Phylum Arthropoda as causative agents

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Theme:
Medical arachnoentomology.
Arthropods as causative agents and carries
of causative agents of infections.

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Phylum Arthropoda: general
characteristics
The name “arthropod” comes from two Greek words,
arthros - jointed, and podes - feet.
All representatives of the Phylum Arthropoda share the
following characteristics:
1. Arthropods have jointed appendages.
2. Limbs are segmented.
3. Arthropod body is segmented.
4. Arthropods have an exoskeleton.
5. Arthropods have a ventral nervous system, an open
circulatory system, a digestive system, a respiratory
system, an excretory system and specialized sensory
receptors.

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Phylum Arthropoda
includes
3 classes of medical
importance:
• Class Crustacea:
cyclops, crabs.
• Class Arachnida
(Octapoda):
scorpions, spiders,
ticks and mites.
• Class Insecta
(Hexapoda):
mosquitoes, flies,
bugs, lice, fleas.

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Class Crustacea
Most crustaceans have two
pairs of antennae, three pairs
of chewing appendages, five
pairs of limbs.
Crustaceans differ from the
arachnids and insects in that
they have legs on their
abdomen as well as on their
thorax.

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Medical importance of Crustacea
1. Cyclopes are intermediate hosts of the
fish tapeworm - Diphyllobothrium latum
and Dracunculus medinensis.
2. Crabs or crayfish are intermediate hosts
of the human lung fluke - Paragonimus
westermani.

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Class Arachnida
1. The Class Arachnida is a group of more than 100,000
species, including scorpions, spiders and mites.
2. Most arachnids are adapted to kill prey with poison
glands, stingers, or fangs.
3. Arachnids have a body that is divided into a
cephalothorax and an abdomen.
4. Attached to the cephalothorax are 4 pairs of limbs, a
pair of chelicerae, and a pair of appendages called
pedipalps. The pedipalps aid in chewing; in some
species pedipalps are specialized to perform other
functions.
5. Arachnids undergo incomplete metamorphosis.

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Class Arachnida - 3 orders with medical
importance
Order Scorpions Order Araneae (spiders)
Order Acari (mites)

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Scorpions differ from spiders in two
ways:
- Scorpions have greatly enlarged pedipalps, which
they hold in a forward position.
- They also have a large stinger on the last segment
of the abdomen.
Scorpion Sting Symptoms:
• Intense pain at the sting site,
• Mild swelling around sting site,
• Numbness in area of sting,
• Sensitivity to touch,
• Nausea or vomiting,
• Excessive salivation.

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Stepwise first aid
If a scorpion stings you, follow this scorpion sting first aid plan
for minimization of pain:
• Wash the affected area: If possible, get the site of the sting
under cold water immediately.
• Medicate topically: Apply a layer of ointment containing an
antihistamine, a corticosteroid, and an analgesic.
• Apply ice: Hold a bag of ice over the ointment on the area.
The ice will reduce the pain and inflammation.
• Medicate orally: Take one dose of Benadryl (antihistamine)
and one dose of a pain killer (acetaminophen).
• Go to the hospital: Because some scorpion stings can be
fatal, you will need to go to the emergency room to get
evaluated for scorpion anti-venom. If possible, get someone
else to drive you.
• Ice as needed: Keep applying ice until pain is tolerable. You
may experience pain for any length of time between a few
hours to a couple days.

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Order Acari
• Most mites are small, less than 1 mm long,
the adult length from 100 nm to 2 cm.
• Cephalothorax and abdomen are fused into an
unsegmented ovoid body.
• Respiration occurs either by means of
tracheae or directly through the exoskeleton.
• They are found in virtually every terrestrial,
freshwater, and shallow marine habitat known
and feed on fungi, plants, and animals.
• They act as predators and as internal and
external parasites of both invertebrates and
vertebrates.

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Sarcoptidae - Scabies Mites
Sarcoptes scabiei - itch mite of
humans
Distribution: Worldwide.
Disease: not vectors of any disease,
but causative agent of scabies.
Morphology: male (0,2 mm) is
smaller than female (0,4 mm).
Body is oval, convex dorsally and
flat ventrally. Mouthparts:
rudimentary hypostome without
teeth. Chelicerae end in pincer-
like structures. Pedipalps are short
and 3-segmented.
The whole life cycle takes about 2
weeks.

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small male large female
Burrowing initially occurs in thinner skin of the body.
- Bend of knee and elbow;
- Webbing between fingers and folds of the wrist;
- Genitalia and buttocks;
- Breasts.

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Scabies Rash

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Life cycle of Sarcoptes scabiei

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Transmission
Spread by ovigerous female mites through:
– Personal (prolonged close) contact;
– Occasionally by infested sheets (rare);
– Touching or shaking hands;
– Sexual activity;
– Among children (outbreaks);
– Mites can survive up to 24 hours off host.
Diagnosis:
- itching of affected surfaces at night;
- specific lesions;
- finding of the parasite in the tunnels by a needle.
Prevention:
- proper treatment of infected persons;
- sterilization of clothes and bedding;
- personal cleanliness.

