History Of Viruses
Primary causes of diseases in human history
Viruses are microscopic collections of genetic code classified as parasites that need a host to survive. Smaller than bacteria and reliant on a host body to reproduce, they have been primary causes of diseases in human history.
Vaccines and antiviral remedies have made it possible to suppress infections and keep them from spreading widely, helping those affected by diseases caused by viruses recover.
Recent examples include the cure to smallpox ― a viral disease that afflicted many over the course of several centuries in human history. In 1980, the World Health Assembly announced that smallpox was cleared.
Since then, there have been no naturally occurring instances of smallpox recorded. Despite this, smallpox and virus research in the United States continues, focusing on the development of vaccines and diagnostic tests to protect against other virus outbreaks.
In the plethora of viral outbreaks that have occurred throughout history, studying viruses and their origin has allowed scientists to gain a better understanding of what environmental conditions and factors cause viruses.
For example, for viruses like the Ebola virus, environmental factors like population growth and population density may have been contributing factors that led to its outbreak.
Relocation and diffusion throughout history has also been a primary cause of the spread and transfer of diseases. In the sixth century, increased trade with China and Korea brought the smallpox virus to Japan.
In the seventh century, Arab expansion brought smallpox into Northern Africa, Spain, and Portugal, and crusades in the 11th century further diffused smallpox in Europe.
Later, in the 15th century, Portugal’s occupation of Western Africa brought smallpox, spreading it further. Europeans would bring smallpox and other diseases to the New World, killing as many as 90 percent of the native population.
Edward Jenner, a British scientist, hoped that vaccination could eliminate smallpox. He pioneered the idea of vaccination, treating a boy with fluid from a cowpox blister to help him recover.
Two centuries later, the 33rd World Health Assembly declared the world to be free of this disease when it was previously endemic in more than 30 countries.
The 1918 Flu Pandemic or the Spanish Flu, the most severe pandemic in recent history, was caused by the H1N1 virus with genes of avian origin. Scientists are not able to pinpoint where exactly the virus occurred, so its origin remains unknown even today.
Estimated to have infected 500 million people or one-third of the world’s population infected, the virus was responsible for causing 50 million deaths worldwide with 675,000 of those deaths occurring in the United States.
In 1917, when the United States entered World War I, the life expectancy was 54 years for women and 48 years for men.
However, in 1918, spring and fall waves of influenza caused the average lifespan in the United States to drop by 12 years.
In 1919, the third wave of pandemic flu activity occurred as the pandemic began to subside, but the virus continued to circulate for 38 years.
Shortly after, in 1930, the first isolation of influenza proved that the flu was caused by a virus. In 1957, the H2N2 flu virus emerged to trigger a new pandemic, replacing the previous virus.
In 1960, the U.S Public Health Service recommended annual flu vaccinations for people at high risk of severe flu complications and, subsequently, a different variation of the flu virus would emerge later in 1968 as the H3N2 flu virus triggered another pandemic.
In 2005, the genome of the 1918 pandemic flu virus was fully sequenced. Later, in 2009, H1N1 viruses related to the 1918 virus would trigger another pandemic.
Another virus, known as rabies, was extremely deadly in most parts of the world before a vaccine was developed to combat it in the 1920s. It is spread through the saliva of animals or bites.
The virus can lead to damage in the brain and the nerves. When symptoms associated with rabies begin to show, it can nearly always be fatal.
Other viruses, such as HIV, have dominated the modern world since its identification. HIV, also known as human immunodeficiency virus, was first identified in the 1980s by the U.S Center for Disease Control.
Approximately 32 million people have died from HIV. The disease took an exhausting toll on mankind even today when developed countries have synthesized antiviral drugs to prevent the spread of the virus, but middle-income countries and low-income countries continue to be afflicted by the disease.
The dengue virus, another type of virus, was first spotted in the Philippines and Thailand, spreading as a result of warming in tropical and subtropical areas.
Mosquitoes, being the primary carriers of the virus, can cause severe disease with their bites and afflict significantly with dengue fever.
In 2019, a vaccine for dengue was approved for use in children 9 to 16 years old in areas where the virus was prevalent. In other countries, another vaccine is available for those who are 9 to 45 years old, but those receiving the vaccine must have a confirmed case of dengue.
In 1976, Ebola outbreaks were recorded in the Republic of Sudan and the Democratic Republic of Congo. The virus is spread through contact with blood and tissue from those who are infected.
From 2013-2016, an epidemic of the Ebola virus took shape in West Africa to which the virus caused numerous hospitalizations and deaths.
The Ministry of Health of the Democratic Republic of Congo announced, in 2021, the end of the Ebola virus disease that affected many in West Africa.
These viruses are some examples of diseases that have affected humans throughout history. Each virus, through time, has had its unique development within its host.
This process is called pathogenesis, which is the manner of development of a disease.
It is characterized by transmission to the host and accessibility of the virus to tissue, immune system vulnerability to virus multiplication, and the virus’s vulnerability itself to the immune system defenses of its host.
Understanding pathogenesis can help us understand the manner in which a virus forms.
Furthermore, understanding pathogens ― which means any organism that can produce disease ― allows us to understand the primary cause of viruses and where they originate from.
Finally, understanding the history of viruses and how viruses in the past have affected humanity can lead us to a better understanding of contextualizing recent pandemics such as COVID-19.