WIDOW SPIDERS (LATRODECTUS SPECIES)

BACKGROUND

Multiple species of widow spiders (Latrodectus spp.) are found on various continents (North America, Asia, Europe, Africa, and Australia). They are generally black or brown with a red or yellow demarcation on their ventral and/or dorsal abdomen. A lack of a red or yellow demarcation on the spider does not exclude it from being a Latrodectus spp. They live in temperate and tropical latitudes and tend to inhabit shady enclosed spaces such as crevices, wood piles, and sheds. Humans are commonly bitten while in bed during the fall and early winter when the spiders are attempting to find warmth.

PATHOPHYSIOLOGY

Widow spider venom consists of multiple toxins which ultimately result in activation of the nervous system and muscle contraction.2

CLINICAL MANIFESTATION

Patients may or may not feel a pinprick upon the initial bite. A pair of small red spots at the envenomation site may be visible; however, the bite site is often not located.3 Some patients do not develop systemic toxicity. In those patients who do, symptoms typically begin 15 to 60 minutes following the envenomation. The primary symptom is painful muscle cramping, starting at the bite site and progressing towards the center of the body. Patients may develop a painful, rigid abdomen secondary to abdominal muscle spasm which may be mistaken for peritonitis. The pain increases over time and may occur in waves. In some cases, the patient develops a temporary diaphoretic, grimaced, and contorted appearance of the face referred to as “facies latrodectismica.”4 Other symptoms include vomiting, diaphoresis, tachycardia, hypertension (often profound), and restlessness. Symptoms of Latrodectus envenomation last hours to days. Fatalities from Latrodectus envenomation are exceedingly rare and, when they do occur, are secondary to cardiac arrest (presumably from severe hypertension in patients with predisposing medical conditions) and wound infection.5

TREATMENT

Treatment consists primarily of supportive care, pain management, and wound care (to include tetanus prophylaxis). Given the low risk of infection, antibiotics are not routinely recommended.

Depending upon the severity of pain, acetaminophen, nonsteroidal anti-inflammatory agents, and opioids can be used for pain control. Benzodiazepines may improve muscle spasms.6 Pain control and benzodiazepines are often sufficient to manage tachycardia and hypertension. In those patients with severe pain refractory to pain medications, antivenom (if available) may be indicated but may not be readily available.7 Long term injury or death from Latrodectus is extremely unlikely. While rare, fatal allergic reactions to Latrodectus antivenom have occurred.8 Fatal cases due to antivenom anaphylaxis have been reported in patients with asthma. Therefore, Latrodectus antivenom is not indicated in patients with otherwise manageable symptoms, particularly those that may be at higher risk (i.e. history of asthma). If administered, patients should be monitored for 4 hours, but prophylactic treatment for allergic reaction is not recommended. When patients do have significant symptoms meeting indications for antivenom, the antivenom is rapidly effective and curative. When necessary, expired vials of antivenom may be used.9 The dose consists of one 2.5 milliliter vial of antivenom dissolved in one 2.5 milliliter vial of sterile water (provided in the antivenom kit) administered intravenously. While the package instructions permit intramuscular injection, this route is unlikely to provide sufficient absorption to manage symptoms.10 While one dose is usually sufficient, a second dose may be administered if symptoms are not adequately controlled 15-30 minutes after the first dose.

In the event that medical personnel are unable to control the patient’s symptoms with available pain medications and benzodiazepines, then medical evacuation is recommended.