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Podcast Recap: Stings and envenomations with Dr. Ben Grebber

August 17, 2023

Stings and Envenomations

In this episode of PEM Currents: The Pediatric Emergency Medicine Podcast, pediatric resident Dr. Ben Grebber gives an overview of the common signs and symptoms, some pathophysiology, and recommended treatments for bee stings and spider bites.

Podcast length - 16 min., 29 secs.

5 Key Takeaways

1. Risk of systemic reactions increases with a history of multiple honey bee stings, so be mindful of patients with worsening reactions after a second or third bee sting in their lifetime.

Honey bees have one of the highest frequency of stings worldwide, according to the World Allergy Organization, and therefore cause the majority of anaphylactic reactions.

Non-IgE-mediated reactions. For symptomatic treatment, initial management includes removing the stinger. Many hymenoptera have large stingers that can get lodged in the skin, ripping away from the insect’s body as it tries to fly away. Venom is released within the first few seconds and definitely by 2 minutes.

Despite some common misconceptions, pinching the venom sac a few minutes after initial sting will not introduce more venom. However, remaining stingers should still be removed to prevent foreign body reactions. In the first few seconds after a sting, the remaining stinger can be flicked off with a finger or credit card. By the time a patient reaches the ER, forceps should be used and are safe to do so. After a stinger is removed, consider mild analgesics, including acetaminophen and ibuprofen to help with swelling and tenderness. Antihistamines have been shown to reduce localized swelling. Consider ice and cool compresses. There’s limited evidence for low potency prednisone.

Venom-specific IgE-mediated reactions. Local reactions. Look for >10-cm diameter area of induration, which can be mistaken for cellulitis. They can often occur 6 to 12 hours after a sting, and progressively increase in size over 48 hours.

Systemic reactions. Think anaphylaxis involving 1 or more organ systems. Symptoms can range from skin findings, including pruritus, flushing, urticaria, and angioedema. GI symptoms include N/V, diarrhea, and abdominal pain; respiratory concerns include wheezing, stridor, SOB; CV symptoms include hypotension, syncope, and shock. In these cases, serum-triptase (ST) levels may be elevated. However, testing isn't necessary if the offending insect has been identified.

When managing more severe reactions, always start with ABCs.

Treatment. Prompt IM 1:1,000 aqueous epinephrine is indicated. In children give 0.01 mg/kg per dose IM q5-15 min as needed with a maximum dose of 0.3 mg. Can continue symptomatic management once the patient is stabilized, but evidence shows that antihistamines and corticosteroids do not help.

After successful treatment, recommendations vary for observation:

• In patients with milder anaphylaxis reactions, consider two to four hours of observation to monitor for delayed anaphylactic episodes, while more severe reactions might warrant longer (six to eight hours) observation.
• In either case, patients should be discharged with a prescription for an epinephrine auto injector.
• Consider allergist referral for systemic reactions for possible venom immunotherapy and further allergen testing.

Patient counseling. Overall, avoid eating outside, gardening, grilling, and walking barefoot outside, and stay away from trashcans and open beverages. Ineffective avoidance methods include avoiding bright colored clothing, avoiding fragrance, and using insect repellents.

2. Latrodectus or black-widow spiders have not resulted in a death in the U.S. since 1983 but an equine F(ab’)2 antivenin called Analatro is undergoing U.S. trials and is commercially available in Mexico to treat rare cases of severe hypotension.

Only the female spiders have fangs sufficient to penetrate skin. They are found among wood piles and prefer dark, dry places like barns, basements, eaves, and crevices. Sometimes they are found in garden gloves and boots. Black widow spider venom lacks human cytotoxic agents so there will likely be only minimal local injury or tenderness. Patients may present after a pinprick sensation with mild inflammatory response, including lymphadenopathy or a target or halo lesion.

Latrodectism - systemic symptoms, also known as latrodectism. The alpha latrotoxin produced by black widows is a potent presynaptic neurotoxin affecting the neuromuscular junction leading to cation-channel opening. This causes reduced acetylcholine reuptake and muscle cramping. Cramping presents in the legs, abdomen, back, and chest. The toxin can also lead to autonomic nervous system dysfunction, leading to diaphoresis, N/V, tachycardia, irritability, and priapism. Symptoms overall tend to persist for 36 to 72 hours. Be cautious as the abdominal pain be severe and can sometimes mimic appendicitis.

Treatment. Start with analgesics. Benzodiazepines can target central smooth muscles for relaxation and can also be used for anxiolysis. Retrospective studies don't support the use of calcium gluconate. Support hydration, use cool compresses, and provide tetanus immunization if indicated.

In the rare case of severe hypotension, there's an antivenin available, albeit scarce locally. Importantly, this is a horse serum, so be mindful of hypersensitivity. Current U.S. trials are looking at a highly purified equine F(ab’)2 antibody preparation, under the name Analatro, that is commercially available in Mexico.

