More Viruses Than Stars? No Way!

More Viruses Than Stars? No Way!

There are 10 million times more viruses than stars in the universe. But if viruses cause millions of human deaths every year, and many millions more are sickened by these tiny predacious parasites, why would God create such things?

When others learn I’m a virologist, they often respond with questions such as, “Are viruses alive?” When they learn that I’m a Christian, they want to know, “Why would God create viruses?” This question assumes that viruses are bad, causing sickness, suffering, and sometimes even death. But is painting the most abundant organic entities on Earth in such a poor light the only way to understand them?

I love to address questions like these that take a deeper look at viruses and their roles in creation and human sickness, and their use as tools in mitigating suffering and more. I’ll be giving a talk that addresses this topic at the Faith & Science Conference at Evangel University this weekend. I’ll later record it for a 2017 RTB Live! DVD. But for now, here are a few of the highlights.

Are Viruses Alive?

Viruses are comprised of two basic components: proteins and nucleic acid (RNA or DNA). (Some viruses have a third basic component: a lipid envelope.) They display incredible diversity in size, shape, replication strategies, genomic composition, organization, and in the kinds of cells and animals they infect. Estimates suggest that there are 1–3 million different viruses infecting vertebrates. And one study in bats indicates that more than 90 percent of viruses infecting mammals have yet to be identified.1 Despite such huge virodiversity (a phrase indicating viral diversity), all viruses share one thing in common: they cannot replicate or make more viruses on their own. They absolutely require a living cell to provide resources, machinery, and energy to produce and assemble viral components into viral progeny.

Viruses cannot harvest nutrients from their environment. They hijack cellular machinery for protein synthesis and depend on cellular metabolic processes and enzymes for provision of nucleobases and amino acids—building blocks for progeny virions. Viruses also depend on intracellular transport systems for many steps in viral replication and assembly. Without living cells, viruses would never be able to reproduce themselves.

The Seventh Report of the International Committee on Taxonomy of Viruses states, “Viruses are not living organisms.”2 Although not living, viruses carry blueprints for the production of more viruses. And these blueprints can be modified. Some viruses may be engineered to incorporate foreign genes into their viral genomes. Others may pick up extra genes from host cells during replication and packaging. Still other viruses will package defective or truncated genomes that become interfering particles, competing with production of full-length viral genomes in subsequent rounds of infection. Although viruses are not living, they accrue changes over time, and they play a critical role in the history of life on Earth and in sustaining biodiversity today.

How Abundant Are Viruses? 

Viruses are not only incredibly diverse but also incredibly abundant. They outnumber all other living things by a factor of 10 to 1 or even 100 to 1 or more! The vast majority infect single-cell organisms like bacteria and archaea. It is estimated that there are 1031 viruses on Earth, or 10 million times more viruses than stars in the universe. In his book A Planet of Viruses, Carl Zimmer offers two conceptual pictures to help us grasp this abundance of viruses: (1) add all the viruses on Earth together and they would equal the weight of 75 million blue whales, and (2) line up all the viruses end to end and they would stretch out 42 million light-years.3 That’s almost 17 round-trips to the Andromeda Galaxy! Considering most viruses are on the order of 0.1–0.01 microns, or one one-thousandth the width of a human hair, that’s a lot of viruses.

If it were not for viruses, bacteria and other single-cell organisms would rule the Earth, sequestering all nutrients and filling all ecological niches, making higher life and the survival of multicellular organisms impossible. Bacteriophage (viruses that infect bacteria and archaea) kill 40–50 percent of the bacteria in Earth’s oceans on a daily basis. This releases an abundance of organic molecules into Earth’s biogeochemical cycle and food chain for the survival of other organisms. Bacteriophage also help keep our planet’s ecological niches and our bodies’ microbiomes in balance so that we are not overrun by bacteria. If not for a balance between bacterial replication and phage-mediated death, Earth would be a giant ball of bacteria with no room or food source for other organisms to survive and thrive.

