Abstract

VAN DER WALT, Martie. Migration and spread of infectious diseases: From the origin of Homo sapiens up to the Anthropocene. Tydskr. geesteswet. [online]. 2022, vol.62, n.4, pp.647-661. ISSN 2224-7912.  http://dx.doi.org/10.17159/2224-7912/2022/v62n4a2.

A typifying characteristic ofHomo sapiens is its ability to walk upright, which allowed humans to move about in grasslands, enabling them to leave the forests of central Africa and populate the rest of Africa and later the world, a success story like no other. Africa is the place of origin of Homo sapiens. The first major migration of anatomically modern humans, known as the Out-of-Africa migration, was the first of many migratory events of Homo sapiens that continue up to the current era that shaped the world and society. This article aims to describe the defining role of human migration in spreading infectious diseases from pre-history to the present. In future, infectious diseases will continue to spread through migration. However, by contrast, the spread of diseases will be exacerbated due to the opportunities provided in the Anthropocene epoch and will become progressively more challenging. Migration is a term that encompasses the simultaneous movement of large numbers or groups of people away from their original place of living and for a specific reason. The main reasons for migration are emigration/immigration, forced displacement, slavery, migrant labour, asylum seeking and refugees. In addition, war, conflict, and environmental disasters such as droughts, famine and overpopulation are other common causes of migration. Migration is usually unplanned; it happens without warning or advanced planning and is accompanied by a large-scale disruption in the socio-economic structure, health, and well-being of the migrants and/or other affected groups. Such major disruptions to individuals' normal living can weaken the immune system, leading to increased susceptibility to infectious diseases. In addition, temporary housing during migration can often also result in humanitarian disasters that increase opportunities for the transmission of infectious diseases. Migrants are also at risk of contracting new or previously-unencountered diseases prevalent in their chosen resettlement area. Conversely, migrants can carry with them microorganisms absent in the resettlement area. An example of this is the smallpox virus that was brought to South America by the Spanish colonisers. At that stage, poxvirus was absent in this continent, and the indigenous populations had no immunity to the pathogen. The transmission of the poxvirus by colonizers to indigenous populations almost destroyed the indigenous populations of the time. A form of migration that emerged more recently is travel. Travel migration is defined as the large number of unrelated individuals who travel simultaneously across the globe for work or pleasure. Travel migration has been enabled by advances in the speed by which air and train travel takes place. This results in large numbers of individuals being transported across the globe in a short period and over long distances. Travel by water, air and land resulted in the world's population being highly interconnected through the mingling of large numbers of people from geographically remote places but in a relatively short period. Travelling connects people and diseases across the globe. Examples of pathogens that spread through migration and that cause major infectious diseases include the smallpox virus, the human immuno-deficiency virus (HIV), and coronaviruses that cause Middle Eastern respiratory syndrome (MERS), coronavirus disease 2019 (COVID-19) and severe acute respiratory syndrome (SARS). Mycobacterium tuberculosis, the cause of tuberculosis, and Helicobacter pylori, which can cause gastric ulcers, are among the oldest known bacteria that infect humans and were already present in humans when the Out-of-Africa migration occurred. These two pathogens were carried with humans as they migrated and populated new areas of the world, and both have been present in large numbers of humans over millennia. These two organisms can only spread through very close contact between humans and have no host outside the body; therefore, they are great examples of how migration distributes infectious diseases across the world. Mycobacterium tuberculosis is exceptionally well-adapted to spread and cause disease among individuals with lower immunity, such as migrants. Poor housing conditions and crowding, which invariably result from migration due to humanitarian disasters, advance the transmission of pathogens such as tuberculosis. Major lifestyle changes of humans occurred from the Paleolithic to the Neolithic after the Out-of-Africa migration, which directly or indirectly benefited the transmission of diseases. During the Neolithic, animals were domesticated, and agriculture started, allowing people to settle down and establishing the first towns and cities. The domestication of animals created an opportunity for pathogens to cross from animals to humans and adapt to the new host to cause new infectious diseases in humans, called zoonosis. The Anthropocene dawned when deforestation, mining, farming, and other human activities left their mark. As a result, the Anthropocene offers unique opportunities for the emergence and spread of infectious diseases: firstly, by zoonosis or the transmission of diseases from animals to humans, and secondly, the spread of the diseases through migration. Furthermore, changes in the weather and climate can lead to environmental migration. This occurs when people need to abandon their normal place of living because of severe weather events such as droughts and ice ages. Labour migration was responsible for the spread of HIV from its place of origin in Africa. This virus initially landed in humans through inter-species cross-over from primates to humans in the 1950s from eating semi-cooked bush meat. As a result, it became established in the indigenous populations of Africa. HIV is a sexually transmitted disease amongst humans, and migratory labourers from Haiti were infected with the virus while working in the Congo, where they transmitted the virus to people in Haiti upon their return. The MERS and SARS coronaviruses became human pathogens due to bat-human species cross-over, probably due to eating bush meat. However, the rapid distribution of these two viruses to other areas of the world was enabled through travel migration and the highly connected world population. Similarly, the extremely rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) upon its discovery in December 2019 was partly due to travel migration. In future, the negative impact of infectious diseases can be prevented by having disaster preparedness plans to protect the health and well-being of migrants and resident populations. However, events that can potentially be disastrous are difficult to pre-empt: the world was largely unprepared on how to respond to the rapid spread of SARS-CoV-2 and how to control the ensuing pandemic. Other recent examples of similar unforeseen events are the Ukraine-Russian conflict that started in March 2022, which caused many people from Ukraine to flee to other countries for safety. The second example is the heavy rain of April 2022 in the KwaZulu-Natal Province of South Africa, which caused massive destruction of houses and infrastructure, resulting in affected people being displaced. In both cases, the reasons for migration can have a detrimental impact on the health of the affected people, which renders them susceptible to disease transmission.

Keywords : Helicobacter pylori; Anthropocene; infectious diseases; migration; tuberculosis; Helicobacter pylori; HIV/AIDS; coronaviruses; inter-species; smallpox; Out-of-Africa; Ukraine; KwaZulu-Natal; zoonosis.

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