Parasitology is the scientific study of parasites, their hosts, and the relationship between them. It examines the biology of parasites and parasitic diseases, including their distribution, biochemistry, physiology, ecology and how they affect hosts. Parasites can be unicellular, worms, or arthropods. They either live on the outside surface of a host's body as ectoparasites, or inside the host's body as endoparasites. Hosts are organisms that harbor parasites and can take various forms, such as definitive, intermediate, paratenic, reservoir, or compromised hosts.

1. Parasitology
Parasitology is the study of Parasites, their
host and the relationship between them.
Parasites are living organism which recieves
nourishment and shelter from another organism
where it lives.
Host are organisms which harbour parasites.

2. Parasitology
Finally,
Parasitology is the scientific discipline
concerned with the study of the biology of
parasites and parasitic disease, including, the
distribution, biochemistry, physiology,
molecular biology, ecology, evolution and
clinical aspects of parasites including the host
response to these agents.

3. Parasitology
A parasite could be unicellar, worm or an
arthropods.
Medical parasitology has included the study of
three major groups of animals; parasitic
protozoa, parasitic helminthes (worm) and
those arthropods that directly cause diseases
or act as a vector of various pathogens.

4. Parasites
 On the basis of their location, parasites can
be divided into two types;
1. Ectoparasites (live on the surface of the body
e.g., Human louse, ticks, mites etc).
2. Endoparasites (live within the the body of
host. eg. All protozoan parasites, helminthes
etc.

5. Host
Organism which harbour parasites
Following types;
1. Definitive host
2. Intermediate host
3. Paratenic host
4. Reservoir host
5. Compromised host

6. Host Parasites Relationships
1. Symbiosis
2. Commensalism
3. Parasitism