Five species of widow spiders are found in the United States: Latrodectus mactans (black widow; Fig. 118–2A), Latrodectus hesperus (Western black widow), Latrodectus variolus (found in New England, Canada, south to Florida, and west to eastern Texas, Oklahoma, and Kansas), Latrodectus bishopi (red widow of the South), and Latrodectus geometricus (brown widow or brown button spider; Fig. 118–2B). They are present in every state except for Alaska. Dangerous widow spiders in other parts of the world include L. geometricus and Latrodectus tredecimguttatus (European widow spider found in southern Europe), Latrodectus hasselti (red-back widow spider found in Australia, Japan, and India; Fig. 118–2C), and Latrodectus cinctus (found in South Africa). These spiders live in temperate and tropical latitudes in stone walls, crevices, wood piles, outhouses, barns, stables, and rubbish piles. They molt multiple times and as a result can change colors. The ventral markings on the abdomen are species specific, and the classic red hourglass-shaped marking is noted in only L. mactans. Other species may have variations on their ventral surface, such as triangles and spots.
Widow spiders. (A) The North American black widow spider, Latrodectus mactans. Note the hourglass on the abdomen. (B) The brown widow spider, Latrodectus geometricus. (C) The Australian redback spider, Latrodectus hasselti. (Used with permission of The American Museum of Natural History.)
Typically, the female L. mactans is shiny, jet-black, and large (8–10 mm), with a rounded abdomen and a red hourglass mark on its ventral surface. Her larger size and ability to penetrate human skin with her fangs make her more venomous and toxic than the male spider, which resembles the immature spider in earlier stages of development and is smaller, lighter in color, and has a more elongated abdomen and fangs that usually are too short to envenomate humans (Table 118–3). Black widow females are trappers and inhabit large, untidy, irregularly shaped webs. Webs are placed in or close to the ground and in secluded, dimly lit areas that can trap flying insects, such as outdoor privies, barns, sheds, and garages.5
TABLE 118–3.Brown Recluse and Black Widow Spiders: Comparative Characteristics ||Download (.pdf) TABLE 118–3. Brown Recluse and Black Widow Spiders: Comparative Characteristics
| ||Brown Recluse (Loxosceles spp) ||Black Widow (Latrodectus spp) |
|Description ||Female brown, 6–20 mm, violin shaped mark on dorsum of cephalothorax; female greater toxicity than male ||Female jet black, 8–10 mm, red hourglass mark on ventral surface, female greater toxicity than male |
|Major venom component ||Sphingomyelinase D ||α-Latrotoxin |
|Pathophysiology of envenomation ||Vascular injury, dermatonecrosis, hemolysis ||Massive presynaptic discharge of neurotransmitters; lymphatic and hematogenous spread, neurotoxicity |
|Epidemiology ||Bites more common in warmer months ||Bites more common in warmer months in subtropical and temperate areas; perennial in tropics |
| ||North America (southern and midwestern states): L. reclusa ||North America: L. mactans, L. hesperus, L. geometricus |
| ||South America: L. laeta, L. gaucho ||Europe: L. tredecimguttatus |
| ||Europe: L. rufescens ||Africa (southern): L. indistinctus |
| ||Africa (southern): L. parrami, L. spiniceps, L. pilosa, L. bergeri ||Australia: L. hasselti |
| ||Asia/Australia: Rare ||Asia/South America: Rare |
|Clinical effects ||Cutaneous ||Cutaneous |
| ||Initial (0–2 hours after bite): Painless, erythema, edema ||Initial (5 mintues–1 hour after bite): Local pain |
| ||2–8 hours: Hemorrhagic, ulcerates, painful ||1–2 hours: Puncture marks |
| ||1 week: Eschar ||Hours: Regional lymph nodes swollen, central blanching at bite site with surrounding erythema |
| ||Months: Healing || |
| || ||CVS: Initial tachycardia followed by bradycardia, dysrhythmias, initial hypotension followed by hypertension |
| || ||GI: Nausea, vomiting, mimic acute abdomen |
| ||Hematologic ||Hematologic: Leukocytosis |
| ||Methemoglobinemia, hemolysis, thrombocytopenia, disseminated intravascular coagulopathy || |
| || ||Resolution over several days |
| || ||Metabolic |
| || ||Hyperglycemia (transient) |
| || ||Musculoskeletal: Hypertonia, abdominal rigidity, “facies latrodectismica” |
| || ||Neurologic |
| || ||CNS: Psychosis, hallucinations, visual disturbance, seizures |
| || ||Peripheral nervous system: Pain at the site |
| || ||Autonomic nervous system: Increased secretions; sweating, salivation, lacrimation, diarrhea, bronchorrhea, mydriasis, miosis, priapism, ejaculation |
| ||Renal: Kidney failure, acute tubular necrosis ||Renal: Glomerulonephritis, oliguria, anuria |
| || ||Respiratory: Bronchoconstriction, acute respiratory distress syndrome |
|Treatment ||Analgesia ||Analgesia |
| ||Wound care ||Muscle relaxants |
| ||Dapsone (?) ||Antivenom |
| ||Hyperbaric oxygen (local) (?) || |
| ||Antivenom (?) not available universally || |
| ||Corticosteroids || |
