ARTHROPODS OF
MEDICAL
IMPORTANCE
Arthropods (2 hours)
• 1. Defines “Arthropod’’
• 1.1 Lists the arthropod classification.
• 2. Lists the clinical tables related with arthropods
• 2.1. Defines the cklinical importance of arthropodsi.
• 2.2. Lists the prevention methods from arthropods.
• 2.3. Lists the laboratory diagnostic methods.
ARTHROPODA
Arachnidia
 Diplopoda
 Chilopoda
 Insecta
 Crustacea
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Myriapoda/Centipedes
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The centipedes are elongated,
multisegmented (15 to more than 181
segments), many-legged, tracheate
arthropods.
They possess a distinct head and trunk.
The body is dorsoventrally flattened, and
each trunk segment bears a single pair of
legs.
Maxillipeds or poison claws are situated on
the first segment and are used for capturing
prey.
commonly found in dark, damp
environments such as the areas
beneath logs, among rubbish, and
inside old buildings.
 Human bites are almost invariably the
result of accidental exposure to the
organism during outdoor activities.
 Centipede bites may be extremely
painful and cause swelling at the site of
the bite.
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Pentastomida/
Tongue Worms
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The pentastomids, or tongue worms, are
bloodsucking endoparasites of reptiles, birds,
and mammals.
Many vertebrates, including humans, may
serve as intermediate hosts.
contaminate vegetation or water, which is in
turn ingested by one of several possible
intermediate hosts (fish, rodents, goats,
sheep, or humans).
Humans may also become infected by
ingesting the inadequately cooked flesh
of infected reptiles or other definitive
hosts or by eating the infected flesh of
intermediate hosts (e.g., goats, sheep)
containing infective larvae.
 In this case, the human host is
considered a temporary definitive host.
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the infection is acquired by ingesting
raw vegetables or water contaminated
with pentastome eggs or by consuming
raw or undercooked flesh of infected
animals.
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Treatment is not usually warranted.
Crustacea/
Copepods,Decapods
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The crustaceans are primarily gill-breathing
arthropods of fresh and salt water.
found in fresh water and serve as intermediate hosts
of various worms
Copepods
 small, simple aquatic organisms. They lack a
carapace, have one pair of maxillae, and have five
pairs of biramous swimming legs. Free and parasitic
forms exist. The genera Diaptomus and Cyclops are
medically important.
intermediate host in the life cycle of several
human parasites, including
Dracunculus medinensis (dracunculiasis),
Diphyllobothrium latum (diphyllobothriasis),
 Copepods have a worldwide distribution
 the chlorination and filtration of water and
thorough cooking of all fish.
 Infected people must not be allowed to
bathe in water used for drinking, and
suspected water should be avoided.
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Decapods
include the prawns, shrimps,
lobsters, crayfish, and crabs.
 Crabs and crayfish are medically
important as the second
intermediate hosts of the
lung flukeP. westermani.
 Thorough cooking of crabs
and crayfish is the most effective
means of preventing infection with P.
westermani.
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Chelicerata
(Arachnida)
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Spiders
characteristic features that permit easy identification.
Specifically, they possess eight legs, no antennae, a body
divided into two regions (cephalothorax and abdomen), and an
unsegmented abdomen with spinnerets posteriorly. All true
spiders produce venom and kill their prey by biting
Venomous spiders may be classified as those that cause
systemic arachnidism and those that cause necrotic
arachnidism.
Systemic arachnidism is primarily caused by tarantulas and
black widow spiders.
Tarantulas (family Theraphosidae) are large, hairy spiders of
the tropics and subtropics. The tarantulas are of little
importance because they are not very aggressive and avoid
human habitations.
The black widow spider, Latrodectus mactans, is widespread
through the southern and western United States.
 Related species of Latrodectus are found throughout temperate
and tropical regions of all continents, but none is primarily
domestic; thus their contact with humans is limited.
Black Widow Spiders
 The female black widow spider (L. mactans) is easily
recognized by the presence of a globose, shiny, black abdomen
bearing the characteristic orange or reddish hourglass marking
on the ventral surface. The venom of the black widow spider is
a potent peripheral neurotoxin
 Only the female Latrodectus spider is dangerous to humans;
the small, feeble male delivers an ineffective bite.
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These spiders frequent wood and brush piles, old
wooden buildings, cellars, hollow logs, and privies.
Given these locations, the bite is often located on
the genitalia, buttocks, or extremities.
Healthy adults usually recover, but
small children or weakened people
suffer considerably from these bites
and may die without treatment.
Muscle spasms may be severe and may
require the intravenous administration
of calcium gluconate or other muscle
relaxant agents.
