Chapter 53 Scorpion Envenomation
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Scorpion stings occur commonly in tropical and subtropical regions around the world (Figure 53-1). Among causes of animal-related human fatalities, scorpion stings rank second only to snakebites.196 The estimated annual number of scorpion stings worldwide is nearly 1.2 million, resulting in over 3000 deaths.54 More than 1800 scorpion species can be found, distributed on all continents except Antarctica.165 The stings from most scorpion species cause local pain and inflammation, similar to bites or stings from other arthropods; mild systemic symptoms may also occur, but these stings are not serious. Basic first aid and symptomatic therapy, often only with nonprescription medications, are the only interventions necessary to treat most scorpion stings.
FIGURE 53-1 Scorpion sting incidence around the world.
(Modified from Chippaux JP, Goyffon M: Epidemiology of scorpionism: A global appraisal, Acta Tropica 107:71, 2008. With permission from Elsevier.)
Nevertheless, about 30 scorpion species are recognized as medically important and potentially fatal to humans. These dangerous scorpion species are distributed in both the Old World and New World, and all but one are from a single taxonomic family (Buthidae). Even among stings from dangerous scorpion species, many cases do not result in severe morbidity or mortality. Small children are particularly prone to developing more serious envenomation syndromes, probably because of the greater venom dose delivered per unit body weight. Stings are more common during the warmer months of the year, and in many countries they often occur in rural areas where access to health care may be more difficult. Seriously envenomed patients should certainly receive aggressive symptomatic and supportive care; however, the role of antivenom remains controversial, mostly because of the paucity of controlled clinical studies demonstrating its efficacy.
Some differences exist between the full-blown envenomation syndromes that are typically seen. Most of the dangerous scorpions, including Tityus species in the Caribbean region and in South America, Androctonus and Buthus species in North Africa, Leiurus species in the Middle East (particularly L. quinquestriatus), and Hottentotta tamulus (formerly Mesobuthus tamulus) in India, cause an “autonomic storm” with prominent neurologic and cardiopulmonary effects, including hypertension, myocarditis, and pulmonary edema. A generally similar syndrome, but without the severe cardiopulmonary effects, occurs from stings of Centruroides species in the southwestern United States and Mexico and from Parabuthus species in southern Africa, which produce prominent neurologic effects associated with excess cholinergic tone. The non-Buthid scorpion Hemiscorpius lepturus, most commonly found in Iran, is the only dangerous species typically associated with local tissue necrosis and may also cause hemolysis and renal failure.
Identification of new scorpion species and changes in taxonomy continue to occur. Names of scorpion genera, species, and even some families have changed since earlier editions of this book. Several species’ Linnean taxonomic names mentioned in the medical literature are now obsolete, and such changes will be generally noted in the text discussing those scorpions. The information provided in this chapter is believed to be current as of early 2010.
Scorpions are predatory arthropods of the class Arachnida. They have a lobster-like body shape with seven sets of paired appendages (Figure 53-2, online): the chelicerae, the pedipalps (claws), four sets of legs, and the pectines, a pair of comblike structures on the ventral surface. The segmented tail curves upward dorsally, ending in a terminal bulbous segment called the telson, which contains paired venom glands and the stinger (Figure 53-3).
FIGURE 53-2 Anatomy of a scorpion.
(Redrawn from Keegan HL: Scorpions of medical importance. Oxford, Miss, 1980, University Press of Mississippi.)
Scorpions feed primarily on ground-dwelling arthropods and small lizards. Scorpions grasp prey in their pedipalps and then rapidly thrust the tail overhead to sting. The chelicerae tear the food apart. The scorpion consumes only the juices and liquefied tissues of its prey, discarding the solid parts. Scorpions envenom by stinging, not biting, even though cases are occasionally misattributed to “bites” in the medical literature.20,165 Scorpions can sting multiple times; however, it appears that the first sting depletes or nearly depletes the telson of venom. A case series of three pairs of scorpion sting victims from India found that consecutive stings by Hottentotta tamulus caused severe cardiovascular manifestations in the first victim but not in the second.23 This author has anecdotally noted a similar difference in the severity of neurologic manifestations from consecutive Centruroides sculpturatus stings in Arizona.
