Glimpse into world of viruses


THE world around us is infested with billions of extremely tiny organism that are not visible to our physical sight. Some of them play important roles in our many ecosystems and shape life, to a large extent, sustaining our livelihood on earth. And then, there are those that cause many diseases that affect us in varying degree of their severity. Every single day, in one way or the other, we humans are repeatedly exposed to these microorganisms.
Though the proposition may sound scary, it is a matter of fact that viruses have been present everywhere and throughout all of human history and evolution. They are the most abundant form of microorganism, and are omnipresent in all of our lives. In a broader sense, they may be considered non-living, because of the fact that they lack the ability to survive and reproduce independently, a characteristic typically, attributed to living organisms. Like other known microorganisms – bacteria, fungi, and parasites, they are one group of minute infectious agents that are associated with many diseases in humans. However, unlike other infectious agents, viruses absolutely need living host cells for their energy requirements and survival, and for replication and propagation. It is only in living hosts that they can reproduce with genetic continuity and a high possibility of mutation.
During the first half of the twentieth century, many scientists considered viruses to be the smallest living entities, a set of primitive life forms, somehow, placed between the lifeless world and the highly evolved cells. However, with the development of molecular biology, it was clear that viruses were simple and yet complex agents of infection. It was further determined that they were strict molecular parasites, and therefore would penetrate and hide inside living cells, thereby, using the host cell machinery for their own benefit. In so doing, they hijack the host cellular mechanism for their own survival. Thus, the often-debated question of whether they are a group of living or non-living organisms is a matter of definition, and inasmuch, does not affect their biological and pathogenic reality.
Viruses come in different sizes, shapes and forms. They range from 15 nanometers to 300 nanometers in size (a nanometer is one billionth of a meter). They occur as rod-shaped, spherical (circular), or polyhedral (e.g. cube, prism, pyramid), and tad-pole shaped forms. The individual particle, or virion, possesses a genome that consists of a nucleic acid, basically, deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), respectively, but not both. This is contained and protected by a protein shell or capsid. In a nutshell, RNA and DNA are fundamentally, the most basic essential biological molecules that serve as backbones or the blueprints to every life forms on earth.
Customarily, viruses are separated into three subgroups on the basis of host specificity, namely, bacteria viruses, plant viruses, and animal viruses. The animal viruses, and specifically, the viruses associated with human diseases are further classified in relation to their origin (e.g. reoviruses), mode of transmission (e.g. arboviruses’, tick-borne viruses), or the manifestations they produce (e.g. polioviruses, polyomaviruses, poxviruses). Sometime, they are named for the geographical location in which they were first isolated (e.g. coxsackievirus)
There are more than two hundred and nineteen species of virus that are known to cause infections in humans. The first of the human viruses, the yellow fever virus, was discovered in 1901. Thereafter, three to four new species of viruses are being identified every year. Some of the important infectious disease caused include, common cold, influenza, rabies, measles, many forms of diarrhoea, hepatitis, Dengue fever, yellow fever, polio, smallpox, AIDS, and now, COVID-19. Cancers such as, cervical cancer, Burkitt’s lymphoma, and liver cancer, are also associated with viruses.
Over the course of human history and evolution, viruses have become very successful parasites. They have adapted to proliferate in and around us, and to spread from human to human. Their unpredictable ability to evolve accords them that advantage to survive and to propagate. As such, it thus seems almost inevitable that new species of human viruses will continue to emerge in the not too distant future.
The picture at right hows schematics of 12 viruses that cause diseases in humans; and they are SARS-CoV/COVID-19, Influenza, Hepatitis A, Hepatitis B, Hepatitis C, HIV, Zika/Dengue, Rabies, Ebola, Norovirus, HPV, and HSV. Picture from The European Physical Journal Plus (2021), 136:675
In this article, we have only glimpsed a very small portion of their world, the mystical world of viruses. And yet, there is so much more to be discovered about this ever-present and pervasive form of microorganism.
I am indebted to the authors of following scientific articles from which information was extracted: 1. Lopez-Garcia, P and Moreira, D 2012, Viruses in Biology, Evo Edu Outreach, 5:389–398, viewed 13 October 2021,; 2. Sohrabi F, et al. 2021, Role of plasmonics in detecting deadliest viruses: a review, Eur. Phy. J. Plus, 136:675, viewed 21 October 2021,; 3. Uecker, H and Trubenova, B 2019, A glimpse into the world of human viruses, viewed 13 October 2021,; and 4. Woolhouse, M, et al. 2012, Human viruses: discovery and emergence, Phil. Trans. R. Soc. B, 367, 2864-2871, viewed 13 October 2021,

  • Gelinde Narekine is a technical officer with Discipline of Medical Laboratory Science, School of Medicine & Health Sciences, UPNG