4-60
Patient Education
General: Material employed for protection against mites function more as toxicants than true repellents.
DEET (diethylmethyltoluamide) provides the best protection when applied to the clothing. Benzyl benzoate is
an excellent chigger toxicant and remains effective after rinsing, washing, or submersion in water.
Follow-up Actions
Evacuation/Consultant Criteria: Evacuation is not normally necessary. Dermatology consultation may be
helpful for further treatment options.
Skin: Spider Bites
(Black Widow [Latrodectus mactans], Brown Recluse [Loxosceles reclusa])
MAJ Daniel Schissel, MC, USAIntroduction: Two dangerous spiders bite in the United States, the black widow and brown recluse. The
Black Widow (BW) spider may be found from southern Canada to Mexico and Cuba. The female is easily
recognized by her coal black globular body and red-orange hourglass marking on the underbelly. It favors
cool, dark, little-used places to set its web, including outdoor toilet seats. The Brown Recluse (BR) has a
1cm oval light tan to dark brown body, and a leg span over 2.5 cm. A classic dark brown violin-shaped dorsal
marking extending from the 3 sets of eyes (rather than 4 seen in other spiders) to the abdomen differentiates
it from other brown spiders. It is found across the United States, and, like the BW, only bites in self-defense.
It is commonly found in storage closets, old shoes or boots, rock bluffs and barns. BR venom is hemolytic and
necrotizing and contains a spreading factor. Other species of Latrodectus and Loxosceles are found in other
areas of the world. Treat their bites similarly. Most other spider bites should be treated supportively as with
the BW, or with wound care and shock precautions as with BR. Some spiders have neurotoxic venom, which
should be treated with antivenin if available.
Subjective: Symptoms
BW: Pinching bite followed by local swelling and burning at the puncture site; abdominal cramping and pain
begins within 10 min to an hour, peaking at about 3 hours.
BR: Painful, stinging bite with gradual development of severe pain in 2-8 hours; slow progression over the
following weeks of a necrotic ulcerating process spreading from the bite; 25% of patients will also have a
systemic reaction also, with nausea, vomiting, fever, chills, muscle aches and pains.
Objective: Signs
Using Basic Tools:
BW: Bite with two, red, punctate markings on an erythematous plaque, most commonly found on the buttocks
or groin area.
BR: Tender, swollen bite that progresses to hemorrhagic vesicle or bullae, and later (5-7 days) to a slowly
enlarging gangrenous eschar with a border of erythema and edema; lymphangitis; wound granulates, leaving
a large fibrous scar; systemic symptoms (25% patients) include generalized erythema, purpuric macular
eruption, thrombocytopenia, hemoglobinuria, hemolytic anemia, renal failure and shock.
Assessment: Diagnosis based on clinical morphologic criteria and history of exposure.
Differential Diagnosis
BW - acute abdomen, tick or other arthropod bite.
BR - necrotizing fasciitis for localized wounds; anaphylaxis for systemic reactions.
Plan:
Treatment
BW: Pain control, calcium gluconate 3 mEq IV and tetanus prophylaxis.
BR: Tetanus prophylaxis, ice and elevate bite site to decrease the localised reaction; pain control; good