The venom is more potent on a volume-per-volume basis than the venom of a pit viper and contains six active components with molecular weights of 5000 to 130,000 Da.5 The six components are five latroinsectotoxins (α-, β-, γ-, δ-, ε-LITs) (insect-specific neurotoxins), and α-latrocrustatoxin (α-LCT) (crustacean-specific neurotoxin).105 α-Latrotoxin binds, with nanomolar affinity, to the specific presynaptic receptors neurexin I-α and Ca2+-independent receptor for α-latrotoxin (CIRL), otherwise known as latrophilin.30,114,126 The binding triggers a cascade of events: conformational change allowing pore formation by tethering the toxin to the plasma membrane; Ca2+ ionophore formation; translocation of the N-terminal domain of α-LTX into the presynaptic intracellular space, and intracellular activation of exocytosis of norepinephrine, dopamine, neuropeptides, acetylcholine, glutamate, and γ-aminobutyric acid (GABA), respectively. This massive release of neurotransmitters is what causes the clinical envenomation syndrome known as lactrodectism.5,171,174
Widow spiders are shy and nocturnal. They usually bite when their web is disturbed or upon inadvertent exposure in shoes and clothing. A sharp pain typically described as a pinprick occurs as the victim is bitten. A pair of red spots may evolve at the site, although the bite is commonly unnoticed.53,155 The bite mark itself tends to be limited to a small puncture wound or wheal and flare reaction that often is associated with a halo (Table 118–3). However, the bite from L. mactans may produce latrodectism, a constellation of signs and symptoms resulting from systemic toxicity. Some cases do not progress; others may show severe neuromuscular symptoms within 30 to 60 minutes. The effects from the bite spread contiguously. For example, if a person is bitten on the hand, the pain progresses up the arm to the elbow, shoulder, and then toward the trunk during systemic poisoning. Typically, a brief time to symptom onset denotes severe envenomation. One patient developed latrodectism following the intentional intravenous injection of a crushed whole black widow spider.47
One grading system divides the severity of the envenomation into three categories.60 Grade 1 envenomations range from no symptoms to local pain at the envenomation site with normal vital signs. Grade 2 envenomations involve muscular pain at the site with migration of the pain to the trunk, diaphoresis at the bite site, and normal vital signs. Grade 3 envenomations include the grade 2 symptoms with abnormal vital signs; diaphoresis distant from the bite site; generalized myalgias to back, chest, and abdomen; and nausea, vomiting, and headache.
The myopathic syndrome of latrodectism involves muscle cramps that usually begin 15 minutes to 1 hour after the bite. The muscle cramps initially occur at the site of the bite but later may involve rigidity of other skeletal muscles, particularly muscles of the chest, abdomen, and face. The pain increases over time and occurs in waves that may cause the patient to writhe. Large muscle groups are affected first. Classically, severe abdominal wall spasm occurs and may be confused with a surgical abdomen, especially in children who cannot relate the history with the initial bite.44 Muscle pain often subsides within a few hours but may recur for several days. Transient muscle weakness and spasms may persist for weeks to months.
Additional clinical findings include “facies latrodectismica,” which consists of sweating, contorted, grimaced face associated with blepharitis, conjunctivitis, rhinitis, cheilitis, and trismus of the masseters.155 A fear of death, pavor mortis, is described.155 Nausea, vomiting, sweating, tachycardia, hypertension, muscle cramping, restlessness, compartment syndrome at the site of the bite, and, rarely, priapism are also reported.5,61,119,214 The mechanism of compartment syndrome developing after a black widow spider envenomation is unclear, but two postulated theories include rhabdomyolysis and the venom affecting the blood vessels leading to engorgement and obstruction of the venous outflow. In one case, the compartment syndrome was treated with antivenom, and the patient recovered without the need for a fasciotomy.61 Recovery usually ensues within 24 to 48 hours, but symptoms may last several days with more severe envenomations. Life-threatening complications include severe hypertension, respiratory distress, myocardial infarction, cardiovascular failure, and gangrene.47,60,61,81,165,179,183 In the past 20 years, more than 40,000 presumed black widow spider bites have been reported to the American Association of Poison Control Centers. Death is rarely reported. There have been two fatalities in Madagascar from envenomation by L. geometricus, one from cardiovascular failure and the other from gangrene of the foot.183 The most recent fatality reported from Greece resulted from myocarditis secondary to envenomation by L. tredecimguttatus,182 confirmed by a local veterinarian. The patient developed severe dyspnea, hypoxemia, cyanosis, cardiomyopathy, and global hypokinesis of the left ventricle confirmed by echocardiography, followed by death 36 hours later; antivenom was not available. On autopsy, diffuse interstitial and alveolar edema, with mononuclear infiltrate of the myocardium and degenerative changes, were noted, and toxicologic analysis for xenobiotics, as well as all blood, urine, bronchial, and serologic viral cultures, were negative. The paucity of mortalities is presumed to result from the improvement in medical care, the availability of antivenom, or the limited toxicity of the spider.