 A specific antivenin is available and
remains the treatment of choice. It is
valuable if given shortly after the bite.
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Brown Recluse Spiders
 Spiders producing necrotic arachnidism belong to the
genus Loxosceles. These spiders are yellow to brown
and are of medium size (5 to 10 mm long) with
relatively long legs. They commonly display two
distinguishing characteristics: a dark fiddle- or violinshaped marking on the dorsal side of the
cephalothorax, and six eyes arranged in three pairs
forming a semicircle.
 The venom injected by the female or male spider is
a necrotoxin (that may also have hemolytic
properties) and causes necrotic lesions with deep
tissue damage. Humans are bitten only when the
spider is threatened or disturbed.
Initially, the bite of Loxosceles species tends
to be painless; however, several hours later,
itching, swelling, and soreness may develop
in the area of the bite.
 Intravascular coagulation and hemolysis may
occur and be accompanied by
hemoglobinuria and cardiac and renal failure.
This hemolytic syndrome may be life
threatening and occurs more commonly after
the bite of L. laeta. In South America, this
syndrome is known as visceral
loxoscelism.
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Cleansing the bite wound and providing
tetanus prophylaxis and antibiotics to
prevent secondary infection may all be
indicated.
 Healing is generally uncomplicated, and
debridement or excision should not be
performed for 3 to 6 weeks to allow
natural healing to commence.
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Excision and skin grafting may be necessary
for bites that have not healed in 6 to 8
weeks.
Systemic therapy with corticosteroids may be
useful in treating the hemolytic syndrome
Preventive measures are similar to those
recommended for black widow spiders.
Loxosceles (and other) spiders may be
controlled in dwellings with insecticide
compounds.
Scorpions
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The typical scorpion is elongated with conspicuous,
pincher-like claws (or pedipalps) at the anterior
end of the body, four pairs of walking legs, and a
distinctly regimented abdomen that tapers to a
curved, hollow, needle-like stinger.
When the scorpion is disturbed, it uses the stinger
for defense. Both male and female scorpions can
sting. Venom is injected through the stinger from
two venom glands in the abdomen. Most scorpions
are unable to penetrate human skin or inject enough
venom to cause real damage; however, a few
species are capable of inflicting painful wounds that
may cause death.
 Children
under the age of 5 years are
most likely to be fatally stung by
scorpions.
 Scorpions are nocturnal, and during the
day they remain concealed under logs,
rocks, and other dark, moist places.
They invade human habitations at
night, where they may hide in shoes,
towels, clothing, and closets.
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The effect of a scorpion sting in a patient is highly variable and
depends on factors such as the species and age of the
scorpion, the kind and amount of venom injected, and the age,
size, and sensitivity of the person who was stung.
Although the sting of many scorpions is relatively nontoxic and
produces only local symptoms, other stings may be quite
serious.
Scorpions produce two types of venom: a neurotoxin and a
hemorrhagic or hemolytic toxin. The hemolytic toxin is
responsible for local reactions at the site of the sting, including
radiating, burning pain; swelling; discoloration; and necrosis.
The neurotoxin produces minimal local reaction but rather
severe systemic effects, including chills, diaphoresis, excessive
salivation, difficulty speaking and swallowing, muscle spasm,
tachycardia, and generalized seizures. In severe cases, death
may result from pulmonary edema and respiratory paralysis.
Local or systemic signs and symptoms
coupled with physical evidence of a
single point of skin penetration are
usually sufficient to establish the
diagnosis.
 An entomologist or parasitologist
should be consulted if there is a
taxonomic question.
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The management of scorpion stings varies.
In the absence of systemic symptoms,
palliative treatment may be all that is
necessary. Pain may be relieved by
analgesics or local injection of Xylocaine;
however, opiates appear to increase toxicity.
Local cryotherapy may reduce swelling and
retard the systemic absorption of the toxin.
Hot packs produce vasodilatation and may
accelerate toxin distribution systemically and
are therefore contraindicated.
Antivenin is available and is effective if
administered soon after the sting. Very
young children with systemic symptoms
should be treated as medical
emergencies. Systemic symptoms and
shock should be treated supportively.
 The use of chemical pesticides to
reduce scorpion populations. Removal
of debris around dwellings can reduce
hiding and breeding places.
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Mites
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small, eight-legged arthropods characterized by a
saclike body and no antennae. A large number of
mite species are free-living or are normally
associated with other vertebrates (e.g., birds,
rodents) and may cause dermatitis in humans on
rare occasions.
The number of mites that are considered true human
parasites or present real medical problems is quite
small and include the human itch mite (Sarcoptes
scabiei), the human follicle mite (Demodex
folliculorum), and the chigger mite.
