medical importance of arthropods
DESCRIPTION
a short note on arthropodsTRANSCRIPT
• Arthropods are small invertebrate animals
with jointed legs.
•They have an external shell-like skeleton
made of a tough, rigid material called
chitin.
•Their body parts and appendage segments
are joined by flexible membranes which
allow the various parts to move.
•The majority of arthropods are not harmful
to humans.
•Most of species are medically important as
they can cause annoyance,or diseases in
humans.
•These arthropods can be put into four
main categories :
•Harmful cause nuisance, discomfort,
and blood-loss by their bites (mosquitoes,
bugs, fleas); or cause nuisance by their
mere presence (gnats).
• Ectoparasites live & feed permanently
on the exterior of the host without
transmitting germs (head lice, pubic lice,
scabies mites).
•Mechanical transporters transmit
disease passively,by picking up infections
from faeces, and then contaminating
human food so that disease is contracted
orally (flies, cockroaches).
•Vectors actively transmit parasitic
disease-causing organisms. The pathogen
develops and multiplies in the vector,andis transmitted to humans via arthropod’s
bite or excreta (mosquitoes, tsetse-flies,
body lice, fleas).
• Arthropods of medical importance include
insects (class Insecta) and arachnids
(class Arachnida). Of the arachnids, only
mites and ticks (order Acarina) are vectors
of diseases.
• Of the insects, five groups are of medical
importance: true flies (order Diptera),true
bugs(order Heteroptera,or Hemiptera),lice
(orderAnoplura),fleas(orderSiphonaptera),
and cockroaches (order Dictyoptera).
• Insects can be easily distinguished from
arachnids in the following ways:
INSECTS ARACHNIDS
• 3 distinct body
regions (head,
thorax, and
abdomen)
2 distinct body regions
(cephalothorax, and
abdomen)
• 3 pairs of legs 4 pairs of legs (except
larval mites, which
have 3 pairs)
• often have wings never have wings
•1 pair of antennae no antennae
• segmented
abdomen
abdomen usually not
segmented
• The change in form during an insect’s
development is called metamorphosis.
• Insects which undergo complete metamorphosis
(ex:flies) have four stages of development: egg,
larva,pupa,and adult.
• Insects which undergo incomplete
metamorphosis (ex:bugs) have three stages of
development : egg,nymph,and adult.The nymph
look like adult but is smaller and its size is rougly
proportional to its age.
Phylum Arthropoda includes
3 classes of medical importance:
1.Class Crustacea: cyclops, crabs.
2. Class Arachnida (Octapoda):
scorpions, spiders, ticks and mites.
3.Class Insecta (Hexapoda):
mosquitoes, flies, bugs, fleas.
Class CrustaceaMost crustaceans have
Two pairs of antennae,
Three pairs of chewing appendages.
Various numbers of pairs of legs.
Crustaceans differ from the insects in that they have legs on their abdomen as well as on their thorax.
Medical importance: Cyclopes are intermediate hosts of the fish tapeworm (Diphyllobothriumlatum) and Dracunculusmedinensis.
Class Arachnida.
The Class Arachnida is a group of more than 100,000
species, including spiders, scorpions, ticks, and mites.
Most arachnids are adapted to kill prey with poison
glands, stingers, or fangs.
Arachnids have a body that is divided into a
cephalothorax and an abdomen.
Attached to the cephalothorax are 4 pairs of legs,
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.
Incomplete metamorphosis.
Class Arachnida includes 3 orders
of medical importance:
Order Scorpiones. Order Araneae (spiders)
Order Acari (ticks and mites).
Order Scorpionoidae
• Four pairs of legs.
• Body divided into two tagmata: cephalothorax
and the abdomen.
• Adult arachnids have
eight legs,two claws and
distinguishable easily
from insects.
• The bigger the claws
are, the less venom it has.
Characterstics:
Medical importance:
• Compounds found in scorpion venom can be used for
creating new drugs.
• Malayan pit viper venom -used as a hypertension drug.
• A toxin found in the North African deathstalker scorpion
has shown potential for treating brain tumours.
• Black mamba venom has powerful painkilling potential.
Pathogenicity:
• Symptoms of bite include severe
pain, inflammation and swelling.
• Muscular spasm occur in severe cases. Fatal outcome
is caused by respiratory failure, pulmonary edema and
shock.
Order Araneae (spiders)
Characterstics:
• There are about 35,000 named species of spiders (order Araneae).
• Spiders hunt their prey or catch it in webs.
• They have either six or eight eyes, even though they
can’t see far away.
• The hair on their bodies used as sensors to feel their
way around and to tell when other animals are near.
