PEM Board Review Series: Bites & Stings
Overall concepts:
First, do no harm—many historically recommended interventions (incision, suction,
tourniquests, electric shock, ice directly on the wound, alcohol on the wound) only add
insult to injury when applied to snakebites—make sure the potential benefits exceed risk
Antivenom is the definitive treatment for serious snake envenomation. The sooner
antivenom is given, the more likely that irreversible damage can be prevented. Dosing is
not based on the patient’s weight
The diagnosis of spider bites is overused for wounds of uncertain etiology—there is no
accepted specific treatment for brown recluse spider bite in the USA
Envenomations and the treatment of such can cause severe allergic reactions so be
prepared to treat these potentially life-threatening complications.
Bee (hymenoptera) stings with IgE mediated anaphylaxis, are the most common cause of
death from venomous bites; Removal of the stinger by gently scraping the stinger off
with a blade or credit card is recommended; avoid squeezing the stinger with fingers or
forceps as this can inject more venom.
Snakebites:
A huge range of effects—children may suffer little more than a fang puncture mark or
they may develop MSOF and die. Benadryl has NO ROLE in the treatment of snakebites
(except if there is an allergic reaction to the anti-venom):
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Viperidae/Crotalidae(pit vipers—they have a heat-sensing pit between the eye &
nostril): rattlesnakes, cottonmouths (water moccasins), adders, and copperheads.
o Toxins cause coagulopathies, tachycardia, and “progressive edema”, and a
“metallic taste in mouth”; venom is cytolytic resulting in edema; therefore,
removal of jewelry and clothing distal to the site is vital to ensure
perfusion distal to the site of the bite
o Treatment is first clothing/jewelry removal, antivenin, pressure
immobilization (with the pressure aspect serving to decrease venous and
lymphatic drainage) and splinting (essentially immobilization without the
pressure) is useful within 1 hour of the bite; Incision and suction can be
done within one hour of the bite (controversial).
Elapidae: cobras, coral snakes, kraits, and mambas
o Toxins cause neurotoxicity (ptosis, weakness, paresthesias, fasciculations)
o Coral snakes have wide black and red bands that are separated by
narrower yellow bands, while king snakes (non-venomous) have red bands
directly bordered by black bands and the yellow rings are within the black
bands: “red on yellow, kill a fellow; red on black, venom lack”
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Venom can lead to capillary leak, abnormal clotting, paralysis, neurotoxicity, tissue
digestion—the more time venom is in there, the more digestion takes place—
rhabdomyolysis can occur.
Antivenom is indicated for progressive effects of the venom, including:
 Worsening local injury (pain, swelling, ecchymosis)
 Coagulopathy
 Systemic effects (hypotension and altered mental staus)
Immediately after a snakebite, the only apparent manifestations may be fang puncture
wounds. If a patient presents very early, an envenomation syndrome might not have
developed yet.
The common venomous snakes present with a pair of puncture wounds from the fangs,
while non-venomous snakes (with the exception of the coral snake) have either no fangs
or have fangs with an additional row of teeth.
The venom of the coral snake is a neurotoxin and would produce muscle weakness over
time.
Snakebites cause pain around the bite site as tissues distort with swelling, there may be
taste changes, difficulty breathing that progresses to respiratory distress or failure.
Patients may experience N/V/D and coagulopathies (pit vipers) can lead to hematemesis
or hematochezia.
Insufficient evidence exists for splinting or positioning (above or below heart)
Immediate first aid: any rings or other constricting jewelry and clothing should be
removed in anticipation of severe swelling. Tenderness (mark the extent of tenderness
with a marker and repeat every 15 minutes) is more sensitive than swelling for detecting
progression; it can be difficult to distinguish limb swelling and blue/pallor discoloration,
pain, and paresthesias of a snakebite from compartment syndrome—however, if the
effects are caused by envenomation and the patient does not have compartment
syndrome, capillary refill should be normal and compartmental pressures should not be
elevated.
There are two antivenoms for pit vipers (Antivenin Crotalidae and CroFab)—starting
dose is 4-6 vials irrespective of weight—RSI & anaphylaxis supplies and equipment
should be available. Endpoint is arrest of progression of symptoms and then a lower dose
until all symptoms resolved.
All children with snake envenomations should be admitted to the hospital. If patient is
only believed to have suffered a “dry bite”, they should be observed for at least 8 hours to
see if any envenomation symptoms develop, especially progressive edema; No ABX but
update Td.
