In epidemiology, a virgin soil epidemic is an epidemic in which populations that previously were in isolation from a pathogen are immunologically unprepared upon contact with the novel pathogen. [1] Virgin soil epidemics have occurred with European settlement, particularly when European explorers and colonists took diseases to lands they settled in the Americas, Australia and Pacific Islands. [2]
When a population has been isolated from a particular pathogen without any contact, individuals in that population have not built up any immunity to that organism and also have not received immunity passed from mother to child. [3] The epidemiologist Francis Black has suggested that some isolated populations may not have mixed enough to become as genetically heterogeneous as their colonizers, which would also have affected their natural immunity, due to the potential benefits to immune system function due to genetic diversity. [3] That can happen also when such a considerable amount of time has passed between disease outbreaks that no one in a particular community has ever experienced the disease to gain immunity. [4] Consequently, when a previously unknown disease is introduced to such a population, there is an increase in the morbidity and mortality rates. Historically, that increase has been often devastating and always noticeable. [2]
Diseases introduced to the Americas by Europeans and Africans include smallpox, yellow fever, measles and malaria as well as new strains of typhus and influenza. [5] [6]
Virgin soil epidemics also occurred in other regions. For example, the Roman Empire spread smallpox to new populations in Europe and the Middle East in the 2nd century AD, and the Mongol Empire brought the bubonic plague to Europe and the Middle East in the 14th century. [6]
The term was coined by Alfred Crosby [1] as an epidemic "in which the populations at risk have had no previous contact with the diseases that strike them and are therefore immunologically almost defenseless." His concept is related to that developed by William McNeill, who connected the development of agriculture and more sedentary life with the emergence of new diseases as microbes moved from domestic animals to humans. [7]
In one early use of the term, in 1973, Peter Moodie remarked that measles and chickenpox, which are usually childhood diseases, may in ‘virgin soil’ epidemics “affect all age-groups”, and may also produce a-typically dangerous sequelae such as pneumonia. [8]
The concept would later be adopted wholesale by Jared Diamond as a central theme in his popular book Guns, Germs and Steel as an explanation for successful European expansion. [9]
Due to limited interaction between communities and more limited instances of zoonosis, the spread of infectious diseases was generally hampered in Native American communities. This contrasted with Eurasia, where a large number domesticated animals in close contact with large human populations would lead to more frequent zoonotic diseases, which would then in turn spread between human populations more easily due to trade and warfare. Native Americans were not exposed to this latent pool of circulating Eurasian diseases until the European colonization of the Americas, which then led to frequent virgin soil epidemics among Native Americans. [10]
A series of epidemics of unknown origin caused major population collapses in Central America in the 16th century, possibly due to little immunological protection from previous exposures. While the pathogenic agents of these so-called Cocoliztli epidemics are unidentified, suspected pathogenic agents include endemic viral agents, Salmonella, or smallpox. [11] [12]
The European colonization of Australia led to major epidemics among Australian Aboriginies, primarily due to smallpox, influenzas, tuberculosis, measles, and potentially chickenpox. [13] [14] [15]
With malaria spreading in the Caribbean islands after European-African contact, the immunological resistance of African slaves to malaria in contrast to the immunologically defenseless locals might have contributed to African slave trade. [16]
Novel and rapid-spreading pandemics such as the Spanish flu are occasionally referred to as virgin soil pandemics. [17]
Research over the last few decades has questioned some aspects of the notion of virgin soil epidemics. David S. Jones has argued that the term "virgin soil" is often used to describe a genetic predisposition to disease infection and that it obscures the more complex social, environmental, and biological factors that can enhance or reduce a population's susceptibility. [9]
Paul Kelton has argued that the slave trade in indigenous people by Europeans exacerbated the spread and virulence of smallpox and that a virgin soil model alone cannot account for the widespread disaster of the epidemic. [18]
The debate, as regards smallpox (Variola major or Variola minor), is sometimes complicated by problems in distinguishing its effects from those of other diseases that could prove fatal to virgin soil populations, most notably chickenpox. [19] Thus, the famous virologist Frank Fenner, who played a major role in the worldwide elimination of smallpox, remarked in 1985, [20] "Retrospective diagnosis of cases or outbreaks of disease in the distant past is always difficult and to some extent speculative."