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Ixodidae - hard-bodied ticks,
Argasidae - soft-bodied ticks
They are blood-feeding
ectoparasites
(parasites that occur on the
surface of their host).
Representative of Ixodae –
Ixodus ricinus.
All stages of its will feed on
humans, and their bite can be
painful. This tick can also
transmit several diseases that
affect humans, including
Crimean–Congo hemorrhagic
fever and Lyme disease.

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Anatomy of IXODES ticks

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TICK LIFE CYCLE- Female lays eggs.
- Larvae hatch,
feed on blood and
then drop to the
ground.
- Larvae molt into
nymphs.
- Nymphs feed on
blood and molt into
adults.
- Adult male and
female feed on
blood.
Life cycle takes
several months (1-
2 years in some
species).

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Medical importance of Ticks
- Mechanical injury by the bite.
- Tick paralysis: progressive flaccidity due to a failure of
acetylcholine liberation in the neuromuscular junction. Tick’s
toxin produces a block in the motor nerve fibers. The toxin is
elaborated by the tick’s ovaries and is secreted by salivary
glands.
Vectors of diseases:
• hard-bodied ticks (Ixodidae) are carriers of rickettsial,
spirochaetal, viral, bacterial, and protozoan diseases.
• soft-bodied ticks (Ornithodorus) are vectors of endemic
relapsing fever (caused by Borrelia duttoni) and Q-fever.
Control of ticks:
• Repair of cracks.
• Insecticide spraying on floors and cracks.
• Infested animals are dusted by insecticide agents or dipped in
special solution.
In endemic areas: wear light-colored, tightly woven slacks and a
long sleeved shirt; spray clothing with an insect repellant
containing N,N-diethyltoluamide.

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Class Insects
Insects have:
- three body sections: head,
thorax, abdomen;
- three pairs of legs, all
attached to the thorax;
- one pair of antennae;
- one or two pairs of wings.
The mouthparts of insects
are elaborate.
There are two different
kinds of metamorphosis
in insects: simple and
complete.

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Class Insecta have 4 medical important
orders:
1. Order Anoplura - lice.
2. Order Siphonaptera - fleas.
3. Order Hemiptera - bugs.
4. Order Diptera - mosquitoes and flies.

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Order Anoplura - lice
• Body is flattened dorso-ventrally.
• Lice are wingless insects with short legs.
• Order Anoplura displays incomplete metamorphosis.
Pediculus humanus - Head louse
Morphology: adult louse is 2-5 mm in size, male is
smaller than female.
These are insects that can’t jump or fly.
Their style of movement relies on 6 legs, each of which
ends in a claw which can grasp human hair.
The head louse found on humans is specific to people. It
can’t be contracted from the family dog, cat or any
other animal. Mammals and birds can have lice but
they are species specific.

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Pediculus humanus life cycle
- Female louse lays
about 10 eggs
daily.
- Eggs are cemented
to hairs or to fibers
of clothes.
- Eggs hatch in about
one week.
- Nymphs feed on
blood and pass
through 4 instars.
- Adult louse
emerges in about
two weeks.

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Transmission of Head Lice
• Host-to-host (direct contact from
someone who is infested)
• By wearing infested clothing (hats,
scarves, coats, hair ribbons etc.)
• By using infested combs, or
brushes
• By lying on a bed, couch or carpet
that has recently been in contact
with an infested person.

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About 2500 species, most are
parasites of mammals only approx.
100 species on birds.
Temporary obligate parasites,
blood-feeding exclusively as adults.
Most fleas of medical and
veterinary importance are not host
species-specific increases the
potential for acquisition and
transmission of pathogens.
Order Siphonaptera - fleas

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Flea life cycle

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Important Flea Species
Xenopsylla cheopis
(Oriental rat flea) -
primary urban plague
vector.
Pulex irritans (human
flea) - occasional
epidemic plague vector.
Ctenocephalides felis,
C. canis (cat and dog
flea) - primary pest
species.
Tunga penetrans (sand
flea (chigoe).

