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Skin Diseases Caused by Arthropods
and Other Noxious Animals
Various cutaneous symptoms, including blistering and contact dermatitis, allergic reaction and secondary infection, are caused by arthropods. Pathogens transmitted by insects or other noxious animals may cause systemic
symptoms. Infestation by arthropods or insects may result in cutaneous symptoms, and various pathogens carried by arthropods and other noxious animals can infect humans.
A. Diseases caused by insects and other noxious animals
1. Insect bite
Insect bite is a general term for the dermatitis that is caused by
the bite or sting of a mosquito, gnat, horsefly, bee or other insect.
It is thought to be an allergic reaction to the salivary components
that the insect discharges while sucking blood or to the venom of
stings. The severity of the clinical symptoms depends largely on
the age of the patient and the severity of allergic reaction. Immediately after an insect bite, itching wheals or erythema appears.
There are two major clinical types of insect bites: those of immediate hypersensitivity, in which symptoms subside in 1 to 2
hours, and those of delayed hypersensitivity, in which erythema
or blistering may occur 1 to 2 days after a bite (Figs. 28.1-1 and
28.1-2). Treatments are topical steroid application for eruptions,
and oral antihistamines for itching lesions. A bee sting may cause
an anaphylactic reaction.
Clinical images are available in hardcopy only.
g
h
h
i
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Fig. 28.1-1 Insect bite.
a: Itching erythema on the lower leg. b: A tense
blister on the lower leg. c: Insect bite on the eyebrow. Severe edema occurred around the lesion.
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a
b
c
d
e
f
Clinical images are available in hardcopy only.
2. Hypersensitivity to mosquito bite
After a mosquito bite, an allergic reaction occurs against the
protein in the salivary components of the mosquito, sometimes
leading to systemic symptoms such as high fever, liver dysfunction and lymph node enlargement, and cutaneous symptomsa
including blistering. Later, swelling, induration, necrosis and
ulceration occur. During the course of hypersensitivity to mosquito bite, the histopathological symptoms may resemble those of
hydroa vacciniforme. Recent study has found the Epstein-Barr
virus (EBV) to be associated with hypersensitivity to mosquito
bite. Cases have proven the association between chronic EBV
infection and NK/T cell lymphoma.
a
MEMO
Flies lay eggs in necrotic tissue. Eggs and maggots are present at the
site, requiring curettage.
Myiasis
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b
b
c
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g
Clinical images are available in hardcopy only.
c
d
e
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Skin Diseases Caused by Arthropods and Other Noxious Animals
3. Caterpillar dermatitis
Clinical images are available in hardcopy only.
The urticating hairs of larval moths and butterflies (caterpillars) including those of the tussock moth, tea tussock moth and
browntail moth cause caterpillar dermatitis. The affected site has
tingling pain. Punctate, itching erythema is followed by a red
wheal (Fig. 28.2) that progresses to vesicles and papules.
4. Dermatitis linearis
Fig. 28.1-2 Insect bite.
Small, itching papules of about 5 mm in diameter
occur, most frequently on the lower legs.
The hemolymph of the beetle Paederus fuscipes Curtis comes
into contact with the skin, causing dermatitis linearis (Fig. 28.3).
Two to three days after contact, characteristic linear skin lesions,
reddening, vesicles, swelling, burning sensation and sharp pain
occur.
5. Scabies
Outline
● It
Clinical images are available in hardcopy only.
is an infestation caused by the mite Sarcoptes scabiei
var. hominis. Multiple papules occur. Intense itching is
present, worsening at night.
● The genitalia, trunk and interdigital areas are most frequently involved. It is characterized by “tunnels” (burrows) in the interdigital area.
● It may be transmitted by bedclothes or skin-to-skin contact. It often occurs as a STD or in-hospital epidemic.
● Benzyl benzoate, topical g -benzenehexachloride and
oral ivermectin are the main treatments.
Fig. 28.2 Caterpillar dermatitis.
Punctate, itching erythema occurs, accompanied
by pruritus and blistering in some areas of the
lesion.
Clinical images are available in hardcopy only.
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Fig. 28.3 Dermatitis linearis.
Clinical images are available in
hardcopy only.