3. The diagnosis of brown recluse spider bite can be difficult without a witness to observe the bite, leading to a broad diagnosis and differential, including cutaneous anthrax; treatment is mostly symptomatic as an antivenin doesn't exist.

While found in Southern U.S., these spiders can also hitchhike in baggage or cargo and make their way north. Bites often occur from April to October. After an initial bite, early symptoms include erythema, pruritus, and edema within two to eight hours. In the next 24 to 48 hours, a blue-gray halo begins to form that eventually becomes more vesicular in nature, occasionally with serous or hemorrhagic fluid. This lesion will progress over the course of seven to 10 days with ischemia and necrosis into a black eschar. Eventually, the eschar sheds over two to five weeks, leaving behind an ulcer. Systemic manifestations of brown recluse spider bites (less common) are termed loxoscelism. They include fever, chills, malaise and lymphadenopathy after 24 hours with other symptoms including N/V, diarrhea, a macular papular rash, and hemolytic anemia to name a few.

Unfortunately there are no arachnid venom lab tests to confirm the diagnosis.

Treatment. Treatment is mostly symptomatic as an antivenin does not exist. Provide tetanus prophylaxis if indicated. Consider splinting, clean the wound if open, and apply cool compresses. Local symptoms do not require hospitalization.

For more systemic reactions: consider monitoring for signs of hemolysis and treat for any signs of cellulitis. Other therapies have not been heavily studied but some data supports the use of corticosteroids, antibiotics, antihistamines, dapsone, and lastly surgical incision.

4. Most tarantula (mygalomorph) bites are no more severe than a bee sting.

Found in the tropical and subtropical desert areas of the Southwestern U.S., these spiders are also common arachnid pets.

Patients can present with localized erythema, swelling and pain. Occasionally, agitated tarantulas release and shoot their hair, which can embed in skin leading to pruritis. If they end up in a patient’s eyes, consider a thorough ophthalmologic exam as the hairs can lead to chronic keratitis and retinitis. For skin hairs, try using adhesive tape to effectively lance out the hairs or saline solution to rinse the area. Treat with local wound care, antihistamines, or oral analgesics as needed.

5. The potent neurotoxin of the bark scorpion activates neural sodium channels and systemic reactions leading to symptoms within 60 minutes; antivenin became available in 2011 and should be reserved for persistent signs of severe envenomation or neurotoxicity.

The bark scorpion (Centruroides exilicauda) is primarily found in the Southwestern U.S. and is the most venomous scorpion in the country. Scorpions that are capable of injecting venom belong to the Buthidae family, with the deadliest scorpions actually living in North Africa and the Middle East. Envenomation is described as severely painful, with patients often describing the sensation of an electric shock. Venom components are often found in aphrodisiac formulations in the U.S.; nonetheless, bark scorpion envenomation can lead to adrenergic and parasympathetic activation.

The potent neurotoxin activates neural sodium channels and systemic reactions leading to symptoms within 60 minutes. Neurologically, patients may present with uncontrolled jerking movements of the extremities, peripheral muscle fasciculation, tongue fasciculation, facial twitching, and rapid disconjugate eye movements. They may also describe temporary dysfunction of the affected extremity, such an arm or a hand if stung in that region. The adrenergic and parasympathetic surge can result in agitation, extreme tachycardia, hypertension, salivation, and respiratory distress. Venom can also cause non-specific ST changes, ST elevation, or ST depression.

A definitive history of scorpion sting is most useful as the differential diagnosis includes seizures, phenothiazine, or organic phosphate poisoning, to name a few.

Initial management should include the ABCs.

For mild symptoms: Consider supportive cold compresses, tetanus prophylaxis if applicable, and analgesics.

For more severe reactions: Benzodiazepines are appropriate for seizures and opioid analgesics for pain. There’s no clear studied cardiac therapy but calcium channel blockers can assist with hypertension, as well as alternative afterload reducers. Atropine will improve hypersecretion, but should be used with caution.

Antivenin became available in 2011 and should be reserved for persistent signs of severe envenomation or neurotoxicity. Anascorp Centruroides Immune F(ab’)2 equinine injection is available in many regional trauma centers around bark scorpion habitats. Treatment requires 3 vials reconstituted in 5 mL of sterile, normal saline combined and then diluted further to a total of 50 mL infused over 10 minutes. Antivenin can be repeated a second time if necessary.

Patient counseling. Avoid areas where scorpions congregate and physical barriers such as elevated door thresholds.

Any views, thoughts, and opinions expressed in this podcast recap are solely that of the host and guests and do not reflect the views, opinions, policies, or position of epocrates and athenahealth.

Source:

Sobolewski, B. (Host). (2023, June 27). Stings and Envenomations. Dr. Ben Grebber (Guest). PEM Currents: The Pediatric Emergency Medicine Podcast. https://www.pemcincinnati.com/podcasts/