1. The document discusses the classification of parasites, beginning with an overview of parasitology and definitions of key terms like parasite, host, and types of parasite-host associations. 2. Parasites are classified into three main phyla - Protozoa, Platyhelminthes, and Nemathelminthes. Protozoa are single-celled parasites while the latter two contain multicellular worms. 3. Key parasitic groups are described in more detail, including characteristics, examples of genera/species, and life cycles. This includes intestinal and tissue protozoa, cestodes, trematodes, and nematodes.

1. Classification of
parasites

2. DR ABDUL SAMI
MPHIL EASTERN MEDICINE
The Islamia University of
Bahawalpur
Pakistan

3. Parasitology
• Parasitology is the branch of Science which mainly deals about all the Parasites
and its infectious diseases. Whole Parasitology covers mainly Parasites, Host
and its association between them.

4. Parasite
• A living organism which receives nourishment and shelter from another
organism where it lives is called parasites.
• A parasite does not necessarily cause disease.
• Simply parasitism is living in association with the host.
• The parasite derives all benefits from the association and the host may either
not be harmed or may suffer the consequences of this association, a parasite
disease.
• A parasite is an organism that is entirely dependent on another organism,
referred to as its host, for all or part of its life cycle and metabolic
requirements.

5. Host
• An organism which harbors the parasite.

6. Terms for association of Parasites
• Introduction and Classification Parasites also describes different terms
associated association of parasites.

7. Symbiosis
• An association in which both are so dependent upon each other that one can’t
live without the help of the other. None of the partners suffers any harm from
the association.

8. Commensalisms
• An association in which the parasite only is deriving benefit without causing
injury to its host.

9. Parasitism
• An association in which the parasite derives benefit and the host gets nothing
in return but always suffers some injury, however slight the injury may be.

10. Classes of parasites
• Parasite are mainly classified into following two catagories; along with some
other types of Parasites;
• Ecto-parasite (ectozoa): lives outside on the surface of the body of the host.
• Endo-parasite (entozoa): lives inside the body of the host: in the blood, tissues,
body cavities, digestive tract and other organs.

11. Classification of parasites
• The parasites which are divided into three main groups
1. Phylum Protozoa- single-celled organism, multiply in human host, Medical
Protozoology
2. Phylum Platyhelminthes and Phylum Nemathelminthes- multicellular worms,
do not normally multiply in human host, medical Helminthology.
3. Phylum Arthropoda – Medical Entomology

12. Classification of parasitic protozoans
• Protozoa
A) Sacromastigophora
1) Mastigophora
2) Sarcodina
B) Apicomplexa
Sporozoa
a)Coccidia
b)Haematozoa
C) Ciliophora
Microspora

13. 1)Mastigophora
• All are flagellates.
• They have one or more whip like flagella for locomotion at some stage of their
life cycle. In some cases, there is the presence of undulating membrane (Eg.
Trypanosoma).
• The mastigophore includes the intestinal and genitourinary flagellates and the
blood and tissue flagellates.
• The intestinal and genitourinary flagellates are Giardia, Trichomonas,
Dientamoeba, Chilomastik, etc.
• The blood and tissue flagellates are Trypanosoma, Leishmania, etc.
• They reproduce asexually by binary fission.

14. 2)Sarcodina
• They are all typically amoeboid and include Entamoeba, Endolimax,
Iodamoeba, Naegleria, Acanthamoeba, etc. amoebae consist of a shapeless
mass of moving cytoplasm which is divided in to granular endoplasm and clear
ectoplasm.
• They move by pushing out the ectoplasm to form pseudopodia (false feet) into
which the endoplasm then low.
• Amoebae reproduce asexually by simply dividing into two (binary fission)

15. Sporozoa
• The members of this super-class undergoes complex life cycle with alternating
sexual and asexual reproductive phases involving two different hosts.
• Coccidia are intacellular parasites that reproduce asexually by a process called
schizogony (merogony) and sexually by sporogony.
• Class Coccidia includes Isospora and Toxoplasma and class Haematozoa includes
the malarial parasites-Plasmodium species.

