Arachnid Envenomations
Wilderness Medical Consortium
Matt Sholl
General
Class Arachnida and phylum Arthropoda
comprise ~ 70,000 species
Divided into 9 orders
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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
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Acari
Through direct envenomation
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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
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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
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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
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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
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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
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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
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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
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Spitting spiders
Scytodes genus
Common violin shape
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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
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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
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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
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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