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Summer 2021 - Vaccines

Emerging Novel Viruses

With trillions of viruses living in the human and other species’ microbiomes, the possibility of novel viruses such as COVID-19 emerging is high, but the threat they may pose is unknown.

With the ongoing global pandemic courtesy of the coronavirus, novel viruses have become a topic of discussion in the medical community — and among laypeople. But the nature of novel viruses, what they are, how they appear and the threat they pose to public health are not widely understood.

What Are Novel Viruses?

Viruses as defined by the Merriam-Webster dictionary are “nonliving extremely complex molecules, that typically contain a protein coat surrounding an RNA or DNA core of genetic material but no semipermeable membrane, that are capable of growth and multiplication only in living cells.”1 Simply put, a novel virus is one that has not previously been identified by the scientific community and, thus, has not been named or categorized. In fact, novel viruses may have existed for years, but they were never encountered by human researchers. On the other hand, novel viruses may newly develop since genes in RNA and DNA are subject to mutation.

Almost 7,000 viruses have been described in detail, according to a March 24, 2020, article in The New York Times, and that number has undoubtedly grown. Still, it’s estimated there may be hundreds of thousands, even millions, of viruses that have not yet been discovered. And, every one of them is a novel virus.

Viruses reproduce by latching onto a specific molecule on the membrane of a cell and then inserting themselves into the cell’s interior where they hijack the cell’s own replication processes to make copies of themselves. For instance, when a person has the influenza (flu) virus, that person’s body may contain up to 100 trillion copies of that flu virus alone.2

And, because viruses penetrate a cell’s exterior membrane by latching onto a specific molecule, they tend to specialize. This means a virus that can infect one life form is generally unable to infect another since different species’ cells have different chemical makeups, including their membranes. A virus that will fit into one specific molecule will be unable to fit into all other molecules.

Yet, the same instability that allows new viruses to arise from old ones via genetic mutation also leads to viruses jumping from birds to humans (such as various forms of avian flu over the years) and, apparently, in the case of the novel coronavirus, from bats to humans: A mutation allows the virus to latch to a molecule unique to its new host. 

In late April, the Centers for Disease Control and Prevention (CDC) reported the discovery of three novel influenza viruses — most recently, a child in Wisconsin infected with an (A(H1N1)v) virus, thought to have been acquired during contact with pigs.3 

How Are Novel Viruses Discovered?

A virus’s environment is cytoplasm. Viruses cannot survive outside a host cell, at least not for long.2 Lacking a cellular membrane to protect their genetic coding, viruses are extremely vulnerable to environmental factors such as heat, cold, radiation, exposure to caustic materials and other factors that can cause them to quickly disintegrate when they are outside of a cell. Viruses also lack any means of locomotion, relying on their hosts for mobility.

Since viruses are only found, by and large, within the cells of organisms, searching for viruses is not like searching for new plants, animals or even microbes. Because viruses are so small that they live inside of cells, all but a handful (known as giant viruses) are too tiny to be seen with standard microscopes. Electron microscopes can capture images of viruses and are one tool used to discover viruses. Today, however, most recent and ongoing searches for novel viruses are conducted using chemical tests that look for specific genes known to be associated with viruses.4

Still, while technology such as electron microscopes and polymerase chain reactions allow us to search for viruses at their submicroscopic scale, most of those 7,000 viruses we currently know about were discovered the same way health officials became aware of the novel coronavirus: through the symptoms of infected hosts, human or otherwise.

The symptoms of COVID-19 were just distinct enough to make researchers wonder if there was a new disease in late 2019 and early 2020. As researchers studied people exhibiting symptoms of this outbreak, they were able to determine there was a new, or novel, virus not previously known about: a coronavirus.

While the World Health Organization (WHO) continues to try to determine the exact origins of this novel coronavirus, the Wuhan Institute of Virology, a research laboratory in Wuhan province in China, is part of that investigation because it engages in the search for and identification of novel viruses, and the first cases of COVID-19 were diagnosed in that area. Whether this novel coronavirus infected a lab worker studying bat-borne viruses, and from there escaped into the general human population, is not yet known. WHO is conducting additional study after the original report dismissed that possibility but faced widespread criticism for its methodology.5  

Still, laboratories such as the Wuhan Institute of Virology continue to search for new viruses in hopes of expanding our limited knowledge of viruses. 