Fig. 28.4-1 Scabies on the scrotum.
Scabies is characterized by small multiple nodules.
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A. Diseases caused by insects and other noxious animals
Clinical features
Small, multiple, light pink papules 2 mm to 5 mm in diameter
occur on the trunk, genitalia, thighs, inner arms and interdigital
areas (Figs. 28.4-1 and 28.4-2). Small nodules may form in the
genitalia and axillary fossae. Both the papules and nodules are
accompanied by intense itching that worsens when the skin is
warmed, such as at bedtime. Patients with scabies often complain
of difficulty of sleeping from itching. Scratching of the skin
lesions may lead to formation of eczematous plaques. When the
interdigital areas and palms are involved, there may be slightly
elevated, grayish-white linear lesions (mite burrows) several millimeters long where female insects lay eggs. Blistering occurs in
some cases (Fig. 28.4-2).
Pathogenesis
Scabies is an infestation in the epidermal horny cell layer by the
mite Sarcoptes (S.) scabiei var. hominis. This mite is ovoid and
has body dimensions of 0.4×0.3 mm for males and 0.2×0.15
mm for females, with 4 pairs of legs at the adult stage (Fig. 28.5).
A mated female forms a mite burrow in the horny cell layer and
lays 1 or 2 eggs daily there, dying in 4 to 5 weeks. Eggs incubate
for 3 to 5 days. S. scabiei var. hominis inhabits creases of the skin
or the hair follicles and grows to adult stage in 14 to 17 days.
Scabies infestation is caused by direct skin-to-skin contact or
indirect contact through bedclothes or clothing. The incubation
period is about 1 month. Scabies often occurs within a family and
at hospitals and eldercare homes. Infection may be direct, from
sexual transmission.
Norwegian (crusted) scabies is caused by a large number of S.
scabiei var. hominis in persons with poor nutrition, poor hygiene
or immunosuppression. Under such conditions, scabies is highly
contagious and may cause severe symptoms including generalized hyperkeratosis and crusts.
Diagnosis
When disseminated small papules accompanied by intense
itching are found on the trunk, mite burrows should be carefully
searched for in the interdigital areas. Multiple papules on the
genitalia, particularly on the scrotum or labia majora, should be
carefully examined. To confirm the diagnosis, a specimen including the horny cell layer is removed from the skin by pinching
with tweezers, scraping the skin with a scalpel, pricking with a
needle, or exfoliating with adhesive tape for direct identification
of the mite body or eggs by light microscopy. Inquiry on symptoms of scabies among the patient’s family members and partners, and history-taking on sexual activity are helpful.
Differential diagnosis
Insect bite, eczema and urticaria are differentiated from scabies. Mite burrows and the nodules on the genitalia are useful for
differentiation.
Clinical images are available in hardcopy only.
Clinical images are available in hardcopy only.
Fig. 28.4-2 Scabies on the hand and foot of
an elderly person.
Distinct blistering is present.
a
b
c
d
e
f
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b
c
d
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f
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Fig. 28.5 Sarcoptes scabiei var. hominis.
a: S. scabiei var. hominis has four pairs of legs. b:
Eggs of S. scabiei var. hominis.
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Skin Diseases Caused by Arthropods and Other Noxious Animals
Fig. 28.6 Eggs of the louse Phithilus pubis
on pubic hair.
Treatment
Topical application of ointments containing sulfur, crotamiton
and benzyl benzoate is helpful. Previously, g -BHC (benzene
hexachloride) was most commonly used in the U.S. and Europe.
It is important to apply the ointment to the entire body skin below
the neck of all family members and partners, regardless of
whether they are symptomatic. In recent years, oral ivermectin
has become available for use. It is extremely effective, requiring
only one administration a day. Antihistamines may be used, if
necessary. Thorough laundering and sun drying of bedclothes is
recommended.
6. Pediculosis
Definition, Classification
Allergic reaction is induced by a louse that parasitizes human
skin to suck blood, causing intense itching. Lice are host-specific
and spend their entire life on the host. The three main causative
lice of pediculosis are Pediculus capitis (head lice, 2 mm to 4
mm long, inhabiting head hair), Pediculus humanus (clothing or
body lice, 2 mm to 4 mm long, inhabiting clothing), and Pthirus
pubis (pubic or crab lice, 1 mm long, inhabiting pubic hair; Figs.