So God’s creation certainly included bacteriophage for keeping life on Earth well regulated, whether in the human gut or the global biogeochemical cycles. But what about viruses that make us sick?

Where Did Viruses Come From? 

Historically, viruses were identified because of the diseases they caused (e.g., rabies virus, tobacco mosaic virus, smallpox). The advent of metagenomics has changed this. We now realize that Earth is filled with a vast array and diversity of viruses. Everywhere we find life, we find viruses. Yet only a very small fraction of viruses are associated with human disease. Viruses that infect humans, like all other viruses, are of unknown etiology. Apart from direct creation, some subset of viruses may originate from the natural order of decay. Many scientists who consider the origin of viruses think of them in terms of cellular castoffs or escape genes from once (or current) living organisms.

I find it interesting to think of this in the context of retroviruses. Endogenous retroviruses (ERVs) are highly repetitive sequences in the genomes of many animals that resemble the sequence and genetic organization of modern retroviruses. The prevailing paradigm is that ERVs are the result of ancient retroviral infections and insertion events. However, we are finding that some ERVs have specific and critical developmental functions in the genomes of the organisms that harbor them. It seems a safe assumption that only a fraction of associated ERV functions have been identified to date, since they have been largely unexplored in functional capacities and were relegated to evolutionary junk heaps—even though they compose more than 8 percent of the human genome.

Some ERVs, like jumping genes, translocate to other places in the genome. Some (but not those characterized in humans) even produce viruses that may be transferred from cell to cell or host to host. Perhaps some ERVs are the result of ancient retroviral infections, but perhaps some ERVs are the originating source of various retroviruses. Considering that we know so little of the highly repetitive genomic sequences of humans and other extant animals, not to mention knowing practically nothing of repetitive genomic elements in extinct animals, this is at least a plausible scenario for the origin of some viruses.

I admit that this is a bit far-fetched in light of current dogma, but it is within the realm of the possible, and it suggests that other cellular castoffs or escape genes from other animals (long extinct or even extant and yet unidentified or yet to be discovered) may hint at multiple other virus origins as well.

Viruses: Part of the Fall or God’s Providence?

Certainly, many viruses associated with human disease have animal origins. These zoonotic viruses are transferred to humans when humans come in contact with animals that harbor the virus even in the absence of disease. It is unclear what roles these viruses may have in nature before making the jump into human hosts. It’s possible that some may exist to regulate animal populations, similar to the way bacteriophage regulate bacterial populations. It is also possible that some may have symbiotic effects in nature (like some plant viruses do) and only result in disease when exposure and transmission to susceptible hosts occur from imperfect management of creation.

Viruses may even be part of God’s creation, providentially given for our management as they supply an abundant matrix of untapped genes and delivery systems to address many of the challenges we face in human health and disease. Regardless of their origins (or associated diseases), many viruses are already harnessed as tools allowing scientists to uncover keys of cellular biology and to mitigate disease. To name just a few ways that we wield viruses for good, they are utilized in gene therapy, cancer therapy, gene-editing, vaccine production, and nanomedicine delivery.

So although some viruses are bad, we cannot paint all viruses with the same brush. Some were certainly part of the created order. Some may be associated with the natural order of decay or the mismanagement of creation. Still others are being harvested for mitigating disease and suffering. With such an abundance of still-unknown viruses, we have so much more to discover.

  1. Simon J. Anthony et al., “A Strategy to Estimate Unknown Viral Diversity in Mammals,” mBio4 (September 2013): e00598-13, doi:10.1128/mBio.00598-13.
  2. Marc H. V. Regenmortel et al., eds., Virus Taxonomy: Seventh Report of the International Committee on Taxonomy of Viruses (San Diego: Academic Press, 2000), 4.
  3. Carl Zimmer, A Planet of Viruses, 2nd ed.(Chicago: University of Chicago Press, 2015), 48.