Symptom in search of a toxin: muscle spasms following bites by Old World tarantula spiders (Lampropelma nigerrimum, Pterinochilus murinus, Poecilotheria regalis) with review.

BACKGROUND Tarantula spiders are widely kept and bred in captivity by both adults and children. Their bites are generally considered harmless. AIM To explore the effects of envenoming by Old World tarantulas. DESIGN AND METHODS Clinical studies and review of conventional literature and hobbyist web sites. RESULTS Two men bitten on their index fingers by pet Old World tarantula spiders, Lampropelma nigerrimum (Ornithoctoninae) and Pterinochilus murinus (Harpactirinae) in England, developed intense local pain, swelling and episodic, agonising, generalised muscle cramps. In one of them, cramps persisted for 7 days and serum creatine kinase concentration was mildly elevated. A third man bitten on a finger by Poecilotheria regalis (Poecilotheriinae), suffered persistent local cramps in the affected hand. Reports since 1803, including recent ones on hobbyist web-sites, have been largely overlooked. They mentioned muscle spasms after bites by these and other genera of Old World tarantulas, including Eumenophorus, Selenocosmia and Stromatopelma. The severe muscle spasms seen in two of our patients were a challenge to medical treatment and might, under some circumstances, have been life threatening. They demand a toxinological explanation. CONCLUSION Bites by several genera of African, Asian and Australasian tarantulas can cause systemic neurotoxic envenoming. In the absence of available antivenom, severe persistent muscle spasms, reminiscent of latrodectism, pose a serious therapeutic challenge. Discovery of the toxin responsible would be of scientific and potential clinical benefit. Tarantula keepers should be warned of the danger of handling these animals incautiously.