Bio 311
Information for this section was taken from the URLs
indicated in each section and from the following books:
Alcamo, I.E. 2001. Fundamental of Microbiology. Jones
and Bartlett Publishers, Sudbury, MA.
Wistreich, G.A. 1992. The Sexually Transmitted Diseases: A Current Approach. Wm. C. Brown Publishers, Dubuque, IA.
Certain forms of
disease-causing agents are able to live on or in the skin of their hosts. Such forms of life are called ectoparasites
and the relationship is referred to as an infestation.
Scabies and phthiriases,
or the crabs, are two examples of sexually transmitted diseases that fall into
the category of infestations.
Scabies
http://www.ashastd.org/stdfaqs/scabies.html
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Scabies is an
infestation caused by the mite Sarcoptes scabies. This
mite which can barely be seen by the naked eye, is spread only through close
contact. The ectoparasite can barely
survive being off the human body for more than a few minutes.
·
Scabies is one of the
few sexually transmitted diseases which is also often spread nonsexually in
hosuselholds and other areas. It
may be transmitted by close contact with infected persons such as bedding,
family members, or patients in a variety of health care facilities. Cases of scabies can occur where
children exchange clothing or spend the night at one another’s homes. Infected dogs also may be a source of
mites.
·
The adult female itch
mite has a round body and four pairs of legs, which allow it to walk rapidly on
skin surfaces. After finding a
suitable location, the female mite digs or burrows into the top skin layers. Within a few hours, she begins to lay 2
or 3 eggs per day. These hatch and
eventually develop into adult mites in about 10 days. It is not unusual to find ten or more mites on one infected
person. The greater the mite load
in an individual, the greater is the likelihood of transmission.
Signs and Symptoms
·
The first signs of
scabies appear within 4 weeks after contact with an infected person. Normally, all parts of the body except
that face may be infested by the scabies mite. Infants and individuals with an immunocrompomised system,
may have face involvement.
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The characteristic
feature of the disease is the skin burrow or irregular ditry-appearing line
formed by the movements of a pregnant female mite. At times, reddened blisters formed near the end of the
burrow indicate an allergic reaction.
Infested individuals generally experience intense itching at night in
involved areas. Since the mite
favors the cooler parts of the body, burrows and blisters often are located on
the penis, scrotum and breasts.
Fingers often are the first areas involved. Other body parts frequently infected include the waist,
buttocks, ankles, abdomen, and the area around the armpits.
Diagnosis
·
Scabies is generally
diagnosed by finding any stage of the mite or its typical black fecal pellets,
know as scybala, in lesions. Skin
specimens may be obtained by vigorous scraping with an oiled sterile scalpel
over the involved area to remove the tops of several burrows. This material is transferred to a glass
slide and examined microscopically.
·
Shave biopsies may also
be examined microscopically, as well as needle extraction of mites.
·
Anther approach used is
the burrow ink tests or BIT. Here
a burrow is rubbed with the underside of a fountain pen so as to cover it with
ink. An alcohol-soaked pad then is
used to remove the excess ink from the surface. The remaining ink flows into the mite burrow forming a
characteristic dark, zigzag line extending across and away from the entrance to
the burrow.
Treatment
Several miticides are
available for treatment of infested individuals. Topical creams such as
permethrin and lindane can be used.
In addition, an oral medication ivermectin can be used.
Pubic Lice
http://www.ashastd.org/stdfaqs/crabs.html
·
To date, 3 types of lice
are known to afflict humans. These
are the body louse, head louse and the pubic or crab louse.
·
Phthiriases or crab louse infestation, is easily spread by sexual
contact, the major means of tranmission.
The crab louse, Pthirus pubis, favors the pubic region, where it resides and
feeds. However, these lice can
find a home elsewhere on the body, wherever there is hair. Such sites include the armpits,
eyebrows, and eyelashes.
·
Infestation can also
result from contact with lice containing bath towel, bedding, and toilet seats.
·
The crab louse is
broader than it is long. Its
second and third pairs of legs have crablike claws which help the louse to
firmly attach to pubic hairs. The
life cycle of this ectoparasite, egg to egg is about 25 to 30 days. It can live away from the body of a
host for only a few days since the louse must have a blood meal on a regular
basis for survival.
Signs and Synptoms
·
The most common area
affected in the case of crabs is the pubic region. Intense itching is the most obvious symptom of the infestation.
Other areas that may be involved include the thigh, the trunk of the body, and
the hairy regions such as eyelashes, eyebrows, mustache and beard.
·
At times, characteristic
sky-blue spots may develop on the thigh and trunk. These lesions generally fade within a short time.
Diagnosis
Most commonly, the
diagnosis is made by finding and identifying adult lice and/or their numerous
eggs, or nits, on or near pubic hairs.
Pubic lice infestation is one of the few STDs that can be diagnosed by
physical examination alone.
Treatment
Medications such as
lindane are applied to the infested hairy and surrounding areas, with specific
attention to the pubic area and perianal region. Possible infested underclothes, sheets and pajamas should be
washed and cleaned by machine with hot water and dried in a hot dryer
cycle. A hot cycle is necessary to
insure that all lice and their eggs or nits have been destroyed. Washing with hot water and drying with
very hot heat will also get rid of scabies.
Permethrin cream and
Pyrethrins with peperonyl butoxide shampoo can also be used in addition to
Lindane shampoo. To treat infested
eyebrows and eyelashes, a prescription ointment must be used.