Loxoscelism

Loxoscelism is the set of clinical effects caused by a bite or sting from a Loxosceles species of recluse spider, most commonly Loxosceles reclusa in North America and Loxosceles laeta in South America. The venom contains sphingomyelinase D, a dermonecrotic phospholipase that damages skin, subcutaneous tissue, and occasionally deeper structures. The resulting syndrome can range from a mild local reaction to severe systemic illness.

Initial symptoms usually include intense pain at the bite site, erythema, blistering, and swelling within hours. Within 24 to 48 hours, the lesion may develop a necrotic eschar. Systemic manifestations can appear 48 to 72 hours post-bite and may involve fever, malaise, nausea, vomiting, hemolysis, renal failure, and, rarely, disseminated intravascular coagulation. Laboratory findings may show leukocytosis and elevated C-reactive protein, and a prolonged clotting profile.

Diagnosis is based on clinical presentation and confirmed by a history of potential exposure to Loxosceles; laboratory confirmation is limited and typically not used in routine practice. Imaging may be employed to assess tissue depth or organ involvement.

Treatment consists of wound cleansing, debridement of necrotic tissue, and antibiotic coverage for secondary infection. Systemic antivenom (tixanosul or related preparations) can be used in severe cases, but evidence of efficacy varies. Corticosteroids and antithrombotic therapy may be considered for extensive inflammation or coagulopathy. Supportive care for renal failure or hemolysis is essential.

Prevention involves avoiding dense vegetation, using protective clothing, checking mattresses and clothing for spiders, and controlling rodent populations. Loxoscelism remains a public health concern in regions where recluse spiders are endemic, and education on prompt medical evaluation after a suspected bite can reduce morbidity.