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CLASSIFICATION OF MEDICALLY IMPORTANT PARASITES
 Parasites = Kingdom Protista & kingdom Animalia.
 Kingdom Protista subdivided into subkingdom:
1. Protozoa - Unicellular; a single ‘cell-like unit’ Example amoeba
 Kingdom Animalia subdivided into subkingdom:
2. Metazoa (Heliminths) - Multicellular; a number of cells, making up a complex individual
Example Tapeworm
1. PROTOZOA
 Protozoan parasites of medical importance have been classified into kingdom Protista,
subkingdom Protozoa which is further divided into the following four phyla:
A. Phylum Sarcomastigophora
B. Phylum Apicomplexa
C. Phylum Microspora
D. Phylum Ciliophora
A. PHYLUM SARCOMASTIGOPHORA
Phylum Sarcomastigophora has been subdivided into 2 subphyla based on their modes of
locomotion;
i.
subphylum sarcodina
ii. Subphylum Mastigophora
i.
Sarcodina (Amoebae)
(Sarcos meaning - flesh or body): Subphylum Sarcodina includes those parasites, which have no
permanent locomotory organs, but move about with the aid of temporary prolongations of the
body called pseudopodia.
(a) Genus, Entameba:
E.g. Entameba histolytica
(b) Genus Endolimax
E.g. Endolimax nana
(c) Genus Iodameba
E.g. Iodameba butchlii
(d) Genus Dientmeba
E.g. Dientameba fragilis
ii.
Mastigophora (Flagellates)
(Mastix, meaning whip or - flagellum): Subphylum Mastigophora includes those protozoa which
possess whip-like flagella . Flagellates parasitic for man are divided into 2 groups:
a) Kinetoplastida: These possess a kinetoplast from which a single flagellum arises. They are the
hemoflagellates comprising the trypanosomes and Leishmania, which are transmitted by bloodsucking insects and cause systemic or local infections.
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b) Flagellates without kinetoplast: These bear multiple flagella. Giardia, Trichomonas, and other
luminal flagellates belong to this group. Because most of them live in the intestine, they are
generally called intestinal flagellates
(a) Genus Giardia
E.g. G. lamblia
(b) Genus Trichomonas
E.g. T. vaginalis
(c) Genus Trypanosoma
E.g. T. brucci
(d) Genus Leishmania
E.g. L. donovani
B. PHYLUM APICOMPLEXA (SPOROZOA)
 Phylum Apicomplexa was formerly known as sporozoa.
 Members of this group possess, at some stage in their life cycle, a structure called the apical
complex serving as the organ of attachment to host cells.
i. They are tissue parasites.
ii. They have a complex life cycle with alternating sexual and asexual generations.
(1) Genus Plasmodium
E.g. P. falciparum
(2) Genus Toxoplasma
E.g. T. gondi
(3) Genus Cryptosporidum
E.g. C. parvum
(4) Genus Isospora
E.g. I. beli
C. PHYLUM CILIOPHORA
 These protozoa are motile by means of cilia, which cover their entire body surface. The only
human parasite in this group is Balantidium coli, which rarely causes dysentery.
Ciliates
E.g. Balantidium coli
D. PHYLUM MICROSPORUM
 Phylum Microspora contains many minute intracellular protozoan parasites, which frequently
cause disease in immunodefficient subjects. They may also cause illness in the
immunocompetent, rarely.
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2. METAZOA (HELIMINTHS)
 The helminthic parasites are multicellular (metazoa) bilalerally symmetrical animals having 3
germ layers (triplobastic metazoa) and belong to the kingdom Metazoa.
 The term 'helminth' (Greek helmins-’worm’) originally referred to intestinal worms, but now
comprises many other worms, including tissue parasites as well as many free-living species.
 Helminths, which occur as parasite in humans belong to 2 phyla:
A. Phylum Platyhelminthes (flatworms) – It includes 2 classes:
Class – Cestoda (tapeworms)
Class – Trematoda (flukes or digeneans)
B. Phylum Nemathelminthes – It includes class nematoda and 2 subclasses:
Subclass – Adenophoraea (Aphasmidia)
Subclass – Secernentea (Phasmidia).
A. PHYLUM PLATYHELMINTHES
 The platyhelminths are tape-like, dorsoventrally flattened worms.
 They either lack alimentary canal (as in cestodes) or their alimentary canal is incomplete,
lacking an anus (as in trematodes).
 Body cavity is absent, viscera is suspended in gelatinous matrix.
 They are mostly hermaphrodites (monoecious).
 Phylum Platyhelminthes includes 2 classes:
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i.
ii.
i.





Class Cestoda
Class Trematoda
Class Trematoda
Trematodes have flat or fleshy, leaf-like unsegmented bodies.
The alimentary canal is present but is incomplete i.e., without an anus.
They possess suckers but no hooks.
The sexes are separate in the schistosomes, while the other flukes are hermaphroditic.
They are oviparous.
(a) Genus Schistosoma
E.g. S. mansoni
(b) Genus Fasciola
E.g. F. hepatica
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ii.
Class Cestoda
 Cestodes have tape-like, dorsoventrally flattened, segmented bodies.
 They do not possess an alimentary system.
 The head carries suckers and some also have hooks.
 They possess scolex, neck, and proglottids.
 They are monoecious and body cavity is absent.
 They are oviparous.
(a) Genus Diphylobotrium
E.g. D. latum
(b) Genus Taenia
E.g. T. saginata
(c) Genus Echinococcus
E.g. E. granulosus
(d) Genus Hymenolepsis
E.g. H. nana
B. PHYLUM NEMATHELMINTHES (NEMATODA)
 Nematodes are elongated, cylindrical worms with an unsegmented body.
 They possess a relatively well-developed complete alimentary canal, with an anus. Body
cavity is present.
 The head does not have suckers or hooks, but may have a buccal capsule with teeth or cutting
plates.
 The sexes are separate (diecious).
 They are either oviparous or larviparous.
Intestinal Human Nematodes
Somatic Human Nematodes
Small Intestine
• Ascaris lumbricoides (Common round worm)
• Ancylostoma duodenale (Old world Hook worm)
• Necator americanus (American or New World Hook worm)
• Strongyloides stercoralis
• Trichinella spiralis
• Capillaria philippinensis
Large intestine
• Trichuris trichiura (Whip worm)
• Enterobius vermicularis (Thread or pin worm)
Lymphatics
• Wuchereria bancrofti
• Brugia malayi
• Brugia timori
Skin/subcutaneous tissue
• Loa loa
• Onchocerca volvulus
• Dracunculus medinensis (Guinea worm)
Mysentery
• Mansonella ozzardi
• Mansonella perstans
Conjunctiva
• Loa loa
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