LICE
Lice are nonflying insects that live off the blood meal from a human host. They have been human pathogens for thousands of years and continue to cause millions of cases of disease annually. Three variants of the louse exist: the head louse, the body louse, and the pubic louse. For the most part, lice cause localized skin disease from the biting they do to secure their blood meal. However, some lice have been known to transmit other diseases to humans. The most important infectious agents transmitted by body lice are the bacteria that cause epidemic typhus, relapsing fever, and trench fever. These infections are uncommon in the United States and North America but are still seen, and one should be aware of their causes and vectors.
Clinical
Findings: Lice are capable of infesting any human, independent of age, sex, or
race. Body lice are seen more frequently in patients of low socioeconomic
status and especially in homeless individuals. Underlying mental health issues
in this subset may also predispose one to conditions that are opportune for
infestation. Pubic lice, or “crabs,” is a sexually transmitted disease that is
seen in younger adults more frequently than in other age groups; however, it
has been reported to occur in people all ages.
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| CLINICAL MANIFESTATIONS OF PUBIC LICE |
Pediculosis
capitis (head lice infestation) is probably the most common louse infestation
in North America and Europe. The louse, Pediculus humanus capitis, preferentially
locates to the scalp and lives between the hair shafts. These lice are
transmitted by close contact and from fomites such as combs, pillows, and head
rests. Patients complain of severe itching on the scalp and neck. On
inspection, small (1-2 mm), red, excoriated papules are seen. Evidence of
scratching becomes prominent as time goes on without a diagnosis. The diagnosis
is confirmed by finding a louse, which is typically 2 to 4 mm long and light
brown in color. On occasion, the abdomen of the louse can appear red, which is
the case directly after a blood meal. These insects are not particularly fast
moving, nor can they fly or jump; as a result, they are easy to capture and
identify. Egg sacks (nits) are firmly adhered to the hair. This is in contrast
to the common hair cast, which can easily be moved up and down the hair shaft
with minimal effort. The nits are laid in close proximity to the scalp, usually
within 0.5 mm. The nits hatch within 2 weeks. Therefore, nits found more than 2
cm from the scalp are often nonviable, and the larva has already emerged from
the nit. Persistent infections can lead to bacterial superinfection and
pyoderma with cervical adenopathy.
Pediculosis
pubis (pubic lice infestation) is a commonly acquired sexually transmitted
disease. The pubic louse, Phthirus pubis, is structurally different from
the body or head louse and can easily be distinguished. Patients complain of
itching and often note pinpoint drops of blood in their undergarments. This is
caused by small amounts of bleeding after the pubic lice feed. These lice have
specialized arms that allow them to climb around the entire human body, and
they may be seen at any location. They have a tendency to affect the eyelashes and eyebrows.
This is important to look for clinically, to appropriately treat all affected
regions.
Pediculosis
corporis (body lice infestation) is commonly seen in homeless individuals and
in those with poor hygiene. Historically, body lice have been associated with
epidemics during times of war, because close contact for extended periods leads
to easy transfer from one host to another. The body louse, Pediculus humanus
corporis, is indistinguishable from the head louse on inspection with the
naked eye. Entomologists trained in differentiating the species are capable of
discerning the two. Body lice live on the clothing and leave it to feast on
human blood. Patients present with multiple pruritic, red to pink, excoriated
papules anywhere on the body. On inspection of the skin, one typically will not
find lice. It is only with close inspection of the clothing or bedding material
that the infestation becomes apparent. Hundreds to thousands of lice may be present on the
clothing, particularly in small hiding spaces such as the seams. Along with the
lice, many eggs and larvae may be seen.
The body
louse has been shown to be a carrier of the bacterial agents that cause
relapsing fever, trench fever, and epidemic typhus: Borrelia recurrentis,
Bartonella quintana, and Rickettsia prowazekii, respectively. The
louse carries the bacteria within its gut.
B.
recurrentis is responsible for causing the disease relapsing fever. It is
transmitted from one human to another when the fecal material of a human body
louse gains entry into the bloodstream. This bacterium is unique in that it can
rearrange its surface proteins. This is believed to be the reason for the
relapsing and recurrent fevers: The host immune system reacts in a periodic
manner to the changing surface of the bacteria.
B.
quintana is
a bacterium that is transmitted through the feces of the louse. After a louse
defecates on a patient’s skin and the patient scratches, the stool and the
bacteria are implanted into the skin, which causes infection. Also, the louse
often bites after defecating and causes skin trauma that transfers the bacteria
into the skin. B. quintana is the etiologic agent of trench fever, bacillary
angiomatosis, and peliosis and has also been shown to cause endocarditis. B.
quintana infections are most commonly seen in patients who are infected
with the human immunodeficiency virus and in homeless individuals.
R.
prowazekii is an obligate intracellular parasite that is transmitted to humans
through the feces of the human body louse. The natural environmental reservoir
for this bacterium is the flying squirrel (Glaucomys volans). The
infected louse feeds on the human, and the fecal material that contains the R.
prowazekii bacteria is deposited into the fresh wound, allowing for
infectious transfer. This infection is most frequently seen during times of
war, when individuals are in close contact with one another for significant
periods. Signs and symptoms of epidemic typhus include fever, rash, pain,
delirium, and other constitutional symptoms.
Pathogenesis:
P.
humanus capitis affects humans and has a high propensity to infest the scalp. These lice
live on the host and periodically take a blood meal from the scalp or neck
area. In patients with very long hair, the blood meal may be taken from the
back or any area of skin that is in contact with the hair. The lice are able to
reproduce rapidly. The females, which are a bit larger than the males, lay eggs
that hatch and develop into adults capable of reproducing within 4 weeks.
Histology:
The
histological findings on skin biopsy are similar among all forms of louse
bites. Histological evaluation cannot differentiate a louse bite from any other
insect bite with certainty. Skin biopsies are rarely performed in these cases,
because the diagnosis is made clinically. Biopsy specimens show a nonspecific,
mixed superficial and deep inflammatory infiltrate with eosinophils. This may
suggest a bite reaction. Unlike tick bites or scabies, in which occasionally
tick parts or scabies mites are seen in a biopsy specimen, a biopsy from a
patient with a lice infestation will never show mouth parts or other elements of the louse.
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| CLINICAL FINDINGS AND MANAGEMENT OF LICE |
Therapy for
body lice also requires complete disinfection of the household or living areas.
Overtly infested clothing should be thrown away. Professional fumigation should
be considered.
