treatment and observation.
Funnel-Web Spiders
Funnel-web spiders (see Plate 17) are large, aggressive spiders that deliver a potent neurotoxin.
Signs and Symptoms
1. Intense pain at the bite site, with or without a local wheal surrounded by erythema lasting for 30 minutes; localized sweating
a. Begins minutes after venom injection, with local piloerection and muscle fasciculation; becomes generalized over the next 10 to 20 minutes
b. Intense pain at the bite site; perioral tingling, nausea and vomiting, diaphoresis, salivation, lacrimation, diarrhea
Treatment
1. In the field, apply the pressure immobilization technique for venom sequestration at the bite site (see Chapter 37).
2. Give specific antivenom, which is developed in rabbits and is the mainstay of treatment. Adult and pediatric dose is two ampules (100 mg purified IgG per ampule) of antivenom administered intravenously every 15 minutes until symptoms improve.
3. Be aware that general management, in addition to antivenom administration, is supportive.
Banana (Brazilian Wandering or Armed) Spiders
Signs and Symptoms
1. Severe local pain that radiates up the extremity into the trunk, followed within 10 to 20 minutes by tachycardia, hypertension, hypothermia, profuse diaphoresis, salivation, vertigo, visual disturbances, nausea and vomiting, and priapism.
2. If death occurs (usually in 2 to 6 hours), it is usually caused by respiratory paralysis.
Treatment
1. Treat mild envenomation symptomatically by infiltrating the bite site with a local anesthetic.
2. Be aware that narcotics may potentiate the venom’s respiratory depressant effect and should not be used.
3. For severe envenomation, administer monovalent antivenom (Belo Horizonte) or polyvalent antivenom (Sero Antiaracidico Polivalente, Instituto Butantan, available in Brazil).
Wolf Spiders
Wolf spiders are diurnal predators that are usually a mottled dark gray or brown (Fig. 38-1).
Tarantulas
Tarantulas are large, slow spiders (Fig. 38-2) capable of inflicting a painful bite when threatened. Several varieties possess urticating hairs, which they flick by the thousands through the air into an attacker’s skin and eyes.
FIGURE 38-2 Mature female tarantula Aphonopelma iodius. (Courtesy Michael Cardwell & Associates, 1997.)
Treatment
1. Therapy is supportive and based on symptoms. To remove urticating hairs, apply and remove sticky tape from the skin in a few repeated applications.
2. Elevate the bitten extremity and immobilize it to reduce pain.
3. Administer analgesics as needed.
4. Topical or systemic corticosteroids and oral antihistamines may be used for urticating hair exposure.
5. For eye exposure, irrigate the eyes, and then consider ophthalmic antibiotic/corticosteroid ointment (e.g., combination bacitracin/neomycin/polymyxin B/hydrocortisone ophthalmic ointment q3-4h for 5-7 days) for keratoconjunctivitis, and follow up with an ophthalmologist as soon as possible.
Hobo Spiders
Treatment
1. Apply cold compresses intermittently for the first 4 days after the bite. Do not apply heat.
2. If the wound appears infected, apply a topical antiseptic (mupirocin, bacitracin) under a sterile dressing. Administer an oral antibiotic such as cephalexin, dicloxacillin, or erythromycin (see Appendix H).
Hymenoptera (Bees, Wasps, and Ants)
By far the most important venomous insects are members of the order Hymenoptera, including bees, wasps, and ants (Fig. 38-3). The abdomen and thorax are connected by a slender pedicle, which may be quite long in certain wasps and ants.
Signs and Symptoms
1. Instantaneous pain, followed by a wheal-and-flare reaction, with variable edema. Most stings are on the head and neck, followed by the foot, leg, hand, and arm. Stings may occur in the mouth, pharynx, or esophagus if the insects are accidentally ingested.
2. Fire ant stings may produce vesicles that subsequently become sterile pustules; this is caused by the ant grasping the skin with mouthparts and inflicting multiple stings (Fig. 38-4).
FIGURE 38-4 Fire ant lesions.
3. In the case of multiple bee, wasp, yellow jacket, or hornet stings, vomiting, diarrhea, generalized edema, dyspnea, hypotension, and collapse may develop. The lethal dose of honeybee venom has been estimated at 500 to 1500 stings.