Mites affect humans in three ways: by causing
dermatitis, by serving as vectors of infectious
diseases, and by acting as a source of allergens.
The itch mite (S. scabiei)
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causes an infectious skin disease variably known as scabies,
mange, or the itch. The adult mites average 300 to 400 μm
in length with an oval, saclike body in which the first and
second pairs of legs are widely separated from the third and
fourth pairs. The body has dorsal transverse parallel ridges,
spines, and hairs. The ova measure 100 to 150 μm.
Adult mites enter the skin, creating serpiginous burrows in the
upper layers of the epidermis. The female mite lays her eggs in
the skin burrows, and the larval and nymph stages that develop
also burrow in the skin. The female mites live and deposit eggs
and feces in epidermal burrows for up to 2 months.
Characteristically, the preferred sites of infestation are the
interdigital and popliteal folds, the wrist and inguinal regions,
and the inframammary folds. The presence of the mites and
their secretions cause intense itching of the involved areas. The
mite is an obligate parasite and can perpetuate itself in a single
host indefinitely.
Scabies
 is cosmopolitan in distribution, with an estimated global
prevalence of about 300 million cases. The mite is an obligate
parasite of domestic animals and humans; however, it may
survive for hours to days away from the host, thus facilitating
its spread.
 Transmission is accomplished by direct contact or by contact
with contaminated objects such as clothing.
 Sexual transmission has been well documented. Spread of the
infection to other areas of the body is accomplished by
scratching and manual transfer of the mite by the affected
person.
 Scabies may occur in epidemic fashion among people in
crowded conditions such as daycare centers, nursing homes,
military camps, and prisons.
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The outstanding clinical diagnostic symptom is intense itching,
usually in the interdigital folds and sides of the fingers,
buttocks, external genitalia, wrists, and elbows. The
uncomplicated lesions appear as short, slightly raised
cutaneous burrows.
At the end of the burrow, there is frequently a vesicle
containing the female mite. The intense pruritus usually leads
to excoriation of the skin secondary to scratching, which in turn
produces crusts and secondary bacterial infection.
Patients experience their first symptoms within weeks to
months after exposure; however, the incubation period may be
as little as 1 to 4 days in persons sensitized by prior exposure.
Host hypersensitivity (delayed or type IV) probably plays an
important role in determining the variable clinical
manifestations of scabies.
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Some immunodeficient people may develop a variant of
scabies, so-called Norwegian scabies, characterized by
generalized dermatitis with extensive scaling and crusting and
the presence of thousands of mites in the epidermis. This
disease is highly contagious and suggests that host immunity
also plays a role in suppressing S. scabiei.
The clinical diagnosis of scabies is based on the characteristic
lesions and their distribution. The definitive diagnosis of scabies
depends on the demonstration of the mite in skin scrapings.
Because the adult mite is most frequently found in the terminal
portions of a fresh burrow, it is best to make scrapings in these
areas.
The scrapings are placed on a clean microscope slide, cleared
by the addition of 1 or 2 drops of a 20% solution of potassium
hydroxide, covered with a coverslip, and examined under a
low-power microscope. With experience, the mite and ova may
be recognized. Skin biopsy may also reveal the mites and ova
in tissue sections.
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The standard, and very effective, treatment for
scabies is 1% gamma benzene hexachloride
(lindane) in a lotion base. One or two applications
(head to toe) at weekly intervals is effective against
scabies. Lindane is absorbed through the skin, and
repeated applications may be toxic. For this reason,
it is not advisable to use it in treating infants, small
children, or pregnant or lactating women.
Recently, a 5% permethrin cream (Elimite) has
replaced lindane lotions as the treatment of choice
for scabies. Clinical trials have shown permethrin to
be more effective and less toxic than lindane.
Other preparations used to treat scabies include
crotamiton sulfur (6%) preparations, benzyl
benzoate, and tetraethylthiuram monosulfide.
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Primary prevention of scabies is best achieved with
good hygiene habits, personal cleanliness, and
routine washing of clothing and bed linens.
Secondary prevention includes the identification and
treatment of infected people and possibly their
household and sexual contacts. In an epidemic
situation, simultaneous treatment of all affected
people and their contacts may be necessary. This is
followed by thorough cleansing of the environment
(e.g., boiling clothing and linens) and ongoing
surveillance to prevent re-occurrence.
Human Follicle Mites
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include two species of the genus Demodex, D. folliculorum and
D. brevis. These mites are minute (0.1 to 0.4 mm) organisms
with a wormlike body, four pairs of stubby legs, and an
annulate abdomen.