A characteristic physical property of scorpions is that they fluoresce when illuminated by ultraviolet light, as from a black light or a medical Wood’s lamp (Figure 53-4). This property is used in collecting scorpions for breeding or venom harvesting and in providing pest control. The fluorescent pigment in the scorpion cuticle is probably riboflavin.125
Scorpion venoms are complex mixtures containing mucopolysaccharides, hyaluronidase, phospholipase, acetylcholinesterase, serotonin, histamine, protease inhibitors, histamine releasers, and protein neurotoxins.63,177 Neurotoxins are pharmacologically the most important venom constituents.177 The neurotoxins are single-chain, basic polypeptides of 60 to 70 amino acids, reticulated by four disulfide bridges. Each of the dangerous scorpion species’ venoms contains several neurotoxins, but they all share a similar structure and homologous sequences.91,177 In neuronal membranes, these toxins cause two effects with regard to fast sodium channels involved in action potential transmission: (1) incomplete inactivation of sodium channels during depolarization, resulting in a widening of the action potential, and (2) a slowly developing, inward sodium current after repolarization, leading to membrane hyperexcitability. The net result is repetitive firing of axons, enhancing release of neurotransmitters (acetylcholine, norepinephrine, dopamine, glutamate, aspartate, γ-aminobutyric acid) at synapses and at neuromuscular junctions.60,74,82,171,195 This is clinically demonstrated as excessive neuromuscular activity and autonomic dysfunction. Some scorpion neurotoxins also have effects on calcium-activated potassium channels,86,169 chloride channels,64 and L-type calcium channels.17
A few scorpion species have been demonstrated to produce a first droplet of “prevenom,” which has a different composition (less protein) and in vitro pharmacologic properties than does the subsequent normal venom.109 The clinical impact of prevenom, as compared with venom, is not known.
Regional Considerations: Epidemiology, Risk Factors, and Treatment
Although scorpions are found throughout the world, the bulk of the published medical literature originates from only a few countries. The absence of data about a specific country here does not exclude the possibility of scorpion envenomation occurring there, particularly if that country is near a known scorpion-endemic area; it simply means that such information is not available.
Scorpion stings are a common problem throughout countries on Africa’s Mediterranean coast, where about 100,000 stings are reported annually.139
Scorpion stings are a major endemic hazard, accounting for 30% to 50% of all cases reported to the Moroccan Poison Control Center.2 The annual number of stings in Morocco has been estimated at 25,000 to 40,000.2,89 The majority of stings are caused by Androctonus mauretanicus, known as the “black scorpion” (Figure 53-5), and Buthus occitanus, the “yellow scorpion.”89 Stings are more commonly reported from Morocco’s southwestern provinces of El Kalaa, El-Jadida, Agadir, and Tan-Tan. Stings occur more commonly in rural areas, in the early evening when scorpions are active seeking prey.89 Most cases occur during the warmer summer months.2
FIGURE 53-5 Androctonus mauretanicus, the “black scorpion” of North Africa.
(Courtesy Jan Ove Rein.)
Serotherapy has been advocated by some clinicians as the major therapeutic measure in Morocco since the 1970s.89 F(ab′)2 fragment antivenom is made by hyperimmunizing horses with crude A. mauretanicus venom; this product is cross-reactive with B. occitanus venom. In southwestern Morocco, 49% of patients are treated with antivenom, 35% with other drugs (calcium, steroids, antihistamines), and 16% with both. Patients given higher doses of antivenom (10 mL versus 2 to 5 mL or no antivenom) showed a decrease in serum venom levels and an increase in clinical improvement.89 However, in a 2009 series of 163 pediatric cases treated in Fez (north-central Morocco), none was treated with antivenom; the specific reason for symptomatic treatment was not explained, although the controversy regarding antivenom use was cited.2 Traditional first aid often includes scarification, which consists of local incision to induce bleeding that may result in venom release. Scarification was observed in nearly 40% of children evaluated at a university hospital in Fez, but this practice is considered medically contraindicated. Ninety percent of all fatal cases occur in children younger than 10 years old, with mortality rates ranging from 5.3% to 6.7%.2
Hundreds of deaths per year are caused by scorpion stings in Algeria.130 Most lethal scorpion stings in Algeria are caused by Androctonus australis. Antivenom therapy is advocated as the only indicated treatment for severe scorpion envenomation.173
Much of the published scorpion research from North Africa comes from Tunisia. Almost all stings are caused by five scorpion species: Androctonus australis, Androctonus bicolor, Buthus tunetanus (these first three are Buthid species), Scorpio maurus tenetanus, and Euscorpius sicanus.92 A. australis, locally known as the yellow scorpion (Figure 53-6), is the most common scorpion in Tunisia and accounts for most severe envenomations.80,92 A. aeneas is a dangerous black scorpion found only in the southern part of Tunisia, which constitutes only 1% to 2% of collected scorpion specimens. The non-Buthid scorpions are both relatively harmless and have thin tails and thick claws. The more dangerous Tunisian scorpions have long, thin claws and a thick tail (Figure 53-7).92,124 Stings occur most often outdoors (92%) on the victim’s extremities (95%) during the summer months.124 About 80% of all envenomations occur between June and September, with a peak in August.47,92 Scorpion envenomation occurs more in the less-populated middle and south of the country, so severely affected patients are usually admitted to rural hospitals with limited resources.47
FIGURE 53-6 Androctonus australis, responsible for many severe scorpion envenomations in North Africa.
