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updated 27. may 22 at 18:43
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Unfortunately, epidemics and pandemics are nothing new. All you need is a glimpse into human history the struggle of our species against infectious diseases is constant. Not to mention the recent Covid, black death, cholera, tuberculosis, flu, typhus or smallpox are just some of the ones that have left indelible marks …
Each disease requires specific action and the introduction of various prevention, response and treatment mechanisms. This is why it is necessary to identify the origin and modes of occurrence of pathogenic agents.
In this respect, they account for approximately 60% of the world’s emerging zoonotic infectious diseases (which are transmitted between animals and humans). It is estimated that approximately a billion people in the world get sick and that millions die each year as a result of zoonotic events.
And of the more than 30 new human pathogens identified in recent decades, 75% come from animals.
Recent outbreaks of several zoonoses – H5N1 avian influenza, H7N9 avian influenza, HIV, Zika, West Nile virus, Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), Ebola or Covid-19 (SARS-CoV-2) outside other – poses a serious threat to human health and global economic development.
They are generally unpredictable because many come from animals and are caused by new viruses that are only subsequently detected. However, it exists the least ten factors which we already know for sure are associated with a future epidemic or pandemic. They are collected and explained below.
1. Wars and famines
The damage caused by the war is clearly numerous and complex: deaths, injuries and the mass displacement of people to flee the fighting are most noticeable. However, the emergence of infectious epidemics is closely related to conflicts.
In 2006, a cholera epidemic was reported in 33 African countries, 88% of them in conflict-affected countries. In recent years, several countries in the Middle East and Africa have experienced infectious epidemics as a direct result of the war, exacerbated by food and water shortages, displacement and damage to infrastructure and health services.
2. Land use change
Land use change is a major ecosystem modification directly caused by the human population. The consequences are very wide.
Indeed, these changes can affect the diversity, abundance and distribution of wild animals and make them more susceptible to infection by pathogens. In addition, by creating new contact opportunities, they facilitate the circulation and spread of pathogens among species, which can ultimately lead to human infection.
Through deforestation and forest fragmentation, we support the extinction of specialized species in these habitats and the development and settlement of more general species.
Some wild-type species that host pathogens, especially bats and other mammalian species, such as rodents, are relatively more abundant in such transformed landscapes, such as agricultural ecosystems and urban areas, than in adjacent undisturbed localities.
Establishing pastures, plantations or intensive livestock farming near forest edges can also increase the flow of pathogens from wildlife to humans.
4. Uncontrolled urbanization and population growth
Changes in population size and density due to urbanization again affect the dynamics of infectious diseases. For example, the flu tends to have more permanent epidemics in more populated and densely populated urban areas.
5. Climate change
Climate change increases the risk of interspecies virus transmission. Many types of viruses are still unknown, but they probably have the ability to infect our species. Fortunately, the vast majority of them currently circulate quietly among wild mammals.
However, the expected increase in temperature with climate change will lead to massive migration of animals in search of milder environmental conditions, which will facilitate the emergence of “biodiversity hotspots” (endangered biogeographical area with at least 1500 species of plants and endemic animals). If they reach areas with a high human population density, especially in Asia and Africa, new opportunities will arise for zoonotic spread to humans.
According to recent predictions based on climate change scenarios, virus transmission between species will increase by around 4000 times by 2070.
Globalization has made it possible to spread many infectious agents to all corners of the globe.
The transmission of infectious diseases is the best example of the growing porosity of borders. Globalization and increased connectivity are accelerating the potential for a pandemic and its rapid spread due to the constant movement of micro-organisms through international trade and transport.
7. Hunting, trade and consumption of bush meat
Zoonoses can be transmitted at any point in the bushmeat supply chain, from hunting in the forest to the point of consumption. There are many pathogens that have been transmitted to humans from bushmeat and include, but are not limited to, HIV, Ebola virus, monkey foaming virus and monkey pox virus…
8. Illegal cash trade and wildlife markets
An ecosystem with high species richness reduces the rate of encounters between susceptible and infectious individuals, which reduces the likelihood of pathogen transmission. Live animal markets and other hidden illegal trade enclosures, on the other hand, are places where the most diverse species are crammed into overcrowded cages.
Under these conditions, they not only share the same unhealthy and unnatural space, but also ectoparasites and disease-transmitting endoparasites. Animals bleed, drool, mud and urine: this leads to the exchange of pathogenic microorganisms and parasites, leading to interactions between species that should never have happened.
9. Microbial evolution
Microorganisms are constantly evolving, naturally and in response to direct and indirect selection pressures from their environment. A well-established example is influenza A viruses, whose original reservoir is waterfowl, from which they have managed to infect other animal species.
The worldwide development of many types of antimicrobial resistance in common human pathogens is clear evidence of the enormous ability of microorganisms to adapt rapidly.
10. Collapse of public health systems
In recent decades, financial support for public health systems has been phased out in many countries.
This has decimated the critical infrastructure needed to deal with sudden outbreaks. The recent and rapid emergence of new threats from infectious diseases such as Covid-19, together with the recovery of older diseases such as measles and tuberculosis, has important implications for global public health systems.
We must be aware that preparing for possible future epidemics and pandemics requires careful and careful study of the potential factors that facilitate the development of infectious diseases. Careful and critical analysis will help design future forecasting and prevention strategies.
Raúl Rivas González, Department of Microbiology, University of Salamanca
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