D. folliculorum parasitizes the hair follicles of the face of most
adult humans, whereas D. brevis is found in the sebaceous
glands of the head and trunk. Infestations are uncommon in
young children and increase at the time of puberty. It is
estimated that 50% to 100% of adults are infested with these
mites.
The role of Demodex species in human disease is uncertain.
They have been associated with acne, blackheads, blepharitis,
abnormalities of the scalp, and truncal rashes. More recently,
extensive papular folliculitis resulting from Demodex infestation
has been described in people with acquired immunodeficiency.
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Factors such as poor personal hygiene, increased
sebum production, mite hypersensitivity, and
immunosuppression may increase host susceptibility
and enhance the clinical presentation of Demodex
infestation. Most people infested with these mites
remain asymptomatic.
Mites may be demonstrated microscopically in
material expressed from an infested follicle. They
may be seen as incidental findings in histologic
sections of facial skin.
Effective treatment consists of a single application of
1% gamma benzene hexachloride.
Chigger Mites
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the larvae of mites of the family Trombiculidae. The adult trombiculid
mites infest grass and bushes, and their larvae (i.e., chiggers) attack
humans and other vertebrates, producing severe dermatitis. The
larvae have three pairs of legs and are covered with characteristic
branched, featherlike hairs.
The larvae appear as minute, barely visible, reddish dots attached to
the skin, where they use their hooked mouth parts to ingest tissue
fluids. Chiggers typically attach to the skin areas where clothing is
tight or restricted such as the wrists, ankles, armpits, groin, and
waistline.
Chiggers are a particular problem for outdoor enthusiasts such as
campers and picnickers. In Europe and the Americas, they are
associated with intensely pruritic lesions; however, in Asia, Australia,
and the western Pacific rim, they serve as vectors of the rickettsial
disease scrub typhus or tsutsugamushi fever (Rickettsia
tsutsugamushi)
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Saliva injected into the skin at the time of mite
attachment produces an intense pruritus and
dermatitis. The skin lesions appear as small
erythematous marks that progress to papules and
may persist for weeks. Mite larvae may be visible in
the center of the reddened, swollen area. The
irritation may be so severe that it causes fever and
sleep disruption. Secondary bacterial infection of the
excoriated lesions may occur.
Treatment for dermatitis caused by chiggers is
largely symptomatic and consists of antipruritics,
antihistamines, and steroids. The use of insect
repellents such as N,N-9-diethyl-m-toluamide (DEET)
may be of some help in prevention for persons going
into chigger-infested areas
Ticks
bloodsucking ectoparasites of a number of
vertebrates, including humans.
 opportunistic rather than host specific and
tend to suck blood from a number of large
and small animals.
 four-stage life cycle that includes the egg,
larva, nymph, and adult. Although the larva,
nymph, and adults are all bloodsuckers, it is
the adult tick that usually bites humans.
 comprise two large families, the Ixodidae, or
hard ticks, and the Argasidae, or soft ticks.
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Soft ticks have a leathery body that lacks a hard
dorsal scutum, and the mouthparts are located
ventrally and are not visible from above.
Hard ticks have a hard dorsal plate or scutum, and
the mouthparts are clearly visible from above.
Soft ticks differ from hard ticks primarily in their
feeding behavior.
Soft ticks complete engorgement in a matter of
minutes or at most a few hours; hard ticks feed
slowly, taking 7 to 9 days to become engorged.
Hard tick
 Rocky Mountain spotted fever (Dermacentor species), tularemia
(Dermacentor species), Q fever (Dermacentor species), Lyme disease
(Ixodes species), babesiosis (Ixodes species), and ehrlichiosis (D.
variabilis and A. americanum)
Soft ticks
 of the genus Ornithodoros transmit relapsing fever spirochetes
(Borrelia species) in limited areas in the West. In general, people at
risk for tick exposure are involved in outdoor activities in wooded
areas. Tick exposure may also occur during stays in rural cabins
inhabited by small rodents, which commonly serve as hosts for ticks
and other ectoparasites.
 Tick bites are generally of minor consequence and are limited to small
erythematous papules. More serious consequences of tick bite include
the development of a type of paralysis resulting from substances
released by ticks during feeding and transmission of a number of
rickettsial, bacterial, viral, spirochetal, and protozoan diseases of
humans and other animals.
Ticks may attach at any point on the body
but typically favor the scalp, hairline, ears,
axillae, and groin. The initial bite is usually
painless, and the presence of the tick may
not be detected for several hours after
contact.
 After the tick has dropped off or has been
removed manually, the area may become
reddened, painful, and pruritic. The wound
may become secondarily infected and
necrotic, particularly if the mouthparts
remain attached after manual removal
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Three species of tick, D. andersoni, D. variabilis, and A.
americanum, have all been reported to cause tick paralysis.
