“Despite their reputation as harbingers of death and disease, all living cells need viruses.”
Francisco Mojica, molecular biologist, University of Alicante
“Only one form of contagion travels faster than a virus. And that’s fear.”
Dan Brown, American author
Despite their horrific impact on our species, we couldn’t live without viruses. They inspire awe but also evoke fear. Two recent articles may have done the latter: “Scientists have discovered what may be the first ‘vampire’ virus’”; and “Zombie Viruses: Fascinating and a Little Frightening.” It therefore seemed like a good time for a Germ Gems post on how ubiquitous viruses are and to put the newly recognized“vampire” and “zombie” viruses in perspective.
Our planet of viruses. Without viruses, there might not be life on Earth. In his book Planet of Viruses, New York Times journalist Carl Zimmer provides a full accounting of just how astonishing viruses are. He discusses many of the impacts of viruses on us as well as on our planet, including their role in structuring the evolution of life.
Sizing up viruses. It took until 1935 and the newly developed electron microscope for scientists to see a virus (the tobacco mosaic virus) for the first time. Although very small, even viruses vary in size.
Rhinoviruses, the cause of the common cold, are RNA viruses 15-30 nm in diameter. It’s estimated that 500 million would fit on a pinhead. Better known and somewhat larger are SARS-CoV-2 and HIV. Each is about 100 nm in diameter. (SARS-CoV-2 demonstrates that size does matter as most experts concluded that properly worn N95 respirators [masks] do prevent this airborne virus’s entry to the nasal cavity.) At the other end of the size spectrum is the giant Mimivirus(discovered in 2010). It’s a whopping 500 nm in diameter. (An average-size bacterium is about four times bigger.) The Mimivirus is thought to be an evolutionary bridge between nonliving viruses and living organisms.
How many viruses are there? It is estimated that there are 5-10 million times more viruses on Earth than stars that exist in the observable universe. And it’s suggested there may be as many as a trillion different virus species. Fortunately, only a paltry 219 viral species are able to infect humans. But some of these species take an enormously serious toll on humans, for example, HIV, influenza virus, and SARS-CoV-2, to name just a few.
Bacteriophages (aka phages) are viruses found wherever bacteria exist. These viruses kill and selectively target only bacteria. (The term “phage” comes from the Greek phageinmeaning to eat, consume, or destroy.) It is estimated that there are more bacteriophages on the Earth than every other organism, including bacteria combined. (The estimate is more than 10 to the 31st power, that is 1 with 31 zeroes after it.)
Phages clean up most environments inhabited by bacteria. For example, they destroy roughly 40% of bacterial cells in the ocean every day. They do us no harm because human cells lack receptors for phages. (Science journalist Tom Ireland titled hisnew book that focuses mainly on bacteriophages The Good Virus: The Untold Story of Phages.) There’s growing enthusiasm among scientists about the potential pharmaceutical application of bacteriophages to treat multiply antibiotic-resistant bacteria.
What about vampire and zombie viruses? On November 14, 2023, Scientific American published the article “Scientists Discover First-Ever Vampire Virus Latched to Neck of ‘MindFlayer’.” In it, University of Maryland investigatorsannounced the discovery of a satellite virus latched onto its helper virus. The scientists dubbed this satellite phage “MiniFlayer.” MiniFlayer evolved a short appendage that allows it to latch onto its helper virus’s neck like a vampire—reminiscent of Count Dracula—thus the name “vampire virus.”
Biologists have known of viruses that prey on other viruses for decades. They are referred to as “viral satellites.” It’s also been known for some time that most bacterial species have a set of satellite helper viruses. But like other phages, humans lack receptors for satellite viruses as well. Therefore, rather than representing a threat, some scientists think these “vampire” viruses may actually provide insights into new antiviralstrategies. In comparison, the “zombie viruses” are more intriguing and certainly more worrisome.
Recently, European researchers digging into the permafrost of Siberia unearthed a group of viruses referred to as “zombie viruses.” As journalist Caitlin Taylor So reported in a November 13, 2023 article in WebMD News, “Zombie Viruses: Fascinating and a Little Frightening,” of all the consequences of climate change, nobody predicted the recent reviving of 13 types of prehistoric viruses, as the ancient frozen ground slowly loses its “perma.”
Researchers observed that these zombie viruses were only able to infect amoebae. Nonetheless, the scientists involved in on-going studies take very seriously the small risk that a frozen virus would get unearthed and start an infection chain that ends up in humans.
Along this line, a sobering letter appeared in the June 2023 issue of New Microbes New Infections. In their letter “Zombie virus revitalized from permafrost: Facts and fiction,” a group of Indian scientists points out that one-fourth of the landmass of the Northern Hemisphere is covered in permafrost, which is home to countless numbers of viruses. They refer to the zombie virus tale phenomenon as “growing infectious types of literature,” which is analogous to “emerging infectious diseases.” And they note, “Some of the most recent works of literature involving virusesare horrific science fiction or thrillers…. After researching live cultures, specialists concluded that all ‘Zombie viruses’ are communicable and pose a ‘health risk.’"
A cautionary tale. There is uniform agreement among public health experts that “it is not a matter of if, but rather of when” the next emerging infection will erupt. But nobody knows“what” the nature of the pathogen will be, or “where” it will start.
From what I’ve read so far, I don’t think we have to “sweat” the vampire viruses. But it seems prudent to me to keep an eye onthose zombie viruses arising from the melting permafrost.