Introduction to Parasitology

PARASITOLOGY
Introduction:
A parasite is an organism that obtains food and shelter from another organism and derives all benefits from this association. The parasite is termed obligate when it can live only in a host; it is classified as facultative when it can live both in a host as well as in free form. Parasites that live inside the body are termed endoparasites whereas those that exist on the body surface are called ecto-parasites. Parasites that cause harm to the host are pathogenic parasites while those that benefit from the host without causing it any harm are known as commensals.
I-Protozoa:
Protozoa are a diverse group of unicellular, eukaryotic organisms. Many have evolved structural features (organelles) that mimic the organs of multicellular organisms .
Classification of Clinically Important Protozoa:
Protozoa are classified according to mode of locomotion as the following:
1. (Sarcodina) Amebas:
Amebas move by extending cytoplasmic projections (pseudopodia) outward from the main cell body. Ex: Amoeba spp.

2. (Mastigophora) Flagellates:
Flagellates move by means of two or more whip-like projections (flagella) that rotate and propel the cells through their liquid environment. ex: Trichomonas.

3. (Ciliophora) Ciliates:
Complex protozoa move by means of many hair-like projections (cilia) or patches arranged in rows that cover the cell surface and beat in synchrony, with two kinds of nuclei in each individual. Although there are some 7000 species of ciliates, only Balantidium coli is pathogenic for humans and pigs,