This is characterized by an ascending flaccid paralysis, fever,
and general intoxication, which may lead to respiratory
compromise and death. The paralysis is due to toxic substances
released in the saliva of the tick and may be reversed by tick
removal. Tick paralysis is observed more commonly in young
children and when tick attachment is in opposition to the
central nervous system (e.g., scalp, head, neck).
Ticks are also involved in the transmission of infections such as
Lyme disease, Rocky Mountain spotted fever, ehrlichiosis,
Colorado tick fever, relapsing fever, tularemia, Q fever, and
babesiosis. The identification of an organism as an adult tick is
usually straightforward and based on the observations of an
organism that is dorsoventrally flattened and possesses four
pairs of legs and no visible segmentation
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An entomologist or parasitologist should be consulted if further
identification is desired.
Treatment, Prevention, and Control
Early removal of attached ticks is of primary importance and may be
accomplished by steady traction on the tick body, grasped with
forceps as close to the skin as possible.
Care should be taken to avoid twisting or crushing the tick, which may
leave the mouthparts attached to the skin or inject potentially
infectious material into the wound.
Because ticks may harbor highly infectious agents, the clinician should
use appropriate infection-control precautions (e.g., use of gloves,
handwashing, proper disposal of ticks and contaminated material)
during tick removal.
Preventive measures used in tick-infested areas include the wearing of
protective clothing that fits snugly about the ankles, wrists, waist, and
neck so that ticks cannot gain access to the skin. Insect repellents
such as N,N-9-diethyl-m-toluamide (DEET) are generally effective.
People and pets should be inspected for ticks after visits to tickinfested areas.
Insecta
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The insects, or hexapods, constitute the largest and most important
of all the classes of arthropods, accounting for approximately 70% of
all known species of animals. Insects include animals such as
mosquitoes, flies, fleas, lice, roaches, bees, wasps, beetles, and moths
to name just a few.
The insect body is divided into three parts-head, thorax, and
abdomen-and is equipped with one pair of antennae, three pairs of
appendages, and one or two pairs of wings or no wings at all. The
medical significance of any insect is related to its way of life,
particularly its mouthparts and feeding habits.
Insects may serve as vectors for a number of bacterial, viral,
protozoan, and metazoan pathogens. Certain insects may serve
merely as mechanical vectors for the transmission of pathogens,
whereas in other insects the pathogens undergo multiplication or cyclic
development within the insect host.
Insects can also be pathogens themselves by causing mechanical
injury through bites, chemical injury through the injection of toxins,
and allergic reactions to materials transmitted by bites or stings.
Bloodsucking Diptera
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All dipterans have a single pair of functional membranous
wings and various modifications of the mouthparts, which have
been adapted for piercing the skin and sucking blood or tissue
juices. Their most important feature is their role as mechanical
or biologic vectors of a number of infectious diseases, including
leishmaniasis, trypanosomiasis, malaria, filariasis,
onchocerciasis, tularemia, bartonellosis, and the viral
encephalitides.
The bloodsucking flies include mosquitoes, sand flies, and
blackflies, all of which are capable of transmitting diseases to
humans. Other dipterans, such as horse flies and stable flies,
are capable of inflicting painful bites but are not known to
transmit human pathogens.
Although the common housefly does not bite, it certainly is
capable of mechanical transmission of a number of viral,
bacterial, and protozoan infections to human hosts.
Mosquitoes
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Adult mosquitoes are small and have delicate legs, one pair of wings,
long antennae, and greatly elongated mouthparts adapted for piercing
and sucking. The two major families of mosquitoes (Culicidae), the
Anophelinae and the Culicinae, share a number of similarities in their
life cycles and development.
They lay eggs on or near water, are good fliers, and feed on nectar
and sugars. The females of most species also feed on blood, which
they require for each clutch of 100 to 200 eggs. Females may take a
blood meal every 2 to 4 days. In the act of feeding, the female
mosquito injects saliva, which produces mechanical damage to the
host but also may transmit disease and produce immediate and
delayed immune reactions.
the genus Anopheles contains the species responsible for the
transmission of human malaria. In the tropics, these mosquitoes breed
continually in relation to rainfall. A. aegypti, the yellow fever mosquito,
usually breeds in man-made containers (flower pots, gutters, cans)
and is the primary vector of yellow fever and dengue in urban
environments throughout the world. Body_ID:
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The bite is usually followed within a few minutes by
a small, flat weal surrounded by a red flare. The
delayed reaction consists of itching, swelling, and
reddening of the wound region. Secondary infection
may follow as a result of scratching.
