Examples of Pathogens

bacteria-108895_1920Pathogens are infectious agents that can cause a disease in a host. This kind of agents can be, bacterias, viruses, prions, fungi, parasites and viroids. There is a definition for pathogenicity which stands for disease-causing potential in pathogens, and virulence is the level of the pathogenicity, which tells us about the strength of the pathogens. A word pathogen comes from Greek words pathos which means “suffering, passion” and genēs which means “producer of”. A term came into use in the 1880s.


There are opportunistic or good bacteria and bad or pathogen types of bacteria. The opportunistic ones are inside our body and they help our digestive system work by creating some sorts of substances and even help some vitamins absorption. They can damage the body if our immune system is compromised which can lead to some disease. They are capable of direct influence on the body, or indirect through toxins which some of them produce. Some important bacterias are Streptococcus, Mycobacterium tuberculosis, Shigella, Campylobacter, Salmonella, Staphylococcus and other. They can cause many diseases like tuberculosis pneumonia, tetanus, diphtheria, syphilis, typhoid fever and more. There are vaccines which we get in early life for some of the dangerous illness. And for bacteria infections we use antibiotics for cure.


They can invade the DNA of an organism, reproduce and invade the host, leading to reproduction with that DNA. The effects can be some mutations and diseases. The most common disease is flu or cold, which is usually by viruses. This kind of agent can be virus Influenca and they belong to Orthomyxoviridae family. There are other families of viruses such as Adenoviridae, Picornaviridae, Flaviviridae, Retroviridae, Papovaviridae, Polyomavirus, Rhabdoviridae, Togaviridae, Paramyxoviridae, Herpesviridae and Hepadnaviridae. They can cause some viral diseases like smallpox, rubella, influenca, measles, mumps, ebola, chickenpox. They are smaller than bacteria and they have either DNA or RNA structure.


The fungus can be a cell or multiple cell organism. They can be found in any part of living world, from soil to sea and water. For humans, they can usually cause some skin diseases like thrush, athletes’ foot and ringworm. Single cell funghi are yeasts. They are important for cancer study research. An example of this kind of fungus is Candida which is an opportunistic pathogen but can cause disease in a reduced immune system organism. As a multicellular funghi, there are mushrooms.


They are unicellular organisms which were introduced in 1818s. They can cause diseases from mild to life-threatening and can affect humans and animals. Plasmodium can cause malaria, which was a devastating disease for the human race. Other protozoa, like Trichomonas, can cause sexually transmitted diseases. There are a few phyla inside protozoa: Euglenozoa, Amoebozoa, Choanozoa, Loukozoa, Percolozoa, Microsporidia and Sulcozoa. Amoebozoa can cause amoebic dysentery that have symptoms from a digestive system like diarrhea.


They are the smallest microorganisms and they have small circular RNA without any protein coat on top. They are rarely human pathogens, but some of them can be Hepatitis D viruses which are an RNA small viroids.


Prions come from a name of proteinaceous infectious particle which stands for a pathogen that causes  transmissible spongiform encephalopathies (TSE). This kind of disease attacks the nervous system and leads to degenerative disease. They are extremely small and they can’t reproduce by themselves because they lack in the nucleic acid. They use protein refold process which damages the brain and cause nervous tissue death.


Human parasites come in a lot of forms, from worms to protozoa. They can be endoparasites, which invade the body from inside and ectoparasites, that affect the skin. The worms can lay eggs in the organs and skin, and also, they can lead to creating cysts. This kind of eggs and cysts can be found in feces because they are usually inside digestive system. They live and feed on a host’s nutrients and live at the other’s expenses. Contaminated water can lead to Giardia infection, and cats can transfer Toxoplasmosis. There are obligate and facultative parasites, where the obligate ones depend on a host’s nutrients and substances for their life cycle. There are also direct and indirect ones. Direct parasites have one host, but for indirect one, there will be some intermediate hosts in between.

Pathogens Path Of Spreading

It is important to know the spreading of a pathogen to know how to prevent it and to protect yourself from this kind of diseases.

  • Direct contact. This way you can infect another person with contact with their fluids like blood, saliva, genital fluids. Example for this is sexually transmitted diseases and athlete’s foot.
  • Droplet cloud. When you sneeze or talk, a cloud of small droplets can spread in the air leading to someone else’s mouth and nose, where they can inhale them. This can cause an infection through the respiratory
  • Fecal-Oral Transmission. Pathogens can go inside the body through contaminated water and food and cause diseases like salmonella and cholera.
  • Vectors. Through insects and animals. Like house flies that cause dysentery and mosquitoes that cause malaria.


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