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Some viruses look like moon landers.

Called phages, they hijack bacteria by landing on the hapless cells and injecting them with a ream of genetic material. Then, the phages use the commandeered cells to multiply.

Similar to the new coronavirus, these phages are excellent parasites. They can be aggressive, dogged, and seem to act with purpose. Yet, many microbiologists who know viruses best say it's a stretch to call any virus truly alive. And so, they can't be killed — only disarmed, like pulling the plug on an appliance.

But today, with a rapidly spreading viral pandemic that's stirring serious unease in American emergency rooms, it doesn't really matter if a virus meets biologists' definitions of dead or alive. Whatever these entities are, they're powerful.

"It's more of a philosophical question," said Ryan Relich, a medical microbiologist at Indiana University's School of Medicine, of whether viruses are alive or not.

"What's more important is that they're winning," he said.

Today, the coronavirus isn't just winning. It's dominating us. It's closed our arenas. Shut down our bars. Emptied California beaches. The increasingly austere governor of New York is now demanding ventilators from the federal government. Our best, and most critical, defense — until a vaccine is developed in a year at the earliest — is social distancing: We're avoiding infected persons and hiding from the microbes themselves, which are basically genes surrounded by a shell.

Viruses, like coronavirus, have become globally dominant because they evolved to become master replicators. But they can't multiply alone, so they take over other cells and exploit this cellular machinery to multiply. It's exquisite parasitism. A single coronavirus-infected cell can manufacture millionsof coronaviruses.

"Parasitism is an old, venerated way of making a living," said Siobain Duffy, who researches the evolution of viruses at Rutgers University.

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Yet, unlike parasites such as intestinal worms, viruses are almost completely dependent upon the cells they hijack. "Viruses don't actually do anything on their own," explained Relich.

They don't breathe. They don't eat. They don't make energy. They appear mindless, floating around with the possibility of landing on a cell. "They don't get up and go to work every day," said Relich. "I don’t consider them to be living. But hey, maybe you want to consider them to be alive so that it’s easier to personify them or rationalize things in a more palatable way."

So, microbiologists can make a good argument that viruses don't have the same hallmarks of living as do amoebas, elephants, and emus.

But maybe viruses are alive — just in another sense of alive. After all, life has been evolving on Earth for some 3.8 billion years, noted Duffy. There are all kinds of curious things out there that might blur the boundary between alive and not alive. For example, there are viruses with longer genomes than bacteria (which we all agree are alive), and viruses that make some bacteria better at things, like photosynthesis. Our human DNA is embedded with some viral genetic material, too, noted Relich.

"People want a clear dividing line between life and non-life," said Duffy. But that line might be blurrier than we think, she added.

The quandary of whether a virus can ever be killed, then,is a bottomless philosophical hole that may never have a certain answer. But it's safe to say, at least, that there are effective ways "to inactivate viruses or otherwise render them kaput," said Relich.

Chemicals — like bleach and rubbing alcohols — can massively damage the exterior wrappings of viruses, which for some include a fatty membrane envelope, making viruses useless. Thorough hand washing destroys these viral shells, too. Though there are no proven antiviral medications for coronavirus (and there may not be for many months), these types of drugs are designed to disrupt a virus' activity. For instance, the HIV drug Enfuvirtide blocks the virus from even attaching to human cells. Other drugs stop viruses from replicating, once they've already slipped inside a cell.

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There's another very certain thing about viruses. Humanity has a ton to learn about them. There are countless species, and they're everywhere. "There are more viruses in this world than there are cells," said Duffy. But only 6,828 virus species have been formally named by scientists. Meanwhile, there could be millions more species out there. Finding and understanding theses microscopic entities could reveal much more about their nature, and "lives."

"We need more research, we need more researchers, we need more funding for research," said Relich.

Only in 1977 did humanity discover the third domain of life, a massive, ancient group of organisms called archaea (the other two domains are bacteria and eukaryotes — which include humans.) What might the great diversity of viruses in this domain, still being discovered, tell us?

"Life continues to astound us," said Duffy. Indeed.

For now, we're focused on the minority of viruses that can threaten our ability to breathe, like the new coronavirus which can result in the serious respiratory disease COVID-19. And for good reason.

"It's to our own advantage to know our enemies as well as possible," said Relich.

Even if they can't be killed.

"Whether or not they’re alive, viruses influence life," said Duffy.

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