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Spider Bites:
Latrodectus (Black widow spider): 2 cm long, shiny black, with a red-orange hourglass
or spot on the ventral abdomen and a chaotic web. The predominant clinical effects are
neurologic and autonomic—typically, the bite site has a “target” appearance. There may
be a central reddened, indurated area around the fang puncture sites surrounded by an
area of blanching and an outer halo of redness which is pruitic. The wound does NOT
become necrotic.
Venom is a neurotoxin that causes continuous release of Ach and NE at the presynaptic
junction leading to stimulation of the myoneural junction and consequent muscle rigidity.
Symptoms are painful muscle cramping and back pain that progresses centrally along
with diaphoresis locally around the bite site (distinctive for widow spider envenomation);
this can mimic a rigid or acute abdomen; also may have HTN, tachycardia, N/V, H/A,
shock, respiratory arrest, and death. Symptoms begin within an hour and peak by 3
hours; rhabdomyolysis.
2 basic treatment options: Antivenom or a combination of pain medications and
sedatives (but if you choose this, it may need to last days to weeks!); Antivenom is
effective but potentially deadly! ABX not indicated but should update Td.
Black widow bites do NOT leave impressive skin lesions; steroids and antibiotics have
NO treatment role.
Indications for antivenin include:
1) Age < 5 years
2) Respiratory difficulty
3) Hypertension
Loxosceles reclusa (Brown recluse spider): 1-2 cm with violin shaped marking on the
dorsum of the cephalothorax; primary toxin is sphingomyelinase D causing subcutaneous
fat necrosis and a “growing ulcer”; symptoms start with mild stinging followed by
aching, fever, malaise, joint pain, and morbilliform eruption with petechiae. Lesions
develop a violacious center with a ring of pallor and a halo of erythema and edema the
“red, white, and blue” sign”. After 24-72 hours a eschar forms; after 2-5 weeks, it
sloughs, leaving an ulcer; monitor for hemolysis/renal failure; urticaria NOT a feature
Because spiders are not parasitic and only bite humans out of defense, multiple lesions
are suggestive of an etiology other than spider bites; tx; cold compresses.
There are no brown recluse spiders in the NE USA. These spiders are found in the midsouthern, SW, and NW USA.
Yellow-sac spider (Cheiracanthium): is in the mid-eastern USA (most common house
spider in large cities) and causes “yellow-green” skin at the site with an eschar and ulcer;
treatment is local skin care
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Tarantulas: bite is painful but not dangerous; can have eye exposure to hairs flicked
from the abdomen that needs ophtho consult for removal.
Rabies
The boy described in the vignette has suffered multiple bites by a raccoon, one of the
wild mammals most likely to be infected with rabies in the United States (along with
bats, skunks, and foxes). The goal of postexposure prophylaxis for rabies is to prevent the
virus from entering the nervous system. Good wound care, including copious irrigation
and cleaning with soap and water, are the critical initial steps. The additional use of
iodine-containing solutions can be considered. In high- or uncertain-risk situations,
postexposure prophylaxis (PEP) should be initiated, with both passive (immune globulin)
and active (vaccine) immunization, according to the schedule detailed below.
Rabies is a zoonotic disease presenting as an acute, rapidly progressive
encephalomyelitis. Symptoms can include paresthesias, anxiety, dysphagia, delirium,
seizures, and varying degrees of paralysis. It is caused by an RNA virus in the family
Rhabdoviridae, genus Lyssavirus. Virus particles in the saliva of the biting animal are
deposited in the wound, later entering local nerves and traveling to the central nervous
system. The incubation period in humans ranges from a few days to several years, with
an average of 4 to 6 weeks. The time frame is shorter with wounds in the head and neck
region. Once symptoms of infection have developed, there are no effective therapies to
improve outcomes. Very few patients have survived symptomatic rabies infection, and
most survivors had received pre-exposure prophylaxis. For this reason, attention is
focused on control measures and immunoprophylaxis.
Although all mammals are potentially susceptible to rabies infection, small rodents
(squirrels, mice, rats) and lagomorphs (rabbits, hares) rarely represent a risk of rabies
transmission. The routine use of domestic cat and dog rabies vaccination in the United
States has reduced dramatically the rate of rabies infection and, therefore, the risk of
rabies transmission by these animals. Bats are the predominant source of human rabies in
the United States. Worldwide, however, dogs remain the most common source of human
rabies cases.
