7.3: Types of Pathogens
Below are the categories of pathogens that we currently know about. Some are more well-known than others. It is important to remember that often the symptoms - and even disease processes - that we associate with infection are in fact our body’s own immune response to the pathogen. However, knowing the type of pathogen that causes the disease is helpful at not only preventing its transmission but discovering treatment or prevention methods. For example, antibiotics are effective at treating bacterial upper-respiratory infections, but will not be effective against viral upper-respiratory infections.
- Viruses: Composed of either RNA or DNA packaged in a protein sheath, viruses invade host cells and cause the host cell’s nucleus to reproduce the virus, often killing the host cell in the process (NHGRI, 2024). As the virus is reproduced within the host organism, it may “shed” the virus by releasing virus-laden mucus through coughing or sneezing. Viral shedding is essentially when the infected person is most infectious to others (ACHI, 2020).
- Bacteria: These are single-cell organisms that come in a variety of shapes, many of which are symbiotic to humans and animals (ex: gut microbiota). Some cause diseases by reproducing so rapidly that they invade healthy tissues, or by releasing toxins that kill off healthy cells (Drexler, 2010).
- Worms: (aka helminths, also commonly known as a parasite rather than a pathogen). Worms attach themselves - usually to the intestines - of the host that ingests them, in order to gather nutrients. They can spread to various parts of the body and reproduce.
- Fungi: These are multicellular organisms that reproduce by creating spores that can be airborne or waterborne, including molds, yeasts, and mushrooms. Most fungi don’t cause illness. When they do, fungal infections can affect the surface (skin) or internal organs (lungs or blood). Sometimes exposure to fungi can simply cause asthma or allergy symptoms ( About Fungal Diseases , 2023).
- Protozoa: Also single-cell organisms, these act like parasites and cause diseases such as malaria, trichomoniasis, and giardia, among other diseases (Contributors to Wikimedia projects, 2023).
- Prions: A relatively newly discovered pathogen, prions are only proteins that are abnormally folded. When this protein comes in contact with other proteins, it can change their structure, causing holes to form in tissue. Creutzfeldt-Jakob disease and “mad cow disease” are thought to be caused by prions.