How Are Novel Viruses Named?

Unlike animals, plants, fungi and bacteria, viruses are not necessarily named for those who discover them. Instead, they are given a name by the International Committee on Taxonomy of Viruses (ICTV).6

Nor are viruses necessarily categorized by species, genus, family, order, class, phylum, etc. As viruses are not currently considered part of the kingdom of life, they are described and categorized by their molecular structure and any infections they are known to cause.6 Hence, the novel coronavirus that causes COVID-19 is officially known as “severe acute respiratory syndrome coronavirus 2,” which is shortened to SARS-CoV-2. (The term “coronavirus” refers to the globular shape of the virus.)

Since viruses reproduce and are self-described by their genetic code (RNA or DNA), there is ongoing reconsideration of whether viruses are indeed a life form. ICTV is formulating a new classification similar to that used for cellular life.7 The organization has also been charged by WHO with creating a universal database of all known viruses.

The Threat of Novel Viruses

Although some 320,000 viruses are thought to be able to infect mammals,8 most viruses do not pose a high risk to humans. Only approximately 200 of the 7,000 currently cataloged viruses are known to infect humans.9 Other viruses that enter the body through airborne droplet transmission, by mosquito bites or by touching one’s face after shaking hands are unable to penetrate the body’s cells so they cannot cause infection. (Interestingly, the human body is naturally host to untold types of viruses that cannot penetrate human cells. These viruses live on the bacteria that inhabit the body, which is the so-called good bacteria in the digestive tract.10)

However, some of those 200 viruses are very deadly. Hemorrhagic fevers such as ebola, dengue and yellow fever are among the most feared diseases known. Other viruses cause AIDS, encephalitis and polio. And, seasonal flu is also caused by viruses.

So, it is difficult to gauge what the health threat of a novel virus will be. It depends entirely on the type of virus, how infectious it is and how it affects its host. Ebola, for instance, has a mortality rate of up to 90 percent, but it does not seem able to spread much beyond its original source in equatorial Africa. The common cold, on the other hand, is highly contagious and endemic around the world, but it rarely causes serious health concerns.

Treating Novel Virus Infections

Since the specific nature of a novel virus is not known in advance, specifying treatment is also impossible. However, if a patient is exhibiting symptoms of an infection for which no obvious cause can be found, and blood work does not reveal any known bacterial or viral markers, the patient can be referred to a specialist. 

For any unidentified infection, physicians carefully monitor a patient for any sudden deterioration in his or her condition. Any change in or appearance of a rash, a spike in fever, a persistent cough, difficulty breathing, severe headaches or body aches are all signs of a potential viral infection.

Relatively few viruses have an antiviral treatment on the market, and none will be approved for a novel virus, so the unfortunate reality is treatment for an infection caused by a novel virus will be rest and fluids unless the patient suffers such severe symptoms that hospitalization or other intervention becomes necessary.

It is important, when a new pathogen is suspected, doctors notify local and state public health agencies, as well as the CDC.

Ongoing Research

Even modern technology has some inherent limitations in aiding scientists’ search for new viruses. For instance, polymerase chain reactions that can take a small sample of RNA or DNA and mass-produce copies of it so researchers can identify it via chemical tests only helps if there are common genetic strains already associated with known viruses.

When viruses are found that do not share RNA or DNA patterns with any known viruses (in one recent case, a virus residing in a South American amoeba), confirming a new virus has been found takes a lot more work.11 In addition, the recent discovery that there are likely thousands of viral types living in the gut bacteria of human beings only hints at the scale of trying to identify and categorize as many viruses as possible. Just in homo sapiens, it is estimated there are more than 1,000 species of bacteria living in our digestive tracts.12 Another recent study found there are likely 140,000 different virus types living in those 1,000 bacteria species in the human microbiome alone.13

Because most animals have gut bacteria involved in digesting food (among other functions), and since this microbiota varies from species to species, the number of separate bacteria to be studied — and the viruses that live within them — is astronomical. There are 6,000 different species of mammal alone, and a similar number of amphibians. Add to that 1,000 species of reptile and 9,000 or more bird species. This only hints at the number of potential undiscovered viruses. 