16. Ciliophora
• These are the complex protozoa bearing cilia (short hairs) distributed in rows or
patches by which they move.
• They have two kinds of nuclei (macronucleus and micronucleus) and a large
contractile vacoule.
• Balantidium coli, a giant intestinal ciliate of humans and pigs, is the only human
parasite representative of this group.

17. Classification of Parasitic Helminths
• Classification of Parasites includes; parasitic worms, or helminths, of human
beings belong to two phyla- Platyhelminthes (flatworms) and
Nemathehelminthes (Round worms).
• Helminths
A) Nemathelminthes
Nematoda( Round Worms)
B) Platyhelminthes
1)Cestoda(Tapeworms)
2)Trematoda(Flukes)

18. Nematodes
• Their body is elongated, cylindrical and unsegmented. Sexes are separate
(diecious). They also lack hooks and suckers.
• They possess the complete alimentary canal and body cavity. Examples are:
1. Intestinal
2. Somatic (inside the tissues and organs)

19. 1. Intestinal
i. Small intestine only: Ascaris lumbricoides (Common round
worm), Ancyclostoma duodenale (The old world hook worm), Necator
americanus (American hookworm)
ii. Caecum and vermiform appendix: Enterobius
vermicularis (Threadworm or pin worm), Trichuris trichuria (Whipworm).

20. 2. Somatic (inside the tissues and organs)
i. Lymphatic system: Wuchereria bancrofti, Brugia malayi
ii. Subcutaneous tissue: Onchocerca volvulus, Dracunculus medinensis
iii. Lungs: Strongyloides stercoralis
iv. Conjunctiva: Loa loa

21. 1)Cestodes
• These are tape-like, segmented and hermaphrodite organism. They have
suckers in their head and in some species also hooks that attach he tapewor to its
host.. It consists of a head (scolex) and many proglottids.
• Alimentary canal and body cavity are absent. Examples are
Diphyllobothrium, Taenia, Echinococcus, Hymenolepsis, etc.

22. 2)Trematodes
• They are leaf-like unsegmented organism. Sexes are not separate except
Schistosomes which are diecious. They don’t have hooks and suckers in their
head. Alimentary canal is present but is not complete (anus absent).
• The body cavity is absent.
• Examples are Schistosoma, Gastrodiscoides, Fasciolopsis, Fasciola, Clonorchis,
Heterophyes, etc.

23. Scheme followed in parasitological studies
The Introduction and Classification of Parasites along with the study of animal parasites infecting man and
producing clinical manifestations should include:
• History of discovery of the parasite
• Geographical distribution
• Habitat inside the human host
• Morphology and life cycle
• Modes of infection: Reservoir host, source of infection, portal of entry, vehicle of transmission
• Effects of the parasites: pathogenic lesions, clinical manifestations
• Immunological responses
• Methods for specific diagnosis
• Approved therapy for eradication of parasitic infection
• Prophylactic measures for the prevention of parasitic infection of the individual as well as of the
community.

24. Protozoa
• Protozoal parasite consists of a single “cell-like unit” which is morphologically
and functionally complete.

25. Differences between protozoa and metazoan
• Protozoa
Morphology---- Unicellular
A single “cell like unit”
Physiology ----- A single cell performs all the functions: reproduction, digestion,
respiration, excretion
• Metazoan
Morphology---- Multicellular
A number of cells, making up a complex individual
Physiology ----- Each special cell performs a particular function.

