Is a Virus Alive or Not?

Electron micrographs of an HIV-infected T-cell, MERS virus particles, swine flu virus particles and Ebola virus particles. Photos: NIAID/Flickr, CC BY 2.0.

I want to raise the question here of what exactly it means to be ‘alive’, especially if you happen to be a virus. Viruses are composed entirely of RNA (although others do indeed have their own DNA), encased in a protein shell, and inhabit a ‘twilight zone’ between living and nonliving. One of the reasons why they are not regarded as fully alive is that they cannot reproduce themselves. Biologists define life using the acronym GRIMNER: living things have growth, respiration, irritability, movement, nutrition, excretion and reproduction. Viruses are not cellular, do not grow, move or breathe, and they do not divide to produce offspring.

While this definition of life fits even tiny life forms like bacteria, my argument here is that life might also be defined in terms less bound to the familiar creatures that share these features with us. Think of reproduction, for example. Are celibates and mating members of society who choose not to have offspring not alive? Were the children who died before having a chance to produce offspring not ever alive? No, for all these people do have the means of producing offspring, but have for various reasons not used it. Then what about people who were born without the capacity to produce viable sperms or ova. Should we place them in a ‘twilight zone’?

I think we would agree that people who have not produced progeny have been able to have a profound impact on humankind, because they have as teachers, writers and thinkers been able to influence people they had no role in bringing to life. Their influence kicked in much later, when their students, readers and followers were not only already born, but fairly mature, and capable of taking the information they received and acting on it. Once we agree that these ‘influencers’ are alive, it’s impossible to exclude others who had no children but had little or no impact on anyone else. We have an understanding of ‘life’ that encompasses them all. ‘Living’ is an attribute of species, not their individual members.

When I think of life, be it human, bacterial or immaterial things like a language, I look for vitality, something that makes an entity more than just the sum of its parts. A dead body, however physically present it may be, is not alive. Lenin and Mao, ‘asleep’ forever in their mausoleums, are never going to get up and lead us again, though their parts are there, and any that might have been removed would not be sufficient to bring them back to life if restored. A language that is spoken natively by no community, a language that is the first language of no infant, is not alive, however present it might be in old manuscripts, because it is no longer capable of evolving in concert with its environment. It needs to be preserved, like the remains of Lenin and Mao, as it is dead.

What does this vitality consist of? This article is an attempt to move past what looks to me like an anthropocentric perspective to arrive at a broader view. To start, I would say vitality involves a cycle – a beginning, growth, a mature phase and an end. Along with this, there needs to be some sense of a drive, something the living entity feels impelled to do. To borrow a concept from thermodynamics, it has to resist entropy: it must not be a temporary assemblage that all too readily falls apart. Despite missing some abilities attributed to other living things, a virus is in its own sense complete.

If viruses had no impact on other creatures, we wouldn’t be spending so much time thinking about them. What a virus does is not random: it is a creature driven to locate and penetrate a living cell, and what most viruses proceed to do is hijack the innate programming of that cell so that it does not make copies of itself, but instead helps the viruses reproduce. In the process, the virus usually harms the larger creature the cell is a part of, if enough cells are taken over in this way, and that is why we speak of a virus causing infection. Causing infection would appear to be a virus’s ‘motivation’.

Viruses have been a part of life on this planet for at least 3 billion years, long before sexual reproduction evolved as a means of producing offspring. In those days, they were the only creatures tiny enough to penetrate other cells and add to their DNA, which made them important drivers of evolution. And this has not always been a bad thing.

In the early days of sexual reproduction, there was one problem would-be parents faced. Any offspring gestating inside its mother had DNA from two parents, and that technically made it a foreign object, something the body was primed to expel at once. Reptiles, dinosaurs and birds solved this problem by allowing their embryos to be expelled, but they encased them inside egg-shells, and incubated them outside the body. Then came marsupials, mammals like kangaroos who gave birth to tiny embryos with strong fore-limbs capable of propelling them to their mothers’ pouches, where they would gestate externally. Pregnancy, in those times, could not last more than a few weeks.

In The Tangled Tree: A Radical New History of Life (2018), science writer David Quammen talks about the work of the biologist Thierry Heidmann on the syncytin genes that cause immunosuppression. He relates the story of a retrovirus, similar to HIV, the virus that causes AIDS (Acquired Immunodeficiency Syndrome), that infected an early mammal. But instead of harming or killing her, as most viruses would do, it was captured and lived on in her genome. In fact, it located itself in her chromosomes, making it a part of her genetic heritage that would be passed on to all her progeny.

What this virus did was suppress the immune response that made mothers expel their embryos early and created what we now call the ‘immunosuppressive’ state of placental pregnancy, where embryos get time to develop inside their mothers until they are fully viable. In fact, many newborn mammals, unlike baby marsupials, are able to get up and walk as soon as they are born.

Is it possible to make a case that a virus ceases to ‘live’ when it is no longer capable of infecting a living cell? There is no doubt these two states exist: a time when the virus is capable of causing infection and a time when it is not. That is why we speak in terms of ‘how long a virus can be harmful’ outside of a host, calculating this time in seconds, hours or days. It doesn’t matter to a virus whether we regard it as alive or not. All I wish to do here is question the definition of life that has been in use up to now.

This definition may be carefully nuanced within the scientific community, but medical professionals in India speaking to the media have gone so far as to portray a virus as something analogous to the ‘contents of a pen-drive’, just information, and therefore not alive. This simplification has been a source of confusion to a people weathering a pandemic – people who have been wondering if the thing that has taken away so many human lives was itself something ‘alive’ or not.

The implicit belief the people have that something that they are told was never ‘alive’ might be indestructible. This has led to all sorts of fears, like the smoke of cremation harbouring the virus.