Tiny agents, massive impacts: five fascinating facts about viruses

The recent outbreak of the novel coronavirus COVID-19 has spread to over 185 countries and infected over 2.4 million people worldwide. Governments across the world are battling the outbreak by putting cities into lockdown, providing aid to the medical staff, and urging their citizens to be vigilant about their hygiene. It is scary. For most of us, viruses are infamous for their disease-causing capabilities. However, it is important to remember that there are other important aspects of viruses that tend to be overlooked.

In 1886, Adolf Mayer, a German chemist published the first paper on viruses. Mayer was investigating a strange disease that affected tobacco plants, which resulted in mosaic patterns on the leaves. The name “virus” was coined in 1398 from the Latin name for poison. The Dutch botanist Martinus Beijerinck, who also studied the tobacco plant disease, reintroduced the name “virus” around 1898 when he believed he had found a new infectious agent.

Viruses are diverse in their shape, structure, the type of genetic material they carry, and the hosts that they can infect. The only features that they have in common are their small size and inability to replicate without the help of a living host. Read on to find out more about the world of viruses that we live in.

1. 1. Viruses are everywhere.

“There are 1×10³¹ viruses on our planet.

That’s 10000000000000000000000000000000 viruses!

If they were all laid out from end to end, they would stretch for 100 million light-years”. For reference, that number is 1000 times the size of the Milky Way galaxy. In our bodies, our cells are outnumbered by viruses 100-fold. A lot of these viruses are beneficial. Some viruses that infect bacteria (known as phages) can protect us from invading bacteria by adhering to the surface of our guts. They can slow down the progression of HIV in HIV-positive patients. Even our genes contain viral genetic material and some of them are essential for placental development.

1. 1. 2. The largest virus is about 35 times bigger than the smallest virus.

Mimivirus, also known as Acanthamoeba polyphaga mimivirus (APMV) was first discovered in 1992. At the time researchers were investigating a pneumonia outbreak in England. They noticed small particles, which they thought were bacteria, growing inside amoebae in a water-cooling tower. When they realized that it was a giant virus, they named it Mimivirus, short for “mimicking microbe”. The virus has a protein coat that has a diameter of 400-500 nanometers, and fibers that extend out from the coat, making it 750 nanometers (or 0.75µm). These viruses are big enough to be visible under the light microscope! The viral genetic material codes for over 900 proteins.

  Mimivirus- giant viruses visualized microscopically. Source.

In contrast, circoviruses are the smallest. They are 17-22 nm in diameter and their genetic material only codes for two proteins. The smallest in this family, the porcine circoviruses, were discovered when a new disease was found in Western Canada during the 1990s. The disease named postweaning multisystemic wasting syndrome, affected mainly nursery pigs. The pigs did not grow well and showed signs of wasting. Although the porcine circoviruses can still be problematic for swine production worldwide, there are vaccines that can reduce their effects.

1. 1. 3. Some viruses can parasitize other viruses.

The vast majority of viruses enter living cells and to hijack the cellular processes for their benefit to replicate and propagate. However, Sputnik and Zamilon viruses utilize the co-infected giant viruses, belonging to the same family as Mimivirus, to replicate. Both viruses are around 50 nm in size. Both of these parasitic viruses replicate inside a host amoeba with the help of ‘virus factories’ that are set up by the giant viruses. These factories recruit specific cell components such as mitochondria, to build a unique structure that supplies the basic needs for virus replication. However, the effect that these viruses have on their virus partners are different. Zamilon does not inhibit the replication of its helper virus. On the other hand, Sputnik inhibits the replication and increases the formation of abnormal viral particles of the helper virus.

Microscopic image of a ‘virus factory’ in an amoeba. The Mont1 virus is co-infected with the Zamilon virus, which can be seen as small particles. The scale bar is 0.1 mm. Source.

1. 1. 4. Neurons can communicate with each other using a viral mechanism.

In 2018, two teams of scientists from the University of Utah and the University of Massachusetts Medical School independently discovered that nervous system cells can interact by using a strategy that is commonly used by viruses. The Arc gene plays an important role in the brain’s ability to store new information. When cells make the Arc protein, the proteins clump together into a form that resembles a viral capsid. Viral capsids are protein shells that contain the virus’ genetic information. The Arc capsids, which are similar to the viral capsids in their physical structure and their behavior, transfer information in the form of mRNA to nearby cells. The researchers hope to use the Arc capsids for genetic engineering and gene therapy to deliver genetic instructions to cells without triggering an immune response in our bodies.

A model of the HIV capsid. The researchers working on the Arc capsid had previously noticed several similarities between the Arc protein and the proteins found in certain viruses like HIV. Source.

1. 1. 5. Viruses can be made in the lab from scratch.

Viruses are essentially a string of genetic information inside a coat. Making them from scratch does not present as big a problem as making cells. Cells have many more components, all of which need to work together. In fact, scientists were able to create the poliovirus in 2002. The researchers from the State University of New York, Stony Brook, built the virus by using the chemical code of its genetic material, which was publicly available. They injected mice with the synthesized virus and saw that the mice became paralyzed after about a week. The mice that were infected with normal poliovirus also showed the same effects.

It soon became evident that this technology could be used for bioterrorism. To prevent such a possibility, the companies that manufacture DNA decided to limit access to dangerous genes. This technology has again been pushed into the spotlight due to the COVID-19 pandemic. Researchers from the University of North Carolina are attempting to recreate the virus based on the computer readouts of its genetic sequence that was posted online by Chinese labs. Building a synthetic virus is useful if scientists can’t obtain them directly from patients, which has been a problem with COVID-19. If they succeed, they can examine what causes the virus to spread, how it gains access to human cells, and what drugs can stop it.

Author:

Ananya Sen is currently a Ph.D. student in Microbiology at the University of Illinois at Urbana-Champaign. When she’s not studying oxidative stress, she is busy pursuing her passion for scientific writing. Currently, she contributes articles to ASM,  ScienceSeeker, and her own blog where she discusses the history of various scientific processes. She is an ardent reader and will happily discuss anything from Jane Austen to Gillian Flynn. Her graduation goals include covering all the national parks in the U.S. with her sidekick Oscar, a Schnauzer/Pomeranian mix.

Editors:

Sumbul Jawed Khan received her Ph. D. in Biological Sciences and Bioengineering from the Indian Institute of Technology Kanpur, where she studied the role of microenvironment in cancer progression and tumor formation. During her post-doctoral research at the University of Illinois at Urbana-Champaign, she investigated the gene regulatory networks that are important for tissue regeneration after damage or wounding. She is committed to science outreach activities and believes it is essential to inspire young people to apply scientific methods to tackle the challenges faced by humanity. As an editor, her aim is to simplify, translate, and excite people about current advances in science.

Roopsha Sengupta is the Editor-in-Chief at ClubSciWri. She did her Ph.D. at the Institute of Molecular Pathology, Vienna and postdoctoral research at the Gurdon Institute, University of Cambridge, UK, specializing in the field of Epigenetics. During her research, she was involved in many exciting discoveries and had the privilege of working and collaborating with a number of inspiring scientists. As an editor for ClubSciWri, she loves working on a wide range of topics and presenting articles coherently, while nudging authors to give their best.

Cover image- Pixabay

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