Arachnid Envenomations

Arachnid Envenomations Wilderness Medical Consortium Matt Sholl

General • Class Arachnida and phylum Arthropoda comprise ~ 70,000 species • Divided into 9 orders • Acari (mites and ticks) • Araneae (true spiders) • Scorpiones (true scorpions) • Opiliones (harvesters/daddy-long-legs) • Pseudoscorpionidae (false scorpions) • Pedipalpi (whip scorpions) • Palpigradi (microwhipscorpions) • Ricinulei (hooded tick spiders) • Solpudida (sun spiders)

Of Those…. • … The classes important to us are those that cause injury or illness to humans by: • Acting as a vector of disease • Acari • Through direct envenomation • Aranae and Scorpiones

Outline • Focusing on arthropod envenomations • Discussing spiders and scorpions • Will discuss ticks and tick borne diseases another time • Focusing on spiders and scorpions indigenous to North America Hiking the Royces -- WMC Spring trip 2005

Scorpions - General • 1200 species grouped into 7 families • Buthidae family contains the majority of clinically important scorpions • Vary in size from a few millimeters to 15 cm • Size does not correlate with its danger • In No America - smaller scorpions (Centrurooides) accounts for most envenomations • Typically night stalkers and remain hidden during the day • Under rocks, plant matter, in burrows or in clothing • Incredibly heat tolerant but can live in cold temperatures and at altitude (up to 14,000)

Scorpions - Recognition • Resemble miniature lobsters • Small heads (prosoma) • Variable sized claws (pedipalps) • 8 paired legs • Segmented tail (part of abdomen) • Ending in venomous telson • Telson composed of a vesicle that stores the venom and a stinger (aculacea) • Stinger is a single, slender spike used to pierce the shell or skin of prey/victim • Muscular action squeezes venom into the prey through twin openings in its base

Recognizing Centurodies • One of 41 species of bark scorpions • Responsible for the bulk of severe envenomations in No America • Slim, yellow-brown scorpion 4 - 7.5 cm in length at maturity • Slender pincers • Triangular shaped sternum • Tubercle at the base of its stinger • Limited to Arizona, the base of the Grand Canyon, and the area surrounding Las Vegas and western New Mexico

Scorpions - Incidence of Envenomations • 2001 American association of Poison Control Centers • 14,599 calls related to scorpions stings • 851 (6%) required no medical attention • No deaths in 2001 • Although there are an estimated 5000 deaths world wide per year

Scorpion Venom • Make-up is variable from species to species but in general: • Mixture of single-chain polypeptides containing neurotoxins that block ion channels • esp. sodium and potassium channels • Secondary effects from release of acetylcholine and catecholimines • Hyaluronidase allows spread of the venom • Serotonin, lipids, amino acids also reported

Dry Stings • Scorpions can vary the amount of venom released per sting depending on the victim’s size • Several rapid stings can deplete the venom stores • Dry stings with no apparent envenomation are common

Envenomation - Local Effects • Local symptoms are the most notable • Include localized, intense pain at the puncture site • Pain increases significantly with tapping lightly over the site • No focal erythema or edema • Symptoms begin shortly after sting and may last for hours • May last for weeks

Envenomation - Systemic Effects • The cause of morbidity and mortality • Usually in children and elderly • Initially manifested by increased cholinergic tone • Salivation, lacrimation, urinary incontinence, defication, gastroenteritis and emisis • SLUDGE phenomenon

Systemic Effects - cont. • Subsequent norepinephrine release causes tachycardia, hypertension, hyperpyrexia, myocardial depression, pulmonary edema • Leads to most of the mortality • Cardiac effects - MI w/out lesions • CNS effects - confusion, agitation, ataxia, myoclonic and dystonic movements • Other effects - hyperglycemia, pancreatitis • Anaphylaxis rare but has been reported • Onset of systemic symptoms is usually with in 6 hours and usually peaks at 12 hours

How Common are Systemic Symptoms? • 5000 scorpion stings occur each year in Arizona • Of these, around 250 result in systemic symptoms • 5%

Management of Scorpion Stings - Field Treatment • Attempts should be made at identification • Can be difficult… • Treatment begins with local therapy • Rest, ice, elevation, splinting and light, compressive dressing • Pain management (NSAIDs, Tylenol, narcs) • Keep patient calm and resting • Six hour observation period to determine if systemic symptoms may manifest • ? Evacuation vs. observation

Management of Scorpion Envenomation - Antivenom • Use of antivenom controversial • Even for pt’s with systemic signs • Antivenom appears to be species specific • Must be administered within 1 hour • These factors limit use to areas with known single species and easy access to health care • In the US, University of AZ holds antivenom to Centurodies venom • Antivenom derived from goat serum • 3% incidence of immediate sensitivity • 60% incidence of serum sickness

More on Antivenom • Antivenom appears to assist with local pain and paresthesias • Does not appear to help with systemic symptoms, ie. pulmonary edema, MI, CVA • These symptoms due to pronounced catecholamine release not toxic effects of venom • BUT this is why antivenom must be administered with in 1 hour • Not FDA approved and therefore can not be transported over state lines • ONLY IN AZ!!!