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Features
– Piercing & sucking mouth parts
– When present, 2 pairs of wings
(hind pair reduced)
– Incomplete life cycle
• Immature stages = nymphs
• Nymphs are mostly small
wingless replicas of adults
• No pupal stage
Of lesser medical importance
– Most are phytophagous or
predators of arthropods
– Few blood suckers – 2 families
Order Hemiptera – True Bugs

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Family Cimicidae - bed bugs
• Identification
– Small, apricot-coloured &
wingless
– Circular body & flattened
extensions of prothorax
behind eyes
• Medical importance
– Most species are
ectoparasitic on rodents,
poultry, birds & bats
• 3 species parasitic on
humans
• Cimex lectularius occurs
worldwide
– Do not appear to vector any
pathogens

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Life cycle
– Adults & tiny nymphs hide in day
• Any cracks & crevices
• Mattresses, clothing & under
wallpaper
– Emerge at night to feed on blood
• Survive without food for
several months, but need
blood to moult & lay eggs
– Bites are painless; no response
during sleep
• Many show allergic reactions
(large red discs around bites;
swelling & irritation for days)
• High densities can cause
anaemia in children
Adult & nymphs feeding

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Family Reduviidae - assassin bugs
• Identification
– Large robust bugs = ambush
predators of arthropods
– Strong recurved beak for
biting
• Inject paralytic toxin to
subdue prey
• Bite very painful to
humans
• No species in SA usually
bite mammals
• Medical importance
– South American subfamily
Triatominae (kissing bugs)
• Feed on human & animal
blood
• Transmit Chagas’ disease

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Triatominae - kissing bugs
– Live in woodland & forest habitats
– Colonized human dwellings
• Live in ceilings, cracks &
crevices etc.
– Behave like bed bugs & attack
humans at night
– Spread protozoans which cause
Chagas’s disease (American
trypanosomiasis)
– Most notorious species are
Triatoma infestans & Rhodnius
prolixus
Triatoma infestans
Rhodnius prolixus

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Order Diptera - Flies
• The key distinguishing adult
structure: two wings.
• All Flies are Holometabolous
(having a complex
metamorphosis
– i.e. egg, larvae pupa, and
adult).
The habitat of the larval stage is
basically “aquatic or semi-
aquatic,” and they have
adapted to live in very, very
“challenging” environments.
Allows them to invade
dead and living tissues

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Diptera – flies as parasites
• Ectoparasites
1. Adults are free living
but blood feeding
with the larvae
stages aquatic or in
moist semi-aquatic
habitats.
(Nematocera and
Brachycera)

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Diptera – flies as parasites
2. Adults ectoparasites
(or blood feeding)
but larvae develop
within female and
essentially pupate
after emerging from
mother (Glossina,
Hippoboscidae)

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Diptera – flies as parasites
• Endoparasites
3. Adults free living but
larvae are internal or
partially internal
(flesh feeding)
parasites of
vertebrates (Oestrus,
Gasterophilus,
Cochliomyia
hominovorax)
Gasterophilus intestinalis

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Myiasis defined
The invasion of organs and tissues of humans or other
vertebrate animals with dipterous larvae, which for at
least a period feed upon the living or dead tissue or, in
the case of intestinal myiasis, on the host’s ingested
food.

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Metallic Flies
Cochliomyia hominivorax

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Lucilia spp.
Calliphora spp.

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Musca domestica
Housefly is a medium-sized fly, 6- 10 mm
in length; the female is generally slightly
larger than the male.
Distribution: cosmopolitan.
Morphology. Adult fly has a gray color, 4
dark stripes, red eyes.
Life cycle. 1. Eggs are laid into masses of
decaying organic substances, garbage,
refuse or manure.
2. Larvae hatch in 6-24 hours and feed on
organic matter.
3. They molt 2 times giving 3 larval stages.
4. The third larva pupates inside the larval
skin.
5. The adult emerges after a few days .The
whole cycle takes about one week.

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Medical importance of House fly
1. Indirect mechanical transmission of
microorganisms (as typhoid, poliomyelitis and
bacillary dysentery), eggs of helminthes and cysts
of protozoa.
2. Accidental myasis.
Control
1.Sanitary disposal of refuses, garbage and manure
(breeding media) by dumping, burning or
application of insecticides.
2.Control of adult flies by screening or space
spraying of insecticides.

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Mosquitoes - Bloodfeeding - only
females take blood
- Males feed on plant
sugars
- Gonotrophic cycle - feed,
egg development,
oviposition (half-gravid,
gravid)
Disease transmission
Some species of
Anopheles transmit:
1. Human malaria
2. Wuchereri bancrofti
Some species of Culex
transmit
1. Wuchereria bancrofti
2. Encephalitis
3. Rift valley fever

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Eggs – 3 strategies
• Singly on water surface
– Anopheles
• Singly in a pile, on moist substrates
– Aedes/Ochlerotatus
• Form of a raft, on water surface
– Culex
– Culiseta
Differences between Anopheles and Culex

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Larval Stage
• Larval instars (4)
• Aquatic, Filter feeders
• Respiration
Anopheles

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Pupa
• Non-feeding
• Respiration
Anopheline Culicine
Pupal Stage ComparisonPupal Stage Comparison

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Mosquito - pupa and larvae

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Anopheline
Culicine
Adult stage
comparison

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Aedes aegypti
Anopheles Culex

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