Insect and Scorpion Stings

Epidemiology and Species

Epidemiology

Insect stings:

• 9.3 million people are stung by ants each year.
• > 1 million stings yearly by other insects
• Anaphylaxis occurs in approximately 3% of cases.
• Approximately 10 deaths per year in the United States

Scorpion stings:

• Majority of stings are nonlethal, but young children are at higher risk (if not treated):
  • < 1% in adults
  • 25% in children < 5 years
• More common in: 
  • Temperate and tropical regions
  • Rural areas
  • Summer months
  • During the evening

Clinically relevant species

The Hymenoptera order includes the following stinging insects:

• Apids: bees
• Vespids:
  • Wasps
  • Yellow jackets
  • Hornets
• Formicids: fire ants

Venomous scorpions in the United States include:

• Centruroides sculpturatus (Arizona bark scorpion)
• C. exilicauda (Baja California bark scorpion)
• C. vittatus (striped bark scorpion)

Pathophysiology

General Hymenoptera venom characteristics

• Proteolytic enzymes → degrade surrounding tissue
• Proteins act as allergens → histamine release → vasodilation and inflammation

Apids

• Barbed stinger becomes lodged in the skin → only stings once → kills insect
• Venom contains melittin → pain producing and cytolytic

Vespids

• Stingers do not stay in the skin → allows multiple stings
• Venom contains antigen 5 protein → allergenic

Formicids

• Ant anchors itself to the skin → stings repeatedly while rotating in an arc
• Venom is made of alkaloids → cytotoxic → characteristic sterile pustules

Bark scorpions

• Can sting multiple times → venom depletes with each sting
• Neurotoxic venom → incomplete inactivation of sodium channels → prolonged depolarization and hyperexcitability: 
  • Cranial nerve and somatic dysfunction
  • Excessive acetylcholine release → parasympathetic dysfunction
  • Excessive epinephrine and norepinephrine release → sympathetic dysfunction

Clinical Presentation

Presentation of insect stings

Local signs and symptoms:

• Pain
• Urticaria
• Redness
• Swelling
• Induration
• Warmth
• A stinger may still be attached (bee sting).
• Sterile pustules (fire ant stings)

Systemic signs and symptoms (anaphylaxis):

• Generalized urticaria
• Angioedema
• Flushing
• Wheezing and respiratory distress
• Hypotension

Presentation of scorpion stings

Local signs and symptoms:

• Mild swelling
• Warmth
• Pain and tenderness
• Paresthesia
• Regional lymphadenopathy

Systemic signs and symptoms (envenomation):

• Vital sign findings:
  • Hypertension
  • Tachycardia or bradycardia
  • Tachypnea
• Nausea and vomiting
• Muscle spasms and fasciculations
• Abnormal movements:
  • Neck
  • Head
  • Eyes
• Anxiety and restlessness
• Sialorrhea (excessive salivation)
• Diaphoresis
• Weakness
• Pulmonary edema

Complications:

• Respiratory failure
• Anaphylaxis
• Pancreatitis

Diagnosis and Management

Diagnosis

Insect and scorpion stings are clinical diagnoses.

Insect sting management

General management:

• Clean with soap and water.
• Remove the stinger (with a scraping motion, not by squeezing).
• Apply cold compresses.
• Medical therapy:
  • NSAIDs or acetaminophen for analgesia
  • Antihistamines
  • Topical corticosteroids
  • Oral prednisone for large, localized reactions

Management of severe allergic reactions and anaphylaxis:

• Assess and stabilize the airway.
• Medical therapy:
  • Antihistamines (H1 and H2 antagonists)
  • Epinephrine
  • Corticosteroids
  • IV fluids

Prevention:

• Venom immunotherapy is effective at reducing the chance of recurrent anaphylaxis.
• Patients with previous anaphylaxis to stings should carry an epinephrine syringe.

Scorpion sting management

Most stings only require supportive care. Care for venomous scorpions may include:

• Observation for at least 4 hours
• Intubation for impending respiratory failure
• Medical therapy:
  • NSAIDs or opioids for pain
  • Benzodiazepines for muscle spasms
  • IV antihypertensives, as needed
• Antivenom for skeletal muscle and/or cranial nerve dysfunction

Differential Diagnosis

• Spider bite: the brown recluse spider contains a necrotizing venom that can lead to a painful, blistering, necrotic wound; fevers; myalgias; hemolysis; seizures; and renal failure. A black widow spider’s neurotoxic venom can cause muscle cramping and rigidity, vital sign instability, lacrimation, salivation, ptosis, and respiratory distress. The diagnosis is clinical. Management includes wound care, pain management, antivenom for black widow spider bites, and delayed debridement of necrotic tissue in brown recluse bites.
• Snakebite: Evidence of envenomation at the bite site includes edema, erythema, warmth, bullae, and necrosis. Systemic symptoms such as nausea, diaphoresis, paresthesias, and altered sensorium may be present. In addition, coral snake venom can cause flaccid muscles. The diagnosis is clinical. Management includes supportive care, pain control, hydration, and antivenom. Patients are monitored closely for shock, coagulopathy, respiratory failure, and renal failure.
• Asthma: a chronic inflammatory condition resulting in bronchial hyperresponsiveness and airflow obstruction. Patients typically present with wheezing, cough, and dyspnea. Urticaria and hypotension are not generally seen. Diagnosis is confirmed with a pulmonary function test showing a reversible obstructive pattern. Management is based on symptom severity and may include oxygen therapy, bronchodilators, inhaled corticosteroids, systemic steroids, and intubation for respiratory failure. 
• Hereditary angioedema: an autosomal dominant disorder characterized by recurrent episodes of severe swelling (angioedema). Swelling in the airway can restrict breathing and lead to a life-threatening airway obstruction. The diagnosis is made by evaluating levels of C1 inhibitor in the blood. Management includes danazol, kallikrein inhibitors, and C1 inhibitors. 
• Botulism: a poisoning from Clostridium botulinum toxin that may lead to symmetric cranial nerve palsies and descending muscle paralysis. Electromyography and toxin assays may be used in the diagnosis. Management includes supportive therapy, intubation for respiratory impairment, and antitoxin administration.