Systemic Effects - Treatment • Supportive care likely more benefit than antivenom • In the hospital, look for concerning signs and blunt their effects before irreversible damage is done: • EKG, cardiac enzymes, FSBG,  MS, Sz • Hypertension - Nitroprusside agent of choice • Pulmonary Edema - O2, Dig, Diuretics, -Blockers (if EF > 50%) and mechanical ventilation • Steroids have not been proven helpful • Morphine can provoke arrhythmias • Nifedipine can initiate heart block and hypotension

Prevention of Scorpion Envenomation • Wear protective footwear especially at night • Exercise caution when lifting rocks, logs and when collecting firewood • Do not handle scorpions with bare hands • When camping try not to sleep directly on the ground • Shake out footwear, clothing and bedding to expel unwanted creepy crawlies • Learn how to distinguish a highly venomous scorpion from a harmless one and the area they occur in

Spiders • Diverse group of 34,000 species divided into 105 families • All of the true spiders have unsegmented bodies and the ability to make silk • Not all true spiders use silk to make webs • Spiders use venom to subdue their prey and begin digestion (no teeth)

Can the Venom Injure Humans • In order for a spider’s venom to injure a human it must: • Have fangs strong enough to pierce a human’s skin • Have venom that causes injury to humans • Have enough venom to cause injury • Several spider families meet these characteristics…

Incidence of Spider Encounters • Worldwide distribution and thrive in populated areas • Results in many bites/year • American Association of Poison Control Centers data • 2001 - 20,204 calls for spider bites • 50% not linked to specific species • 1890 (19.7%) sought medical attention • No deaths • World wide incidence is not known

A General Rule for Arachnid Exposures • The importance of identifying the culprit spider that caused a bite can not be overstated • The diagnosis of spider envenomation DEPENDS on identifying the culprit spider • Diagnosis of “spider bite” with out positive identification of the spider is dubious

Two General Categories • Spiders can be divided into two general categories • Spiders that cause local tissue damage • Spiders that cause systemic symptoms • Some spiders may cause both local and systemic symptoms • Some cause injury through other mechanisms

Necrotic Arachnidism • Defined as local tissue necrosis caused by a spider bite • Venom in necrotic arachnids contains • Hyaluronidase • Levarterenol - like substance • Spider fangs may host numerous bacteria • End result of envenomation is local tissue distruction via liquifactive necrosis • Spectrum of disease from major to minor • Loxosceles is the only proven class in the US

Other Spiders • Many other spiders have been reported to cause necrosis although recently many question the reality of this • Wolf Spiders • series of 515 documented bites from wolf spiders in brazil showed no necrosis • Hobo spiders • Introduced from Europe in 1920’s • Spread to Pacific NW • Allegedly causes necrotic wound and HA • Little documentation to confirm and nontoxic in Europe

The Main Actor - Loxosceles • Characteristic eye pattern • Six eyes arranged in pairs • Other spiders characteristically have 8 eyes in 2 rows of 4 • Pigmented “violin shape” on back • Unreliable and commonly misinterpreted • May or may not be present in young

Brown Recluse Mimics • Many other North American spiders mimic the appearance of Brown Recluse spiders • Common Eye Pattern • Spitting spiders • Scytodes genus • Common violin shape • Cellar spiders • NEJM article - attempting to collect any spider identified as Brown Recluse by public • > 1700 spiders submitted from 36 spider families • Genus Kukulcania most commonly submitted

Loxosceles - Distribution • Again - only confirmed necrotic arachnoid • 11 species of loxosceles in No America • Brown Recluse responsible for most envenomations • Only active in a specific range in the US • May be transported outside this range BUT has little effect on epidemiology • Spiders are RARELY verified in states where they are not epidemic • Must be very suspicious of a reported bite in a non endemic state

