Introduction

Abstract

Parasitology is a branch of Zoology as well as a part of the medical science also. The science of parasitology has a long history and has its foundations in zoology with its importance on identification, classification and the interpretation of lifecycles with their concern for the disease caused by parasites. Parasites are those organisms which cannot sustain without the help of others. They are dependent on others for food and shelter but the relation is heterospecific. The organisms which give them food and shelter are hosts. Once entered within the host, parasites take complete control on its host and establish an intimate relationship between them. Parasites establish combinations of physiological, biochemical and nutritional adaptations to set up themselves within the host. Parasites also create mechanism for evading the immune responses of the host so that they can reside permanently within the host until death without any resistance. Parasites are threat to the millions of human and animals throughout the world. They are the reason of human misery and immense income loss to the country. There are innumerable numbers of parasitic organisms in the globe. It is believed that the number and type of parasites are far more than non-parasitic organisms. Though we exclude viruses and bacteria those are all parasites yet the number of parasites across those of non-parasitic free living organisms.