We move forward from our recent article and show you this time the five major types of infectious agents that exist around us. While researchers make good use of various equipment like microscopes to take on the field to identify these agents, a lot of work is put by other health care professionals into finding treatments and cure.


Viruses are microorganisms that enter the human body in various ways. They are invisible to the naked eye, as they can have as little as 20 nanometers in diameter. Billions of them can exist in tiny areas which is why it is impossible to protect yourself entirely against their action. While they are small, they have all sorts of shapes.

They are made of nothing else but their DNA and a shell made of protein, intended to protect the genetic material inside. What you should know about viruses is that they are dormant when they are not in a type of environment that would allow them to thrive.

As soon as they find a gateway to living cells, they begin to reproduce. But they do not do it by themselves, but they use the metabolism of those cells to replicate themselves. That makes them parasites.

They will reproduce to the point that they can take over the living cells. Because they can’t be observed by themselves to create cures and treatments, some biological material like tissue or cells, is necessary for experiments.

You may have heard of some viruses as they are quite widespread, primarily through the unfortunate fame that the diseases they cause have, such as influenza or AIDS.



The second infectious agent we will discuss here is bacteria. These microorganisms may look gigantic compared to viruses, as they can be 100 times bigger, but they are still invisible, and we cannot learn of their existence without the assistance of a microscope. They usually have three different shapes: spherical, rod-like, and curved.

Like viruses, bacteria have a core made of their DNA, but they are a bit more evolved, as they also contain some structures that act as guardians against attacks, such as those that could come from antibiotic treatments.

However, bacteria are not much-evolved microorganisms, and they only contain one set of chromosomes. When they reproduce, they produce clones of themselves. Sometimes, under various circumstances, they can mutate, and that’s when they become resistant to multiple treatments.

Bacteria have been around since ancient times. There are even studies that show that they have been here for the last three billion years, as some fossils can attest. Their high adaptability makes them so resilient and a problem when they become an infectious agent. Throughout millennia, they learned how to make use of other living organisms to thrive.

Also, they have developed their weapons against what could destroy them, which is why human medicine must always evolve, as well. Attacking the immune system, bacteria can even kill the organism they choose to inhabit. Various infections, such as blood-related, those found in the urinary tract, tuberculosis, and strep throat, are caused by bacteria.


The significant difference between fungi and the other infectious agents mentioned so far is that the former are multi-cellular. That means that they are more evolved, and their way of reproducing slightly differs, as well. An interesting aspect of fungi is that they use spores with a single cell, even if they are made from multiple cells.

With 51 million types of fungi on the planet, it is quite clear that fighting the infections caused by them is no easy task. Usually, fungi live on the skin and, as soon as there is a bruise, a cut, a breaking of the skin, they can use this opportunity to get inside the bloodstream, from where they can wreak havoc.

Sometimes, people can inhale fungal spores, and from their respiratory tract, a fungal infection can develop. When fungi infections affect the entire body, they are called systemic diseases.

What you should bear in mind is the particular relationship between fungi and bacteria. There are plenty of good bacteria living on the human skin and inside the body. If someone is under medication with antibiotics, bacteria may reduce, and that’s when fungi take over.

Some fungal infections are related to antibiotic treatments. That’s why prolonged administration of such drugs is not recommended. Also, people with a weak immune system are more likely to suffer from fungal infections. They can be located in many parts of the body, such as the mouth, the nose, the eyes, or the vagina.



The three categories of infectious agents mentioned above are the most widespread. However, there are still some others which are not as well-known but can still be made responsible for various diseases. Among them, there are protozoa, which are most evolved than fungi, bacteria, and viruses.

One aspect about them you should know is that they can live outside your body, unlike the other agents that remain dormant. Their evolution is quite interesting since they are mobile and can share some features with the animal reign.

The most common way of transmission is through feces, which is why washing your hands thoroughly after using the bathroom is highly recommended. One known infection caused by protozoa is amebic dysentery, to give you an example.


While this scientific name might tell you nothing, it is the one chosen by scientists to describe some parasites that are well known to humankind. Helminths are worms, more specifically flatworms and roundworms. They can be tiny in their first stages of development, but, when they mature, they can be visible to the naked eye.

Most of the population is exposed to helminths and the infections they cause regularly, but the incidence of diseases is higher in tropical and subtropical areas. One explanation is the lack of proper sanitation in the countries found here.



1 Star2 Stars3 Stars4 Stars5 Stars (1 votes, average: 5.00 out of 5)

Leave a Reply

Notify of
Real Time Analytics