parasite

Parasitology د.صادق الشيخ
Helminthology
Introduction
Helminthology: The science which deals with the study of helminthes.
Helminthes: The term used for all groups of worms that live as parasites.
The Classification of Organisms :
It is a procedure of putting organism's in-groups according to their food need.
Basis of classification according to structural similarities called Taxonomy,
General appearance.
Arrangement of body parts. 3 -DNA and PCR .
The five kingdoms are:
Manerous: are simple, single cell, some can make their own food others cannot. Ex: Bacteria.
Protist : are complex single cell, some can make their own food others cannot . Ex: in a drop of pond water Paramecium, Amoebae, Euglena. Phylum protozoa.
Fungi: are many –celled organisms that absorb food from dead and livings things, Ex: Mushrooms.
Plants: are many- celled organisms that make their own food, Ex: Roses, trees.... etc.
Animals: are many – celled organisms that cannot make their own food. Ex: Mice, birds, worm, man.
Taxonomy: the science which deals with classification of animals, plants ... etc.
The six subdivisions of the kingdoms :
Include :- Phylum Class Order Family Genus Species
Animal kingdom


Vertebrates (40.000) spp invertebrates 3millions one phylum with skeleton inside animals without back bone
Their bodies 8 phyla

Classes:-

1
Mammalian 6000spp

2
Birds 8000 spp

3
Amphibian Frog 2000 spp

4
Reptile korekodile 2000 spp

5
Fish carp 220000 spp

1
Sponge
e.g. sponge
2
Coelenterate
e.g. hydra
3
Platyhelminthes
e.g. Tapeworms ,Flukes
4
Round worm
e.g. Ascaris
5
Annelids
e.g. leech and earthworm
6
Molluscus
e.g. snails
7
Echinoderms
e.g. Sea star
8
Arthropods
e.g. Grass hopper, insects e.g. flies ,fleas ,bugs ,lice

General characters of helminthes :

1:- They are multicellular bilaterally symmetrical animals .
2:-Very few worms' infections are potentially dangerous and the ability of these to produce clinical diseases is more often associated with:
No. of the parasites.
Unusual site in which they occur.
Re – infection.
Immunity of the host.
3- Unlike protozoa, most helminthes are unable to multiply within the host, so most helminthes infections are light.
4- Many helminthes have a limited distribution because they require a particular climate and the presence of reservoir or a suitable vector.
5- Many helminthes require another host to complete their life cycle.
6- The worms obtain their nourishment from hosts tissues or intestinal contents through their digestive system, but tape worms have no digestive system so they obtain their nourishment by absorption of predigest nutrients through their body wall.
7- The worms have parasite protective mechanisms which prevent the host damaging outer surface.

Methods of transmission

Fecal – oral route: infective eggs or larvae may swallowed by contaminated food or water e.g. Ascaris and Enterobius.
Swallowing of an infective larvae in the tissue of another host e.g. Tania solium, Tania saginata and Trichinella spiralis.
Active penetration of the skin by the larva e.g. Hook worms and Shestosoma sp.
Bite of blood sucking insects e.g. filarial worms
Inhalation of the infective eggs with air-dust, eggs too light to be spray with air-dust. E.g. Enterobius vermicularis.
Contact with contaminated people clothing sticky eggs adheres on the underwear of infected host e.g. E. vermicularis.
Cestodes or Tapeworms
General characters
The adult is usually found in the intestine of vertebrate and the larva develops in the tissues of various intermediate hosts.
The adult body is composed of scolex (head) ,neck and ribbon – like chain of segments (strobili) { immature ,mature and gravid segments}
All the tapeworms of man are hermaphroditic.
There is no mouth and no trace of an alimentary system, so nutrients are absorbed directly from host gut through the body wall.
Three groups of tapeworms infect humans:-
Tania group {Giant adult tapeworms} and Echinococcus {minute tapeworms}.
Hymenolepis group and Dipylidium caninum.
Broad fish tapeworm Diphyllobothrium latum.
All cestodes have indirect life cycle except Hymenolepis nana.


Pathogenesis
Irritation
Injuries produced by the worms are due to:-Movements and migration

Obstruction

Size and numbers
Adults
Atrophy
Pressure

Mechanical Action

Catarrhal inflammation
Attachment

Sharing host's nutrients
Loss of weight

Larvae

Macrocytic anemia
Sucking blood


Hemolysis
Adults
Tissue lysine

Chemical action

Anticoagulins

Larvae

Inflammation
Local necrosis
Repairing
Encapsulation
Reaction
Direct absorption of toxins

General allergic responses

Indirect nervous reflexes
Cestodes larvae (Metacestode):
Solid metacestodes : subdivided into :-
Procercoid sac-like solid structure with caudal appendage at its posterior end which contain hooks.





Plerocercoid: chalky white solid structure composed of caudal solid appendage and invaginted head in the neck.

Bladder metacestodes : subdivided into –

Cysticercoid: has a bladder filled with parenchyma e.g. Hymenolepis spp.andD.caninum.

Cysticercus : has fluid filled bladder with invaginated scolex .e.g.Taenia sp

Hydatidcyst :metacestode of Echinococcus composed of bladder filled with fluid and surrounded by germinal and laminated layers . from germinal layer brood capsules arise which contain number of scolices .





Coenurus : with multiple scolices , inside non laminated bladder ,arise from germinal layer e.g. Tania multiceps