The 4 Types Of Pathogens (and Their Characteristics)
There is no doubt that one of the great advances of humanity has been medicine. Thanks to this science, our longevity has been significantly extended in a matter of decades.
However, infectious diseases continue to be one of the most frequent causes of death in the world today, and their study has never ceased. Thanks to these lines of research, we know that these conditions are caused by the infection of the patient by some type of pathogenic agent.
To understand this process a little more, here we will see a summary of the most important types of pathogens
We understand as a pathogen or infectious agent any microorganism that infects other organisms, causing damage and injuries
Traditionally, any organism was considered invasive, although it is now separated into two terms: pathogenic, which includes acellular microorganisms, prokaryotes and fungi; and parasites, for the rest of the eukaryotes (protozoa, helminths and ectoparasites) that cause parasitic diseases.
Thus, pathogenic agents are studied by fields of science such as Medicine or Biology.
Types of pathogens
Microorganisms are the main cause of diseases in humans Pathogens are adapted to living inside other organisms (host), since they themselves cannot meet all their needs, such as feeding or reproducing. Due to this fact, they induce damage to the host cells, which triggers the disease.
The way the types of pathogens are classified depends on the taxonomic category to which they belong, that is, if it is a bacteria or a virus, for example. In this case we will name these types of pathogens from the simplest to the most complex (at a structural level).
1. Prions
This strange type of pathogen is, fundamentally, a protein. It does not even have genetic material, but it has a great capacity to damage the organism; It causes transmissible spongiform encephalopathy (TSE), a lethal neurodegenerative disease for which there is no cure. Various variants are known, and there is one that affects mammals, including humans.
The protein that causes this infection in these cases is “prp” (Prionic Protein). The curious thing is that It is a protein found in our cells, which is mainly present in neurons and the gene that produces it is in the genome of mammals, which is why it originates from this group of vertebrates.
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 acquire the ability to self-reproduce, to gain resistance to proteases (enzymes that degrade certain proteins) and to accumulate amyloid bodies, which causes the death of neurons, degenerating into the disease.
Prions are linked to conditions such as kuru diseases (due to human cannibalism), Creutzfeldt-Jakob disease (genetics) or bovine spongiform disease, which was commonly called “mad cow disease.”
2. Viruses
The next type of pathogenic agent is viruses. Acellular, these are generally a protein structure (Capsid) that houses genetic material inside They are obligate intracellular parasitic microorganisms, since they cannot reproduce on their own, and they need the machinery of a cell to multiply in number. This fact causes the disease to be generated by damaging the host’s cells. Several criteria are used to classify them, according to their genetic content or their structure.
Viruses cause a large number of infections in humans, and they act in very diverse ways. They can cause temporary (such as the flu virus), chronic (chronic Hepatitis B virus) or latent (herpes virus) conditions This last case refers to pathogens that enter the host and generate a condition, but upon recovery from it, the infectious agent is not completely eliminated from the body and goes unnoticed, activating periodically, causing a new condition. In some cases, they can degenerate into cancer with the insertion of genetic material into the cell’s chromosome, as is the case with human papillomavirus (HPV) and cervical cancer.
3. Bacteria
The next type of pathogen is bacteria, although not all of them act like this, since this is a very diverse biological category, covering an entire kingdom of prokaryotic cells. Prokaryotic cells differ from eukaryotic cells (the one we have) by not having a nucleus inside to house their genetic material (DNA), not having membranous organelles (cell machinery) and having a cell wall that protects them. (with some exceptions).
Many criteria are used to classify bacteria, but mainly by the composition of the cell wall (gram stain), its structural form (Bacillus, coccus or spirochete) and its interaction with oxygen (aerobic or anaerobic).
When acting as pathogens, bacteria are differentiated according to their way of interacting with the host
Like viruses, there are bacteria that are obligatory intracellular pathogens, because they do not have their own mechanisms to obtain ATP, the cell’s energy. Example of this is Chlamydia.
Other bacteria have the ability to enter cells, but it is not necessary for their survival, and can also be outside the cells; in this case, it is known as a facultative intracellular pathogen. That does not mean that it must be inside another organism, that is, it does not live in an open environment. An example of this group of pathogens is Salmonella.
Last we have extracellular pathogens, is that they are found inside the organism, but they never enter the interior of the cells. An example of this group is Streptococcus.
Although we are not aware, we are surrounded by microorganisms, and millions of bacteria live on our skin, mouth or digestive system. Whether we get the disease is sometimes nothing more than the product of a combination of factors, such as the initial amount of the pathogen or the state of the host’s immune system, our body. In the case of infectious bacteria, their damage may be due to their own action on the cells or due to the effect of the toxins they secrete, which sometimes cause tissue destruction.
4. Mushrooms
The last type of pathogen is fungi. These are eukaryotic organisms, which, unlike prokaryotes, already have an intracellular nucleus and membranous organelles. Additionally, fungal cells are reinforced with a cell wall. Its cellular organization can be unicellular (yeasts) or in filamentous hyphae (chains)
In the case of infectious fungi, they act in two different ways. The first are superficial infections in this case the pathogen is dermatophytes, and they attack the skin, hair or nails (for example, athlete’s foot).
In the second case it would be the fungal infection which is when its action is inside the host, either on the mucous membranes or in organs (for example, Candida).
What about parasites?
Although they are no longer usually included in the types of pathogenic agents, in the past they were. Let’s look at its different categories.
Protozoa are single-celled eukaryotic microorganisms Like bacteria, this category encompasses different ways of living, including parasitic organisms, both extracellular and intracellular. He Plasmodiumwhich causes the disease Malaria, would be the most lethal protozoan currently, wreaking havoc in developing countries.
Another group of parasites are helminths, which are worms, that is, multicellular eukaryotic organisms As before, it exists free-living as a parasite, and normally has a very complex life cycle, with phases of sexual reproduction (union of sexual cells or gametes) and asexual (identical copies). Examples are intestinal tapeworms, Ascaris (intestinal nematode) or Trichinella (nematode that causes Trichinellosis).
Finally, there are ectoparasites These are arthropods, specifically insects (such as the louse) and arachnids (the mite) that adhere to or burrow into the host’s skin for a long period of time. They usually do not cause great harm. The greatest danger of arthropods is when they act as vectors, in other words, when they carry within themselves a pathogen (such as the Borrellia bacteria and the tick in Lyme disease) or parasites (Plasmodium and the mosquito in Malaria) and transfers with its bite.