Medical attention is usually not sought for a bite
unless secondary infection occurs. Local anesthetics
or antihistamines may be useful in treating reactions
to mosquito bites.
Preventive measures in mosquito-infested areas
include the use of window screens, netting, and
protective clothing. Insect repellents such as DEET
are generally effective. Mosquito-control measures
that involve the use of insecticides have been
effective in some areas.
Gnats and Biting Midges
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Ceratopogonids represent an assortment of tiny flies with
names such as gnats, midges, and punkies. The majority of
the flies that attack humans belong to the genus Culicoides;
they are minute (0.5 to 4 mm long) and slender enough to pass
through the fine mesh of ordinary window screens. The
females suck blood and typically feed at dusk, when they may
attack in large numbers.
Biting midges may be important pests in beach and resort
areas near salt marshes. Those of the genus Culicoides are the
main vectors of filariasis in Africa and the New World tropics.
The mouthparts of biting midges are lancet-like and produce a
painful bite. Bites may produce local lesions lasting hours or
days.
Local treatment is palliative, with lotions, anesthetics, and
antiseptic measures. The treatment of breeding sites with
pesticides and repellents may be useful against some of the
common species of these pests.
Sand flies
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Sand flies, or moth flies, belong to a single subfamily of the
Psychodidae, the Phlebotominae. They are small (1 to 3 mm),
delicate, hairy, weak-flying insects that suck the blood of
humans, dogs, and rodents. They transmit a number of
infections, including leishmaniasis. Female flies become
infected when they feed on infected people.
Phlebotomine larvae develop in nonaquatic habitats such as
moist soil, stone walls, and rubbish heaps. In many areas, sand
flies cause problems as pests. They also serve as vectors of
infectious diseases such as leishmaniasis in the Mediterranean,
the Middle East, Asia, India, and Latin America.
The bite may be painful and pruritic around the local lesion.
Sensitized people may have allergic reactions. Sand fly fever
is characterized by severe frontal headaches, malaise, retroorbital pain, anorexia, and nausea.
very sensitive to insecticides, which should be applied to
breeding sites and window screens. Various insect repellents
may also be useful.
Blackflies
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Members of the family Simuliidae are commonly called
blackflies or buffalo gnats. They are 1 to 5 mm long, are
humpbacked, and have mouthparts consisting of six "blades"
that are capable of tearing skin
Blackflies are bloodsucking insects and breed in fast-flowing
streams and rivers. They are of major importance as vectors of
onchocerciasis. m species), the vector of onchocerciasis.
Blackflies are common in Africa and South America, where they
serve as vectors of onchocerciasis. In North America, they are
common around the lake regions of Canada and the northern
United States. They are pests to hunters and fisherman in
these areas. In large numbers, they may cause significant
blood loss and pose a major threat to wild and domestic
animals.
The bite is painful and accompanied by local inflammation,
itching, and swelling.
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The local reaction may also be accompanied by a systemic
response that varies according to the number of bites and the
sensitivity of the person. This syndrome is known as blackfly
fever and is marked by headache, fever, and adenitis. It
usually subsides within 48 hours and is considered a
hypersensitivity reaction to the salivary secretions of the fly.
a hemorrhagic syndrome has been described after bites of
blackflies in certain areas of Brazil. This syndrome resembles
thrombocytopenic purpura and is characterized by local and
disseminated cutaneous hemorrhages associated with mucosal
bleeding.
the usual palliative measures (e.g., anesthetics, antihistamines,
lotions) to relieve local pruritus and swelling. Patients with the
hemorrhagic syndrome have shown marked improvement with
corticosteroid therapy.
Preventive measures include protective clothing. In general,
insect repellents are ineffective against blackflies. Some control
is achieved by pouring insecticides into rivers and streams.
Horse and Deer Flies
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They are large, ranging in length from 7 to 30 mm. The males feed on
plant juices, the females on blood. In the act of biting, the female fly
leaves a deep wound, causing blood to flow, which the fly laps up.
The fly may serve as a mechanical vector of infectious diseases when
the fly's mouthparts become contaminated on one host and transfer
organisms to the next. These flies are not considered important
vectors of infectious disease in humans.
the housefly, Musca domestica; the stable fly, Stomoxys calcitrans;
and the tsetse flies of the genus Glossina. The stable fly, often
mistaken for the housefly, is a true bloodsucker capable of serving as
a short-term mechanical vector of a number of bacterial, viral, and
protozoal infections. The tsetse fly is also a biting fly and serves as the
biologic vector and intermediate host for the agents of African
trypanosomiasis, Trypanosoma brucei rhodesiense and T. b.
gambiense.
The common housefly represents a host of genera that are
nonpiercing or contaminating flies. Because of their living and feeding
habits, they mechanically transmit diverse agents to humans.