26. Structure of Protozoa

27. Morphology
• The structure of a protozoal cell is composed of;
1. Cytoplasmic body
2. Nucleus

28. 1)Cytoplasm
• It may be divisible in to two portions:
1. Ectoplasm: the external hyaline portion; its function is protective,
locomotive and sensory.
2. Endoplasm: the internal granular portion; its function is nutritive and
reproductive

29. Structures developed from ectoplasm
• Organelles of locomotion
1. Pseudopodia: prolongation of temporary ectoplasmic process, seen in Rhizopodea (E.
histolytica)
2. Flagella: long delicate thread-like filaments, seen in Zoomastigophorea. (Giardia
intestinalis)
3. Cilia: fine needle-like filaments covering the entire surface of the body, seen in
Ciliatea. (B. coli)
4. Contractile vacuoles: situated inside the endoplasm; excretory function.
5. Rudimentary digestive organ, such as cytostome (cell mouth) and cytopharynx, seen in
Balantidium coli.
6. Cyst wall: a thickened resistant wall, seen in the cystic stage

30. 2)Nucleus
• It is the most important structure, as it controls the various functions and
regulates reproduction.
• It is situated inside the endoplasm and its structure is often of great help
in the differentiation of genera and species.
• Its structure comprises of the following:
• bound externally by a well-defined nuclear membrane
• chromatin granules, lining the inner side of the nuclear membrane
• karyosome (plastin) situated inside the nucleus either centrally or
peripherally

31. Encystment
• The protozoal parasite possesses the property of being transformed from
an active (trophozoite) to an inactive stage, losing its power of motility and
enclosing itself within a tough wall.
• The protoplasmic body thus formed is known as a cyst. At this stage, the
parasite loses its power of growth and multiplication.
• The cyst is the resistant stage of the parasite and is also infective to its
human host.

32. Reproduction
• The protozoal parasites may exist in two stages: trophozoite and cyst, as
in intestinal flagellates and amoebae.
• In such cases the parasite multiplies only in the trophic stage.

33. The methods of reproduction or multiplication among the parasitic
protozoa are of the following types:
1. Asexual multiplications:
i.) by simple binary fission:

34. In this process, the individual parasite divides either longitudinally or
transversely into two more or less equal parts.Before division all the
structures are duplicated.
ii. by multiple fission or schizogony:

35. • In this process more than two individuals are produced, as in Plasmodia.
• The nucleus of the parent cell at first undergoes repeated divisions which are
then surrounded by the cytoplasm.
• When the multiplication is completed, the parasitic body or the schizont
ruptures and liberates these daughter individuals which in their repeat their life
cycle.

36. 2. Sexual reproduction
i. By conjugation:
• In this process, a temporary union of two individuals occurs during which time
interchange of nuclear material takes place.
• Later on, the two individuals separate, each being rejuvenated by the process,
as in Ciliatea.
ii. By syngamy:
• In this process, sexually differentiated cells, called gametes, unite permanently
and a complete fusion of the nuclear material takes place.
• The resulting product is then known as a zygote, as in Plasmodia.

37. Life cycle
 A protozoal parasite may multiply vigorously by asexual method for a
long time, and later by a change of process it either has recourse to
sexual method of reproduction or undergoes encystment for a change
of its host.
 The sexual method of reproduction often occurs in a different host
other than the one utilized for asexual multiplication; the process is
known as alternation of generation accompanied by alternation of host,
as seen in Plasmodia.
 A protozoal parasite may pass its life cycle in one or two hosts.

38. Second host not required
examples are Rhizopodea, intestinal flagellates and
Ciliates.
1) The parasite in this group adapts themselves for passive transfer from
one host to another by encystment.
2) The species multiplies asexually in its trophic stage and in
circumstances unfavorable for its existence, secretes a resistant cyst-wall,
transforming itself into a cyst.
3) When the condition becomes favorable again, the organism leaves the
cyst (excystment) and continues its life in the trophozoite stage.

39. Second host required
examples are Trypanosoma, Leishmania and Plasmodia.
In Trypanosoma and Leishmania the second host is required for the
development of a special cycle which is essential for the continuation of
the species from one host and the sexual method of reproduction in
another host.

40. Helminthology
• The helminthic parasites are multicellular, bilaterally symmetrical animals
having three germ layer (triploblastic metazoa).

