Writer: Charlotte Leung

Image: https://www.lysol.com/clean-and-protect/protect-against-germs/other-illnesses/what-are-viruses

“Viruses” is an omnipresent term, consistently plastered in the media and our lives for the past three years. From the mass epidemics of the polio virus to over two years of self-isolation, viruses have unveiled themselves as diminutive yet evasive and invisible threats that have impacted numerous lives over the existence of humanity. With the most recent case being the worldwide COVID-19 pandemic, one might wonder how these “small but mighty” microorganisms are in action in our bustling day-to-day lives.

There are currently over 10^31 viruses worldwide, most found in the ocean. This means if all viruses were to line up together, their line would extend into space! A virus is a small infectious pathogen replicating inside animals, plants, or bacteria’s living cells. The name “virus” comes from a Latin word meaning “slimy liquid” or “poison.” They comprise genetic material encircled by a protein coat known as a capsid and nucleic acid. They are also sometimes surrounded by an external membrane envelope. Every virus is unique, like a fingerprint, varying in shape and structure. They all consist of various kinds of genomes and infect different hosts.

Viruses are classified according to multiple deviations: morphology, chemical composition, and replication strategy.

First and foremost, viruses can be categorized by their physical characteristics, meaning their shape and size. This is called morphological classification. There are four main kinds of virus shapes.

  • Helical: A cylinder-shaped virus with genetic information curved inside a spring structure. (E.g. influenza virus)
  • Icosahedral or polyhedral: A virus shape consisting of many sides. This virus shape primarily affects people. (E.g. adenoviruses)
  • Spherical: Helical or polyhedral viruses that have an envelope that encircles them. The vast majority are shaped like a ball. (E.g. poliovirus)
  • Complex: Viruses that are made up of more than one shape. For example, a virus can have a polyhedral “head” attached to a helix “body.” (E.g. poxviruses)

Secondly, viruses can be classified through their chemical composition and mode of replication. A virus’s genome, or the instructions inside a cell, can have DNA or RNA (genetic material used to store genetic information), which can be single-stranded or double-stranded, linear or circular). The whole genome can take either one nucleic acid molecule or several molecules. The various types of genomes can call for different replication techniques.

Furthermore, there are several diverse types of viruses, which are often seen in medical diagnosing. Here are some examples:

  • Coronavirus: a group of RNA viruses that infect mammals and birds. They cause respiratory tract infections that can go from mild to lethal. An example of a specific classification of coronavirus is the betacoronavirus, one of the four genera of coronaviruses.
  • Enteroviruses: a category of viruses that can cause mild to severe infections. A typical example is the common cold, hand, foot, and mouth disease, or polio.
  • Flavivirus: a genus of viruses that can be spread to humans through infected mosquitoes or tick bites. They can lead to an extensive range of diseases as well as deaths.
  • Hepatitis Virus: A group of viruses that cause liver inflammation. They have five primary types: A, B, C, D, and E. Most hepatitis viruses are of significant concern and can lead to more severe diseases due to the possibility of a long-lasting/chronic infection.

Animal viruses rely on host cells to spread. To replicate, a virus must infect and reprogram a host cell to produce more virus particles. The process has multiple steps: recognition, entry, assembly, and exit.

  • Recognition: The virus uses unique surface molecules that recognize the host cell membrane.
  • Entry: Following the attachment, different possibilities exist for how the virus enters.  

-Endocytosis: the membrane folding, where the membrane forms a pocket to allow entry of the virus molecules.

-Channel Creation: creating channels within the host membrane.

-Fusion: Enveloped viruses fuse with the host membrane and release the capsid inside the cell.

  • Assembly: Following the entry, the virus uses the host cell’s machinery to replicate its DNA, RNA, and proteins. The replicated virus particles form new virus particles within the host cell.
  • Exit:

-Enveloped animal viruses take away a piece of the plasma or internal membrane in their escape process.

-Non-enveloped virus: builds up infected cells until the death or bursting of the cell to exit.

  • Repeat: The virus molecules repeat the process to attack each cell in the body, compromising a complete “takeover” of the virus causing the infected person to begin feeling ill. In addition, the repetition leads to a battle between the immune system and the virus.

After the replication of the virus particles, the body of the host cell typically begins to exhibit signs of the infection. Some common examples of how viruses affect the bodily systems of the human body include:

  • The common cold: includes viruses like rhinovirus, and symptoms include a runny nose and sore throat.
  • Pneumonia: includes viruses like Influenza A and B, which cause respiratory issues.
  • Hepatitis: involves all types of Hepatitis, A through E. They cause liver damage.

There are various patterns in which viral infections follow; they include the following:

  • Acute infections: Sudden emergence of severe symptoms for a short time, usually stopped by the immune system.
  • Chronic Infections: Infections that last long and typically cause long-term health issues. An example is Hepatitis C.
  • Asymptomatic Infections: Infections that do not cause noticeable symptoms during/after replication. Examples include herpesviruses 6 and 7.

 In closing, viruses are classified and replicated using a multitude of methods, from chemical composition to endocytosis. This process reminds us of how easy and dangerous viral infections may be, warning others to be more meticulous regarding epidemics, pandemics, or even just a visit to the hospital. It emphasizes the importance of mask-wearing, sanitation, and hygiene daily. Nowadays, countless research facilities have attempted various solutions to aid those with viruses, as seen with the vaccine development for COVID-19. So, what is your take to stop this invisible enemy?

References

Animal & human viruses (article) | Viruses. (n.d.). Khan Academy. Retrieved July 18, 2024, from https://www.khanacademy.org/science/biology/biology-of-viruses/virus-biology/a/animal-viruses-hiv

Boutet, E., & Brito, A. (n.d.). Intro to viruses (article) | Viruses. Khan Academy. Retrieved July 18, 2024, from https://www.khanacademy.org/science/biology/biology-of-viruses/virus-biology/a/intro-to-viruses

Coronavirus. (n.d.). Wikipedia. Retrieved July 18, 2024, from https://en.wikipedia.org/wiki/Coronavirus

Hepatitis. (2019, September 1). World Health Organization (WHO). Retrieved July 18, 2024, from https://www.who.int/news-room/questions-and-answers/item/hepatitis

Kelser, E. A., & Alli, B. (n.d.). What Are Enteroviruses? Symptoms, Causes, Diagnosis, Treatment, and Prevention. Everyday Health. Retrieved July 18, 2024, from https://www.everydayhealth.com/enterovirus/guide/

Kutasi, O. (n.d.). Flavivirus. Wikipedia. Retrieved July 18, 2024, from https://en.wikipedia.org/wiki/Flavivirus

Structure and Classification of Viruses – Medical Microbiology. (n.d.). NCBI. Retrieved July 18, 2024, from https://www.ncbi.nlm.nih.gov/books/NBK8174/

Virus | Definition, Structure, & Facts. (2024, June 18). Britannica. Retrieved July 18, 2024, from https://www.britannica.com/science/virus

Viruses: Definition, Types, Characteristics & Facts. (2023, March 29). Cleveland Clinic. Retrieved July 18, 2024, from https://my.clevelandclinic.org/health/body/24861-virus