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The tsetse fly is found in the eastern and central
regions of Africa, where it is of major medical and
veterinary importance as the intermediate host and
biologic vector of a number of trypanosomes that
infect humans and animals. The housefly and stable
fly are cosmopolitan in distribution and serve as
indicators of poor sanitation.
problematic because of their widespread distribution
in primarily rural and undeveloped areas. Insect
repellents and insecticides may be effective against
adult flies. Improved sanitation is important in
controlling houseflies.
Myiasis-Causing Flies
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Myiasis is the term applied to the disease produced by maggots that
live parasitically in human tissues. Clinically, myiasis may be classified
according to the body part involved (e.g., nasal, intestinal, or urinary
myiasis). The number of myiasis-producing flies and the diversity in
lifestyle requirements are enormous.
Only the host relations and sites of predilection of some of the more
important species are covered in this section.
One important example is the human botfly, Dermatobia hominis,
which is found in the humid regions of Mexico and Central and South
America. The adult botfly attaches her eggs to the abdomen of
bloodsucking flies or mosquitoes, which in turn distribute the eggs
while obtaining a blood meal from an animal or human.
The larvae enter the skin through the wound created by the biting
insect. The larvae develop over 40 to 50 days, during which time a
painful lesion known as a warble appears. When the larvae reach
maturity, they leave the host to pupate. The resulting lesion may take
weeks to months to heal and may become secondarily infected. If the
larva dies before leaving the skin, an abscess forms.
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Semispecific myiasis is caused by flies
that normally lay their eggs on decaying
animal or plant matter; it develops in a host
if entry is facilitated by the presence of
wounds or sores. Representatives of this
group include the greenbottle fly, Phaenicia;
bluebottle flies, Cochliomyia; and blackbottle
flies, Phormia.
These flies are worldwide in distribution, and
their presence is encouraged by poor
sanitation. T
hey occasionally lay their eggs on the open
sores or wounds of animal and humans.
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Another group that causes myiasis in humans is the
flesh flies, or sarcophagids. These flies have a
worldwide distribution and normally breed in
decomposing matter. They may deposit their larvae
on foods that, if ingested, may serve as a source of
infection.
Flies that produce accidental myiasis have no
requirement for development in a host. Accidental
infection may occur when eggs are deposited on oral
or genitourinary openings and the resulting larvae
gain entry into the intestinal or genitourinary tract.
Flies that may produce accidental myiasis include M.
domestica, the common housefly.
Sucking Lice Body
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only the body louse is important in medicine as the vector of the rickettsia of
typhus and trench fevers and the vector of the spirochetes of relapsing fever
The body louse, Pediculus humanus, and the head louse, P. humanus
capitis, are elongated, wingless, flattened insects with three pairs of legs and
mouthpieces adapted for piercing flesh and sucking blood
The pubic or crab louse, Phthirus pubis, has a short, crablike abdomen with
clawed second and third legs.
Epidemics of head lice are reported frequently in the United States, particularly
among school children. The head lice inhabit the hairs of the head and are
transmitted by physical contact or sharing of hair brushes or hats. Crab lice
survive on blood meals around the hairs of the pubic and perianal areas of the
body.
They are transmitted frequently from one person to another by sexual contact
and contaminated toilet seats or clothing. Body lice are usually found on
clothing. Unlike head or crab lice, they move to the body for feeding and return
to the clothing after obtaining a blood meal. All of the lice inject salivary fluids
into the body during the ingestion of blood, which causes varying degrees of
sensitization in the human host.
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Intense itching is the usual characteristic of infestation by lice (pediculosis).
The patient may have pruritic, red papules around the ears, face, neck, or
shoulders. Secondary infection and regional adenopathy may be present.
The eggs, or nits, are white, round objects that may be found attached to the
hair shafts (head and crab lice) or on clothing (body lice).
Gamma benzene hexachloride (lindane) lotion applied to the entire body and
left on for 24 hours is an effective treatment for lice.
Shaving the hair of affected areas is a desirable adjunct. Adult lice in clothing
must be destroyed by the application of lindane or DDT powder or by boiling.
Lice may survive in the environment for up to 2 weeks; thus items such as
brushes, combs, and bedding must be treated with a pediculicide or by boiling.
The best strategy for primary prevention is education and practice of good
hygiene habits. Secondary prevention may be practiced by a policy of routine
surveillance (e.g., scalp inspections) in schools, daycare centers, military
camps, and other institutions. Repellents may be necessary for people who run
a high risk of exposure in crowded conditions.