28.6 and 28.7). It is impossible to distinguish between Pediculus
capitis and Pediculus humanus by appearance.
Fig. 28.7 Pediculosis.
Clinical features
A louse parasitizes a hair shaft and lays eggs on the hair. The
eggs incubate for about 1 week. The lice mature and suck human
blood. In most cases, intense itching begins 1 to 2 months after
infection. Eruptions do not usually occur.
a
b
c
d
e
f
g
Clinical images are available in hardcopy only.
a
b
c
d
e
f
g
h
Fig. 28.8-1 A tick bite.
a: Shoulder 2 hours after the bite. The legs of the
tick are still moving (the patient is Hiroshi
Shimizu, the author of this textbook). b: A tick
bite on the eyelid.
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Pathogenesis
Pediculus capitis infestation may become epidemic among
p
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m at schools
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schoolchildren
during kgroup activities
oro daycare centers. Pthirus pubis infestation is caused most frequently by sexual
intercourse. The eyebrows are involved in rare cases. Pediculus
humanus infestation is epidemic among individuals under environments with poor hygiene, such as in the homeless.
Diagnosis, Treatment
Itching on the head or genitalia is the main complaint of a
p
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o important
patient,
is m
suspected.
toqsearchr
for lice and eggs attached to the hair. Phenothrin shampoos and
Skin diseases caused by jellyfish,
coral and sea anemones
MEMO
An eruption may be caused by the sting of jellyfish, coral or sea
anemones in the ocean. Some marine organisms sting humans with the
nematocysts on their tentacles or otherwise injure human skin by contact. Systemic symptoms may be severe.
r
503
B. Skin diseases transmitted by insects and other animals
powders are helpful treatments. The family members and sexual
partners are also treated to avoid “ping-pong” infestation, in
which the disease repeatedly rebounds from untreated to treated
persons.
Clinical images are available in hardcopy only.
7. Tick bite
Clinical features
a
b
Tick bite is caused by ixodid (hard) ticks. Because ticks of the
family Ixodidae tend not to be felt when crawling on human skin,
they are able to attach insidiously to the face, arms or even the
trunk or genitals of humans (Figs. 28.8-1 and 28.8-2). The bite
tends to be painless. The main symptoms are inflammation
around the bite, erythema, edematous swelling, bleeding and blistering. The mouthpart is firmly fixed in the skin while sucking
blood; a tick bite is often found when the complaint has been a
wart or skin tumor. A tick that has sucked its fill of blood falls
naturally from the skin. Borrelia spirochetes may be transmitted
by a tick bite, leading to Lyme disease (described later).
Pathogenesis
Ixodidae are 2 mm to 8 mm long (Fig. 28.9) and tend to inhabit grasslands or woods. They burrow into the skin of humans and
animals to suck blood.
c
d
e
f
g
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Fig. 28.8 A tick bite.
c: A tick on the neck.
Fig. 28.9 An ixodid tick removed from human
skin.
It is generally 5 mm to 8 mm long.
Treatment
If a tick is forcefully pulled while sucking blood, it may tear,
leaving the mouthpart in the skin. This can lead to foreign-body
granuloma. The whole tick, including the mouthpart, should be
removed by either inserting scissors into the bite spot or punching the site out with the tick attached. Oral administration of
tetracycline 1 week after removal is advised as a prophylactic
against Lyme disease.
B. Skin diseases transmitted by insects and other animals
Table 28.1 Classification of Borrelia species.
is an infection caused by the spirochete bacteria Borrelia burgdorferi sensu lato, transmitted by ticks of the family Ixodidae.
● It occurs most frequently in USA, Scandinavia and central Europe, during spring and summer.
● It begins as erythema chronicum migrans (first stage)
and progresses to arthritis and cerebral meningitis (second stage) and then to dysfunction of the joints and central
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" "!
B. burgdorferi
B. burgdorferi sensu lato B. garinii
B. afzelii
Outline
● It
!
1. Lyme disease
Borrelia
Other Borrelia species
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