Difference Between Parasite and Pathogen

Main Difference – Parasite and pathogen

Parasite and pathogen are two types of organisms that can be harmful to hosts. A parasite grows, feeds, and is sheltered in or on the host organism without contributing to the survival of the host. A pathogen is an organism that causes a disease in the host. Pathogens can be any type of microorganisms such as bacteria, virus, prions, fungi, protists, and parasites. The main difference between parasite and pathogen is that parasite is a type of pathogen whereas pathogens are disease-causing agents in host organisms. However, not all parasites are pathogens. But, parasites are eukaryotic organisms while pathogens except parasites and fungi are prokaryotic organisms.

Key Areas Covered

1. What is a Parasite
– Definition, Features, Examples
2. What is a Pathogen
– Definition, Features, Examples
3. What are the Similarities Between Parasite and Pathogen
– Outline of Common Features
4. What is the Difference Between Parasite and Pathogen
– Comparison of Key Differences

Key Terms: Bacteria, Fungi, Host Organism, Parasite, Pathogen, Protists, Virus, Worms

What is a Parasite

A parasite is an organism that lives in or on another organism and benefits at host’s expense. Ideally, parasites refer to organisms that are visible to the naked eye. Therefore, parasites are macroscopic organisms. Mainly, protozoans and helminths are considered as parasites. They are host specific. Hence, they only cause diseases only in specific organisms. Approximately, 36,400 species of protozoans have been identified as pathogens in other organisms. On the other hand, about 70 species of protozoans and 300 species of helminths are known as parasites in humans. Among them, about 90 species cause diseases in humans. On that account, not all parasites cause diseases in humans. Plasmodium is one of the well-known examples of protozoan, which is a parasite in humans. A human louse is shown in figure 1.

Figure 1: Human Louse

Tapeworm, roundworm, flatworm, fluke, and pinworm are examples of worm parasites including helminths. Other than these two groups, lice and fleas are also considered as parasites in humans. They are called ectoparasites since they live on the host. The most characteristic feature of parasites is the high rates of reproduction.

What is a Pathogen

A pathogen is an agent that causes a disease to its host. It can be a bacterium, fungus, virus, prion or parasite. The host organism can be a plant, animal or microorganism. Bacteria are less than 10 micrometers in size and may cause typhoid, cholera, food poisoning, and gonorrhea. Viruses are much smaller than bacteria. They reproduce inside the host cell. Influenza, common cold, and AIDS are caused by viruses. Fungi are eukaryotic organisms. Fungal infections are more common in the skin. Athlete’s foot and ringworm contagious are examples of diseases caused by fungi. Clostridium tetani, the bacterium causing tetanus is shown in figure 2.

Difference Between Parasite and Pathogen

Figure 2: Clostridium tetani

Protists such as amoeba and Plasmodium cause diseases in humans. Amoebic dysentery and malaria are diseases caused by these organisms.

Similarities Between Parasite and Pathogen

Both parasite and pathogen can cause disease in host organisms.
Both parasites and pathogens are specific to the host.
Both parasites and pathogens exhibit high multiplication rates.

Definition

Parasite: A parasite is an organism that lives in or on another organism at the host’s expense.

Pathogen: A pathogen is an agent that causes a disease to its host.

Examples

Parasite: Protozoans and helminths are parasites.

Pathogen: Pathogens can be bacteria, fungi, virus, prions, protists, and parasites.

Level of Organization

Parasite: Most parasites are prokaryotic organisms, except parasites and fungi.

Pathogen: Pathogens are eukaryotic organisms.

Microscopic/Macroscopic

Parasite: Parasites are macroscopic organisms.

Pathogen: Pathogens can be either microscopic or macroscopic organisms.

Pathology

Parasite: Not all parasites cause diseases in the host organism.

Pathogen: All pathogens cause diseases in the host organism.

Types of Diseases Caused

Parasite: Malaria and amoebic dysentery are examples of diseases caused by parasites.

Pathogen: Common cold, influenza, aids, tetanus, and food poisoning are diseases caused by pathogens.

Conclusion

Parasite and pathogen are two types of organisms that can cause diseases in host organisms. Parasites depend on the host organism for their benefits. Most parasites are macroscopic organisms. Worms, protists, and ectoparasites are the different types of parasites. They sometimes cause diseases in the host. All pathogens cause diseases in the host. Bacteria, viruses, fungi, and protists are the main types of pathogens. The main difference between parasite and pathogen is the relationship between the two types of organisms and their pathology.

Reference:

1. Nordqvist, Christian. “What is a Parasite? What do Parasites do?” Medical News Today, MediLexicon International, 26 Feb. 2016, Available here.
2. Alberts, Bruce. “Introduction to Pathogens.” Molecular Biology of the Cell. 4th edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.

Image Courtesy:

1. “Male human head louse” by Gilles San Martin (CC BY-SA 2.0) via Flickr
2. “Clostridium tetani 01” By CDC – Centers for Disease Control and Prevention’s Public Health Image Library (Public Domain) via Commons Wikimedia