Yaws is a systemic treponematosis
caused by Treponema pertenue, a spirochete that is morphologically and
serologically indistinguishable from T. pallidum.
Visit:
Pathology of Syphilis;
Neurosyphilis;
Congenital Syphilis
;
Bejel
Like syphilis, yaws
has three stages and a period of latency, but it is non-venereal and
late lesions are limited to bone and skin.
T. pertenue does not cause late
lesions of the cardiovascular system, the central nervous system, or
other deep organs.
Children and adolescents living in
deprived tropical regions are at risk.
Transmission is by skin to skin contact
and is facilitated by a break or abrasion.
Two to five weeks after inoculation, a
single “mother yaw” appears at the site of inoculation, usually on an
exposed part.
It begins as a papule and becomes a “raspberry-like” papilloma, 2 to 5 cm across.
The disseminated or secondary stage
begins with the eruption of a similar, but smaller, raspberry-like
lesion on other parts of the skin.
Microscopically the mother lesion
and the disseminated lesions resemble each other.
There is
hyperkeratosis with a finely lobulated contour, papillary acanthosis ,
with elongation and pointing to the tips of the rete ridges , and an
intense infiltrate of the epidermis by neutrophils.
The epidermis
dissolves at the apex of the papilloma , where neutrophils are
concentrated, to form a shallow erosion of the surface.
The dermal
papillae are hyperemic and edematous. Plasma cells invade the upper
dermis.
Spirochetes are numerous in the dermal papillae, particularly
in foci of neutrophils and in superficial exudates.
Unlike the
causative organism of syphilis, T. pertenue does not invade,
compromise, or destroy vessels.
Painful papillomas on the soles, lead
the patient to walk on the sides of his feet like a crab, a condition
called crab yaws.
Shortly after inoculation the treponemes are borne by
blood to bone, lymph nodes, and skin.
Here they grow during a latent
period of 5 or more years.
This is followed by lesions of the late
stage, which include gummas of the skin and periostitis, both of which
are destructive.
Periostitis of the tibia causes “saber shins” or
“boomerang legs”.
Gummas of the skin are destructive in the face and
upper airway.
Darkfield examinations of exudates,
silver impregnation techniques on tissue sections, and all the
serologic tests for syphilis are useful in the diagnosis of yaws.
A single dose of long-acting penicillin
is curative.
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