Cristobal Silva has re-examined accounts by colonists of 17th-century New England epidemics and has interpreted and argued that they were products of particular historical circumstances, rather than universal or genetically inevitable processes. [21] [22]
Historian Gregory T. Cushman claims that virgin soil epidemics were not the major cause of deaths due to disease among Pacific Island populations. Rather, diseases like tuberculosis and dysentery were able to take hold in Pacific Island populations that had weakened immune systems because of overworking and exploitation by European colonizers. [23]
Historian Christopher R. Browning writes that "Disease, colonization, and irreversible demographic decline were intertwined and mutually reinforcing" in reference to virgin soil epidemics during the European colonisation of the Americas. He contrasts the rebound of the European population following the Black Death with the lack of such a rebound across most Native American populations, attributing this differing demographic trend to the fact that Europeans were not exploited, enslaved, and massacred in the aftermath of the Black Death like the indigenous inhabitants of the New World were. "Disease as the chief killing agent," he writes, "does not remove settler colonialism from the rubric of genocide". [24]
Following this work, historian Jeffrey Ostler has argued that, in relation to European colonization of the Americas, "virgin soil epidemics did not occur everywhere and ... Native populations did not inevitably crash as a result of contact. Most Indigenous communities were eventually afflicted by a variety of diseases, but in many cases this happened long after Europeans first arrived. When severe epidemics did hit, it was often less because Native bodies lacked immunity than because European colonialism disrupted Native communities and damaged their resources, making them more vulnerable to pathogens." [25]
A pandemic is an epidemic of an infectious disease that has a sudden increase in cases and spreads across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. Widespread endemic diseases with a stable number of infected individuals such as recurrences of seasonal influenza are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide.
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.
Herd immunity is a form of indirect protection that applies only to contagious diseases. It occurs when a sufficient percentage of a population has become immune to an infection, whether through previous infections or vaccination, that the communicable pathogen cannot maintain itself in the population, its low incidence thereby reducing the likelihood of infection for individuals who lack immunity.
In biology, immunity is the state of being insusceptible or resistant to a noxious agent or process, especially a pathogen or infectious disease. Immunity may occur naturally or be produced by prior exposure or immunization.
In epidemiology, the basic reproduction number, or basic reproductive number, denoted , of an infection is the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection. The definition assumes that no other individuals are infected or immunized. Some definitions, such as that of the Australian Department of Health, add the absence of "any deliberate intervention in disease transmission". The basic reproduction number is not necessarily the same as the effective reproduction number , which is the number of cases generated in the current state of a population, which does not have to be the uninfected state. is a dimensionless number and not a time rate, which would have units of time−1, or units of time like doubling time.
In epidemiology, an infection is said to be endemic in a specific population or populated place when that infection is constantly present, or maintained at a baseline level, without extra infections being brought into the group as a result of travel or similar means. The term describes the distribution of an infectious disease among a group of people or within a populated area. An endemic disease always has a steady, predictable number of people getting sick, but that number can be high (hyperendemic) or low (hypoendemic), and the disease can be severe or mild. Also, a disease that is usually endemic can become epidemic.
The first European contact in 1492 started an influx of communicable diseases into the Caribbean. Diseases originating in the Old World (Afro-Eurasia) came to the New World for the first time, resulting in demographic and sociopolitical changes due to the Columbian Exchange from the late 15th century onwards. The Indigenous peoples of the Americas had little immunity to the predominantly Old World diseases, resulting in significant loss of life and contributing to their enslavement and exploitation perpetrated by the European colonists. Waves of enslaved Africans were brought to replace the dwindling Indigenous populations, solidifying the position of disease in triangular trade.
Population figures for the Indigenous peoples of the Americas before European colonization have been difficult to establish. Estimates have varied widely from as low as 8 million to as many as 100 million, though many scholars gravitated toward an estimate of around 50 million by the end of the 20th century.
An emergent virus is a virus that is either newly appeared, notably increasing in incidence/geographic range or has the potential to increase in the near future. Emergent viruses are a leading cause of emerging infectious diseases and raise public health challenges globally, given their potential to cause outbreaks of disease which can lead to epidemics and pandemics. As well as causing disease, emergent viruses can also have severe economic implications. Recent examples include the SARS-related coronaviruses, which have caused the 2002–2004 outbreak of SARS (SARS-CoV-1) and the 2019–2023 pandemic of COVID-19 (SARS-CoV-2). Other examples include the human immunodeficiency virus, which causes HIV/AIDS; the viruses responsible for Ebola; the H5N1 influenza virus responsible for avian influenza; and H1N1/09, which caused the 2009 swine flu pandemic. Viral emergence in humans is often a consequence of zoonosis, which involves a cross-species jump of a viral disease into humans from other animals. As zoonotic viruses exist in animal reservoirs, they are much more difficult to eradicate and can therefore establish persistent infections in human populations.
Globalization, the flow of information, goods, capital, and people across political and geographic boundaries, allows infectious diseases to rapidly spread around the world, while also allowing the alleviation of factors such as hunger and poverty, which are key determinants of global health. The spread of diseases across wide geographic scales has increased through history. Early diseases that spread from Asia to Europe were bubonic plague, influenza of various types, and similar infectious diseases.