Laboratory data generally are not helpful in management or predicting outcome. According to one study, the most common findings include leukocytosis and increased creatine phosphokinase and lactate dehydrogenase concentrations.60 Currently, no specific laboratory assay is capable of confirming latrodectism. However, the clinical situation may warrant the need to check laboratory tests and other studies to evaluate the sequelae of the black widow spider envenomation.
Treatment involves establishing an airway and supporting respiration and circulation, if indicated. Wound evaluation and local wound care, including tetanus prophylaxis, are essential.236 The routine use of antibiotics is not recommended.
Pain management is a substantial component of patient care and depends on the degree of symptomatology. Using the grading system, grade 1 envenomations may require only cold packs and orally administered nonsteroidal antiinflammatory agents. Grade 2 and 3 envenomations probably require intravenous (IV) opioids and benzodiazepines to control pain and muscle spasm.
Traditionally, 10 mL 10% calcium gluconate solution was given IV to decrease cramping. However, a retrospective chart review of 163 patients envenomated by the black widow concluded that calcium gluconate was ineffective for pain relief compared with a combination of IV opioids (morphine sulfate or meperidine) and benzodiazepines (diazepam or lorazepam).60,141 Another study found greater neurotransmitter release when extracellular calcium concentrations were increased, suggesting that administration of calcium is irrational in patients suffering from latrodectism.192 The mechanism of action of calcium remains unknown, and its efficacy is anecdotal; therefore, we do not recommend calcium administration for pain management.
Although often recommended, methocarbamol (a centrally acting muscle relaxant) and dantrolene also are ineffective for treatment of latrodectism.141,197 A benzodiazepine, such as diazepam, is more effective for controlling muscle spasms and achieves sedation, anxiolysis, and amnesia. Management should primarily emphasize supportive care, with opioids and benzodiazepines for controlling pain and muscle spasms, because the use of antivenom risks anaphylaxis and serum sickness.
Latrodectus antivenom (Wyeth) is rapidly effective and curative. In the United States, the antivenom formulation is effective for all species but is available as a crude hyperimmune horse serum that may cause anaphylaxis and serum sickness. The morbidity of latrodectism is high, with pain, cramping, and autonomic disturbances, but mortality is low. Hence controversy exists over when to administer the black widow antivenom. The antivenom can be administered for severe reactions (eg, hypertensive crisis or intractable pain), to high-risk patients (eg, pregnant women suffering from a threatened abortion), or for treatment of priapism.141,183 Use of antivenom probably should not be considered for patients unless systemic effects are designated as grade 3.61 The usual dose is one to two vials diluted in 50 to 100 mL 5% dextrose or 0.9% sodium chloride solution, with the combination infused over 1 hour (Antidotes in Depth: A34). Skin testing may identify a highly allergic individual but does not eliminate the occurrence of hypersensitivity reactions; therefore, we do not recommend skin testing. Recently, an anaphylactoid reaction to the black widow spider antivenin was reported after a negative skin test in both a boy and a man124,168 who subsequently died from the anaphylactoid reaction. Both were being treated for intractable pain after failing intravenous opioid management. Pretreatment with histamine H1- or H2-blockers, or both, and epinephrine may be beneficial in preventing histamine release and anaphylaxis. Patients with allergies to horse serum products and those who have received antivenom or horse serum products are at risk for immunoglobulin IgE-mediated hypersensitivity reactions and, though efficacy is largely unproven, may benefit from the pretreatment with antihistamines and corticosteroids.
A purified F(ab)2 fragment Latrodectus mactans antivenom, Analatro¯, is currently undergoing clinical trials (Antidotes in Depth: A34).
In Australia, a purified equine-derived IgG-F(ab)2 fragment antivenom for the red-back spider L. hasselti (RBS-AV) is available. The RBS-AV (CSL, Melbourne, Australia) is administered intramuscularly and given as first-line therapy to patients presenting with systemic signs or symptoms in Australia. Since its introduction in 1956, no deaths are reported, and the incidence of mild allergic reactions to RBS-AV is only 0.54% in 2144 uses.223
However, an underpowered prospective cohort study of confirmed red-back spider bites failed to show that intramuscular antivenom was better than no treatment when all patients were followed up over one week.129 This study did note that only 17% of patients were pain-free at 24 hours with antibody treatment. Therefore, intramuscular antivenom appears to be less effective than previously thought, and the route of administration requires review. Recently in Italy, an FM1 Fab fragment specific for the α-latroxin has been highly effective in neutralizing the toxin in vivo in mice and shows some promise for possible use in humans.12,45 This single monoclonal antibody shows great promise in the treatment for severe black widow envenomation. Inadvertent use of RBS-AV successfully treated envenomations from the comb-footed spider (Steatoda spp),130 and the Steatoda venom and clinical effects are similar to the Latrodectus venom but milder in clinical presentation.103