B. DISEASES DUE TO ANIMAL PARASITES

PEDICULOSIS

Synonyms.—Phthiriasis; Morbus pedicularis; Morbus pediculosis; Malis pediculi;
Lousiness; Fr., Phtiriase; Maladie pédiculaire; Ger., Läusesucht.

Pediculosis, while signifying mere lousiness, is commonly under­
stood as a designation of that condition of local or general cutaneous
irritation due to the presence of the animal parasite—the pediculus,
or louse. The parasite belongs to the class insecta, of the subdivision
hemiptera, and the family pediculidæ. Three species of the parasite are
encountered, each having its particular field of operation—pediculus

Fig. 312.                                      Fig. 313.                           Fig. 314.

Pediculus capitis.                      Pediculus corporis.              Pediculus pubis.

(Female; dorsal surface; X 25) (courtesy of Dr. L. A. Duhring).

capitis, pediculus corporis, and pediculus pubis. The first is found upon
the scalp region, and only accidentally and temporarily on other parts­;
the second has the general body surface, or in reality the clothing, as its
special habitat, while the pediculus pubis, especially the pubic region,
but also other parts where there are short stiff hairs, as the axillae, the
breast and leg hairs, the eyebrows, and the eyelashes. Only rarely do
these three parasites invade other than their own special regions named,¹
and then, as a rule, only accidentally and temporarily. Depending upon

¹ Grindon, “The Migration of Pediculi,” The Med. Fortnightly, March 15. 1893,
gives á few examples and cites others, with references.

1174

PARASITIC AFFECTIONS

this fact, three varieties of the malady are presented, named, according
to the parts involved, pediculosis capitis, pediculosis corporis, and pedic­
ulosis pubis.

In appearance, shape, and other features the head and body-lice
are practically alike, the former being from 1¹/₅ to 3¹/₅ mm. in length, or
averaging about one-third less in size than the latter, which varies from
1¹/₅ to 4¹/₅ mm. long. Upon the whole, clinical observation shows the body-
louse to be predominantly much the larger—much more so than these
figures would indicate. Their breadth is about, or a little less than,

half their length. The male is smaller than
the female; the sexual organ of the former
is on the dorsal surface, and consists of a
conic or wedge-shaped, protruding, and
relatively large structure; the vaginal open­
ing in the female is on the ventral surface.
These pediculi are of an elongate, ovalish
shape, having six strongly jointed legs
with stout claws coming off from the
thoracic portion; the longer abdominal
part shows laterally well-defined deep
notches. The rounded, acorn-shaped head,
somewhat ovalish in the body-louse, has
two prominent eyes and two antennae.
Both the head-louse and body-louse are
grayish in color, with blackish margins.
After feeding, the contained blood imbibed
gives the parasite a slight or decided red­
dish tinge, more noticeable, as a rule, in
the pediculus corporis. The pediculus
pubis, or crab-louse, averages much shorter
than either the head- or body-louse, the
thoracic and abdominal portions show
apparently no division, and the head seated
squarely upon the body. It varies in length
from 1 to 2¹/₁₀ mm., and is almost as broad
as it is long. In addition to the usual
number of jointed claws it has eight strong,.
teat-shaped, prehensile feet going off from
the margin of the abdomen. In color it
is grayish, with a yellow tinge, and is more or less translucent. In other
respects it is similar to the other varieties, except that there are no well-
defined notches laterally. The reproductive capacity of these parasites
is very great, from fifteen to twenty eggs for the pubic variety to fifty
or more for the others. The ova, or nits, are found attached to the hair-
shafts in the scalp and pubic varieties, and in the clothing and on the
lanugo hairs in pediculosis corporis. The ova are minute, dirty-white or
grayish-looking, pear-shaped bodies, visible to the naked eye, and glued
to the hair by a chitinous substance, with the projecting butt end point­
ing toward the distal end of the shaft. They hatch out within a week

Fig. 315.—Ova of the head-
louse attached to a hair (mag­
nified) (after Kaposi).

PEDICULOSIS

1175

and the young are sexually competent in less than two weeks more.
It can readily be seen how rapidly they multiply. While the parasites
cannot be said to be elective in the choice of subjects, yet some individ­
uals seem to be less desirable as hosts than others.

The symptoms produced by the parasites primarily or secondarily
vary within considerable limits, and this is not always necessarily de­
pendent upon the number present, but to some extent upon the irritabil­
ity of the skin and other individual factors. In marked examples of
pediculosis, owing to the constant irritation and itching, and sometimes
to the consequent disturbed sleep, the general health may be influenced.
In fact, in some instances there seems to be an appearance of impaired
nutrition, the skin being of a dingy, unhealthy color, and, especially in
the scalp variety, the hair dry and lifeless looking. This may possibly
be in a measure due to the absorption of some toxic substance from the
pediculi themselves, transferred when pricking the skin for nourishment.
At all events, the changed general appearance, the healthier tone of the
skin, and improved nutrition ensuing upon a cure of the malady are some­
times striking and scarcely otherwise explainable.

While the symptoms of pediculosis are to a great extent the same in
the three varieties of the malady, they are somewhat modified by the
locality invaded, and are therefore best described separately.

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