Viruses All Around Us
What comes to mind when you hear the word “virus”?Perhaps the common cold, a cold sore, or maybe even aglobal pandemic, such as the one we are living in now,caused by a coronavirus that may have originated in bats.
In fact, viruses are ever-present in the living world, infecting,affecting, and interacting with all organisms, from the minuscule to thegigantic, and can be found in every ecosystem on the planet.They are as ubiquitous and essential to our lives as the air webreathe, the water we drink, and the food we eat. But what,exactly, are they? Are they alive? What do they do, and howdo they do it?
Small, but Mighty
Viruses are the smallest of all microbes. It would take 500million rhinoviruses, the virus known to cause the commoncold, to cover the head of a pin. They exist by hijackingthe cellular machinery of another living thing in order toreproduce. An individual virus known as a virion does this byinjecting its genetic material, packets of nucleic acids knownas RNA and/or DNA, into a host cell. They then replicatewithin, and ultimately explode out of, the cell in the formof new virions ready to infect other cells. These minusculemicrobes can pack a powerful punch, infecting us with anarray of diseases from chicken pox to AIDS.To see how a virus enters a host cell, check out this animation.
Viruses are Everywhere
Viruses do not only infect humans. They are, in fact, ever present in our world, occupying nearly all organisms, and found in virtually every type of habitat, even in the air we breathe and the deepest depths of the ocean. They are also ancient, predating some of the earliest forms of life. Scientists believe they are at least as old as the first cells, which emerged around 4 billion years ago, but viruses could be even older, existing in the precellular world as self-replicating entities that subsequently evolved into forms that parasitize other cells.
Coronavirus
COVID-19 is the disease caused by the new coronavirus, seen below, an airborne virus that emerged in China in December 2019, and subsequently led to the global pandemic of 2020. Harvard Medical School created an online learning module on how the human body reacts to viruses like Covid-19. You can find it here.
Are Viruses Alive?
Viruses occupy a space on the tree of life that blurs theline between existence and nonexistence. Life is generallydefined as an organism that can live and reproduceautonomously using its own energy-producing biologicalmechanisms.
Viruses, on the other hand, are essentiallyparasites that, in order to multiply, must harness a host cell’sreplication mechanisms. Because they are unable to do anyof this on their own, some argue that they are not among theliving. However, other scientists suggest that because virusesare made up of the same building blocks of life, DNA andRNA, they verge on life. It’s an ongoing debate that hasremained largely unresolved in the scientific community forthe last 100 years.
Viral Shapes
Viruses come in many different shapes and sizes, but allare made of two essential components: a core of geneticmaterial, either DNA or RNA, which is surrounded by aprotective protein coat called a capsid. Packaged together,a single virion comes in four different shapes: helical,polyhedral, spherical, and complex.
Viral Assemblies
How can you fight something you can’t see? Viruses likeinfluenza spread so effectively, and as a result can beso deadly, because of their ability to spontaneously self-assemble in large numbers.
Researchers at the Harvard JohnA. Paulson School of Engineering and Applied Sciences haveengineered a new way to observe and track viruses as theyassemble. This new method may spot weaknesses in virusesthat drug makers can exploit to design drugs that preventviruses from assembling in the first place.
Studying the Invisible
Virus are extremely tiny, even tinier than bacteria, so howdo scientists study them? Hannah Gavin, a microbiologist atHarvard, shows us how she does just that in this video.
Viral Alliances
Though viruses are most often associated with illness, theycan be a friend as well as a foe. Scientists have learned tomanipulate their unique characteristics as a scientific tool.
Bacteriophages are types of viruses that attack bacteria byattaching to bacterial cells and injecting their genetic materialinto them. Harnessed correctly, this can stop a bacterialinfection in its tracks. In this way, phage therapy has beenused to treat bacterial infections in humans by injecting thebacteria causing the infection with bacteriophages thatessentially stop it from spreading. Similarly, viruses mayultimately save the American Chestnut, an iconic tree speciesnearly wiped out by a bacterial infection called ChestnutBlight. Scientists have figured out a way to superchargea virus that attacks the Blight, preventing infection fromspreading throughout the tree.
American Chestnut
The American Chestnut, once considered one of the mostimportant forest trees in North America, was nearly wiped outby Chestnut Blight in the first half of the twentieth century, butmay recover with the help of viruses.