(Courtesy Jan Ove Rein.)
FIGURE 53-7 Androctonus amoreuxi, demonstrating the thin claws and thick tail characteristic of most dangerous scorpion species.
(Courtesy Jan Ove Rein.)
Between 30,000 and 45,000 scorpion stings are reported annually in Tunisia, correlating to an incidence of 4.5 to 20 stings per thousand inhabitants, depending on the location. About 2.5% of stings (900 to 1100 per year) result in systemic manifestations requiring hospital admission.92 The mortality rate ranges from 0.25% to 0.4%, which is about 10% of victims with systemic envenomations, or 35 to 105 deaths per year.7,92,124–126 Two-thirds of reported stings affect adults and older adolescents, but nearly all fatalities occur in younger children; the mortality rate for children is about 1%.92,124 In a study of 951 patients admitted to the ICU between 1990 and 2002, the mortality rate was 7.5%.47
Scorpion antivenom is available in Tunisia and is commonly given to patients with systemic toxicity, but without good evidence of improved outcome.47 A randomized controlled trial of 825 patients given antivenom or placebo regardless of presenting clinical severity did not show any benefit of antivenom.5 Whether a subset of patients exists who would benefit from antivenom is not known. Horses are used as host animals to produce antivenom, although research has also been conducted with camels.139 Corticosteroids are often administered when treating scorpion stings in Tunisia, but this treatment appears to have no benefit; in fact, it is independently associated with the need for hospitalization.154 Dobutamine infusions are also used to treat severely affected patients with pulmonary edema.80
The majority of scorpion stings in South Africa, Zimbabwe, and neighboring countries do not cause systemic effects, although fatalities occasionally occur. The more dangerous scorpion species are members of the Buthidae family, most notably Parabuthus transvaalicus (centered around Zimbabwe and northernmost South Africa) and P. granulatus (found throughout the region).40,142 Parabuthus scorpions are some of the largest Buthid species in the world, ranging in size from 50 to 149 mm (2 to 6 inches).39,142 At least 20 Parabuthus species are distributed throughout South Africa, Namibia, Botswana, Zimbabwe, and Mozambique, also extending northward along the eastern coast into the Sahara and Arabia.142,149 It is recognized that Parabuthus scorpions have thin pincers and thick tails (Figure 53-8), whereas the relatively harmless species have thick pincers and thin tails (Figure 53-9).40,129,142 Parabuthus scorpions also have stridulatory granules on the dorsal aspects of the two proximal tail segments. When alarmed, these scorpions can scrape their stingers over these granules, making a warning sound.150 Also, several Parabuthus species are able to squirt their venom, an ability that has not been reported in other scorpions.149 Opistophthalmus glabrifrons, a member of the Scorpionidae family widespread in southern Africa, has infrequently caused systemic symptoms in addition to local swelling, but its sting is not considered potentially fatal.38
FIGURE 53-8 Parabuthus transvaalicus, a dangerous scorpion of southern Africa.
(Courtesy Jan Ove Rein.)
FIGURE 53-9 Hagodenes troglodytes, an impressive-looking yet relatively harmless scorpion of southern Africa, has large claws and a thin tail.
(Courtesy R. David Gaban.)