• Body is divided into cephalothorax and abdomen and
fused into an unsegmented ovoid body.
• Respiration- tracheae or directly through exoskeleton.
Medical importance :
• Black Widow Spider- most dangerous species.
• They are found in 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.
• The venom is neurotoxic, effecting the human nervous
system, and cramps in the legs, arms and chest occur
concurrently with the local swelling.
• Symptoms may include headache, nausea, tremors,
stuttering, and a slight rise in body temperature.
Order Acari(ticks & mites)
Ticks are divided into hard-bodied ticks (family Ixodidae)
and soft-bodied ticks (family Argasidae)
Ticks are blood-feeding ectoparasites
Medical importance:
• 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.
• Soft-bodied ticks (Ornithodorus) are vectors of endemic relapsing fever (caused by Borrelia duttoni) and Q-fever.
• Hard-bodied ticks (Ixodidae) are carriers of rickettsial,
spirochaetal, viral, bacterial, and protozoan diseases.
Mites:
Sarcoptes scabiei
Also called the “itch mite” of humans
Morphology: male (0,2
mm) is smaller than
female (0,4 mm).
Body is oval, convex
dorsally and flat
ventrally.
Not Vectors of any disease.
• Insects are relatively small,
ranging in size from 0.1mm.
• Most insects have compound eyes, and many
have ocelli as well. The mouth parts of insects
are elaborate and Haustellate.
• One pair of antennae and one or two pairs of
wings.
• Three pairs of legs, all attached
to the thorax.
• Body is divided into head,
thorax, and abdomen.
House fly
• Metamorphosis in insects: simple and
complete.
• Immature stages are of
insects called nymphs.
• Larvae in insects are
worm-like, which differ
greatly in appearance
from the adults.
• Larvae do not have compound eyes.
• Insects with complete metamorphosis
include the moths, and butterflies; bees.
• As vectors of the agents of bacterial, viral or
parasitic infection.
• As parasites in their own right, spending part
or all of their lifespan on humans
• As instigators of allergic responses that vary
in severity.
• They are 2 types of vectors:
1.Biological vectors
2.Mechanical vectors
Biological vectors:
• Pathogens do not undergo multiplication
ordevelopment inside their bodies.
• Serve as mere contaminators.
• Transmit pathogens by way of their secretions
and the contaminated external surfaces of body.
Mechanical vectors:
• Acquire pathogenic agents in act of blood feed.
• Undergo multiplication, propagation and
development inside the arthropod’s body.
Class Insecta is divided into 4 orders of medical importance:
1. Order Anoplura (lice).
2. Order Siphonaptera (fleas).
3. Order Hemiptera (bugs).
4. Order Diptera (mosquitoes and flies).
Order Anoplura (lice)
• Body is flattened dorso-ventrally.
• Lice are wingless insects with short legs.
• Order Anoplura displays incomplete
metamorphosis.
Head louse
•Morphology (Pediculus humanus):
• Adult louse is 2-5 mm in size, male is smaller than female.
• Body is divided into head, thorax and abdomen.
Order Siphonaptera( Fleas)
About 2500 species, most
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.
Xenopsylla cheopis (Oriental rat flea) - primary
urban plague vector.
Order Hemiptera( Bed Bugs)
• Bed bugs get their name
from their proclivity.
• They feed on blood,
climbing on you as you
sleep and feasting.Their bites can cause severe
redness and itching.
• Some of tem are not a big deal.But they're fast
breeders and hard to kill. They can hide in your
carpet, your clothes or even inside your walls.
• Bed bug bite causes anemia and lack of energy
-- in extreme cases, death.
Mosquitoes
• Mosquitoes are one of the
main disease carriers
among insects.
• When they bite, they
regurgitate a small amount of their stomach
contents into the new host.
• If a mosquito previously bit an infected person
or animal, he can transfer that disease to the
new host.
Ex: Malaria, typhoid and cholera.
Flies
• Flies often eat food we
consider undesirable, such as
rotting vegetation and feces.
• Their bodies are covered with
diseased particles, including their mouth parts,
feet and legs.
• Deposition of those diseased particles on food
we eat, leads to food poisoning.
• Flies also transmit diseases such as typhoid
and cholera.
Bees and Wasps
• Bees and wasps don't typically
spread disease,stings are common.
• Depending on where you're stung and
the power of your immune system,
most stings are fairly benign,leading to a red,
painful, sometimes itchy bump that fades
in a few days.
• Some people are allergic to the toxin in bee
stings. They can experience swelling and
tenderness in a large area around the sting and
die without treatment in extreme cases.