Black Widow Spider

Aka: Black Widow Spider, Latrodectus mactans, Widow Spider, Latrodectism, Widow Spider Bite, Poisoning due to Black Widow Spider Venom, Black Widow Spider Venom

1. See Also
   1. Neurotoxin
   2. Insect Bite
2. Epidemiology
   1. Most commonly active in warmer months
   2. Occurs throughout the United States except for Alaska
3. Types: Widow Spider scientific names
   1. Most common in United States
      1. Latrodectus mactans
         1. South Eastern U.S.
      2. Latrodectus hesperus
         1. South Western U.S. - Arizona, New Mexico, Nevada, Utah, Southern California
      3. Latrodectus variolus
         1. Northern U.S.
   2. Less common in United States
      1. Latrodectus bishopi
      2. Latrodectus geometricus (Introduced brown Widow Spider)
         1. Southern United States
         2. Yellow-orange hour glass and milder venom
4. Identification: Lactrodectus mactans (Southeastern black widow)
   1. Female (only female delivers venomous bite)
      1. Glossy ink-black Spider
      2. Abdomen globular
      3. Red hourglass on underside (ventral) Abdomen may be difficult to visualize
      4. More venomous than males
      5. Leg span : 3-4 cm
   2. Male
      1. Grey coloration
      2. Stripes or spots
      3. Rarely transmit significant venom with bite
      4. Leg span: 1.6 to 2.0 cm (Half the female size)
   3. Spiderlings
      1. Orange, brown and white striped pattern (zebra-like)
      2. Change color with molting
   4. Web
      1. Irregular, chaotic-patterned heavy, strong web
      2. Adult female Spider rarely leaves web
   5. Images
      1. 
5. Habitat
   1. Indoors (Buildings)
      1. Dark garages
      2. Basements
      3. Stables
   2. Outdoors
      1. Yard debris
      2. Rock crevices
      3. Wood piles
      4. Overhangs
      5. Abandoned rodent holes
6. Pathophysiology
   1. Highly venomous Neurotoxin: a-Latrotoxin
      1. Stimulates large presynaptic acetylcholine release
   2. Bite results in systemic toxicity (Latrodectism)
      1. Excessive adrenergic stimulation
      2. Excessive Cholinergic stimulation
7. Symptoms
   1. Initial
      1. Bite felt as pinprick with minimal initial pain
   2. First 10 to 20 minutes
      1. Pain and throbbing at bite site
   3. Next 2 to 3 hours: Latrodectism
      1. Musculoskeletal symptoms
         1. Diffuse, progressive myalgias in 100% of patients
         2. Generalized sweating
      2. Cardiopulmonary symptoms (associated with upper extremity bites)
         1. Crampy Chest Pain or chest tightness
         2. Dyspnea
      3. Gastrointestinal Symptoms (associated with lower extremity bites)
         1. Abdominal cramping (64%)
         2. Board-like rigidity
         3. Nausea and Vomiting (36%)
      4. Facial Symptoms
         1. Flushed sweating face
         2. Contorted, Painful grimace
         3. Conjunctivitis
         4. Trismus of masseters
         5. Facial edema
      5. Neurologic Symptoms
         1. Headache (27%)
         2. Restlessness
         3. Paresthesias
         4. Seizures
         5. Weakness
8. Signs
   1. Bite wound
      1. Two small central red fang marks on blanched skin
      2. Surrounded by erythematous rings (target appearance)
      3. Bite may also appear as wheal and flare pattern
      4. Localized diaphoresis
      5. Muscle fasciculations in the involved extremity
   2. Systemic signs
      1. Hypertension
      2. Diaphoresis
      3. Tachycardia
      4. Shock
      5. Abdominal Pain (with rigid Abdomen)
      6. Back pain
9. Grading
   1. Grade 1
      1. Asymptomatic other than localized pain at Envenomation site
      2. Normal Vital Signs
   2. Grade 2
      1. Muscle pain in extremity with Envenomation
      2. Pain radiation into chest (arm bites) or Abdomen (leg bites)
      3. Local extremity diaphoresis
      4. Normal Vital Signs
   3. Grade 3
      1. Generalized Muscle pain in back, Abdomen and chest
      2. Generalized diaphoresis
      3. Abnormal Vital Signs (e.g. Hypertension, Tachycardia)
      4. Headache
      5. Nausea and Vomiting
   4. References
      1. Clark (1992) Ann Emerg Med 21(7): 782-7 [PubMed]
10. Differential Diagnosis
    1. Toxin Ingestion
    2. Angina
    3. Pneumonia
    4. Asthma
    5. Acute Abdomen (Peritonitis)
    6. Nephrolithiasis
11. Course
    1. Symptoms resolve over 2-3 days
    2. Mortality approaches 1%
    3. Shock or death are more common in children and elderly
12. Labs: Used to differentiate from other conditions
    1. Complete Blood Count
       1. Distinguish from peritonitis
    2. Urinalysis
       1. Distinguish from Urinary Tract Infection
    3. Serum Creatine Phosphokinase or Lactate Dehydrogenase
       1. Distinguish from Rhabdomyolysis
13. Management: General
    1. General
       1. Cold compresses or ice pack (prevents toxin spread)
       2. Thorough Wound Cleansing with soap and water
       3. Steroid ointment
       4. Tetanus Prophylaxis as needed
    2. Muscle spasms, rigidity, pain
       1. First-line therapy: Benzodiazepines
          1. Diazepam (Valium)
             1. Infants/Toddlers: 0.2-5 mg slow IV infusion
             2. Older children and Adults: 10 mg slow IV infusion
       2. Older regimens
          1. Calcium Gluconate
             1. Adult dose: 10 ml of 10% solution) slow IV infuse
             2. Can be repeated every 4 hours
          2. Methocarbamol (Robaxin)
             1. Adult dose: 10-30 ml slow IV infuse
             2. Calcium is more effective
    3. Opioid Analgesics
       1. Monitor for respiratory depression (especially in younger patients)
    4. Disposition
       1. Observe for 6 hours
       2. May discharge home if no concerning symptoms or signs
       3. Consider hospital observation for children and those with cardiovascular disease
14. Management: Antivenin (horse serum)
    1. Indications (rarely indicated)
       1. Critical Envenomation (Grade 3 bites)
       2. Respiratory arrest
       3. Seizures
       4. Hypertensive heart disease
       5. Young Children or elderly
       6. Pregnant women
    2. Dosing
       1. Skin test first before dosing
          1. Evaluate for sensitivity to horse serum
       2. IV: 2.5 ml (1 vial) in 100 to 250 ml NS IV over 2 hours
    3. Adverse effects: Serum Sickness
       1. Risk may be greater than risk of death by Spider Bite
    4. Efficacy
       1. Relieves symptoms within 1-2 hours
       2. Efficacious up to 90 hours after bite
15. Complications
    1. Pulmonary Edema
    2. Cardiomyopathy
    3. Rhabdomyolysis
    4. Cardiovascular Collapse
16. Precautions
    1. Hospitalize severe cases or significant comorbidity
    2. Cohorts to consider hospitalization
       1. Pregnancy
       2. Extremes of age (very young or old)
       3. Coronary Artery Disease
       4. Severe Hypertension
17. References
    1. Cowling and Ferreri (2019) Crit Dec Emerg Med 33(2): 17-25
    2. Diaz (2007) Am Fam Physician 75(6):869-73 [PubMed]
    3. Juckett (2013) Am Fam Physician 88(12): 841-7 [PubMed]
    4. Koh (1998) Postgrad Med 103(4): 235-50 [PubMed]