Stings from the Parabuthus species often cause only pain, although systemic effects occur less commonly. Severe envenomations are characterized by neuromuscular hyperactivity and excessive secretions (particularly hypersalivation and diaphoresis), but without the prominent cardiopulmonary effects from a hyperadrenergic state seen from the dangerous scorpions of northern Africa, South America, the Middle East, and India.39,40,142 This toxidrome appears identical to that seen in the American southwest from the stings of Centruroides sculpturatus. Stings typically occur in the early evening during the warmer months of October through April, with a peak incidence in January and February.39,40,142 Four children died in a series of 42 serious scorpion envenomations in South Africa.142 No fatalities were noted among 244 patients (17 with severe systemic symptoms) in Zimbabwe.40 In another study from Zimbabwe, however, five deaths occurred among 455 patients, with fatalities occurring in children less than 10 years old or adults over 55.39
Antivenom is produced in South Africa against Parabuthus venom, which is recommended for patients with severe systemic toxicity.39,40,129,142,150 Injection of local anesthetics for localized pain and intracutaneous sterile water injection for regional pain have also been advocated.40 Traditional herbal remedies are frequently used but have no apparent beneficial effect; indeed, rubbing the sting site, as commonly practiced with such herbal remedies, more than doubles the chance of developing a severe envenomation.39
Although scorpions are present throughout the country, only a limited number of medical publications about scorpion envenomation in Turkey are available, mostly from the southeastern portions of the country. Potentially dangerous species include Androctonus crassicauda (Figure 53-10), Leiurus quinquestriatus, Mesobuthus species, and a few others.10,46 As elsewhere, stings occur more commonly during warm months, from May through September. Studies from the early 2000s had shown pediatric lethality rates as high as 12.5%, whereas a case series of 170 patients from 2007 involved no deaths.8 In a 2009 case series of 52 children hospitalized in southeastern Turkey, nearly one-half (46.2%) were stung by A. crassicauda, one (1.9%) was stung by L. quinquestriatus, and in the remaining cases the offending scorpion species was not known; one death was recorded. Admission from a rural area was a risk factor for severe envenomation, possibly because of increased time from envenomation to hospital presentation.46
FIGURE 53-10 Androctonus crassicauda, a “black scorpion” from the Middle East with a particularly painful sting.
(Courtesy Jan Ove Rein.)
Antivenom is widely used in Turkey for severe scorpion envenomation. A monovalent antivenom is produced by administering A. crassicauda venom to horses, then enzymatically digesting and purifying the serum. Hydrocortisone and antihistamines are commonly co-administered per the national poisoning treatment procedure.8
Leiurus quinquestriatus, locally often called the “yellow scorpion,” is the most dangerous species found in Israel (Figures 53-11 and 53-12; Figure 53-12, online).44,77,107 Other native species include Hottentotta judaicus (formerly Buthotus judaicus, the “black scorpion”), Androctonus crassicauda, A. bicolor, Nebo hierochonticus, Scorpio maurus, and Orthochirus innesi.43,44,77 More than 90% of all scorpions encountered in neighboring Jordan are either yellow or black scorpions (L. quinquestriatus or B. judaicus), with the yellow being most common.77,107 Most scorpion stings occur during the warmer months of April through October.36 In the Negev desert region, Bedouin children are stung about six times more frequently than are Jewish children, probably because of more time spent outdoors and lack of protective footwear. Males are affected 2.3 times more often than females; this is most likely related to differences in gender roles, such as boys herding sheep or goats.107 The reported mortality rate in children was 18% among Palestinians living on the West Bank in 1965, 3.7% among children in the Jerusalem area in 1991,77 and 1.2% among children in the Negev area in 1985.107 Most scorpion stings have a mild clinical course; 13% of reported sting victims remain asymptomatic, 72% have mild illness, and 15% become moderately to seriously ill.36 In a case series of 18 Israeli pediatric patients stung by L. quinquestriatus between 1988 and 1996, 17 had mild to moderate toxicity, and only one patient was severely affected, suggesting that routine ICU admission was not necessary.35
FIGURE 53-12 The tail segment of Leiurus quinquestriatus just proximal to the telson is characteristically black on this otherwise yellow scorpion.
(Courtesy Jan Ove Rein.)
