Do you know that there are around 260 different kinds of viruses infect human hosts (Professor et al., 2021)? Needless to say, there are billions of viral infections around the world. Furthermore, we briefly talked about the normal biota that lives among humans in the article How Infections Lead to Disease. Research suggests that there are thousands of microbes in a health upper respiratory tract. These bacterium and fungi include Streptococcus pyogenes, Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, and Staphylococcus aureus (pp. 576). Do you remember when we talked about the “defenses” of the upper respiratory tract? They are nasal hair, ciliary escalator, mucus, involuntary responses such as coughing and sneezing, secretory IgA (pp. 576). Microbes that live inside are normally protecting their human host from invading pathogenic microbes. If this happens, microbial antagonism occurs by reducing the chance of the pathogenic ones from invading the body. Also, it prevents these “bad microbes” from colonizing in certain areas and competing for nutrients (from resident microbes). For example, Lactobacillus sakei, a resident microbe of the sinus microbiome, can suppress the pathogenicity from another microbe (pp. 576).
You might be asking, “how does this correlate to the common cold called human rhinovirus?” Our body are exposed to hundreds to thousands bacterium and viruses during our life. Depending on our body’s natural defenses and the severity of the microbe’s colonization, we will eventually catch the cold, or in this case, the common cold!
Caught a Cold?
Before you begin to read more, what symptoms do you think are a result of “the cold”? Many of us have symptoms like sneezing, scratchy throat, and runny nose that begins 2-3 days after initial infection. Well, what if I told you that the common cold is in fact a virus? Also, what if I told you that the common cold is infected by a virus our of 200 different types of viruses (pp. 580)? As unfortunate as it sounds, catching a cold is the same as catching a virus. Yikes! Can you think of one popular virus that might be a part of this virus group? If you are thinking, “coronavirus” then you are correct!
The leading group of viruses that cause a common cold is called rhinoviruses. Rhinitis is a term used to describe inflammation, irritation, and swelling of the mucous membrane in the nasal area. Some people use “hay fever” to describe rhinitis, and a seasonal or non-seasonal reaction to allergens. Do you know that people with asthma and other underlying respiratory conditions often suffer more severe symptoms triggered by the common cold (pp. 580)? It’s important to understand that the rhinovirus can lead to both rhinitis or a common cold. In this case, let’s not confuse rhinitis (or reaction to allergens) with a common cold.
Most Common Modes of Transmission
We come into contact with thousands of bacteria on a daily basis. For example, we touch our computer keys, pet the dog, open the door to the bathroom, and then touch faces without ever thinking about it. Fomites are inanimate objects that can harbor loads of microbes with a single touch. When I write the word “loads” I mean that the fomites are covered with microbes that are invisible to the eye without the help of a microscope.
A single bacterium is about 1 μm (micrometer) unless they are being observed in colonies through a microscope. The size of 1μm is equivalent to the thickness of a very thin piece of paper. Do you think you can see that? Most scientists call 1μm the limit of human vision! On the other hand, viruses are so small that more than 2,000 bacterial viruses could fit into an average bacterial cell, and more than 50 million polioviruses could be accommodated by an average human cell (pp. 128). They are so microscopic that most viruses are measured in nanometers. For example, the influenza virus is 100 nm compared to the poliovirus at 30 nm.
Why not Antibiotics?
Most of you are probably thinking, “why can’t I just take medicine to cure my cold?” Although this is a great question, we need to understand what antibiotics are used for. First, antibiotics target specific functions or disrupt the growth of bacterium (pp. 132). From a biological standpoint, antibiotics disrupt cell wall synthesis (creating the protective layer called a cell wall in bacterium). Also, it disrupts protein synthesis, nucleic acid synthesis, or the synthesis of specific proteins required for bacteria to survive and reproduce (pp. 132).
On the contrary, viruses do not have a cytoplasmic membrane. Also, they cannot synthesize proteins since they either contain a DNA or RNA. Viruses only reproduce by hijacking their host’s genetic material to create new viruses.
Because viruses are not bacteria, antibiotics targeted to disrupting bacterial cells will not work on them (pp. 145). Viruses propagate themselves; scientists find it difficult to use drugs that will affect the virus without affecting the host (pp. 145). Today, scientist turn to vaccines for preventing viral diseases, except that the common cold is just not one of them!
The respiratory tract is the most common place for an infectious agent to gain access in the body (pp. 576). Basically, anything that is in the air we will breathe in. Also, when we breathe in the air, those particles and microbes at least temporarily pass into the organ system (pp. 576). The common cold is one of the most contracted viruses even though we do not have a vaccine to prevent it. As we learned, anatomical features of the respiratory system serve as the only protection against the common cold virus. Our nasal hairs trap particles: the trachea and bronchi propel particles upward and out of the respiratory tract; coughing, sneezing, and swallowing moves trapped microbes along (pp. 576). Nevertheless, the common cold is in fact commonly experienced, but it can be overcome through a strong immune system and proper hygiene techniques!
Professor, C. M. K., Smith, H., & Lusk, J. (2021). ISE Microbiology Fundamentals: A Clinical Approach (ISE HED MICROBIOLOGY). In Microbiology Fundamentals: A Clinical Approach (4th ed., pp. 410–411). McGraw-Hill Education. https://myebooks.mheducation.com/bookshelf/ebooks