Page 98 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 4-13 Integumentary System

ARTHROPODS AND DISEASES THEY CARRY

Phthirus pubis
BUG BITES (Continued)

These methods include burning the end of the tick with Deer ticks that carry Lyme
a cigarette or a match, an approach that is more likely Pediculosis pubis (exposure disease can cause erythema
to cause a skin burn than it is to remove the tick. The of pediculi in hair) migrans (bull’s-eye rash)
best method of removal is to grab the tick as close to
the surface of the skin as possible and gently pull in a Arthropod Disease it transmits Appearance
direction perpendicular to the skin. If the mouthparts
are left embedded in the skin, a small punch biopsy can Blackfly Onchocerciasis
be performed to remove the remaining parts. Ticks are
well known to transmit many infectious diseases,
including Lyme disease and Rocky Mountain spotted
fever. Deer tick Lyme disease, anaplasmosis,
Most spider bites are caused by jumping spiders. As babesiosis
with all spiders, bites frequently occurs after the spider’s
web or nesting location is disturbed. The bites can be
painful and can leave erythema and a papule or nodular
reaction. On occasion, these bites develop secondary Flea Plague
cellulitis. Two spiders are unique in their potential to
cause severe human disease: the black widow spider
(Latrodectus mactans) and the brown recluse spider (Lox-
osceles reclusa). Lice Typhus
The black widow spider is a web-weaving spider that
paralyzes its prey with a potent neurotoxin called latro-
toxin. The venom causes massive release of acetylcho-
line from nerve endings. In humans, this can lead to Lone star tick Tularemia, anaplasmosis
pain, fever, and symptoms of an acute abdomen.
The brown recluse spider is a solitary stalking spider
that lives in dark, hidden locations. It is not aggressive
and typically bites only when a human accidentally dis- Mosquito Malaria, yellow fever, dengue,
turbs its location. The toxin released in its venom con- encephalitis, West Nile virus
tains a mixture of sphingomyelinase-D, hyaluronidases,
proteases, and esterases. Sphingomyelinase-D is the
major component that is believed to be responsible for Reduviid bug Chagas disease
most of the tissue damage caused by the spider’s bite.
It can cause severe pain and aggregation of platelets and
red blood cells, resulting in intravascular clotting with
resultant necrosis of the skin. The characteristic pattern Sandfly Leishmaniasis
seen on the skin is a central bluish region with necrosis
and coagulation, a surrounding vasoconstricted area
that appears to be blanched white and a peripheral rim
of erythema. This has been termed the “red, white, and Tsetse fly African trypanosomiasis
blue” sign of a brown recluse bite. Some bites can prog-
ress rapidly and cause severe necrosis of the skin requir-
ing surgical debridement.
Histology: Most bite reactions are not biopsied, Wood tick Rocky Mountain spotted fever
because they are typically diagnosed clinically. The his-
tological findings for most bug bites are very similar.
There is a superficial and deep inflammatory infiltrate
with many eosinophils. Superficial necrosis of the epi-
dermis may be seen at the site of the bite. Occasionally,
tick mouth parts are located in the biopsy specimen. and treated with preventive tick and flea medications. Narcotics (for pain control) and antivenin have
Brown recluse spider bites show intravascular throm- Flea and bedbug infestations should be treated by a been used to treat black widow spider bites and have
bosis and necrosis of the skin. professional exterminator. Proper use of bug sprays been helpful. The antivenin is derived from horse
Treatment: The treatment of most bites is support- containing DEET (N,N-diethyl-m-toluamide) and serum, and there is a risk of an allergic reaction in
ive. Pruritus can be treated with a potent topical corti- staying in the center of wooded trails can help decrease susceptible patients. Brown recluse spider bites have
costeroid and an oral antihistamine. Avoidance is the one’s chance of being bitten. In endemic areas, any been treated with many agents, including dapsone, to
most important preventive measure. Areas of standing patient with a deer tick bite that has lasted longer than try to mitigate some of the inflammation-induced skin
water provide breeding grounds for mosquitoes and 24 hours should be considered for prophylactic therapy damage. Recognition of these spiders and avoidance
should be drained routinely. Pets should be groomed for Lyme disease. is critical.

84 THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS