ARTHROPODA pdf - د. صادق

ARTHROPODA

ARTHROP ODS

Invertebrate animals with jointed legs and

segmented body which is covered by hard

keratinized exoskeleton , it has a single body cavity

( haemocoel ) which is filled with haemolymph in

which internal organs float

Arthropoda is the largest group of the animal
kingdom

Bilaterally symmetrical, triploblastic and
metamerically segmented

Sexes are usually separate with sexual
dimorphism

Metamorphosis

Jo in t e d le g s

Co mpo un d e ye

Co mpo un d e ye in d e t ails

STRUCTURE AND FUNCTION

Feeding –complete digestive tract
Internal transport –open circulatory

system w/ dorsal heart

Respiration –varied
Excretion –varied
Nervous system –brain + ventral nerve

cord sense organs (sight, smell,
hearing, balance, taste, touch, etc.)

Reproduction –sexes separate

Numerous species of Arthropods play a role in

human health. Most of these are as vectors of

different pathogens such vectors have been dealt

with the specific pathogen.
There are also a number of Arthropods that cause

harm due to their Venom but are not really

parasitic .

PHYLUM ARTHROPODA INCLUDES 3 CLASSES

OF MEDICAL IMPORTANCE :

1–Class 1 :Hexapoda or Insecta : which includes

insects like flies , fleas ,lice , bugs and the

mosquitoes (Anopheles –Malaria and Culex –

Filaria ).

2 –Class 2: Arachnid : includes Ticks ,Scorpions ,

Spiders and Mites .

Black widow spider

Spider s

Tarantula spider

Largest spider

Scorpion

Mites

Dust mites do not feed on blood but the dead
skin cells in the dust.

Some live creating burrows in our skin causing
scabies

3 –Class 3: Crustacea includes Crabs , Water fleas

(Cyclops) the intermediate hosts of some

helminthes .

The science which deals with the study of

medically important insects and Arthropods .

CLASS INSECT A:

The insects are tracheate arthropoda with the body

divided in to 3 parts : Head , Thorax and Abdomen

with 3 pairs of legs and one or two pairs of wings in

winged insects .
We will deal with Arthropods that are parasitic to

and cause diseases in man

MYIASIS

Myiasis means ( burial of larvae in tissue) is

obligatory step in the life cycle of some flies and

incidental for others .
Ectoparasites that cause myiasis are Cochliomyia ,

(Screw worm fly ) ,Calliphora , Osterus ,

Sarcophaga , Gastrophilus , Fleas , Mites and etc..

Myiasis m ay be cutaneous , ar terial ,intestinal or ur inar y in

nor mal tissue or in pr e –existing w ounds aided by ot her

infections , lar vae can bur r ow thr ough necr otic or healthy

tissue using their mandibular hooks aided by t heir

pr oteolytic enzym es .

They cause m echanical damage and t he affected area is a

site of secondar y infection , most ly in childr en .
Cutaneous m yiasis m ay r equir e sur gical r emoval of

bar r ow ed lar vae .
Eggs and m aggots may be w ashed fr om hair ,skin and

wounds w ith soap and w at er . Ur inary m yiasis usually clear s

it self . Pur gat ion w ith ant ihelm inths m ay be necessary for

gastr oint est inal myiasis .

LICE

-Three types of lice are important for human health

•

Pediculus humanus capitis ( Head louse ).

•

Pediculus humanus humanus ( Body louse ) .

•

Phthirius pubis (Crab louse or pubic louse ) .

Lice spend all of their life on one very specific host

and both male and female feed blood and leave one

host only to transfer to another .

HEAD LICE :

In the developed world , 2-10% of children are

infected with head lice .

LIFE CYCLE :

The life cycle of the head louse has three stages :

Egg , Nymph and Adult .

Eggs or Nits : Nits are head lice eggs . They are

hard to see and are often confused for dandruff or

hair spray droplets .

Nits are laid by the adult female and are cemented

at the base of the hair shaft nearest the scalp .

They are o.8 mm. by 0.3mm , oval and usually

yellow to white . Nits take about 1week to hatch

(range 6 to 9 days ) . Viable eggs are usually located

with in 6 mm of the scalp .

NYMPH

The egg hatches releasing a nymph . The nit shell

then becomes a more visible dull yellow and

remains attached to the hair shaft .

The nymph looks like an adult head louse ,but is

about the size of a pin head . Nymph mature after

three molts and become adults about 7 days after

hatching .

ADULT :

The adult louse is about the size of Sesame seeds ,

has 6 legs ( each with claws ) and is tan to grayish –

white . In persons with dark hair , the adult louse

will appear darker .
Females lay up to 8 nits per day . Females are

usually larger than males . Adult lice can live up to

30 days on a persons head .

To live , adult lice need to feed on blood meals

several times daily, Without blood meals , the louse

will die with in 1 -2 days off the host .

SYMPTOMS AND SIGNS

Light infestations cause moderate itching of the

scalp due to sensitizations to louse saliva .
Heavy infestations may result in fever ,aches,

anemia, weakness ,paleness and secondary

infections .

DIAGNOSIS AND TREATMENT

Diagnosis is based on finding live lice or egg shells

(Nits measuring 0.8 x 0.3 mm.) attached to hair

,often behind ears .

Treatment using topical applications of soothing

lotions relives irritation .
Wash hair with shampoo containing ( 1% Benzene

hexachloride ).

Application of a mixture of pyrentins 0.2% and

pipronyl butoxide 2% or copper oleate may be as

effective and less toxic than Benzene hexachloride

or use medical shampoo.

Cleaning ,Washing ,Dressing ,cutting and shorting

the hair as much as you can is the best way to

control and prevent the lice infestations.

BODY LICE :

Body louse is similar to the head louse except

that it is found on the body and clothes .

Diagnosis is based on finding eggs or nits in

seams of clothing .

Symptoms and treatment are the same as those

of head louse

PUBIC LICE :

Pubic lice also known as Crab lice infested widely –

spaced coarse hair in pubic area in adults or

eyelashes in children . Transmission in adults is

usually by sexual contact .

Diagnosis is based on finding lice or nits in the

infested area . Crab lice may be difficult to see at

the base of the hair .

Treatment : pubic area is treated in the same

manner as infested head . Nits and lice may be

removed from eyelashes with forceps.

Ointments with physostigmine 0.25 % or yellow

mercury oxide are effective

FLEAS

Most fleas are of clinical significance to man

because they are vectors for other parasites

.However, the jigger flea or chigoe ( Tunga

penetrans) is a serious pest in the tropical and

subtropical regions of the Americas and Africa.

Bot h sexes feed on blood .The female fleas after

inseminat ion, b urrows it self in t he skin of the toes

and sole of t he foot. The fem ale sw ells t o the size

of a pea , produces eggs and dies in the tissue.
There is local reaction t o t he b ite and t he eggs and

dead flea pro duce r eaction.

The infested tissue can get infected and

gangrenous auto- imputation is common .

Treatments are symptomatic , infestation may be

removed physically, secondary infections are

treated appropriately . Wear shoes in infested

area ..

MITES

Scabies mite ( Sarcoptis scabies ) is the cause of

scabies and is distributed world-wide .
Epidemics of the disease may occur in long periods

but mites may be common at all times in very poor

communities with inadequate washing facilities.

The mit e t ransmitt ed by cont act burro ws in t he

skin on the w ebbing side of finger ,later spreading

to t he wrists ,elbows and the rest of t he body. The

but tocks , wo men s b reast s and external genitalia

may be involved , the scrotum in the male .

The mite tunnels itself through the upper layer of

the skin depositing eggs . Larvae escape the tunnel

and wander on the skin and start new burrows and

mature there to continue the cycle .
Scabies itch is due to the sensitization of the

patient to the mite and eggs and is

characteristically nocturnal. Septic pustules may

Develop after scratching ,if the hygiene is poor .

Diagnosis

is made by characteristic rash ,

smearing black ink on the skin and observing

burrows when ink is wiped .

Microscopic examination of the skin scraping

show mites .

Treatment

involves swabbing of the whole body

from neck down with 1 % Malathion or Benzene

hexachloride ( Crotamiton for infants) .

Topical steroids must not be used. If possible the

whole family should be treated .

Contact with infested person should be avoided.

Clothes should be washed in boiled water .

CHIGGERS

The chigger s or r ed –bugs ( Tr om biculidae ) are an

import ant gr oup of ectopar asit es affecting hum ans . They

att ach to the skin in t he ankles , w aistline, ar m pits and

perianal skin fr om long gr assy envir onment .

These m ites do not feed on blood but on par tially digested

cells due t o r eaction of t heir saline wit h host t issue.

The host reacts t o m outh part s and saliva of t he mite. The

bite causes severe ir r itat ion and sometim es fever .

Tr eatm ent w ith local anest het ic is useful insect r epellent s

may be effect ive in avoiding chigger bites.