Infection 

Introduction

The interaction of micro organisms with the human host is variable.It differs based on the type of micro organisms and the type of host.The immunity plays an important role in the host micro organisms interaction.

Based on their relationship the interaction may be of two types and they are saphrophytes and parasite.

Saphrophytes

The saphrophytes are free living micro organisms that live on dead or decaying organic matter.They are beneficial micro organisms that are found in abundance in soils and water.water play an important role in the degeneration of organic material in nature and help in their recycling.Generally they never cause any infection but occasionally can become pathogen when opportunity is given.

Parasite

The parasite are those micro organisms that can infect and multiply in the host.In Medical micro biology the word parasite refers to a protozoan or helminthic nematodes trematode cestodes organisms.The parasite may be a pathogen or a commensal.

Pathogen 

The pathogen are those micro organisms that can cause disease in the host.The ability of a cause disease is called as pathogenicity 

The pathogen may be of two types

Primary pathogen 

These pathogen are capable of causing disease in a healthy individuals with Normal immunological defences.

Opportunistic pathogen

These pathogen cause disease only to the individual who has an impaired or compromised immunological defence arising due to acquired disease or by the use of immuno suppresive drugs.Most of the normal flora of the human body may turn as opportunistic pathogen e.g Candida and Escherichia coli

Commensal

Commensal are those micro organisms live with the host without causing any diseases to them.The normal flora of human body is mostly commensal and can occasionally turn into opportunistic pathogen.

Infection

Infection is the lodgement and multiplication of a pathogen in the cell or tissue of the host.Disease is the consequences of infection.

Infectious disease 

An infectious disease is any change from the healthy state of the host which may lead to incapability of carrying normal function due to the infection.

Classification of infection

Infection is of different types

Primary infection

Infection for the first time by a pathogen in a host is termed as primary infection.

Reinfection A subsequent infection by the same pathogen in a host is termed as reinfection.

Secondary infection A new pathogenic infects a host whose resistance is damaged due to the already existing infectious disease