4. Large local reactions are relatively common, spreading more than 15 cm (5.9 inches) beyond the sting and persisting longer than 24 hours.
a. Reactions occur in areas remote from the sting and typically include pruritus, hives, difficulty breathing, nausea, papular urticaria, and angioedema. Other symptoms include abdominal pain and vomiting.
b. When reaction is life threatening, there is marked respiratory distress, hypotension, loss of consciousness, and arrhythmias.
c. Most fatalities occur from anaphylaxis, and most of these occur within 1 hour of the sting.
Treatment
1. Be aware that the treatment of anaphylactic reaction follows conventional guidelines, as follows:
a. Maintain the airway, and administer oxygen (if available).
b. Obtain intravenous or intraosseous access. Administer lactated Ringer’s or normal saline solution to support the systolic blood pressure at a level of at least 90 mm Hg.
c. Administer epinephrine. Begin with aqueous epinephrine 1 : 1000 intramuscularly in the deltoid region. The dose for adults is 0.3 to 0.5 mL, and for children 0.01 mL/kg. An alternative is to inject the contents of an EpiPen or EpiPen Jr. intramuscularly into the lateral thigh region. Alternative products are the Twinject or Twinject Jr., or Adrenadick. Repeat in 20 minutes if relief is partial. If the reaction is limited to pruritus and urticaria, there is no wheezing or facial swelling, and the patient is older than 45 years, administer an antihistamine and reserve epinephrine for a worsened condition.
d. In the presence of profound hypotension, when skin is not adequately perfused, 2 to 5 mL of a 1 : 10,000 epinephrine solution may be given by slow IV push, or an infusion may be initiated by mixing 1 mg in 250 mL and infusing at a rate of 0.25 to 1 mL/min.
e. Relieve bronchospasm. Administer micronized albuterol or metaproterenol by handheld metered-dose inhaler.
f. Administer antihistamines. Manage mild reactions with diphenhydramine, 50 to 75 mg IV, IM, or PO. The dose for children is 1 mg/kg. Nonsedating antihistamines, such as fexofenadine 60 mg or cimetidine 300 mg, are adjuncts.
g. Administer corticosteroids. If the reaction is severe or prolonged or if the patient is regularly medicated with corticosteroids, administer hydrocortisone 200 mg, methylprednisolone 50 mg, or dexamethasone 15 mg, IV with a 5-day oral course or 10-day oral taper to follow. The parenteral dose of hydrocortisone for children is 2.5 mg/kg. If the therapy is initiated orally, administer prednisone, 60 to 100 mg for adults and 1 mg/kg for children.
2. For mild hymenopteran stings, apply ice packs to provide relief.
3. Be aware that a honeybee or yellow jacket may leave an embedded stinger. Remove the stinger (and possibly, attached venom sac) as quickly as possible with a sharp edge or forceps. Do not be overly concerned about squeezing the sac—it is more important to remove the stinger and sac as quickly as possible.
4. Note that a home remedy such as a paste of unseasoned meat tenderizer or baking soda is of variable usefulness, although some report the former to be effective. Topical anesthetics in “sting sticks” have limited usefulness.
5. Because infection is common, apply antimicrobial ointment such as mupirocin to cover the wound. Debridement of fire ant blisters is not recommended.
6. Envenomation from multiple hymenopteran stings may require more aggressive therapy, including intravenous calcium gluconate (5 to 10 mL of 10% solution) in conjunction with a parenteral antihistamine and corticosteroid to relieve pain, swelling, and nausea and vomiting. A corticosteroid, such as methylprednisolone, 24 mg the first day then tapered over 5 days, often hastens resolution of a large local reaction to a bee or wasp sting.
7. Manage delayed serum sickness in response to multiple hymenopteran stings with a corticosteroid such as prednisone, 60 to 100 mg for adults and 1 mg/kg for children, tapered over 2 weeks.
Lepidoptera (Caterpillars)
Signs and Symptoms
1. With caterpillars that have hollow spines and venom glands, instant nettling pain, followed by redness and swelling, after direct contact with the live insect
a. Ordinarily, no systemic manifestations; symptoms subsiding within 24 hours
b. Possibly intense pain with central radiation, accompanied by nausea and vomiting, headache, fever, and lymphadenopathy
2. With attached or detached spines from certain caterpillars or moths, itching and erythematous, papular, or urticarial rash within a few hours to 2 days after contact