Stings from L. quinquestriatus initially produce intense local pain, erythema, and edema, which can be followed by an outpouring of catecholamines and acetylcholine from nerve endings. In severe cases, clinical signs of sympathetic overload predominate, with severe hypertension, tachyarrhythmias, and pulmonary edema.3,97,98,162 Parasympathomimetic action of the venom may also cause bradyarrhythmias or atrioventricular block, usually preceding the sympathetic overload. Cardiomyopathy and myocardial damage with electrocardiographic (ECG) and serum marker (creatine kinase [CK], CK-MB, troponin) changes have been reported.77,97,176,183 Other common findings from severe stings include agitation, convulsions, encephalopathy, hypersalivation, diaphoresis, priapism, and pancreatitis.178,179 Treatment recommendations differ, but all emphasize aggressive symptomatic and supportive care for severely envenomed patients. However, some clinicians propose the routine use of antivenom,77 whereas others argue that serotherapy does not significantly alter outcome based on experimental pharmacokinetic data.97,98,101 Antivenom had no demonstrable effect in one clinical series of Israeli patients.180
At least 14 species of scorpions are found in Saudi Arabia; the two species most commonly responsible for significant envenomation are Androctonus crassicauda, a black or dark brown scorpion, and Leiurus quinquestriatus, a yellow scorpion.* The “yellow scorpion” is usually reported to cause more stings than the “black scorpion,” except in one 5-year surveillance survey from the north-central Qassim province, where the distribution was roughly equal.119 Saudi Arabia averages 14,500 annual reported scorpion stings.121 These account for 3% to 4% of all pediatric hospital admissions in northwestern Saudi Arabia between May and August, with few admitted in other seasons.78,79 One author reported the incidence of “scorpion sting syndrome” as 1.3 cases per 1000 emergency department patients,148 whereas a 15-year retrospective analysis from another hospital in the same city (Riyadh), with over 100,000 visits annually, reported only 251 cases.9 Between 70% and 80% of cases occur between May and October, and 73% of stings occur at night between 6 PM and 6 AM.120,148 Many victims are barefoot children playing outdoors or persons tending flocks of goats or sheep. Males are affected at least twice as often as females.15,78,120,148 Mortality rates have decreased from 2% to 8%, as previously reported, to less than 0.05% in more recent studies.15,78,106 Antivenom is recommended and routinely administered for scorpion envenomation in Saudi Arabia; this may be related to decreasing mortality rates.15,78,79,113
L. quinquestriatus envenomations were reviewed earlier, in the section about Israel. A. crassicauda stings are similar to those of the yellow scorpion, causing hypertension and CNS manifestations, but differ in other ways.113 The pain from the A. crassicauda sting has been reported as particularly severe. Generalized erythema was noted in 20% to 25% of children less than 5 years of age; this is not usually seen with other scorpion stings. The cause of this erythema is not clear, especially because elevated catecholamine levels after scorpion envenomation appear to be protective against allergic reaction. Cholinergic effects are seen less often with A. crassicauda stings.
Of special relevance to wilderness medicine, scorpion envenomation became an issue to U.S. soldiers deployed during the Gulf War.93 L. quinquestriatus and A. crassicauda were implicated in 57 scorpion stings over 4 months among 7000 troops of an armored cavalry division stationed in eastern Saudi Arabia. All patients with adequate data for further study recovered fully, usually with only supportive care in the field, probably reflecting that all were healthy adults. No antivenom was available. Typical signs and symptoms included local pain, tachycardia, hypertension, sweating, apprehension, headache, epigastric pain, nausea, restlessness, and local muscle cramping and paresthesias in lower extremity stings. Presumably, victims with only local pain failed to present to battalion aid stations, resulting in an apparently high incidence of systemic effects. Only two persons had serious presentations or subsequent complications. One had a clinical picture consistent with anaphylaxis and required intubation for respiratory support. The other developed a cutaneous ulcer that healed in 3 weeks with oral antibiotic therapy.93
More than 44 scorpion species are found in Iran, including at least seven whose stings are considered medically important.159 Scorpion stings are most prevalent in Khuzestan, a hot and humid province in the southwest adjacent to the Persian Gulf; about 60% of all reported stings in Iran occur in this province. In 1990, the distribution of stings by species to persons seeking medical attention in Khuzestan was 41% Androctonus crassicauda, 45% Mesobuthus eupeus, and 13% Hemiscorpius lepturus, the only non-Buthid scorpion generally recognized as dangerous to humans.160 A more recent collection of 418 scorpions brought with patients evaluated at various medical centers in Khuzestan after being stung found 120 (28.7%) A. crassicauda specimens, 104 (24.9%) H. lepturus, 91 (21.7%) M. eupeus, 86 (20.6%) Compsobuthus matthiesseni, and minor contributions by three other species.66
Nonspecialists can rarely identify species by sight, but most can easily identify the scorpion’s primary coloration. The most dangerous “black scorpions” of Iran are A. crassicauda and Hottentotta schach, whereas the dangerous “yellow scorpions” are M. eupeus, Hottentotta saulcyi, Odontobuthus doriae, and Hemiscorpius lepturus.175 Stings occur more commonly during the warmer months of the year (90% occurring between April and October), and most occur during the night or early morning hours, reflecting times of peak scorpion activity.159,175
In Iran, 90% to 95% of all fatal stings are caused by H. lepturus (sometimes previously called H. lepturus), making it the most dangerous scorpion in Iran.121,159,175 This member of the Hemiscorpiidae family causes a spectrum of disease distinctly different from that caused by the dangerous scorpions of the Buthidae family. Severe envenomation by H. lepturus is characterized by hemolysis, renal failure, and local tissue necrosis. Stings by H. lepturus are stated to not induce an acute painful response (unlike stings from other species), resulting in many patients delaying medical attention until the local tissue destruction is advanced.121,161 This last point sounds similar to many alleged brown recluse spider bites in the United States and alleged white-tailed spider bites in Australia, where dermonecrotic lesions of unknown etiology (often from bacterial infection of the skin and soft tissue) are erroneously ascribed to arthropods by laypersons and health care personnel alike. However, this author is not aware of any published evidence refuting the observation that H. lepturus stings are not initially painful.