PEP should be administered to all people bitten by wild mammalian carnivores and bats
or by domestic animals showing signs of infection. Depending on local rabies risk, PEP
can be withheld for people bitten by cats, dogs, or other domesticated animals when the
animal can be observed for a 10-day period. Any animal displaying signs of illness and
any captured wild animal should be euthanized in a manner to preserve the brain and the
head transported under refrigeration to the nearest laboratory that has rabies testing
capabilities. PEP can be initiated until the test results are available and can be
discontinued if results are negative.
Because animals infected with rabies often exhibit signs of illness or unusual behavior,
nonprovoked bites might carry a higher risk of rabies transmission than provoked attacks
(including attempts to handle or feed the animal). Because most cases of bat-associated
rabies lack a clear history of a bite, PEP should be considered in cases where a bite may
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not be recognized, such as a person who has altered abilities (eg, inebriated adult, infants
and children, mentally handicapped individual, sleeping individual) occupying the same
room where a bat is found.
Passive immunization using rabies immune globulin (RIG) should be administered as
soon as possible after the exposure. Human RIG should be administered in a dose of 20
international units/kg infiltrated into and around the wound(s) whenever possible, with
any remaining volume administered intramuscularly in a large muscle at a site remote
from the site of injection of vaccine (ie, opposite thigh, if the vaccine is administered in
the deltoid). RIG is not required if the patient has received pre-exposure prophylaxis or
has protective antibody titers after a prior rabies vaccine series. RIG provides antirabies
antibody until natural antibody is produced in response to the vaccine.
The Rabies Vaccine is administered as a 1-mL dose intramuscularly, regardless of the age
or weight of the recipient. The initial dose of rabies vaccine (1ml IM) should be
administered intramuscularly in a different syringe and at a different site from the
immune globulin. Studies have shown that antibody concentrations are lower when the
vaccine is administered in the gluteal region, so either deltoid (preferred) or anterolateral
thigh (alternate location for a smaller child) sites should be used. The initial dose is
considered day 0, and four additional doses are administered on days 3, 7, 14, and 28.
Three 1-mL doses of vaccine are administered on days 0, 7, and 21 or 28; repeat
vaccination can be offered every 2 years or as needed, based on antibody titers.
Food poisoning:
Staphylococcal food poisoning: is the most common food-borne illness; symptom onset
is 1-6 hours post ingestion (often salads at picnics)
Ciguatera poisoning: The most commonly reported marine toxin disease in the world;
there is an initial brief period of vomiting followed (often in several hours) by weakness
and paresthesias (especially perioral), pain in the teeth, and a peculiar hot/cold
temperature sensation reversal; cardiovascular signs can be arrhythmias and heart block;
from ingesting contaminated reef fish like barracuda, grouper, and snapper; Treatment is
symptomatic with IV fluids, and antiemetics, BUT must AVOID opioids as they may
cause hypotension due to the combination with one of the biotoxins; Normal cooking will
NOT eliminate the toxin.
Scombroid poisoning (“histamine fish poisoning”): occurs shortly after ingesting spoiled
“oily” fish (tuna, bonita, mahi mahi, and mackerel), which invariably contain high levels
of histamine. Headache, facial flushing, dizziness, nausea and pruitis with frank urticaria
occur; scombroid food poisoning should be reported to the DOH to avoid mass exposure.
Standard treatment include those therapies for systemic allergic reactions (O2,
antihistamines, bronchodilators, and IM Epi)
Botulism: causes weakness in a descending pattern beginning with the cranial nerves
(diplopia, dysphagia, dysarthria) then progressing to the trunk and extremities. Usually
associated with nausea, vomiting, or paresthesias
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Vibrio: species cause cholera—onset of symptoms delayed for 12-24 hours, presents as a
profuse diarrheal illness.
Pufferfish: contain tetrodotoxin, which is a neurotoxin which blocks voltage-gated
sodium channels on the surface of nerve membranes. The first symptom is a slight
numbness of the lips and tongue (appearing between 20 minutes and 3 hours after
ingestion.) The next symptom is increasing paresthesias in the face and extremities,
which may be followed by sensations of “lightness” or “floating”. GI effects may then
occur; The second stage of paralysis is increasing paralysis, respiratory distress, and then
CV effects; The victim, although completely paralyzed, may be conscious and lucid until
shortly before death, which occurs within 4-6 hours. There is no therapy, only supportive
care; Mortality is 50%!
