The black widow spider and other species of the Latrodectus genus are mainly responsible for arachnidism in the US. Although not recognized in most medical texts, the bites of members of the genus Loxosceles also can cause severe reactions. These spiders may be a more frequent source of arachnidism than is realized at present, particularly in the Midwest and Southwest. Spider venoms are either cytotoxic or neurotoxic in action, although Latrodectus and Loxosceles venoms may have mixed effects. The kind and severity of reaction depend primarily on the type of venom and secondarily on such factors as the victim's age and health. Antivenin (Latrodectus mactans) is the preferred therapy in latrodectism. Injectable antihistamines are useful for symptomatic relief in loxoscelism. General measures include avoidance of excessive local treatment, mild antibacterial therapy, and use of muscle relaxants.
Horen WP. Arachnidism in the United States. JAMA. 1963;185(11):839–843. doi:10.1001/jama.1963.03060110043015
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