What is the history of viruses
Viruses, in some sense, have been known to human societies for thousands of years, mainly that some forms of illnesses can be contagious. Even relatively early evidence from nearly 4000 years ago suggests people understood that it was necessary to quarantine infected individuals. While that has been the case, our specific understanding of viruses and the knowledge of their existence is far more recent.
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Early Understanding of Viruses
Viruses such as rabies are known as early as 3000-2000 BC, where texts describe this and related disease that affected both animals and humans. People saw these afflictions being caused by the gods or evil spirits but also understood they could be infectious and could potentially be treated or at least lessen their effects. Early evidence from Mari, a city in modern Syria, indicates by about 4000 year BP, people who had symptoms of the cold or flu were isolated from other individuals (). There is no indication that anyone understood what caused such sicknesses, but it is clear that they understood that viral infections could spread, leading to the creation of a type of quarantine system with isolated rooms built for sick individuals. In Pharaonic Egypt, measles were considered a normal occurrence in childhood. In the Roman Period, we also have detailed accounts of what can be described as small pox. Galen Pergamum, who worked as Marcus Aurelius' personal physician, describes a sickness with fever that caused vomiting and diarrhoea. Boils in the skin were also observed, with the Romans realizing that these disease probably occurred in crowded places. However, there is no evidence of large-scale attempts at prevention, except perhaps isolating infected individuals. Like many cultures, the Roman interpreted outbreaks as punishment from the gods for events or offenses they may have committed.
Increasingly, more texts and descriptions of viruses are found that described what they did to plant and animal life. In the 8th century a plant virus was described by Empress Kōken, where she noticed a yellowing of leaves caused in plants that we can today attribute to tomato yellow leaf curl virus common in some plants. Throughout the Medieval period, many waves of measles and small pox plaques occurred. In the 16th century, a mysterious virus was described in Tutor England, which my have arrived in England during the conquest of the country by the Tudor dynasty. This disease may have been a type of hantavirus, a pulmonary virus, that seemed to kill victims within a day. It had devastating consequences in England and Europe, but it disappeared sometime in the mid-16th century. Isolation and herbal medicines were used to treat this virus. Perhaps the best know impacts of viruses in human history were the various viruses brought to the New World after the 15th century and spread throughout subsequent centuries. This included measles, influenza, and smallpox, which arguably aided the conquest of North and South America as very large numbers of native populations died. Today we know that native populations were vulnerable because these diseases had their origins from domesticated animals that were not native to the Americas. This meant populations there had not developed immunity over centuries as Old World populations had. By the 17th century, at least in the Ottoman Empire, there is evidence that there was an understanding that if you injected someone who did not have a sickness with a small amount of infected material, that person could develop an immunity. The use of variolation was practiced, which included injecting puss from an infected smallpox victim to a person who was not infected. This discovery saved many lives and Lady Mary Wortley Montagu, an English aristocrat, witnessed this form of treatment, which she brought back with her to England. This represents one of the first active attempts to immunize people to a virus.
Later Developments
Variolation continued to be practiced in Europe and Asia in the 18th and 19th centuries, which undoubtedly began to limit viral deaths, particularly from smallpox. This lead to the first compulsory vaccination act, called the Vaccination Act of 1853, which led to free vaccinations for smallpox and made it enforced for anyone over the age of three months. The law was not well enforced and outbreaks continued to occur. One major breakthrough in virus treatment came from Louis Pasteur. He realized that taking spinal cords from dogs that died from rabies could be used to immunize people from rabies. He began crushing these spinal cords of dead dogs and injecting them into health dogs, which went on to survive. However, viruses were still not understood. A key development happened in the 1880s when Charles Chamberland developed a filter small enough to allow bacteria through but not other microbes. This allowed, in 1892, Dmitri Ivanovsky to isolate the agent causing the plant sickness, although he thought it was a toxin and not a virus. In 1898, Martinus Beijerinck became convinced that some other active agent, what he would later call a virus, was likely causing sicknesses in plants.
Modern Understanding
It was not until 1931, when Ernst Ruska and Max Knoll developed an early form of electron microscope (Figure 2), that it now became possible to observe the agents that caused viral spread. Viruses could now be observed and their structure described. By the 1950s, as viruses were increasingly observed, it now also became possible to study their structure through the understanding of DNA. Heinz Fraenkel-Conrat and Robley Williams helped develop the understanding that viruses had genetic structures like other living creatures. Eradication campaigns that began in the post-World War II era have now successfully mostly eradicated smallpox. Today, over 2000 viruses affecting animal, plant, and bacterial life are known, but potentially millions of varieties exist.
Summary
Viruses have long been known to us, with efforts to combat them including isolation, herbal remedies, and even using infected material to create antibodies tried by the 17th century. With the discovery of important filtering techniques, it became possible to isolate viruses from other microbes. However, only since the 1930s have we been able to observe viruses and only since the 1950s do we now know what they are made of. Today's researchers are finding new strains of viruses regulary with more than 2000 currently known to us.