Envenomation by A. crassicauda in Iran produces pain, neuromuscular agitation, and signs of parasympathetic hyperstimulation (e.g., lacrimation, salivation, increased bronchial secretions) similar to other Buthid scorpions.160 However, this report does not comment on signs and symptoms specifically related to the adrenergic/hypertensive crisis seen with many other dangerous species.
Nearly all of the medical literature regarding Indian scorpions relates to Hottentotta tamulus, sometimes called the “red scorpion,” the single most dangerous native species (Figure 53-13).143 Until recent taxonomic changes, this scorpion had been called Mesobuthus tamulus (and before that Buthus tamulus and Buthotus tamulus); therefore the bulk of previously published observations and research now refers to obsolete genus names. H. tamulus is a particular problem in southern coastal India. Stings occur predominantly in April, May, and June at night among young farmers wearing minimal clothing.24,30 In many cases, stings occur at the tip of an extremity, with the only symptom being pain, which can be controlled with local anesthetic injections.30,62 Systemic toxicity occurs from release of catecholamines, with major morbidity and mortality resulting from cardiopulmonary toxicity.* Fatality rates between 30% and 40% were reported in the 1960s and 1970s, but these have fallen to 2% to 3% with treatment using vasodilators and calcium channel blockers.25,27,33 An 11.8% mortality rate, however, was found among 152 children admitted to hospitals in Calcutta from 1985 to 1989, but treatment details were not reported.41
FIGURE 53-13 Hottentotta tamulus, the dangerous “red scorpion” of India. Until recent taxonomic changes, it was most widely known as Mesobuthus tamulus.
(Courtesy Jan Ove Rein.)
H. tamulus antivenom had not been available for clinical use until quite recently. Starting in 2002, scorpion antivenom has been distributed to primary health centers (PHCs) in India free of charge; however, its use is not standard, especially because envenomation cases are commonly admitted, which does not occur at PHCs.33 Bawaskar and Bawaskar, from Maharashtra, a state in western coastal India, are the world’s foremost proponents of using antihypertensive agents (primarily oral prazosin, an α-adrenergic blocker) to treat the catecholaminergic effects of severe scorpion envernomation.22–33 They cite the limited medical resources available for the majority of victims, many of whom live in rural settings and are poor, in addition to the potential risks of transporting unstable patients. Other vasodilators that have been advocated include nifedipine, IV sodium nitroprusside, and captopril.127 Administration of H. tamulus antivenom did not appear to improve clinical outcome compared with treatment with oral prazosin in a nonrandomized observational study of 53 patients.33 A potential confounder is the fact that patients treated with antivenom were all referred from PHCs to the study hospital, whereas those treated with prazosin presented directly to the hospital. Some researchers have instituted protocols relying on oral prazosin for early-presenting patients, but using dobutamine and nitroprusside for those with pulmonary edema.42,147
In 2010, the Bawaskars published a randomized, open-label study comparing patients treated with oral prazosin alone with those treated with prazosin plus H. tamulus antivenom. Enrolled in each group were 35 patients with grade II envenomation (systemic signs and symptoms present, but without pulmonary edema or shock). The recovery time in the antivenom group was reduced (8 hours versus 17.7 hours), and there was no significant difference in clinical deterioration rate. They noted that the total cost of treatment with antivenom “approaches a month’s salary for a laborer in the region” (Rs350, $7.77), whereas prazosin costs less than one-tenth this amount.34
Australia is home to more than 40 named scorpion species and is believed to harbor as many as 200 species in total. However, scorpion stings are uncommon there and do not cause major envenoming.110,111 In a 27-month study in the early 2000s, only 192 scorpion stings were reported to Australian poison centers. The majority of stings occurred during the warmer months of the year, and they tended to occur at night and indoors. These stings generally caused severe pain (defined as greater than that from a bee sting) lasting a few hours, although 11% of the victims had systemic complaints of nausea, headache, and malaise. The majority of victims were managed without seeking additional medical attention. In 95 cases, the offending scorpion was collected and identified by an arachnologist. Most stings (72) were by small Buthid scorpions from the Lychas genus; however, all five stings from Tasmania were from Cercophonius squama, the only known species on that island.110 Urodachus scorpions are larger but less commonly encountered.111 No neurotoxins were found in U. novaehollandiae, the only Australian species that has had its venom studied.185 No antivenom exists for native Australian scorpions. Supportive treatment, often with only oral analgesics, appears to be adequate. Similar to the treatment of some other envenomations, the application of hot water (e.g., immersing a stung finger) has been advocated, but this has not been studied systematically.111,185
