[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 13 The Arthropods
TABLE 13-3
Parameter
Black widow
spiders
Brown recluse
spiders
Hobo spiders
Adult Spiders: Typical
Features at a Glance
Description
Males and females have shiny black
surface
Females larger than males
Females have diagnostic red hourglass
shape on underside
Males and females spin atypical or
chaotic webs
Males and females most active at
night
Exhibit reclusive behavior
Often hide in clothing or bedding
Only bite when threatened
Have trademark brown violin shape
seen on the cephalothorax
Have muted, nondistinct, brown earth
color
Spin distinctive funnel-shaped web
there is no particular pattern or design. These
spiders tend to be more active at night, with the
female hanging upside down in her web, making
the hourglass readily visible. Brown recluse
spiders are so-named because of their reclusive
behavior. They tend to hide in clothing or
bedding and bite only when threatened. In addition,
the trademark brown violin shape can be
seen on the cephalothorax (i.e., the fused head
and thorax section of the body). Hobo spiders
belong to a class of spiders that creates a distinctive
funnel-shaped web. These spiders have a
muted, nondistinct brown earth color.
Life Cycle notes
The life cycle of spiders is less complicated than
that of mites or ticks. After mating, the female
spider generates an egg sack from which as many
as 200 new spiders may hatch as miniature versions
of the adults. As they mature, they increase
in size to the adult level.
Epidemiology and Geography
Human interaction with the arachnids in this
section is through a venomous bite and subsequent
wound and reaction to the venom. These spiders
are by nature not aggressive but will bite when
provoked or disturbed. The black widow spider is
found throughout the United States, with different
species names for variants found in different
geographic regions. The brown recluse spider is
primarily found in the central United States, with
high populations in Oklahoma, Arkansas, and
Missouri. The hobo spider is a resident of the
Pacific Northwest and western Canada.
Clinical Symptoms
All these spiders can cause a very painful bite, with
a secondary reaction to the venom that is simultaneously
injected. The black widow spider is considered
the most venomous spider in North
America but its bite rarely causes a fatality because
so little venom is injected. A severe stabbing pain
at the bite site may be followed by spreading of
the pain, eventually creating nausea, fever, severe
abdominal cramping, and excessive sweating. The
brown recluse spider bite may produce a necrotizing
wound; the size of the wound depends on the
amount of venom that was injected, the body site
location, and the immune status of the individual.
Most severe reactions are in children or those with
a compromised immune system. Approximately
50% of hobo spider bites do not inject venom.
Cutaneous necrosis that resembles that seen in
brown recluse bites has been known to result from
that of a hobo spider. In some instances, the
healing process takes years. Occasionally the condition
from such bites worsens and evolves into
systemic symptoms. For those cases in which
venom is injected, the reaction usually remains
localized, with a blister developing over 24 hours.
This blister eventual ulcerates and healing scabs
form in approximately 3 weeks.
Treatment
To treat a bite by a black widow spider, antivenin
can be given to those with compromised immune
systems, underlying heart conditions, or other
health problems and to older adults. A hospital stay
may also be required to monitor heart conditions.
Antivenin for the bite of the brown recluse spider