Page 97 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 4-12 Rashes

BROWN RECLUSE SPIDERS AND SCABIES MITES

BUG BITES Brown recluse spider bite.
The characteristic red, white,
and blue sign is seen here.
Human skin is exposed to the environment on a con-
stant basis and encounters multiple threats, including
arthropods of many varieties. Each species of arthropod Loxosceles reclusa.
can inflict its own type of damage to the skin; some bites Its venom contains
are mild and barely noticeable, and others can be life- sphingomyelinase-D, which
threatening. The most common bites are those of mos- can cause massive tissue
quitoes, fleas, bedbugs, mites, ticks, and spiders. Not destruction. Also known as
only can these bites cause direct damage to the skin, but the fiddleback spider
these organisms may have the ability to transmit infec-
tious diseases such as Lyme disease, leishmaniasis, and
rickettsial diseases.
Clinical Findings: Mosquitoes are prominent insects
in the spring, summer, and early fall seasons. In warmer
climates, they can be seen year round. Their bite is
often not noticed until after the mosquito has gone.
The recently bitten person is left with a pruritic urti-
carial papule that typically resolves by itself within
an hour or so. Some individuals are prone to severe
bite reactions and develop warm, red papules and
nodules that can last for a week or two and can be
associated with regional lymphadenopathy. Mosquitoes
are essentially a nuisance for the most part, but in some
areas of the world they are the major vectors for trans-
mission of malaria and encephalitis viruses. Sand flies
are similar, but they are the major vector for
leishmaniasis.
Fleas have been around since before the beginning
of human civilization and were responsible in the
Middle Ages for helping transmit the bubonic plague,
which killed millions of people. Fleas are most com-
monly seen in households with pets. Individuals can be
bitten after the pet transfers the fleas to bedding, car-
peting, or clothing. Characteristic bites occur in groups
of three, referred to as “breakfast, lunch, and dinner.”
Flea eggs can lay dormant for years, only to reactivate
in response to movement and vibration that indicate a
meal is likely to be nearby. Many flea bites occur around
the ankles of adults; the fleas jump from the carpeting
to the ankles, take their meal, and leave. The typical
skin lesion is a small papule with a central punctum. It
is self-resolving. Fleas have been known to carry organ-
isms responsible for infectious diseases, including Yer-
sinia pestis (bubonic plague) and Rickettsia typhi (murine Inflammatory
typhus). excoriated
Bedbugs (Cimex lectularius) have made a resurgence papules
in the United States. The are ubiquitous insects that (note penile
can live in any area of the country. Households, hotels, involvement)
and other sleeping quarters become infested with colo-
nies of bedbugs. They emerge in the night, typically 1
to 2 hours before dawn, and search for a blood meal. Scabies (Sarcoptes scabiei) in circle
They find their victim asleep and feed for a few minutes
before retreating back to the nest. The nest is almost
never in the bed; it is most likely to be located within
the baseboard molding or floor boards. In the morning,
the afflicted individual awakens with one to hundreds northern latitudes but can occur at any time of the year are present in the environment and can cause similar
of bites. Most are small papules with a central punctum. in the southern regions. The term chigger refers to the reactions.
Depending on the species of bedbug, a more inflamma- larval phase of the Trombiculidae family of mites; it is Most ticks bite and feed for up to 24 hours before
tory response may occur, causing vesiculation and one of the most common and well-recognized causes falling off after receiving their blood meal. They can
bullae. Bedbugs have been reported to transmit hepati- of human bites. Chiggers are small red mites, so small leave a tick bite granuloma, which is a small red papule
tis B virus. that they are not felt, and they bite quickly. They with a central punctum, at the site of the bite. Many
Encounters with the large mite family of organisms usually leave pinpoint red papules that can be numer- methods have been used to remove ticks; most can
are more likely to occur in the summer months in ous and can cause severe pruritus. Many other mites result in more skin damage than the actual tick bite.

THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS 83