Content Objectives
Evolutionary medicine is using what medical science knows about evolution to improve our health, explain how we can prevent and treat diseases, and explain why we get sick. The evolutionary process matters in our everyday lives through the food we eat, the medicine we administer, and the influences of the environment. For example, these factors impact our microbiome because our body has a variety of bacteria, viruses and other microbes that help or hurt our health, depending on how they react to environmental changes.
The central organizing question of evolutionary medicine—why, in a body of such exquisite design, are there a thousand flaws and frailties that make us more vulnerable to disease?6 The human body is an amazing machine that needs constant care to live to a ripe old age. Food and water intake, exercise, and preventive medicine are natural balancing acts an individual needs to do to beat the odds against survival.
When bacteria or viruses attack the body, underlying factors can kill a person, make the individual very sick, or cause a mild sickness. These pathogens usually can evolve countermeasures faster than we evolve defenses because of their short generational time and immense potential reproductive output.7 These microbes can mutate and change their genetics faster than our cells, and faster than our immune defenses that try to attack them.
Medical doctors and medical and evolutionary scientists need to generate and test the hypothesis of human vulnerabilities to disease and sickness. As part of the maturation of evolutionary medicine, increasingly more care has gone into rigorous formulation and testing of evolution hypotheses relating to our health.8 As long as there are diseases and sicknesses, evolutionary medicine will need to know what, why, and how.
Evolutionary medicine is built upon an edifice of study by evolutionary biologists, medical doctors, functional biologists, and natural theologians that stretches back centuries.9 The pioneers of scientists and doctors tested and practiced using medical vaccines on a trial-and-error basis to find a cure for a particular sickness. These practices of trial and errors helped pave the way in using modern vaccines, such as those important in fighting the COVID-19 pandemic. Evolutionary medicine provides numerous opportunities to help researchers and doctors understand the evolution of humans and why we are vulnerable to certain illnesses and diseases, to have better disease prevention, and to analyze what earlier studies have conducted to see what worked and what did not work which involved historical traits and environmental mismatches. For example, life history evolution research in human traits and the current environment helped paved the way in studying women’s health. Life history includes growth, reproduction, and survivorship dynamics.10 (the future) Life history can identify trends in the future versus the past, like the reproduction of women in our earlier history and how this has changed extensively today. The offspring produced per woman has reduced over time, which can impact the occurrence of short- and long-term health problems, such as postpartum depression, and pelvic organ prolapse later in life.11 (the future)
Researchers also apply lessons from evolutionary medicine to prepare us for future challenges like with COVID-19 pandemic and other novel zoonotic diseases that may occur.12 (future of EM) AIDS, Influenza, and COVID-19 are viral pandemic sicknesses. Doctors and scientists are currently utilizing the understanding of evolution to determine when and how viral mutations can lead to new variants that escape our immune defenses and vaccines.
The curriculum unit will cover topics such as COVID-19, the Influenza pandemic of the early nineteenth century, and asthma. The three topics are respiratory diseases that affect the lungs, due to either pathogen infections or because of allergy responses.
COVID-19
COVID-19 is the disease caused by coronavirus SARS-CoV-2, which has RNA as its genetic material13 The viruses affect humans and some other animals. Contact tracing from humans and animals was challenging to conduct in finding the source of the virus. The Wuhan area had an open market that sold a variety of exotic animals for food, which might have been the original source for early infections in humans. Such a combination of diverse wild animals is a recipe for possible disease spread. Science experts analyzed likely possibilities of SARS-CoV-2 carriers (reservoir species), such as the horseshoe bat, the civet (a cat-like animal), and the possible transmission that happened to humans. Bats are likely a major source of spillover viruses because they contain many different virus species within their bodies, compared to other mammals.14
The frequent transmission of SARS-CoV-2 between different host species gives the virus opportunities to evolve into new strains and various sources of possible spillover into humans. One observed change (mutation) during the virus;’ evolution is an insertion of four amino acids in the spike protein found in the pathogenic, but not in the non-pathogenic coronavirus.15 The pathogenic and non-pathogenic variants are distinguished by their predicted effects of these viruses for causing severe sickness when entering the human body. Another signature trait is in the nuclear localization signal domain of the N protein.16 This part of the protein directs it to the nucleus of host cells.17
On March 11, 2020, the World Health Organization (WHO) declared COVID-19 a pandemic. By this time, the virus had reached 114 countries, with 118,000 known cases and 4,300 deaths worldwide. That was only the beginning.18 These countries’ businesses began to shut down. The stores, banks, schools, and transportation all decreased to a standstill. The United States government, with the Centers for Disease Control (CDC), created mandated guidelines to protect their citizens. The stay-at-home order was announced to try to contain and slow the spread. Within days and weeks, many infected people died, including celebrities, famous musicians, and everyday citizens. Families lost mothers, daughters, sisters, fathers, uncles, sons, grandparents, colleagues, and friends. The four epicenters of the virus spread in the USA were in New York City, Washington State, New Rochelle's New York suburb, and Washington state in Snohomish County. The virus had spread and circulated among the various communities, making it difficult to contain the outbreak.