The 1837 Great Plains smallpox epidemic spanned 1836 through 1840, reaching its height after the spring of 1837, when an American Fur Company steamboat, the SS St. Peter, carried infected people and supplies up the Missouri River in the Midwestern United States. The disease spread rapidly to indigenous populations with no natural immunity, causing widespread illness and death across the Great Plains, especially in the Upper Missouri River watershed. More than 17,000 Indigenous people died along the Missouri River alone, with some bands becoming nearly extinct.
Smallpox was an infectious disease caused by variola virus, which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) certified the global eradication of the disease in 1980, making smallpox the only human disease to have been eradicated to date.
The history of smallpox extends into pre-history. Genetic evidence suggests that the smallpox virus emerged 3,000 to 4,000 years ago. Prior to that, similar ancestral viruses circulated, but possibly only in other mammals, and possibly with different symptoms. Only a few written reports dating from about 500 AD to 1000 AD are considered reliable historical descriptions of smallpox, so understanding of the disease prior to that has relied on genetics and archaeology. However, during the 2nd millennium AD, especially starting in the 16th century, reliable written reports become more common. The earliest physical evidence of smallpox is found in the Egyptian mummies of people who died some 3,000 years ago. Smallpox has had a major impact on world history, not least because indigenous populations of regions where smallpox was non-native, such as the Americas and Australia, were rapidly and greatly reduced by smallpox during periods of initial foreign contact, which helped pave the way for conquest and colonization. During the 18th century the disease killed an estimated 400,000 Europeans each year, including five reigning monarchs, and was responsible for a third of all blindness. Between 20 and 60% of all those infected—and over 80% of infected children—died from the disease.
Although a variety of infectious diseases existed in the Americas in pre-Columbian times, the limited size of the populations, smaller number of domesticated animals with zoonotic diseases, and limited interactions between those populations hampered the transmission of communicable diseases. One notable infectious disease that may be of American origin is syphilis. Aside from that, most of the major infectious diseases known today originated in the Old World. The American era of limited infectious disease ended with the arrival of Europeans in the Americas and the Columbian exchange of microorganisms, including those that cause human diseases. Afro-Eurasian infections and epidemics had major effects on Native American life in the colonial period and nineteenth century, especially.
Before the 20th century, the use of biological agents took three major forms:
The Massachusetts smallpox epidemic or colonial epidemic was a smallpox outbreak that hit Massachusetts in 1633. Smallpox outbreaks were not confined to 1633 however, and occurred nearly every ten years. Smallpox was caused by two different types of variola viruses: variola major and variola minor. The disease was hypothesized to be transmitted due to an increase in the immigration of European settlers to the region who brought Old World smallpox aboard their ships.
The Cocoliztli Epidemic or the Great Pestilence was an outbreak of a mysterious illness characterized by high fevers and bleeding which caused 5–15 million deaths in New Spain during the 16th century. The Aztec people called it cocoliztli, Nahuatl for pestilence. It ravaged the Mexican highlands in epidemic proportions, resulting in the demographic collapse of some Indigenous populations.
Immunological memory is the ability of the immune system to quickly and specifically recognize an antigen that the body has previously encountered and initiate a corresponding immune response. Generally, they are secondary, tertiary and other subsequent immune responses to the same antigen. The adaptive immune system and antigen-specific receptor generation are responsible for adaptive immune memory.
Colonial epidemic disease in Hawaii has greatly threatened the Native Hawaiian population since its introduction to the islands over a hundred years ago. Beginning with the first colonizers led by Captain James Cook that arrived in the islands in 1778, all the way up until today, foreign disease has been present in Native Hawaiians. As Hawaii was so secluded and contained a population of only the Hawaiian people, the islands were considered a "virgin population." This meant that once foreigners arrived, the Native Hawaiian population was decimated by these illnesses while Europeans remained healthy. Some of these diseases included gonorrhea, syphilis, influenza, cholera, tuberculosis, the mumps, measles, smallpox, and leprosy. While each disease brought a different outcome, they all contributed to the reduction of the Native Hawaiian population as they collectively caused more than 100,000 deaths.
European colonisation of Australia was accompanied by epidemic diseases to which the original inhabitants had little resistance. Colds, influenzas, tuberculosis (TB), and measles were major killers. Such diseases devastated Aboriginal populations, weakened their cultures, and often left them in no position to resist the newcomers. Within perhaps as little as six months of the arrival of the First Fleet, venereal disease was already a serious problem for local Aboriginal peoples; but the first disease to produce a major fall in the Aboriginal population around Sydney was the 1789 outbreak, some 16 months after the Fleet arrived, of what Governor Phillip and others referred to as "smallpox". Watkin Tench, a captain in the Marines, wrote that,
pustules, similar to those occasioned in the smallpox, were thickly spread on the bodies; but how a disease to which our former observations had led us to suppose them strangers could at once have introduced itself, and spread so widely, seemed inexplicable.