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.

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 specifically 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 and individuals were often isolated from populations. Nevertheless, outbreaks and major spread of viruses were considered normal. In the Roman Period, we also have detailed accounts of what can be described as smallpox. 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 smallpox plagues 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. To this day this virus is unknown but this disease may have been a type of hantavirus, a pulmonary virus, that seemed to kill victims within a day, making it one of the deadliest recorded. It had devastating consequences in England and Europe, but it disappeared sometime in the mid-16th century almost as quickly as it emerged. Isolation and herbal medicines were used to treat this virus but they may have had little effect. 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 in the New World 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, such as puss from a sick person, the uninfected person could develop an immunity. The practice became the foundation of variolation that was the main form of treatment until the 20th century inoculation efforts. This discovery saved many lives and Lady Mary Wortley Montagu, an English aristocrat living in the early and mid 18th century, witnessed this form of treatment in the Ottoman Empire, which she brought back with her to England. She became the first advocate for variolation in England and this led to experimentation on condemned prisoners, where they were injected with the virus and then purposely exposed to smallpox. Because the prisoners survived, and released for volunteering and surviving, variolation gained in reputation as a form of effective treatment. This represents one of the first active attempts to immunize people to a virus in Europe.

Figure 1. A tablet indicating an attempt to heal sickness and likely viral infection using herbs and medicines.

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. However, viruses, particularly smallpox, led to large-scale outbreaks and this continued to limit the average age of populations to around 40 years even by the early 19th century. Overcrowded conditions and poor sanitation made things worse particularly for the poor. Nevertheless, there was a realization that vaccination could help prevent the spread of 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 healthy dogs, which went on to survive. This led to the first understanding on how to treat rabies, which is still the primary foundation of treatment. However, viruses were still not understood despite these advances. A key development happened in the 1880s when Charles Chamberland developed a filter small enough to allow bacteria and larger microbes through but not others. This allowed, in 1892, Dmitri Ivanovsky to isolate the agent causing a viral 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. Although viruses could not be observed, scientists now began to believe they existed and acted as key agents in many diseases.

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 and later RNA. Heinz Fraenkel-Conrat and Robley Williams helped develop the understanding that viruses had genetic structures like other living creatures. Viruses now became classified as other living beings in the hierarchy of life. 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. Complex DNA makeup and rapid rates of mutation has meant that new viruses could form that are unknown to scientists, including viruses that can go between humans and other life.

Figure 2. The discovery of the electron microscope enabled viruses to be studied in more detail.

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.