Host Parasite Relationships:

Parasite is a type of symbiosis, which lives at the expense of host life and this interaction is called parasitism. Hosts serves as a physical location or microenvironment that provides place for habitat, growth factors, nutrients supply to parasites. Host helps in the multiplication of parasites. The host is under infection when a parasite starts multiplying on it. Ultimately parasites are metabolically dependent on the host for its survival. Parasites are smaller than host size. For instance bacteria, fungi, algae, protozoan, nematodes, virus, plants and animals are parasitic organisms.

Types of host-parasite relationship

Parasite is completely dependent on host and the symbiotic microbial interaction is dynamic. Depending on the recognition of parasite on host it is classified as follows.

• Ectoparasites - Parasites found outside the host surface
• Endoparasites - Parasites that are found inside the host cell
• Final host - Host on which parasites sexually reproduce
• Intermediate host - Host that are not continuous and are temporary
• Transfer host - Tool for reaching final host and it is not involved in completion of life cycle
• Reservoir host – A host that are endangered or infected by parasites resulting in human infections

Factors inducing infection

When the parasite growth is not under control then infection rate increase depending on the following varying conditions.

• Location
• Number of organisms
• Severity

Organisms that induce infectious disease are referred as pathogenicity and the organism is called as pathogen. They are two types of pathogen namely primary pathogen and opportunistic pathogen. When a pathogen cause disease by direct interaction with the host that is healthy, it is referred as primary pathogen. When an organism is partially infected by pathogens that are likely to cause infection is referred as opportunistic pathogen.

Host-Parasite relationship outcome

Factors that decide host parasite relationship are

• Number of organism of host
• Severity or virulence nature of pathogen or degree of pathogenicity
• Resistance degree of host

Only some organism cause diseases when the degree of pathogenicity is not under control or resistible by host. Virulence of pathogen is characterized by infective nature, invasive property and potential of pathogen.