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Difference Between Pathogen and Parasite

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Pathogen 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?

Difference Between Pathogen and Parasite

Microorganism causes disease after infection.

Microorganism will infect other living organisms - a host but that will not result in disease/

Affects the health of the host and can be life-threatening eg: COVID-19 virus.

May affect the fitness of the host which over a period of time can be fatal or not. 

It does not usually require a host to complete its life cycle.

Its mode of living and the completion of life cycle is dependent on the host. 

Viruses are prime examples of a pathogen along with some bacteria, protozoa and fungi. 

Some Bacteria, protozoa and fungi can be parasitic. But viruses aren't usually parasitic. 

Pathogenicity is a state of degradation of health. 

Parasitism is a mode of living for the microorganism.

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.

Parasites vs Pathogens


Parasites are living organisms which live inside or attached to other organisms to draw some benefit from it. The organism on which a parasite lives is called a host. The parasite's life depends on attachment with the host and without the host the parasite will lose its life. Some common examples of parasites are Fungi, lice, ticks, tapeworms and pinworms. Sometimes the parasite causes infection in the host which could also be severe and may cause death of the parasite. 

In most cases parasites depend on the host for nutrition and shelter. Without the host the parasite will die. Some of the parasites manipulate/infect the host in a way that the host will provide the nutrients and shelter to it which is out of the host's natural behavior. This causes the health of the host to deteriorate and may be fatal in some cases.

Most of the parasites are not harmful in nature. In fact some of the parasites cause benefits to the host. In the human body there are parasitic bacteria in our intestine which helps us in digestion of our food and that results in better absorption of nutrients from our food. Few parasitic bacteria also help us in preventing infection from disease causing parasites. The parasite depends on the host to live the whole life so it is always in the best interest of the parasite that the host lives a healthy life. The healthy host will always provide better food and nutrients to the parasite. But remember it is not always the case and parasites can cause disease directly or indirectly to the host organism.


Pathogens are organisms which cause disease in other organisms after infecting them. The pathogens depend on the host organism to achieve some of its life functions and while achieving that it causes the degradation of health for the host. Some common examples of pathogens are Bacteria, Protozoa, Virus and Fungi.

Some pathogens are parasitic in nature and may depend on the host to achieve its nutrients and shelter but they will be called pathogens only if they cause disease in the host. 

All the transmissible diseases in animals are caused by pathogens. Pathogens are by nature harmful to the host and they normally depend on the host to complete one phase of their life cycle.

For example the virus enters the host organism's cell and reproduces its progeny inside it causing the cell to rupture. After that the virus moves out to infect new cells.

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FAQs on Difference Between Pathogen and Parasite

1. What is a Pathogen?

A pathogen is any microorganism that causes a disease which can be fatal if left untreated. A pathogen usually affects the health of other living organisms after infection. Bacteria, fungi, protozoa and virus are all examples of a pathogen.

2. What is Parasite?

A parasite is any microorganism that requires a host which is usually another living organism to complete its life cycle and obtain the necessary nutrients as benefits. It may cause harm or not to the host or do not have any effect on the health of the host body. Some bacteria, fungi and protozoa are parasitic in nature.

3. What is the Difference Between a Pathogen and a Parasite?

A pathogen is a causative microorganism for any disease, whereas a parasite is a microorganism that depends on another host living organism for its life cycle. While doing so, it may or may not cause any disease or affect the health of a person in a detrimental manner.

4. Are there parasites in plants?

Yes there are a lot of parasites available in plants. There are a lot of vines that do not have roots and they grow on top of the other plants to suck its nutrients and survive on top of it. There are a lot of worms who survive on plants and depend on it for its life. They are all examples of parasites on plants. In most cases parasites cause a decrease in the growth of the host plant by consuming the nutrients in the host.

5. Can hosts also depend on parasites?

Theoretically yes hosts can benefit from parasites and can also depend on them. But those relationships are termed as symbiotic relationships. In those relationships, different organisms come together to contribute something for the other organisms so that both can benefit from the relationship. There are a lot of symbiotic relationships available in nature. The best example of it is Lichen. This is a relationship between algae and fungus in which the dominant partner is a fungus. It gives most of its characteristics to the relationship.

6. How do pathogens transfer from one organism to another?

Normally the pathogens depend on hosts for only a phase of their life cycle. Aside from that phase, the pathogens can survive outside the host body. In the non dependent phase the pathogens get out of the host body and can be transmitted to other organisms via multiple methods. Some time they use other vector organism to transmit where as some other time they transmit via air, water,soil and contact/sexual intercourse with infected organisms. They can also be transmitted via use of infected objects.

7. Where can I find more about pathogens and parasites?

We have created notes about all the important concepts and information about the parasites and pathogens which are available in Vedantu. All the notes have been created by the best teacher around India from different boards so that our material will help you irrespective of the board you are studying in. You can sign up and start downloading our course material on parasites and pathogens along with many other important topics in biology. Sign up today and experience a new way of learning biology.

8. How can we save ourselves from pathogens?

The best way to save ourselves from pathogens is to stop them from infecting us. As we know there are multiple ways the pathogens get transmitted. So we have to take care, we take precautions in avoiding the transmission through all the modes. We should keep all our items disinfected by keeping them clean. Wash our hands frequently and use masks to avoid transmission through air. We should always have clean hygienic water and take precautions while attending to the infected person. 

9. Why should I study with Vedantu?

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