In fact, invertebrates have microbiomes, too. Insects have bacteria in their digestive tracts,14 as do spiders15 and shellfish. There are some 925,000 species of insects currently identified. Even organisms without digestive tracts such as sponges, plants, fungi and nonbacterial single-celled organisms such as archaea16 have viruses living within their cells.

In short, it seems there is almost no life form that does not have viruses associated with it. That’s a lot of gut bacteria yet to be studied, and a lot of viruses living in those gut bacteria. 

Looking Ahead

Given how little is known about viruses — how prevalent they are, their genetic diversity and their history — virology is likely to be a rapidly developing field over the coming decades. In fact, virology is at a point at which scientists are trying to determine how much still needs to be understood, according to Jônatas Abrahão, a virologist at the Federal University of Minas Gerais in Belo Horizonte, Brazil.11 

While research into discovering previously unknown viruses in nature continues to accelerate, geneticists are also working on manipulating the RNA and DNA of viruses to better understand how they work and to find new ways of treating infections caused by viruses.

Both prongs of research — discovering existing viruses and modifying the genes of viruses in the laboratory — carry the threat of spillover: Either a virus previously unexposed to homo sapiens makes the leap, or a bioengineered virus accidentally infects a researcher.

Considering what we know so far about viruses, COVID-19 is statistically unlikely to be the last novel virus to cause a major outbreak of disease.


1. Merriam-Webster Dictionary. Virus. Accessed at

2. Wei-Haas M. Viruses, Explained. National Geographic, Feb. 22, 2019. Accessed at

3. Centers for Disease Control and Prevention. FluView Summary Ending on April 10, 2021. Accessed at

4. Racaniello V. How Many Viruses on Earth? Virology Blog, Sept. 6, 2013. Accessed at

5. Rauhala E. WHO Chief, U.S. and Other World Leaders Criticize China for Limiting Access of Team Researching Coronavirus Origins. The Washington Post, March 30, 2021. Accessed at

6. World Health Organization. Naming the Coronavirus Disease (COVID-19) and the Virus that Causes It. Accessed at

7. Lefkowitz E, Dempsey D, Hendrickson R, et al. Virus Taxonomy: The Database of the International Committee on Taxonomy of Viruses (ICTV). Nucleic Acids Research, Jan. 4, 2018. Accessed at

8. Anthony S, Epstein J, and Murray K. A Strategy to Estimate Unknown Viral Diversity in Mammals. mBio, July 30, 2013. Accessed at

9. ViralZone. Human Viruses and Associated Pathologies. Accessed at

10. Pride D and Ghose C. Meet the Trillions of Viruses that Make Up Your Virome. The Conversation, Oct. 9, 2018. Accessed at

11. Pennise E. Scientists Discover Virus with No Recognizable Genes. Science, Feb. 7, 2020. Accessed at

12. Gilbert J, Blaser M, Caporaso J, et al. Current Understanding of the Human Microbiome. Nature Medicine, April 1, 2018. Accessed at

13. Wellcome Trust Sanger Institute. Scientists Identify More Than 140,000 Virus Species in the Human Gut. Science Daily, Feb. 18, 2021. Accessed at

14. Engel P and Moran N. The Gut Microbiota of Insects — Diversity in Structure and Function. FEMS Microbiology Reviews, September 2013. Accessed at

15. Busck M, Settepani V, Bechsgaard J, et al. Microbiomes and Specific Symbionts of Social Spiders: Compositional Patterns in Host Species, Populations, and Nests. Frontiers in Microbiology, July 31, 2020. Accessed at

16. Krupovic M, Iranzo J, Koonin E, et al. Viruses of Archaea: Structural, Functional, Environmental and Evolutionary Genomics. Virus Research, Jan. 15 2018. Accessed at

Jim Trageser
Jim Trageser is a freelance journalist in the San Diego, Calif., area.