41. Difference between cestode, trematode and nematode
• Cestode
Shape-----------Tape-like;segmented
Sexes-----------Not separate,i.e.,Hermaphrdite(monoecious)
Head space-----------Suckers, often with hooks
Alimentary canal--------Absent
Body cavity-------------Absent

42. Trematode
Shape---------Leaf like;unsegmented
Sexes---------Not separate(monoecious),Except Schistosomes
which are diecious
Head space--------Suckers, no hooks
Alimentary canal--------Present but incomplete; no anus
Body cavity--------Absent

43. Nematode
• Shape---------Elongated, cylindrical; unsegmented
• Sexes---------Separate (diecious)
• Head space---------No suckers, no hooks. Well developed buccal capsule in
some species
• Alimentary canal---------Present and complete; anus present
• Body cavity---------present

44. General characters of Cestodes
1. The majority of cestodes are long, segmented and tape-like, hence called tape-
worms. They are flattened dorsoventrally.
2. Sizes vary from a few millimeters to several meters.
3. Adults worms are found in the intestinal canal of man and animal.
4. Head is provided with suckers (cup like) and sometimes with hooks which
serves as organs of attachment.
5. There are three regions in an adult worm: i) a head (scolex), ii) a neck and iii) a
strobila (a body or trunk) consisting of a series of segments (proglottides).
6. Sexes are not separate, i.e., each individual worm is a hermaphrodite.

45. 7. Body cavity is absent.
8. There is no mouth or digestive system. Alimentary canal is entirely absent.
9. Excretory and nervous systems are present.
10. Reproductive system is highly developed and complete in each segment.
11.Fertilization takes place between the segments; it may be a self fertilization or
a cross-fertilization.

46. General characters of Trematodes (Digenetic)
1. These are leaf-shaped, unsegmented flat worms, called flukes.
2. Size varies from 1 mm to several cm in length.
3. The organs of attachment are two strong muscular cup-shaped
depressions, called suckers. The one surrounding the mouth is called the oral
sucker and the other, on the ventral surface of the body, is called the ventral
sucker (acetabulum).
4. Sexes are not separate, i.e., each individual worm is hermaphrodite
(monoecious) except the Schistosomes.
5. Body cavity is absent.
6. The alimentary canal is present but incomplete. The anus is absent. The
oesophagus bifurgates

47. • 7. Excretory and Nervous systems are present.
• 8. Excretory system consists of “flame cells” and collecting tubules which opens
posteriorly, in to excretory pore.
• 9. Reproductive system is highly developed and complete in each individual. The genital
organ lie between the two branches of the intestine.
• 10. The worm is oviparous, since eggs are liberated.
• 11. Eggs are all operculated (with lid) (except those of Schistosomes) and can developed
only in water. Trematode eggs do not float in saturated solution of common salt
Life cycle
• Life cycle passes in two different hosts
• Definitive host: generally man
• Intermediate host: a fresh-water snail or mollusc for larval development.
• A second intermediate host (fish or crab) is required for encystment in some trematodes.

48. General characters of Nematodes
1. The Nematodes are unsegmented worms with out any appendage. They
are elongated and cylindrical in appearance; both ends often pointed.
2. The size show a great variation (5 mm- up to 1 m) D. medinensis
measuring 1 meter or more.
3. The body is covered with a tough cuticle.
4. The worm possesses a body cavity in which the various organs, such as
digestive and genital systems float.
5. Excretory and nervous system are rudimentary.

49. 6. The alimentary canal is complete, consisting of an oral aperature, mouth
cavity, oesophagus, intestine and a subterminal anus.
7. The nematodes of man are all diecious helminths. The male is generally
smaller than the female and its posterior end is curved or coiled Ventrally.
8. Females are either viviparous (produce larvae) or oviparous (lay eggs)
9. The discharged eggs may hatch directly into infective larvae or they may
require special conditions in which to hatch and up to three developmental stages
before becoming infective larvae. Each stage involves a shedding of the old cuticle
(moulting).

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