A case series of 129 patients admitted after scorpion stings in Colombia has been reported.156 The most commonly implicated species were Tityus pachyurus, T. fuehrmanni, and Centruroides gracilis. Most envenomations were mild (76%), and only children less than 6 years old were in the severe group (four patients). A commercially available Mexican antivenom against the venom of four Centruroides species was used in 19 cases with systemic findings, which decreased the duration of some clinical signs and had no reported adverse effects. Thirty-two cases occurred on an Air Force base, where servicemen put on clothes or boots in which scorpions had sought shelter overnight.156
Envenomation by scorpions of medical importance in Venezuela is endemic to the densely populated northernmost sections of the country, with the northeastern states of Monagas and Sucre being particularly affected.71,72 Tityus discrepans is the most common species causing stings, although 184 scorpion species were described by 2006, with 52 from the Tityus genus.71,72,75 Intravenous antivenom is commonly given for severe envenomations, and there appears to be a trend toward a better outcome with earlier administration.136,137
Tityus trinitatis accounts for almost 90% of the scorpion population on Trinidad. Fatalities are rare but occur more often in children. Stings are more frequent in summer months.19 Systemic effects of serious T. trinitatis envenomations include tachypnea, restlessness, vomiting, hypersalivation, cerebral edema, pulmonary edema, hypovolemic shock, seizures, and myocarditis.63 The most striking clinical observation is the high incidence (up to 80%) of acute pancreatitis; scorpion stings are the most common cause of acute pancreatitis in Trinidad.19,88
About 10,000 cases of scorpion envenomation are reported annually in Brazil, with 80% occurring in southeastern regions.141,151 One-half of the reported stings occur in the state of Minas Gerais, although scorpions are also problematic in São Paulo and Bahia.50,141 Most stings occur between December and February.85 Tityus serrulatus, popularly known as the “yellow scorpion,” is the most prevalent species in Brazil and accounts for most fatal stings, as a result of its widespread distribution in populous urban centers and high venom potency.11,59,141 T. serrulatus is considered by some to be “the most dangerous scorpion in South America.”158 T. bahiensis is the second-most common species, although severe envenomations are much more likely from T. serrulatus.49,151 Equine-derived antivenom for either T. serrulatus or both T. serrulatus and T. bahiensis is able to neutralize venom from all Brazilian scorpions studied.151 Children are much more likely than adults to have severe envenomations.84 In Minas Gerais, children less than 14 years of age accounted for 27% of scorpion envenomation admissions but for all cases of significant morbidity and mortality; 16% were treated in an intensive care unit (ICU) setting. Mortality with current treatment now ranges from 0.7% to 1.1% in children and is 0.28% overall.84,104,141,166 A “tripartite approach” has been advocated, which employs symptomatic measures, support of vital functions, and immunotherapy.167 Antivenom from a few manufacturers is available in Brazil and routinely used in severe envenomations.50,84,166
Scorpions of medical importance in Argentina belong to the Tityus genus. Tityus trivittatus is generally recognized as the only species capable of causing severe envenomations or death, although T. confluens has also been implicated in a few cases.69,70 Over a 7-year period, 511 scorpion envenomations were reported to public health authorities. Most cases occurred indoors and during the warmer months, November through April. Scorpions are hyperendemic in the provinces of Córdoba and Santiago del Estero, where 85.6% of the envenomations occurred. Local pain and inflammation were most common, whereas systemic envenomation occurred in 7% of children 10 years and younger and in 2% of older victims. Antivenom therapy was provided in 84% of cases with available treatment records; only three fatalities occurred, and none of these victims had received antivenom. Until 1996, the Argentinians used a cross-reactive Brazilian antivenom against T. serrulatus. Since 1997, Argentina has produced a F(ab′)2 fragment equine antivenom.69
An estimated 250,000 scorpion stings occur annually in Mexico.157 The number of resultant deaths per year has been variously reported from “about 100,” to “700 to 800,” to “over 1000”; regardless of the actual number, this certainly represents a serious public health concern.55,157,164 Of at least 221 native species and subspecies, only eight members of the Centruroides genus (Figure 53-14) are recognized as significantly dangerous.56,65,73,155 The Centruroides scorpions are relatively small and described as yellow, tan, or brown. Clavigero recognized as early as 1780 that “the venom of the small and yellow scorpions is more active than that of the big grey ones.”138 Mexican states on the Pacific Coast, particularly Colima, Durango, Guerrero, Morelos, and Nayarit, report the highest number of scorpion stings.55,65,138,164 In 1999, Morelos had the highest incidence, with a total of 30,663 stings and nine deaths. Nearly 2% of the population in Morelos is stung annually, and in some hyperendemic villages this figure is over 10%.164 In urban areas of Colima, 3 stings per 1000 people occur annually; this figure rises to 18 to 30 stings per 1000 in more rural areas.55 The peak incidence of scorpion stings occurs during the warmer months, but has been variably reported as from “March to July, coinciding with scorpion reproduction,” or between “June and October,” correlating with rainfall statistics.56,155
FIGURE 53-14 Centruroides limpidus limpidus, one of several closely related, dangerous Mexican scorpions.
