Let us trace the history of virology. Several hundred years ago in China, people inhaled powder from scabs of smallpox sufferers in order to immunize others. By the 1700s this was a well-known practice in the Arab world. In 1717 Lady Mary Wortley Montagu observed the practice in Istanbul and attempted to popularize it in Britain, by inoculating the Royal family. But her efforts never became popular because the methods still had a 2-3% chance of transmitting the disease. In 1721, Cotton Mather and Zabdiel Boylston wanted to inoculate citizens of Colonial Massachusetts. They started a program and continued to inoculate many volunteers, despite many adversaries in both the public and the medical community in Boston. As the disease spread, so did the controversy around Mather and Boylston. To make their point, Mather and Boylston used a statistical approach to compare the mortality rate of natural smallpox infection with that contracted by variolation. During the great epidemic of 1721, approximately half of Boston’s 12,000 citizens contracted smallpox. The fatality rate for the naturally contracted disease was 14%, whereas Boylston and Mather reported a mortality rate of only 2% among variolated individuals. This statistical analysis may have been the first time that comparative analysis was used to evaluate a medical procedure. While Cotton Mather is remembered as one of the most influential Puritan ministers and scholars of his day, he is also infamous in his role in the Salem witch trials. Scholars suggest that Mather’s dramatic descriptions of the devil’s activity upon children may have led to the first cry of witchcraft in Salem Village.
In 1796, Edward Jenner developed the much safer technique of vaccination using cowpox instead of smallpox. In 1876, Adolf Mayer described a condition of tobacco plants, which he called “mosaic disease”. He excluded the possibility of a fungal infection and could not detect any bacterium and speculated that a “soluble, enzyme-like infectious principle” was involved. In 1884, the French microbiologist Charles Chamberland invented a filter – known today as the Chamberland filter – that had pores smaller than bacteria and could filter them. In 1885, Louis Pasteur found a vaccine for Rabies and speculated about a pathogen too small to be detected using a microscope. In 1892, the Russian biologist Dmitry Ivanovsky used a Chamberland filter to study tobacco mosaic disease. His experiments showed that crushed leaf extracts from infected tobacco plants remain infectious after filtration. Ivanovsky suggested the infection might be caused by a toxin produced by bacteria, but did not pursue the idea. In 1898, the Dutch microbiologist Martinus Beijerinck repeated the experiments by Adolf Meyer and became convinced that filtrate contained new forms of infectious agents. He observed that the agent multiplied only in cells that were dividing and called it a “virus”.
The cause of Foot and Mouth disease in cattle was first shown to be viral in 1897 by Friedrich Loeffler. He passed the blood of an infected animal through a Chamberland filter and found the collected fluid could still cause the disease in healthy animals. In 1903 it was suggested for the first time that transduction by viruses might cause cancer. In 1908 Bang and Ellerman showed that a filterable virus could transmit chicken leukemia, data largely ignored until the 1930s when leukemia became regarded as cancerous. In 1911 Peyton Rous reported the transmission of chicken sarcoma, a solid tumor, with a virus, and thus Rous became “father of tumor virology”. The existence of viruses that infect bacteria (bacteriophages) was first recognized by Frederick Twort in 1911, and, independently, by Félix d’Herelle in 1917. As bacteria could be grown easily in culture, this led to an explosion of virology research. By 1928 enough was known about viruses to enable the publication of Filterable Viruses, a collection of essays covering all known viruses edited by Thomas Milton Rivers. We have come a long way since then. Let us now delve into what makes viruses special.
Mindnumbing insights into the viral world
Sheer numbers: There are estimated to be 2*10 power 31 viruses in earth. That means 2 followed by 31 zeroes. Zimmer tries to visualize this number, “As in over 10 million times more viruses than there are stars in the universe.” I calculated that if you were to stack one virus on top of another, you’d create a tower that would stretch beyond solar system, milky way galaxy and far beyond, to reach a height of 260 billion light years. This is enough to go to the edge of the known universe and come back 19 times. This number by the way is more than the number of sand grains in earth (8*10 power 18) or the number of drops in the world’s ocean (4.5*10 power 25). This number means that this is the most successful species ever, dwarfing even bacteria (5*10 power 30).
Diversity: Based on research that each species could harbor upto 58 different virus strains, the number of virus species could be at least 100,939,140. This includes the 1,740,330 known species of vertebrates, invertebrates, plants, lichens, mushrooms, and brown algae. To add context just 62,305 vertebrate species are known to exist.
Mobility: Researchers looked at a boundary layer in the atmosphere – the free troposphere. At this height, approximately 8,200 to 9,840 feet above sea level, viruses hitch rides on air currents and on particles of soil or vapor from sea spray, and travel thousands of miles from their point of origin. Researchers noted that “Every day, more than 800 million viruses are deposited per square meter above the planetary boundary layer”.
The human-virus connection: Not many will know that while there are 37 trillion cells in a human, a human body also has 38 trillion bacteria and upto 380 trillion viruses inside it. There is a growing body of research which shows the the human body is not just about human cells, but it should also factor in the bacteria and viruses which outnumber human cells by a 111:1 ratio. What are all these additional microbes and viruses doing?
The greatest massacres of all time: Bacteria and viruses have been involved in an evolutionary tug of war since the beginning of life. Viruses kill 40% to 50% of all bacteria in the oceans each day, which creates considerable organic material that floats to the bottom of the ocean (one billion tons of carbon each day). The carbon footprint of Humans is around 35 billion tons of carbon. This accomplishes in a month what all humans typically create in a year.
Bacteriophages are one group of viruses, found wherever bacteria exist. It’s estimated there are more than 1031 bacteriophages (aka phages) on the planet. That’s ten million trillion trillion, more than every other organism on Earth, including bacteria, combined. Each is evolved to infect a specific bacterial host in order to replicate — without affecting other cells in an organism. They cause a trillion trillion successful infections per second and destroy up to 40 percent of all bacterial cells in the ocean every day.
Research has shown that if a single phage virus is added to a culture of 10 billion E.Coli Bacteria, within two hours, there are 10 trillion viruses and only 10 million E. Coli remaining. This means that 99.9% of the E.Coli have been killed. Bacteria so dread these phages that they decrease their virulence to the host cells in response to phage attacks. Research has shown that in human cholera outbreaks, bacteria which infected humans, mutated their DNA to decrease their ability to make humans sick, in return for increased defense against phages. Hence phage treatment using the ability of viruses to scare bacteria into a meeker version of themself, may be a valuable alternative to antibiotics in the fight against harmful bacteria, in the future.
Reproductive ability: As science columnist Carl Zimmer writes “If you get sick with the flu, for example, every infected cell in your airway produces about 10,000 new viruses.” Within hours viruses can make millions or even billions of copies of itself. “The total number of flu viruses in your body can rise to 100 trillion within a few days. That’s over 10,000 times more viruses than people on Earth.” They also take advantage of the mammalian sneeze reflex to multiply. When an infected person sneezes or coughs more than half a million virus particles can be spread to those close by.
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Photo: Design Cells, iStock https://www.pbs.org/wgbh/nova/article/chatty-bacteria-might-be-most-vulnerable-viruses/
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