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Anascorp and Scorpion Stings in Arizona

Photo: Musides

The other day while working in the Emergency Room I was able to see the anti-venom Anascorp administered for the first time.  The patient, a 3 year old girl, had a history of being very fussy, crying and red “puncture like wound” on her toe.  When she arrived into the ER she was very short of breath, lethargic and tearful.  The mother was not sure what she had been stung by, as she was playing outside in the desert when this started.  She arrived via ambulance and the mother said this began about 15 minutes before she called the ambulance. 

The Arizona Bark Scoprion (Centruroides exilicauda) is found in the Sonoran desert including Arizona and the northern part of Mexico.  This is one of the most venomous scorpions in the Americas and is known for biting humans and pets.  The venom is neurotoxic and symptoms typically begin immediately after the sting has occurred.  Paresthesia (numbness), local pain at the sting site and difficulty moving the extremity are common initial reactions.  More severe envenomations can lead to respiratory distress, difficulty swallowing, nausea/vomiting, tachycardia (fast heart beat), muscles jerks and twitches and neuromuscular dysfunctions. 

Envenomations are graded based on symptoms:

Grade 1- local pain at the site of the sting with paresthesia in the area of the sting

Grade 2- pain and paresthesia distant from the sting site, “trouble swallowing”, victims may feel a need to rub their face, nose and eyes

Grade 3- cranial nerve or somatic neuromuscular dysfunctions such as blurred vision, wandering eye movements (roving eyes), increased salivation, slurred speech, tongue fasciculations and airway obstruction, jerking of the upper extremities, arching of the back and involuntary shaking and jerking (not a true tonic/clonic seizure) 

Grade 4- A combination of both cranial nerve and somatic neuromuscular involvement that may also include hypertension, hyperthermia and tachycardia

The little girl was experiencing symptoms including wandering eye movements and nystagmus, face rubbing, hypersalivation, tongue fasciculations and some muscular tremors of her arms.  She was also have difficulty breathing evidenced with retractions of her chest muscles during inspiration.  She was crying and tachycardic.  After initial stabilization and examination, she was determined to be showing signs and symptoms of a Centruroides’s envenomation. 

The Emergency room I work in is fortunate to be involved in a pilot program testing a form of bark scorpion anti-venom called Anascorp.  This antivenom has been used and produced for many years in Mexico and is not readily available in the United States.  The aim of the study is to evaluate the efficacy of the antivenom for widespread use in America.  Anascorp is derived from horse serum but uses Fab fragments rather than Fc fragments.  The concern with using horse serum based antivenom is that the person may have an allergic reaction to the antivenom.  By using the Fab fragments much of the risk for allergic reaction has been mitigated as the Fc fragments are mostly responsible for the allergic reactions with horse serum administration.  Anascorp is supplied as a five vial package.  The goal is to give an initial loading dose then add additional vials of antivenom as needed, based on clinical signs and symptoms. 

Scorpion Sting First Aid

Initial first aid should center on making sure the sting victim is breathing adequately.  Persons who typically have a bad reaction to the venom include smaller individuals, especially children.  Older individuals and those with chronic medical conditions, especially heart disease, may also have a more severe reaction.  Washing the sting area with soap and water then applying a cold compress typically helps with initial pain control.  The use of acetaminophen (Tylenol) may also assist with pain control.  Symptoms of paresthesia, difficulty swallowing and neurologic symptoms such as muscle twitching or eye roving should prompt a rapid visit to the emergency room.

Rapid Improvement and Case Closed

After the little girl received her appropriate doses of anti-venom she improved quite rapidly.  Within 30 minutes she was much more alert, breathing better and her muscle twitching and eye roving had stopped.  About 3 hours later, she left the emergency room with her mother.  Needless to say, I was quite impressed with the speed and efficacy of Anascorp.

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