I have recently begun a new semester of my graduate studies as well as beginning my graduate project, so posts here might become a bit less frequent. I’m sorry for the inconvenience, but will keep you posted on what I learn from my graduate project regarding allergies and Covid.
Today, I thought it might be useful to talk about the differences between bacteria and viruses (especially given we are in the middle of a viral pandemic). The terms are used somewhat interchangeably in layman circles, but there are significant differences in how they damage the body and how they are treated. Along the way, I will talk a little bit about cell biology and medicine where it is relevant.
Bacteria
All living cells can be sorted into one of two groups; eukaryotes and prokaryotes. All multi-celled organisms (animals, plants, and fungi) and some single-celled organisms (such as amoebas and algae) are eukaryotes, meaning they have a nucleus. The nucleus is a little bit like a “second cell” inside the cell which contains all the cell’s DNA. Having the cell’s DNA contained in its own chamber provides several advantages; anything toxic or dangerous inside the main part of the cell (referred to as the cytoplasm) can’t damage the DNA. Also, there are two layers of security that viruses have to get through in order to infect a cell (see below). But the nucleus is only one difference between these two clades, eukaryotes can grow ten to a hundred times larger than prokaryotes. This additional size allows eukaryotic cells to have far more DNA which means it can build far more complex structures and deal with far more distinct problems. Eukaryotes also contain complex organelles, specialized structures which generate energy, store resources, and move things around. This additional complexity is what has allowed eukaryotes to network together to create multicellular life and become every living thing you can see with the naked eye.
Prokaryotes are a much older clade, from which eukaryotes initially evolved, which includes bacteria. They’re much simpler cells, having their DNA floating freely without a nucleus and not having complex organelles. But this simplicity does have its advantages; prokaryotes can reproduce faster, which means more genetic mutation, which leads to faster adaptation and greater diversity. For just about any location on earth, water, soil, the bodies of animals, there are species of bacteria that can thrive there. Should something happen which kills off almost all the bacteria in a location, their diversity means there will inevitably be a few which have traits which allow them to survive. These survivors can then rapidly reproduce, returning the area to its original bacterial population. And bacteria which can survive in the human body can almost certainly survive indefinitely in other species, in food or water, or on surfaces.
Not all species of bacteria affect humans, certain traits are required to survive inside a body. Of those species that can survive in the body, not all are innately harmful. The intestines are home to thousands of unique species which break down molecules such as fats and carbohydrates, which would otherwise be indigestible. This is why probiotics are a thing, foods which contain these beneficial bacteria or prompt the growth of existing bacteria. The species that do cause disease tend to do so by growing uncontrollably within the body and secreting toxic waste products which damage cells and tissue. Some species can also cause harm by stealing nutrients from one’s cells or by causing the immune system to overreact. Bacterial species you might have heard of include E. coli, Salmonella, Staphylococcus (staph infections among others), Streptococcus (strep throat among others), Gonorrhea, and Tuberculosis.
Fortunately, bacterial infections are something that modern medicine has gotten very good at treating thanks to the invention of antibiotics. Most antibiotics used today are derived from fungi or other bacterial species, which secrete proteins that disrupt the functioning of infectious or competing bacteria. This disruption can work in a myriad of ways, usually by latching onto and breaking a part of a bacteria that it needs to function. This can directly kill roughly 99.9% of an infection, which allows the immune system to kill off the survivors. But as I said before, bacterial colonies are often diverse enough to have survivors. A few bacteria within the swarm will have slightly different parts that the antibiotics can’t latch onto properly or could produce molecules which neutralize the antibiotics. However they do it, they won’t be affected by the antibiotics and can repopulate the body with their immune progeny. This is how antibiotic-resistant bacteria develop, strains evolving to survive against our drugs. Now, research is being done on creating new types of antibacterial drugs, such as viruses which infect bacteria and can adapt with them or antibiotics that attack bacteria in such a way they can’t adapt. But until these drugs become commonplace, it’s important to follow a doctor’s orders when it comes to antibiotics. First off, antibiotics don’t work against viruses (see below), so don’t take them for a cold or any disease that hasn’t been diagnosed as bacterial. While antibiotics are sometimes given to those with serious viral infections, including Covid, this is to prevent opportunistic infections, where bacteria such as pneumonia infect a person while their immune system is weakened by the viral infection. Secondly, if you are being treated with antibiotics, don’t stop the treatment before a doctor tells you to. If there are any infectious bacteria left in your body, giving them ‘room to breathe’ makes it easier for resistant bacteria to proliferate. Don’t take antibiotics meant for someone else, don’t save antibiotics for if you get sick again, and as always, listen to healthcare professionals.