Scorpions:
Buzzword: Can cause “roving” eye movements
Scorpion antivenin is available through the Antivenin Production Laboratory at ASU in
Tempe. Indications include:
1)
2)
3)
4)
persistence of tachycardia
hyperthermia
severe HTN
agitation
Treatment includes supportive care as well as after-load reduction with nifedipine.
There are NO proven benefits to use of steroids, antihistamines, atropine, or cryotherapy.
The systemically poisonous species is Centruroides exilicauda (formerly C sculpturatus);
tapping on the sting site usually produces severe pain (“tap test”)
Most stings result only in local, immediate burning pain. Some local inflammation and
local paresthesias can occur. Symptoms usually resolve within several hours and can be
managed with symptomatic home care consisting of oral analgesics and cool compresses
or intermittent ice packs.
Significant envenomations or those in children < 10 years of age can cause weakness,
restlessness, diaphoresis, diplopia, nystagmus, roving eye movements, hyperexcitability,
fasciculations, opisthotonus, priapism, salivation, slurred speech, hypertension,
tachycardia, convulsions, CV collapse, and death; also coagulopathies, DIC, pancreatitis,
renal failure
Atropine can be considered in cases of significant salivation to aid with supportive
airway management
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Jellyfish:
Mechanism of toxicity is due to nematocysts
Symptoms include stinging, burning pain, pruritis, papular lesions and local
inflammation; severe symptoms from the Portuguese Man-of-War can result in H/A,
myalgias, fever, respiratory distress, hemolysis, renal failure, and coma
Treatment: oral analgesics, flush with sea water, NOT fresh water, application of
vinegar, baking soda, and meat tenderizer will inactivate unbroken nematocysts but will
not alter the effects of toxin already introduced; If present, remove the attached tentacle
with a double-gloved hand or instrument; NO role for steroids
Sea Urchin:
Spines are made of calcium and therefore it is possible to dissolve them with a weak acid
like vinegar.
Stingray:
The venom is a heat labile toxin and can cause vomiting, diarrhea, sweating, and muscle
fasciculations. Can also cause conduction problems and respiratory depression
Initial therapy is irrigation with copious amounts of cold salt water to remove venom.
Then put the injured area in warm water (32-46 degrees Celcius) for 90 minutes; next, reexplore the wound and administer Td
Rat Bites:
Rat Bite Fever is a rare disease that may present after a 1-3 week incubation period with
chills, fever, malaise, headache, and a maculo-papular or petechial rash.
There are 2 types: both respond to IV PCN
1) Haverhill Fever (caused by Streptobacillus moniliformis)
2) Sodoku (caused by Sprullum minus)
Post exposure prophylaxis is NOT recommended
Dog/Cat/Pet/Domestic Farm Animal Bites:
Although the overall rate of infection of dog bites is relatively low (5% to 10% in most
series) relative to cat bites (as high as 25% to 50%), once signs of infection develop, they
need to be treated aggressively. The hand is the highest-risk area of the body for
complications from infection because of the high concentration of tendons, ligaments,
and nerves in a small confined space. A local infection can progress to a tenosynovitis or
lymphangitis and can cause significant short- and long-term morbidity as well as
functional consequences to the hand. Early involvement of hand surgeons is warranted
for this boy to drain and debride this closed space infection and assess for tendon or
ligament injury. Intravenous antibiotics (even before a trial of po), such as ampicillinsulbactam, to cover the most common organisms (Pasteurella sp and other oral
anaerobes, methicillin-sensitive Staphylococcus aureus, and streptococci) are warranted.
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Bites from rabbits and other lagomorphs carry the risk of infection with Francisella
tularensis. Ulceroglandular tularemia is characterized by fever, chills, myalgia, and
headache. A painful maculopapular lesion develops at the bite site, with subsequent
ulceration and regional lymphadenopathy that may suppurate. Streptomycin is the
treatment of choice.
Monkey bite wounds are similar to those from humans but carry the additional risk of
infection with B virus (also known as Herpesvirus simiae), which can cause a potentially
fatal encephalitis.
Bites from farm animals, including horses, pigs, and sheep, carry the risk of infection
with staphylococci, streptococci, actinobacilli, Pasteurella sp, Bacteroides sp, and other
gram-negative rods. As in all bite wounds, local wound management, including cleansing
and debridement of devitalized tissue, is the mainstay of therapy.
Prophylactic antimicrobial agents are recommended for animal bite wounds to high-risk
areas such as hand, face, feet, and genitals and all puncture wounds.
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