(Courtesy R. David Gaban.)
The following signs and symptoms have been reported with Mexican scorpion stings, although not all effects are necessarily seen in the same victim, and no apparent sequence of effects has been observed: hyperexcitability, restlessness, hyperthermia, tachypnea, dyspnea, tachycardia or bradycardia, diaphoresis, nausea, vomiting, gastric distention, diarrhea, lacrimation, nystagmus, mydriasis, photophobia, excessive salivation, nasal secretion, dysphagia with foreign body sensation, dysphonia, cough, bronchorrhea, pulmonary edema, arterial hypertension or hypotension, heart failure, shock, convulsions, ataxia, fasciculations, and coma.65 Unpublished verbal reports by physicians who have treated scorpion-envenomed patients in Mexico suggest that the clinical presentation is virtually identical to that caused by C. sculpturatus in the United States. The higher mortality from Mexican scorpion stings compared with American stings may be the result of differences in venom potency between species, differences in human and scorpion population densities, differences in the ease of access to medical care (e.g., monitoring equipment, ICUs, and antivenom), and perhaps also from cultural differences in housing and protective clothing that promote human–scorpion interactions in Mexico.
Antivenom is recommended and commonly used for severe scorpion envenomation in Mexico.56,65,73,131,155 A F(ab′)2 fragment antivenom is produced domestically and is commercially available. It is prepared from the venoms of four native Centruroides scorpions and is also under investigation for use against C. sculpturatus in the United States.49
More than 40 species of scorpions are found in the United States.51 However, only one American species, the Arizona bark scorpion (Figure 53-15), causes a significant number of systemic reactions and is known to be potentially fatal.37,51,60,172,186 For many years, controversy has existed regarding proper taxonomy and the medical importance of this scorpion.194 This species has at times been called Centruroides sculpturatus, C. exilicauda, or C. gertschi. Current taxonomy holds that the Arizona bark scorpion is properly called C. sculpturatus, which is medically important and found in the southwestern United States (particularly Arizona), of which C. gertschi is a striped subspecies. C. exilicauda is a different species found in Baja California, Mexico; its sting is considered medically insignificant, and no fatalities have been documented.170,194 Nevertheless, a significant proportion of the medical literature regarding scorpions refers to the medically important American species as C. exilicauda. Approximately 30 Centruroides species are found distributed throughout the New World, several of which are medically important and are mostly found in Mexico.172
FIGURE 53-15 Centruroides sculpturatus, the Arizona bark scorpion; the only species in the United States known to cause severe neurotoxic envenomations.
(Courtesy Jan Ove Rein.)
Centruroides sculpturatus is called the “bark scorpion” because of its preference for residing in or near trees. These scorpions also often hide under wood (old stumps, lumber piles, firewood, loose bark, or fallen trees), in ground debris, or in crevices during the daytime. This is troublesome to humans, because the scorpions may hide in shoes, blankets, or clothing left on the floor during daylight hours, as well as under common ground covers and tents. C. sculpturatus is found statewide in Arizona and also in some areas of Texas, New Mexico, northern Mexico, small areas of California, and near Lake Mead, Nevada.60 The bark scorpion is relatively small, measuring up to 5 cm in length. Specimens are variously described as being a uniformly yellow, brown, or tan; stripes are uncommon. The pincers (pedipalps) and tail are thin, giving the scorpion a streamlined appearance (Figure 53-16), in contrast to several of the larger but less dangerous scorpions with thick claws and tails. The presence of a subaculear tooth, a tubercle at the base of the stinger, is distinctive to C. sculpturatus and is helpful in differentiating this neurotoxic scorpion from other species.60,186
FIGURE 53-16 Distinctive features of Centruroides sculpturatus include the nearly uniform yellow/tan color, thin pedipalps and tail, and subaculear tooth (indicated by arrow) on the telson.