Are viruses alive?
This question has led to a long-running debate which has placed viruses in various categories ranging from poisons to life-forms with a brief stop as biological chemicals somewhere in the middle. In the current era of biological sciences viruses occupy an ambiguous area categorizing them as neither living nor non-living. Are these tiny particles of proteins and nucleic acids (and sometimes lipids) alive in any sense, and at the end of the day does it matter what we decide?
In the late 1800s disease-causing particles, much smaller than bacteria, were
linked to conditions such as foot-and-mouth disease and rabies. These filterable agents were termed viruses, with virus being a Latin word for poison. As more and more viruses were discovered that caused disease throughout the late 1800s and early 1900s they were promoted from poisons and possible toxins to life-forms in the eyes of many scientists, albeit parasites that were reliant on cellular life. It was Wendell Stanley’s work in the early 1900s that led to the subsequent view that viruses were merely a complex particle-like structure of biochemicals lacking the necessary parts for metabolism and so demoting viruses to the realm of the biological chemicals.
It is impossible to discuss this topic without first looking at how life is defined. A scientific definition of what constitutes the necessary processes and characteristics essential for life is not an easy thing to pin down, at one point there were over 280 competing scientific definitions of life. Replication, the ability to mutate and metabolise are just a few of the characteristics mentioned. Viruses may not be able to metabolise but they can most certainly replicate and mutate, in fact the entire function of a virus is to replicate. Infection and disease is just a by-product caused by some viruses as they latch on to and enter host cells in order to replicate. For example the respiratory symptoms of influenza may be caused by the viruses attack on cells in the respiratory tract, but the systemic symptoms such as fever and myalgia are caused by the factors involved in the immune response.
As mentioned above the lack of viruses ability to metabolise has been a long-standing argument towards their classification as non-living. Viruses instead rely on host systems to provide the machinery necessary for metabolism in order to provide the energy needed for the virus life cycle. There are a multitude of functions required for viruses to fully replicate and exit a host cell. This requires a virus to hijack and sometimes modify some cellular systems for functions such as genome replication, RNA translation, transport of virus parts and even virus assembly. For example Human Immunodeficiency virus (HIV) recruits a complex used to organise and assist with newly formed viral particles passing through a membrane to gain their outer lipid coat. The hijacking of host systems has led to viruses being described as leading some sort of “borrowed life”. Some viruses have even been shown to steal and use the immune system of its host cell. Andrew Camilli of the Tufts University School of Medicine has said that this discovery adds to the argument that viruses are living things.
Life has also been described as a “self-sustaining system capable of Darwinian evolution” but, as argued by Sohan Jheeta, an astrobiologist, no life is truly self-sustaining. We as humans need oxygen yet we cannot provide our own.
Viruses without a cellular host are dormant particles just waiting to be passed on to a new host. They’re not plotting, they’re not planning, merely lying there dormant. If they degrade during this period have they died? This dormancy and inability to function without another being could be used as an argument against viruses as living things. Although the same could be said of seeds. Yet these are considered living once they leave their dormant phase. Is the potential for life, even borrowed life, enough?
This debate could take an entirely different route if you consider a letter published in the journal of human thermodynamics by Libb Thims in which he discussed the idea that a theory of life was in fact defunct. The point was made that we do not consider a single atom to be alive, nor two atoms, or three. He builds on this statement to say that “it should be very obvious that no matter how many atoms one adds to the argument that an atom or a structure made of two or more atoms cannot be alive”. This is a bold statement as it clearly implies that it is impossible to apply the idea of life to anything, even us. Nikola Tesla also outlined a “defunct theory of life” in 1915 where he said that “There is no thing endowed with life”. This is obviously a very pedantic way to look at the definition of life but a relevant viewpoint nonetheless. Is anything living, or nothing? Or everything?
After all of this though, how important is it that we define viruses as living or non-living? From a scientific perspective defining the boundaries of life is hugely important. If viruses are deemed to be alive then what about prions or viroids? Where is the line drawn and why? The practical use of defining whether or not viruses are alive is relevant to many fields. For example astrobiology in the hunt for other life-forms on other worlds. In this search it seems important that we know what to look for. Whether we define viruses as living or non-living may have no effect on their treatments or the devastation viruses can cause but improving understanding of viruses can have a distinct public benefit. This survey from 2011 shows that the public are lacking some fundamental knowledge about the nature of viruses. This is shown by the fact that over half of people visiting their GP with a respiratory problem such as a cold expected to be prescribed antibiotics. This exemplifies the need for an improved understanding of the nature of viruses in the public domain which can only start with a clear message from the scientific community.
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