• 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.