parasitology

1. Medical Parasitology Classification of Human Parasites
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3rd
year Medicine, Derna 96 Dr. Awad Abd El-Kader
Classification of Human Parasites
Human Parasites can be classified according to their structure into:-
1. Unicellular organisms (Protozoa).
2. Multicellular organisms (metazoa) (Helminthes & Arthropods).
Protozoa: General Features
Protozoa are eukaryotic, single-celled microorganisms belonging to the animal kingdom. Protozoa
(Greek protos—first; zoon—animal). Within its single cell, the protozoon contains all structures
required for performing its various functions.
General Morphology
Protozoa exhibit a wide range of size, shape and structure, but all possess certain essential common
features. The typical protozoan cell is composed of:
 Tri-laminar unit membrane (cell membrane), supported by a sheet of contractile fibrils which
enable the cell to change its shape and to move.
 The cytoplasm can often be differentiated into an outer clear ectoplasm (serves as the organ of
locomotion , engulfment of food materials, discharging waste materials and also as a protective
covering for the cell) and granular inner endoplasm.
 Endoplasm shows a number of structures, the endoplasmic reticulum, mitochondria and Golgi
bodies. Contractile and food vacuoles.
 Nucleus within a nuclear membrane. The nucleus is usually single, but may be double or
multiple
Life Cycle Stages:
a) Trophozoite is the feeding, motile and growing stage of the protozoa (vegetative stage), live
in the host.
b) Cyst is a resting or resistant stage (the inactive, non-motile) which enables prolonged
survival under unfavorable conditions due to the presence of a cyst wall. cyst is infective
stage.
c) Some protozoa has different stages in their life cycle like, oocyst, sporozoite and gametocyte

2. Medical Parasitology Classification of Human Parasites
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3rd
year Medicine, Derna 97 Dr. Awad Abd El-Kader
Reproduction:
Reproduction is usually asexual. The most common method is binary fission
(mitotic division of the nucleus, followed by division of the cytoplasm). Some protozoa, as for
instance the malaria parasites exhibit schizogony (multiple fission ) in which the nucleus undergoes
multiple divisions before the cell divides.
Sexual stages . the sexual process by either conjugation in which two organisms join together and
exchange nuclear material, or by male and female gametocytes.
Binary fission Multiple fission
Classification of Protozoa:
Protozoan parasites can be classified according to organelles of locomotion and morphology into
the following:
1. Phylum: Sarcomastigophora
a) Subphylum Sarcodina
b) Subphylum Mastigophora
2. Phylum Ciliophora
3. Phylum Apicomplexa
4. Phylum Microspora

3. Medical Parasitology Classification of Human Parasites
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3rd
year Medicine, Derna 98 Dr. Awad Abd El-Kader
1. Phylum Sarcomastigophora
Phylum Sarcomastigophora has been subdivided into two subphyla based on their modes of
locomotion:
a) subphylum Sarcodina: which do not have permanent locomotory organs, but move by the
aid of temporary prolongations of the body called pseudopodia (Amoebae)
b) subphylum Mastigophora: which move by whip-like flagella ( e.g. Giardia, Leishmania,
Trypanosoma, Trichomonas).
2. Phyla Ciliophora:
These protozoa are motile by means of cilia which cover their body surface. The only human
parasite in this group is Balantidium coli.
3. Phyla Apicomplexa (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 and penetration to host cells (no locomotion organ).
They have a complex life cycle with alternating sexual and asexual generations.(Plasmodium,
Toxoplasma, Sarcocystis, Isospora, Cryptosporidium , Babesia and Pneumocystis).
4. Phyla Microspora:
Phylum microspora contains many minute intracellular spore forming protozoan
(Microsporidium).
Classification of Protozoa according to their habitat in human:
1. Intestinal Protozoa
2. Urogenital Protozoa.
3. Blood Protozoa.
4. Blood and tissue Protozoa