Diagnosis of Necrotic Arachnoidism • Two important factors • Collection and proper identification of responsible spider • Characteristic skin findings • 600 pts with suspected spider bites at University of AZ or LA County • 80% of bites caused by other arthropods • Bedbugs, hymenoptera, etc • Must be wary of the diagnosis of spider bite in areas where loxosceles is not endemic • Diagnosis remains common in areas where the spider has never been confirmed

DDX of BR Bites • Staph, strep infections • Herpes infections • Diabetic ulcers • Fungal infections • Pyoderma gangrenosum • Lymphomatoid papulosis • Etc. etc. etc. …

True Diagnosis of Loxosceles Bite • Since numerous disease mimic loxoscelism, diagnosis must be suspected UNLESS spider is caught in the act of biting and can be properly identified • Diagnosis remains a clinical judgment • Enzyme-linked immunosorbent assay to detect venom in rabbits • Not commercially available for humans

Treatment • Remains controversial • Initial care includes routine first aid • Rest, immobilization, ice, local wound care, tetanus prophylaxis • Reported therapies include: • Hyperbaric O2 • Dapsone • Steroids • Electric shock • Antibiotics antihistamines, dextran, nitro, excision, antivenom

Dapsone • Sulfone antibiotic • Recommended as treatment for decades • Theory behind use - dapsone inhibits chemotaxis of PMN’s and inhibits generation of oxygen free radicals • Literature on efficacy split • Guinea pig literature suggests decreased lesion size if treated w/in 16 hours • Rabbit literature suggests no benefit • No human data to date

Dapsone - The Down Side • Common side effect • Hemolysis in all patients • Degree is usually not clinically significant • Decrease of 1 - 2 g in Hgb • Dangerous side effect • Severe hemolysis and methemoglobinemia in pts w/ glucose-6-phosphate dehydrogenase deficiency (G6PD) • Other side effects • HA, GI upset with N/V/D, agranulocytosis, lower motor neuron toxicity, hepatitis

Before Dapsone • Prior to initiation of therapy, pt’s need: • Baseline CBC • Baseline LFT’s • Baseline assessment of G-6-PD

Steroids • Commonly administered to pt’s with loxosceles bites • Do not retard the formation of ulcers as much as they ameliorate the systemic effects • Such as reactive erythema and edema • Two studies showed no effects on size or duration of lesions

Hyperbaric Oxygen • In a study w/out controls, benefit reported • Dubious • Another human study w/out controls showed “uneventful healing” • Neither study actually confirmed lesion was from loxoscelism • Rabbit and piglet studies have shown no benefit

Electric Shock • “…rationale for treating loxosceles bites with electric shock arose after reported success of electric stun guns for field therapy of insect stings and poisonous snakebites” • ???? • Therapy = energies of 40 - 50 kilowatt seconds delivered for 1 - 2 seconds per pulse • Human subject reported improvement over 2 - 5 weeks • No controls…. • No benefit in animal studies

Excision and Grafting • Some advocate for excision and graft of all lesions over 1 cm • Some advocate for a course of dapsone prior to excision and grafting • Small cohorts showed improved results vs. dapsone alone

Antivenom • Not available in US • L. laeta anitivenom in So America • Specific or polyvalent antivenom in Brazil • 17 pts w/ documented bites • No difference between dapsone alone, intralesional antivenom, and combo tx • Animal studies suggest that antivenom beneficial if given intralesionally w/in 4 hours of envenomation

Spiders that Cause Systemic Symptoms

Black Widow Spider

Black Widow - General • Females are large enough to envenomate humans • Males too small • 13% of calls to AAPCC for report of Black Widow Bites • Recognized by: • Glassy-black body • Hourglass on ventral surface

Black Widow Venom • Contains  Lacrotoxin • Neurotoxin that results in pre-synaptic neurotransmitter release • Clinical effects are rapid in onset • W/in one hour • Include: • Muscle spasms • Severe abdominal pain • Mimics peritonitis • HTN and diaphoresis are common • Lactrodectus facies • Prostration

Black Widow - Diagnosis • Once again, relies in large part on proper identification of the spider • Can be very difficult • Commonly mis-diagnosed • If diagnosed at all

Treatment • Antivenom available • Allergic reactions to the antivenom seen in 75% of pts up to 14 days out from treatment • One reported death from anaphylaxis • Preliminary test dose mandatory • Due to side effects, antivenom use reserved • Recovery is excellent and usually occurs w/in 3 - 7 days • Pain treated with IV analgesics • IV calcium gluconate ineffective for pain in most case reports

Arachnid Envenomations