Fleas
small, wingless insects with laterally
compressed bodies and long legs adapted for jumping
Their mouthparts are adapted for sucking or "siphoning" blood
from the host.
 Fleas are cosmopolitan in distribution. Most species are
adapted to a particular host; however, they can readily feed on
humans, particularly when deprived of their preferred host.
 Fleas are important as vectors of plague and murine typhus
and as intermediate hosts for dog (Dipylidium caninum) and
rodent (Hymenolepis species) tapeworms that occasionally
infect humans.
 In contrast to the majority of fleas that do not invade the
human integument, the chigoe flea, Tunga penetrans, may
cause considerable damage by actively invading the skin.
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with the bites of other bloodsucking arthropods, flea bites result in pruritic,
erythematous lesions of varying severity, which depends on the intensity of the
infestation and the sensitivity of the bitten person. The irritation caused by the
flea's saliva may produce physical findings that vary from small, red welts to a
diffuse, red rash.
Secondary infection may be a complication.
Cutaneous invasion by the chigoe flea produces an erythematous papule that is
painful and pruritic. Infested tissue can become severely inflamed and
ulcerated. Secondary infection is common.
In severe cases, the infestation may be complicated by tetanus or by gas
gangrene, resulting in amputation.
The diagnosis of flea infestation is inferred in a patient with annoying bites who
is also a pet (dog or cat) owner. Examination of the patient and pet usually
reveals the characteristic insect. Diagnosis of tungiasis is made by detecting the
dark portion of the chigoe flea's abdomen as it protrudes from the skin surface
in the center of an inflamed lesion.
Palliative treatment with antipruritics and antihistamines is indicated for most
flea bites. Surgical removal of the chigoe flea is indicated.
Commercially available insecticides may control fleas at the source. Topically
applied repellents can protect people against flea bites. Flea collars or powders
on pets are also effective preventive measures.
Bugs
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two bloodsucking insects, the bedbug and the triatomid bug.
Both bugs are characterized by a long proboscis that is folded
ventrally under the body when not in use. The bedbug (Cimex
lectularius) is a reddish brown insect approximately 4 to 5 mm
long. It has short wing pads but cannot fly. The triatomid, or
"kissing" bug, has yellow or orange markings on the body
and an elongated head. Triatomid bugs have wings and are
aerial.
Both bedbugs and triatomid bugs are nocturnal and feed
indiscriminately on most mammals. Bedbugs are cosmopolitan
in distribution, whereas triatomid bugs are limited to the
Americas.
Bedbugs hide during the day in cracks and crevices of wooden
furniture, under loose wallpaper, in the tufts of mattresses, and
in box springs.
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Triatomid bugs live in the cracks and crevices of walls and in thatched
roofs. Bedbugs do not play a role in the transmission of human
disease; however, triatomid bugs are important vectors of Chagas'
disease
lesions that range from small, red marks to hemorrhagic bullae.
Bedbugs tend to bite in linear fashion on the trunk and arms, whereas
triatomid bugs bite with higher frequency on the face.
The classic periorbital edema secondary to a triatomid bite is known as
Romaña's sign. The intensity of reaction to a bite depends on the
degree of sensitization of the patient. In addition to causing local
lesions, bedbugs may be associated with nervous disorders and
sleeplessness in children and adults.
The detection of tiny spots of blood on bedding or the dead insects
themselves is frequently the first sign of bedbug infestation.
Antihistamines may be indicated if dermatitis is severe. Control
consists of proper hygiene and the environmental applications of
insecticides.
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order Hymenoptera comprises the bees, wasps, hornets, and
ants. The modified ovipositor of the female, the apparatus for
egg laying, serves as a stinging organ and is used for defense
or to capture prey for food. Members of Hymenoptera are
known for their complex social systems, castes, and elaborate
hive or nest structures. hymenopterans, the bees, or Apidae,
live in complex social organizations such as hives or in less
structured underground nests.
Only honeybees and bumblebees are of concern to humans
because of their ability to sting.
The Vespidae include wasps, hornets, and yellow jackets; all
are aggressive insects and a major cause of stings in humans.
In the act of stinging, the aroused insect inserts the sheath to
open the wound.
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Severe toxic reactions such as fever and muscle cramps can be
caused by as few as 10 stings. Allergic reactions are the most
serious consequence, but others include pain, edema, pruritus,
and a heat sensation at the site of the sting.
Anaphylactic shock from bee stings has resulted in death in
some instances
No satisfactory treatment has been discovered for stings. If left
in the wound, the sting apparatus should be removed
immediately. The injection of epinephrine is sometimes
necessary to counteract anaphylaxis.
Although there are no effective repellents against these insects,
their nests can be destroyed with any of several commercially
available insecticidal compounds.