Immunology and Infectious Disease - What's in the Name?

Now, we've covered what Immunology is (click here), and started to go over the basics of how the immune system works (check out the Basic Immunology posts for more). But what we haven't covered is how immunology fits in to the big picture of infectious disease.

In the age of COVID, I'm sure everyone is familiar with the field of virology. You likely also know about the fields of microbiology and parasitology. These together are the study of viruses, bacteria (and other microorganisms) and parasites.

The question is, how are these different to immunology?

I asked the same question when I was choosing my degree. The answer I was given is that it's a matter of view point.

Microbiology, virology, parasitology, and any other infectious disease/microorganism-related -ology all aim to study these from the point of view of the organism. For example, if you were studying E. coli, you'd want to know how each component of the bacterium works, how it interacts with other bacteria (whether the same or different species), how it modulates its environment for survival, and whether/how it infects any other organisms. The actual stage of infection is only part of the focus and, depending on the organism, may never be part of the study.

Immunology, on the other hand, is entirely focused on how the host's immune cells regulate one another (and other cells of the body, e.g. in the case of cancer), and how they defend against infection. Other components may be of interest (e.g. how the invading organism interacts with others - this would be of especial interest in those who study the bacteria within the gut, AKA the microbiota), but in general the main questions an immunologist asks about microorganisms are:

  • is that organism infectious?

  • does it infect everyone, or is it only an issue in immunocompromised people?

  • how does that organism infect?

  • what cells and cytokines are important in removing it?

  • how does it cause damage - i.e. is it the organism doing the damage, or is it the immune system in an effort to remove it?

  • what happens if the immune system fails - i.e. how dangerous is it?

  • does the immune system need help - i.e. is medical intervention required?

  • can we prevent any disease from occurring (e.g. through the development of a vaccine)?

Not all viral, bacterial, fungal or parasitic organisms are pathogenic to humans. Some are exclusive to animals (e.g. fish, pets, farm animals). As a result, immunologists can specialise in different hosts (this is particularly important in animals related to agriculture).


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