Viruses
Viruses are even simpler than bacteria, to the point they’re not considered to be living organisms. This is...mostly an argument of semantics and what the most useful definitions for scientific terms are (similar to the debate on whether or not Pluto is a planet). But while viruses are made of the same materials as living cells, viruses aren’t able to respond to their environment, they don’t use energy or create waste, and they can’t reproduce on their own, and technically aren’t cells. All cells, eukaryote or prokaryote, are defined as having DNA, a cell membrane (the lipid-based skin of the cell), and cytoplasm (the space inside the cell containing organelles, organic molecules, and room for the chemical reactions that sustain life). Viruses are instead either DNA or RNA that is tightly packed inside a protein shell along with a select few enzymes. They are on average far smaller than bacteria (though the very largest viruses can be bigger than the very smallest bacteria) and contain even less genetic material.
Because viruses can’t reproduce by themselves, they survive via parasitism. Viral particles float through their environment until they happen upon a cell they are able to infect. The outside of the viral shell contains spiky proteins which have evolved to bind to proteins on the membranes of cells and to trick the cell into letting the virus inside. Once inside and past the cell’s defenses, the shell opens and releases its contents. The enzymes splice the viral DNA into the cell’s own genome and trick the cell into ignoring all other functions besides copying and transcribing this one bit of DNA. New viral proteins are manufactured and assembled into new viruses. New copies of viral DNA are copied and inserted into the new viruses. Finally, proteins rip open the cell membrane, killing the cell and releasing thousands of new viruses.
While research is being done into the beneficial effects of certain human viruses, the vast majority of them appear to be harmful. Since killing their host cell is a necessary step to their reproduction, viral infections can directly kill cells and damage tissue. The body can heal the damage to certain tissues, but permanent disability can be caused if viruses infect cells which can’t grow back (i.e. polio causing paralysis by killing motor neurons). The immune system can also cause symptoms as it responds to infections and causes collateral damage. Like bacteria, viruses mutate and adapt very quickly, and their small size means it’s possible for species to spread through a myriad of ways, including through the air, water, or insect bites. Cold and flu are both examples of viral diseases, as are measles, ebola, polio, and coronaviruses.
Certain types of viruses have an additional trick up their sleeve, causing persistent infections. These viruses have additional genetic code which allows their host cell to respond to its environment. If it’s unsafe for the virus to be in the body, such as if the body currently has a strong immune response to the virus or is currently taking drugs that target the virus, the infected cell won’t start manufacturing viruses. It will wait until conditions are right before it begins making viruses and releases them into the body. This is why diseases like HIV are currently incurable, the virus can wait indefinitely ‘inside’ a cell until a patient stops treatments. These dormant infected cells tend to behave the same as any other cell, but not always perfectly. The dormant viral DNA can affect the cell’s behavior, making it less effective at its job or causing it to reproduce faster in order to create more host cells. This faster reproduction makes these cells more prone to becoming cancerous, which is how certain viruses can ‘cause’ cancer. Diseases caused by persistant viral infections include HIV, Hepatitis, HPV, Herpes, and Chickenpox (shingles).
Our current best weapon against viruses are vaccines, which we’ve talked about before. That said, vaccines only work as a preventative measure, they can’t cure an ongoing infection. Antiviral drugs also exist, drugs which bind to viruses in order to block them from entering and infecting new cells. These are typically used against persistent infections in order to hold them in a state of perpetual dormancy, such as the drugs used for AIDS patients. But in recent years, antivirals aimed at severe, common acute infections such as flu and Covid-19 have begun to appear on the market. For the most part though, the treatment for viral infections is to treat the symptoms until the immune system can develop an antibody response.
These are not the only germs that can infect the human body. There are a few diseases that are caused by fungi, such as ringworm and yeast infections. Fungal diseases are fairly rare in humans, but they can be more difficult to treat since fungi are far more closely related to animals than either bacteria or viruses. Some of our worst diseases, such as malaria, dysentery, and sleeping sickness, are caused by protists, single-celled eukaryotes like amoebas. And there are of course parasitic animals, species like tapeworms and lice. But the vast majority of human diseases are caused by bacteria and viruses. Both of these clades can cause any range of symptoms and be spread in a myriad of ways, so it is often difficult to tell what is causing any particular malady without a proper diagnosis. So, be sure to have any illness diagnosed by a doctor and take whatever treatment you’re given as prescribed. What appears simple from afar is often complex and variable from up close.
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