The 4 types of pathogens (and their characteristics)

There is no doubt that one of the great advances of mankind has been medicine. Thanks to this science, our longevity has increased considerably in a few decades.

However, infectious diseases are still one of the most common causes of death in the world today and their study has not ceased. Through these lines of research, we know that these conditions are caused by infection of the patient with some type of pathogen.

To understand this process a little more, here we are going to look a summary of the main types of pathogens.

    What is a pathogen?

    We understand it as a pathogen or an infectious agent any microorganism that infects other organisms, causing damage and injury.

    Traditionally, it was considered to be any invasive organism, although it is now separated into two terms: pathogens, which include acellular microorganisms, prokaryotes, and fungi; and parasites, for the rest of eukaryotes (protozoa, helminths and ectoparasites) which generate parasitic diseases.

    Thus, pathogens are studied by scientific fields such as medicine or biology.

    Types of pathogens

    Microorganisms are the main cause of disease in humans. Pathogens are adapted to live in other organisms (host) because on their own they cannot cover all their needs, such as feeding or reproduction. Because of this, they cause damage to the host cells, which triggers the disease.

    How the types of pathogens are classified depends on the taxonomic category to which they belong.In other words, if it is a bacterium or a virus, for example. In this case, we will name these types of pathogens from the simplest to the most complex (at the structural level).

    1. Let us pray

    This strange type of pathogen is essentially a protein. It doesn’t even have genetic material, but it has a great ability to damage the body; is the cause of transmissible spongiform encephalopathy (TSE), A fatal neurodegenerative disease he doesn’t care about. Several variants are known, and one affects mammals, including humans.

    The protein that causes this infection in these cases is “PRP” (prion protein). The funniest is is a protein in our cells, which is mainly found in neurons and the gene that produces it is in the mammalian genome, so it’s from that group of vertebrates.

    In order for the normal protein (PrPc) to become its pathogenic form (PrPsc), it must produce a change in its protein structure.. This variation causes the protein to lose its natural function and acquires the ability to self-reproduce, to acquire resistance to proteases (enzymes that break down certain proteins) and to accumulate amyloid bodies, causing the death of neurons, degenerating in illness.

    Prions are linked to conditions such as kuru disease (due to human cannibalism), Creutzfeldt-Jakob disease (genetics), or bovine spongiform disease, commonly known as mad cow disease.

    2. Viruses

    The next type of pathogen is the virus. Cellular, it is usually a protein structure (Capsid) that houses genetic material inside. They are obligate intracellular parasitic microorganisms because they cannot reproduce on their own and they need the machinery of a cell to multiply in number. This causes the generation of the disease by damaging the host cells. Different criteria are used to classify them, depending on their genetic content or their structure.

    Viruses cause a large number of infections in humans and act in very different ways. They can cause temporary (such as influenza virus), chronic (chronic hepatitis B virus) or latent (herpes virus) conditions.. The latter case refers to pathogens that enter the host and generate a condition, but upon healing, the infectious agent is not completely eliminated from the body and goes unnoticed, periodically activating, causing a new condition. In some cases, they can degenerate into cancer with the insertion of genetic material into the chromosome of the cell, such as human papillomavirus (HPV) and cervical cancer.

      3. Bacteria

      The next type of pathogen is bacteria, although not all of them work this way.Since it is a very diverse biological category, encompassing a whole kingdom of prokaryotic cells. Prokaryotic cells differ from eukaryotes (the one we have) in that they do not have a nucleus inside to house their genetic material (DNA), do not have membrane organelles (cellular machinery), and have a cell wall that protects them (with a few exceptions).

      Many criteria are used to classify bacteria, but mainly by the composition in the cell wall (Gram stain), its structural form (bacillus, coconut or spirochete) and its interaction with oxygen (aerobic or anaerobic).

      When acting as pathogens, bacteria differentiate based on their form of interaction with the host.

      Like viruses, there are bacteria that are obligate intracellular pathogens because they do not have their own mechanisms for obtaining ATP, the energy of the cell. Chlamydia is one example.

      Other bacteria have the ability to enter cells, but they are also not necessary for survival., And can also be outside cells; in this case, it is known as a facultative intracellular pathogen. It doesn’t mean that you have to be inside another organism i.e. you don’t live in an open environment. An example of this group of pathogens is Salmonella.

      Finally we have extracellular pathogens, Are they found inside the body, but never enter the cells. An example of this group is Streptococcus.

      Even though we are not aware, we are surrounded by microorganisms and millions of bacteria live in our skin, mouth or digestive tract. Sometimes the fact that we have the disease is nothing more than the product of a combination of factors, such as the initial amount of the pathogen or the state of the immune system of the host, our body. . In the case of infectious bacteria, their damage can be caused by their own action in cells or by the effect of the toxins they secrete, which sometimes cause tissue destruction.

        4. Mushrooms

        The last type of pathogen is the fungus. They are eukaryotic organisms which, unlike prokaryotes, already have an intracellular nucleus and membrane organelles. In addition, the cells of the fungi are strengthened by a cell wall. Its mobile organization can be unicellular (yeasts) or in filamentous hyphae (chains).

        In the case of infectious fungi, they work in two different ways. The first are superficial infectionsIn this case, the pathogen is dermatophytes and they attack the skin, hair or nails (eg athlete’s foot).

        In the second case it would be the fungal infection, That is to say when its action is inside the host, either on the mucous membranes or on the organs (for example, Candida).

        What about parasites?

        Although today they are generally no longer included in the pathogen types, they once were. Let’s look at the different categories.

        Protozoa are eukaryotic single-celled microorganisms. Like bacteria, this category includes different ways of life, including parasitic organisms both extracellular and intracellular. Plasmodium, which causes malaria, is believed to be the deadliest protozoan today, wreaking havoc in developing countries.

        Another group of parasites are helminths, which are worms, i.e. eukaryotic multicellular organisms. As before, there are free ways of life as parasites, and generally have a very complex life cycle, with phases of sexual reproduction (union of sex cells or gametes) and asexual (identical copies). Examples are intestinal tapeworms, Ascaris (intestinal nematode) or Trichinella (nematode causing trichinosis).

        for Finally, there are ectoparasites. They are arthropods, especially insects (such as lice) and arachnids (mites) that attach to or burrow into the host’s skin for a long time. They usually do not cause great damage. The greatest danger to arthropods is when they act as vectors, that is, when they carry a pathogen inside (such as the bacteria Borrellia and the tick in Lyme disease) or parasites. (Plasmodium and mosquito in malaria) and transfer with your bite.

        Bibliographical references:

        • Kumar V., Abbas A. and Aster J. (2013). “Robbins, Human Pathology” (9th ed.) Editorial Elsevier Saunder.
        • Cacace V. (2011). “Biology of Prions”. https://arxiv.org/ftp/arxiv/papers/1106/1106.3533.pdf.
        • Iracheta MA (2009). “Bacteria and viruses How do we defend ourselves?”. http://www.rac.es/ficheros/doc/00919.pdf.
        • Permane J. and Salavert M. (2013). “Epidemiology and prevention of nosocomial infections caused by filamentous fungal species and yeasts.” https://seimc.org/contenidos/documentoscientificos/eimc/seimc_eimc_v31n05p328a341.pdf.

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