Classification Of Medically Important Helminths

1. D R . M A H A M O H A M E D A L A B B A S S Y
L E C T U R E R O F PA R A S I T O L O G Y
F O M - S C U
CLASSIFICATION OF
MEDICALLY IMPORTANT
HELMINTHS

2. OBJECTIVES
• Define helminths.
• Identify general characteristics of helminths.
• List different classes of medically important helminths.
• Describe briefly the general characteristics of different classes
of helminths (trematodes, cestodes, and nematodes).
• Describe differences between different classes.
• Identify different developmental stages of helminths (immature
and mature eggs, miracidium, cercaria, larva )
• Identify common examples for each class of helminths.
• List examples of helminths infecting different body organs and
tissues ( intestinal helminthic infections, tissue helminths,
helminths of the blood, hepatic helminths)

3. DEFINE HELMINTHS
• Helminth is a general term meaning worm.
The helminths are invertebrates characterized by
elongated, flat or round bodies.
• The word "helminth" is derived from the Greek
"helmins" (worm). Helminthology is the study of
parasitic worms.

4. IDENTIFY GENERAL CHARACTERISTICS
OF HELMINTHS.
• The outer covering of helminths is the cuticle or
tegument.
• There are both hermaphroditic and bisexual species.
• Helminths develop through egg, larval (juvenile), and
adult stages.
• The definitive classification is based on the external
and internal morphology of egg, larval, and adult
stages.

5. LIST DIFFERENT CLASSES OF
MEDICALLY IMPORTANT HELMINTHS.
1. Trematoda (flukes) ‫المفلطحة‬ ‫الديدان‬
2. Cestoda (tape worms) ‫الشريطية‬ ‫الديدان‬
3. Nematoda (round or cylindrical worms) ‫الديدان‬
‫األسطوانية‬

6. • Flukes (Trematodes)
• Adult flukes are leaf-shaped flatworms. Prominent
oral and ventral suckers (
‫ممصات‬
) help maintain
position in situ.
• Flukes are hermaphroditic except for blood flukes
(Schistosoma), which are bisexual. The life-cycle
includes a snail intermediate host.

7. • Tapeworms (Cestodes)
• Adult tapeworms are elongated, segmented,
hermaphroditic flatworms that inhabit the intestinal
lumen.
• Larval forms inhabit extra-intestinal tissues.

8. • Roundworms (Nematodes)
• Adult and larval roundworms are bisexual,
cylindrical worms.
• They inhabit intestinal (intestinal nematods) and
extra-intestinal (tissue nematods) sites.

9. GENERAL CHARACTERS OF
TREMATODES
• A dorsoventrally flattened body, bilateral symmetry,
and a definite anterior end.
• Flukes are leaf-shaped, ranging in length from a few
millimeters to 7 to 8 cm.
• Flukes possess an oral sucker around the mouth
and a ventral sucker or acetabulum that can be used
to adhere to host tissues.
• Except for the blood flukes (Schistosoma),
trematodes are hermaphroditic, having both male
and female reproductive organs in the same
individual.

10. GENERAL MORPHOLOGY OF
TREMATODES
(A) Hermaphroditic fluke. (B) Bisexual fluke.

11. • Members of Trematodes:
1. Schistosoma mansoni (blood)
2. Schistosoma hematobium (blood)
3. Fasciola hepatica (liver)
4. Heterophys heterophys (intestine)
5. Paragonimus westermani (lung)

13. GENERAL CHARACTERS OF CESTODES
• General Characteristics of Cestodes
• 1. Adult Cestodes: Adult cestodes have tape-like,
ribbon shaped and segmented body and the length
varies from few mm to several meters. They are
flattened dorso-ventrally. An adult worm has three
regions:
• Head or Scolex
• Neck and
• Strobila (a trunk or body) consisting of proglottids or
segments.

14. Tapeworm adult
and scolex

16. • 2. Proglottids or Segments: Each proglottid or
segment is essentially a functional individual, i.e. a
complete unit of a tapeworm. A segment is called
immature if the male and female reproductive organs
are not differentiated, mature if the reproductive
organs are differentiated and gravid if the uterus is
filled with eggs. These are seen from front to
backwards.

17. • Classification of Cestodes
• According to Habitat, the cestodes are the following
types:
• A. Intestinal Tapeworms: Adults live in intestine of
human.
• Taenia saginata (Beef tapeworm)
• Taenia solium (Pork tapeworm)
• Hymenolepis nana (Dwarf tapeworm)
• Hymenolepis diminuta ( Rat tapeworm)
• Diphylobothrium latum (Fish tapeworm)

18. • B. Tissue Tapeworms-Larval Stage
• Hydatid cyst of Echinococcus granulosus (Dog
tapeworm), E. multilocularis
• Cysticercus cellulose of Taenia solium.
• Coenurus cerebralis of Multiceps multiceps.

19. GENERAL CHARACTERS OF
NEMATODA
• Their body is bilaterally symmetrical
• They are cylindrical in shape.
• Their body has a cavity
• The alimentary canal is distinct, with the mouth and the
anus.
• They are sexually dimorphic.
• They are free-living or parasitic.
• Parasitic nematodes cause diseases in the host.
• Fertilization is internal and reproduction is sexual.
• Their cuticle moults periodically.
• The body-wall muscles are longitudinal.

20. Ascaris
Ancylostoma
Entrobius

21. MEMBERS OF NEMATODES
• Intestinal nematodes:
1. Ascaris lumbricoides
2. Ancylostoma duodenale
3. Entrobius vermicularis
• Tissue nematodes as Filaria

22. IDENTIFY DIFFERENT DEVELOPMENTAL STAGES
OF HELMINTHS (IMMATURE AND MATURE EGGS,
MIRACIDIUM, CERCARIA, LARVA )
• Immature egg: usually contain immature ovum or
cells and pass from adult after fertilization in the
excretions of body. Ex: Schistosoma mansoni
• Mature egg: immature egg needs time and
favourable conditions to mature and usually contain
larva capable of infection. Ex: Entrobius

23. • Miracidium : stage present in trematodes only and
present in immature eggs of trematodes, hatching in
water and search for snail as an intermediate host to
complete maturation to another stage.
• Cercaria: infective stage in some trematodes and it
is a mature stage comes out the snail after
maturation to infect the specific host.

24. • Larva : it is a stage immature or mature which
present in nematodes and cestodes, may be in the
eggs or free, may be diagnostic or infective.
•
• In cestodes, the larval stage is modified to a specific
structure and present in tissues. Ex: Hydatid cyst.

26. LIST EXAMPLES OF HELMINTHS INFECTING
DIFFERENT BODY ORGANS AND TISSUES (
INTESTINAL HELMINTHIC INFECTIONS, TISSUE
HELMINTHS, HELMINTHS OF THE BLOOD, HEPATIC
HELMINTHS
• Intestinal helminths:
1. Ascaris lumbricoides
2. Ancylostoma duodenale
3. Entrobius vermicularis
4. Heterophys heterophys
5. Taenia saginata and solium
6. Hymenolepis nana
• Tissue helminths
1. Filarial worms

27. • Blood helminths
1. Schistosoma mansoni
2. Schistosoma hematobium
• Hepatic helminths
1. Fasciola hepatica
2. Echinococcus granulosus (hydatid cyst)

28. Thank you