An infection is a condition that causing health problem to a living organism. In infection a certain part of living organism will hosting foreign substance or species. The foreign species will live, eat from the host, trying to multiply.
In many cases the foreign organism will damage the host where they are trying to live and causing health problem and disease to the host. The foreign organism or also called as pathogens are mostly very small and microscopic.
There will be fight between the foreign species with the host as the host trying to defend itself and eliminate the foreign species and prevent them from multiplying, consume and damage the host with the help of immune system.
Every large organism that consists from various multiple cells (multi-cellular) often become the host and colonized by single cell microorganism in to certain degree. When the population of pathogens are small and do not affect or interfere the main function of the host, then the host and the pathogen will be able to coexist together and causing no problem to the living organism of the host.
But, most if the opposite reaction is happen and the foreign species are trying to interfere the host normal function and activities and threatening the host well-being, it will be called as infection. Therefore, an infection is basically a war between a host which trying to defend itself from a pathogen and pathogen who trying to live out from the host.
There are some types of pathogen that often attack larger organism and cause infection such as; viruses, bacteria, parasite, fungi, viroid and prions. There are some factors that will determine whether the pathogens bring disadvantages to the host or not such as:
The entry route of the pathogen
The area of the host where the pathogens staying and live
The amount of pathogen that are exist in the host
The potential danger severity from the foreign organism
The status and condition of the host’s immune system