The South African fattail scorpion (Parabuthus transvaalicus)(Figure) is one of the most poisonous scorpions in southern Africa.1 A member of the Buthidae scorpion family, it can grow as long as 15 cm and is dark brown-black with lighter red-brown pincers. Similar to other fattail scorpions, it has slender pincers (pedipalps) and a thick square tail (the telson). Parabuthus transvaalicus inhabits hot dry deserts, scrublands, and semiarid regions.1,2 It also is popular in exotic pet collections, the most common source of stings in the United States.
Stings and Envenomation
Scorpions with thicker tails generally have more potent venom than those with slender tails and thick pincers. Venom is injected by a stinger at the tip of the telson1; P transvaalicus also can spray venom as far as 3 m.1,2 Venom is not known to cause toxicity through skin contact but could represent a hazard if sprayed in the eye.
Scorpion toxins are a group of complex neurotoxins that act on sodium channels, either retarding inactivation (α toxin) or enhancing activation (β toxin), causing massive depolarization of excitable cells.1,3 The toxin causes neurons to fire repetitively.4 Neurotransmitters—noradrenaline, adrenaline, and acetylcholine—cause the observed sympathetic, parasympathetic, and skeletal muscle effects.1
Worldwide, more than 1.2 million individuals are stung by a scorpion annually, causing more than 3250 deaths a year.5 Adults are stung more often, but children experience more severe envenomation, are more likely to develop severe illness requiring intensive supportive care, and have a higher mortality.4
As many as one-third of patients stung by a Parabuthus scorpion develop neuromuscular toxicity, which can be life-threatening.6 In a study of 277 envenomations by P transvaalicus, 10% of patients developed severe symptoms and 5 died. Children younger than 10 years and adults older than 50 years are at greatest risk for adverse outcomes.6 Children have a case fatality rate as high as 10 times the adult fatality rate.7
The clinical presentation of scorpion envenomation varies with the species involved, the amount of venom injected, and the victim’s weight and baseline health.1 Scorpion envenomation is divided into 4 grades based on the severity of a sting:
• Grade I: pain and paresthesia at the envenomation site; usually, no local inflammation
• Grade II: local symptoms as well as more remote pain and paresthesia; pain can radiate up the affected limb
• Grade III: cranial nerve or somatic skeletal neuromuscular dysfunction; either presentation can have associated autonomic dysfunction
• Grade IV: both cranial nerve and somatic skeletal neuromuscular dysfunction, with associated auto-nomic dysfunction