The uniqueness of the COVID-19 pathogen allows its patterns to be traced as the virus spreads through the human population, producing data that describes this pandemic spread. Because the coronavirus evolves over time, phylogenetics methods can be used to track its transmission patterns.19 Using these methods will help evolutionary studies in containment protocols, which seek to understand how the virus evolves and how its spread can be limited. The virus evolves more slowly than many other RNA viruses, due to its lower mutation rate. Unlike influenza viruses, coronavirus has a gene that encodes a protein (nsp14) that proofreads the replication of the virus RNA, so that fewer mutations occur.20 Another beneficial factor for the virus is the population size that was infected. The larger the virus population size, the more changes in gene frequencies can occur, causing more mutations to happen, making natural selection efficient in driving evolved changes that make the virus persist in humans. Thus, the large number of active cases of the virus during much of the calendar year 2020 gives the virus more opportunity to evolve by natural selection than if the virus has been checked at low numbers.21 It was difficult to predict the variability of the virus, whether it will become better at transmitting, whether the virus becomes more damaging to cause severe sickness in the population, or whether it will be less damaging. These changes make the virus better to infect, which causes more deaths. From the initial report of the virus till the early fall of 2020, there was only a single change in the virus for which we had evidence that its rise was driven by selection.22
Influenza
The influenza pandemic of the early 1900s killed more people than the soldiers who died in World War I (WWI). An estimated twenty to forty million died around the world from the flu pandemic. It was known as the "Spanish Flu". The name of Spanish Flu came from the early affliction and significant mortalities in Spain, where it allegedly killed eight million in May 1918.23The focus was on men joining the war cause and were busy with transporting war shipments and supplies. As the men crowded, they brought the virus and exposed it to others. The virus killed about 200,000 in October of 1918.23
Influenza, a formidable foe, affected the war, causing entire fleets to become sick. The flu hit both sides, killing more men than their weapons. The Great War and the pandemic tested the resilience of doctors and nurses. They were away with the troops, and only medical students had to care for the sick, or the sickness took them. Despite the shortage of medical staff, the Red Cross asked the civil sector to assist the sick at home and soldiers arriving from overseas. The responses of the public health officials reflected the new allegiance to science and wartime society. The medical and scientific communities have developed new studies and applied them to the prevention, diagnostics, and treatment of Influenza patients.24
As early as 412 BC, Hippocrates, the father of modern medicine, described the first known account of an influenza illness in his sixth "Book of Epidemics".25 Here, he recounted an annual recurring upper respiratory tract infection characterized by pharyngitis, coryza, and myalgia, which peaked around the winter solstice.26 In 1510, 1557, and 1580 were the first documented influenza pandemics that originated in Asia, then spread to Africa, the European continents, and finally to the Americas. The 1830 and 1889 pandemics began in China and spread to Russia rapidly within four months. The virus, suggested to be of subtype H3N8, reappeared at least three more times in successive years, resulting in an estimated one million global fatalities.27
The Influenza of the early 1900s came in the years beginning 1918, 1957, 1968, and 2009. Additionally, each of the pandemics occurring in 1957, 1968, and 2009 were caused by descendants of the 1918 pandemic influenza virus strain, earning the 1918 viral strain the nickname “The Mother of all Pandemics”.28 However, improved understanding regarding the emergence of the 1918 virus and factors (biological, social, environmental) that contributed to viral transmission and pathogenesis have been vital to the development of the current epidemic and pandemic influenza outbreak response effects.29 During the nineteenth and early twentieth century, major outbreaks were increasing, the 1918-1919 Spanish flu, the 1957-1958 Asian flu, the 1968-1970 Hong Kong flu, the 2009-2010 swine flu origins in Mexico causing millions of deaths which effects the world’s economy and healthcare systems. These outbreaks, occurring across different continents, underscore the global impact of Influenza. Within a century, data shows that the flu can evolve rapidly. This is problematic because medical experts worry more about the virus potential in becoming another deadly pandemic. This evolution is why a previous year's flu shot may not be effective on this year's flu and why vaccine developers devote considerable time to attempting to predict the evolutionary tracks viruses will take.30
Flu shots are ineffective because the pathogen is constantly evolving and can invade and continue to threaten the hosts. The virus has two primary mechanisms for antigenic change: antigenic drift and antigenic shift.31 Antigenic drift creates minor changes in viral epitopes through mutations in the viral genome. When epitope-altering mutations occur, viruses containing them are rapidly selected by host immunity, driving antigenic drift.32 The antigenic regions have the highest rate of drifts because viruses with antigenic changes escape the preexisting immunity. A hallmark of influenza virus antigenic drift in humans is the replacement of older viruses by new drifted variants. However, at rates dependent on subtype, the antigenically variant population has been shown to co-circulate for extended periods in A(H1N1) and influenza B viruses. In contrast, turnover is more rapid with A(H3N2) viruses.33 The antigenic shift is another factor that completely exchanges HA or NA genes and only occurs in the Influenza A virus because of many animal reservoirs. Influenza B viruses do not have animal reservoirs and do not go through an antigenic shift. When the human population has limited immunity, the virus's transmission increases and becomes a pandemic. To avoid pandemics, public health entities react with vigor to detections of novel subtypes, such as A(H5N9) and A(H7N9), in humans.34
New vaccines are produced to pinpoint viruses, which require months of production. By the time the vaccines are produced, the virus might have evolved. For example, influenza B viruses undergo a reassortment of deletions and insertions of segments in humans, resulting in good or bad outcomes. Understanding the evolutionary processes in viruses is important for the progress by researchers that was made during the nineteenth century, and we are moving into the twenty-first century. There is no doubt that the virus will constantly evolve, and humans need to keep up with the changes in diseases. There is no perfect vaccine that will cure all pathogens, but analyzing past data will help generate valuable information for future research.
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