Difference Between Pathogen and Parasite

Pathogens and Parasites

Pathogens and parasites are two terms that describe microorganisms that can be harmful to the health of any living being. But the major difference between pathogen and parasite is that the term pathogen describes the effect of a microorganism on another living being which is often harmful, whereas the term parasite describes the mode of living of a microorganism which may or may not be harmful. This becomes more clear as we look at the definitions: 

• Pathogen: 

A microorganism that causes disease after infection can be called a pathogen. It is important to note that any microorganism that causes disease after infecting another organism, which is usually detrimental in nature, then and only then, the said microorganism can be called a pathogen. 

• Parasite:

 A microorganism that infects other living organisms and derives benefits such as nutrients from the host which may or may not cause a decrease in the fitness of the host can be called a parasite. Unlike pathogens, it is a necessity for a parasite to be attached to living inside or alongside another organism i.e. for a parasite to survive it is essential that it infect another organism, in general terms. But this infection may or may not lead to the deterioration of the health and fitness of the host organism. This becomes as mentioned earlier, quite a prima facie difference between pathogens and parasites.

What is the Difference Between Pathogen and Parasite?

Pathogens and Parasites: A more detailed view 

It’s quite easy for anyone to have a mix between the concept of pathogens and parasites. But as stated above, a clear difference between pathogen and parasite exists as a pathogen is the cause of a disease, whereas the same may not necessarily be the case for a parasite. For example, Salmonella typhi is a pathogenic bacteria that cause typhoid fever, whereas, on the other hand, some bacteria can prevent colonisation by microorganisms such as Salmonella enterica - a bacteria that causes food poisoning, thus protecting the human body.  

In another view, it can be easily considered that pathogens are the causative agents of any diseases, whereas parasites may or may not provide these causative agents after infection to the host. As a parasite is dependent on its host to survive its life cycle, it may help the host to survive as well. But this is not necessarily true for every parasite. Some may exchange such benefits whilst others do not. Also, parasites can be pathogenic in nature when they release the causative agents of diseases into the host cell, but pathogens are never necessarily parasites since pathogens can have their own independent life cycle. As mentioned above, bacteria, fungi, protozoa and viruses can be pathogenic and parasitic, both except for the viruses. Viruses are usually pathogenic and not parasitic. 

To conclude, it can be simply stated that any microorganism that can cause the degradation of the health and fitness of another living organism owing to the processes of its own life cycle, can be called a pathogen; whereas, any microorganism that essentially requires another organism to carry out its essential functions during its life cycle can be called a parasite. Hence, one is primarily an effect of life stages and the other is primarily a requirement of the benefits for the life stages.