By Write news
updated May 27 22 at. 18:43
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Unfortunately, epidemics and pandemics are nothing new. A simple glance at the history of mankind is enough to show it our species’ fight against infectious diseases has been constant. Not to mention the recent Covid, the Black Death, cholera, tuberculosis, influenza, typhus or smallpox are just a few examples of those who have left indelible traces …
Each disease requires a specific action and implementation of various prevention, response and treatment mechanisms. This is why it is important to identify the origin and modes of origin of pathogenic substances.
In this respect, about 60% of the new infectious diseases reported worldwide are zoonoses (which are transmitted between animals and humans). It is estimated that approx one 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 discovered in recent decades, 75% are derived from animals.
The recent emergence of several zoonoses – avian influenza H5N1, avian influenza H7N9, HIV, Zika, West Nile virus, severe acute respiratory syndrome (SARS), respiratory syndrome in the Middle East (MERS), Ebola or Covid-19 (SARS-CoV-2)) among others – have posed serious threats to human health and global economic development.
They are generally unpredictable, as many are derived from animals and are caused by new viruses that are only discovered over time. At least it is there ten factors as we already know for sure is associated with the emergence of a future epidemic or pandemic. They are summarized and explained below.
1. Wars and famine
The damage caused by war is, of course, numerous and complex: deaths, injuries and mass displacement of people to flee the fighting are the most obvious. But the emergence of contagious epidemics is also closely linked to conflicts.
In 2006, cholera outbreaks were 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 contagious epidemics as a direct consequence of war, exacerbated by food and water shortages, displacement and damage to infrastructure and health services.
2. Change of land use
Land use change is a major change in the ecosystem that is directly induced by human populations. The consequences are very wide.
These changes can actually affect the diversity, abundance and distribution of wildlife and make them more susceptible to infection with pathogens. By creating new contact opportunities, they also facilitate the circulation and spread of pathogens between species, which can ultimately lead to human infection.
Through deforestation and forest fragmentation, we promote the extinction of special species in these habitats and the development and establishment of more generalist species.
Some animal species that host pathogens, especially bats and other mammalian species such as rodents, are relatively more numerous in landscapes transformed in this way, such as agricultural ecosystems and urban areas, than in adjacent undisturbed places.
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, influenza tends to have more persistent epidemics in more populated and dense urban areas.
5. Climate change
Climate change increases the risk of virus transmission across species. Many virus species are still unknown, but they probably have the ability to infect our species. Fortunately, the vast majority of them are currently circulating silently among wild mammals.
However, the expected temperature rise with climate change will lead to massive migrations of animals in search of milder environmental conditions, which will facilitate the emergence of “biodiversity hotspots” (endangered biogeographical area with at least 1500 plant species and endemic animals). If they reach areas with high population density, mainly in Asia and Africa, new opportunities for zoonotic spread to humans will arise.
According to the latest predictions based on scenarios for climate change, virus transmission between species in 2070 will increase approximately 4,000 times.
Globalization has facilitated the spread of many contagious agents to all corners of the world.
Transmission of infectious diseases is the best example of the growing porosity of borders. Globalization and increased connectivity are accelerating the potential emergence of a pandemic and its rapid spread due to the constant movement of microorganisms through international trade and transport.
7. Bushmeat hunting, trade and consumption
Transmission of zoonoses can occur at any time in the bushmeat supply chain, from hunting in the forest to the place of consumption. Pathogens that have been transmitted to humans from bushmeat are numerous and include, but are not limited to, HIV, Ebola virus, monkey foam virus, and monkey pox virus …
8. Illegal trade in cash and wildlife markets
An ecosystem with high species richness reduces the encounter rate between susceptible and infectious individuals, reducing the likelihood of pathogen transmission. Conversely, markets for live animals and other hidden illegal trade fences are places where the most diverse species are crammed together in overcrowded cages.
Under these conditions, they share not only the same unhealthy and unnatural space, but also disease-carrying ectoparasites and endoparasites. Animals bleed, drool, defecate and urinate on each other: this leads to the exchange of pathogenic microorganisms and parasites, thus forcing interactions between species that should never have occurred.
9. Microbial evolution
Microorganisms evolve constantly, naturally and in response to direct and indirect selection pressures from their environment. A well-established example is influenza A viruses, whose ancestral reservoir are waterfowl, from which they managed to infect other types of animals.
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, there has been a gradual withdrawal of financial support for public health systems in many countries.
This decimated the critical infrastructure needed to deal with sudden outbreaks. The recent and rapid emergence of new infectious diseases, such as Covid-19, combined with the resurgence of older diseases, such as measles and tuberculosis, have important implications for global public health systems.
We need to be aware that preparing for possible future epidemics and pandemics requires careful and careful examination of the potential factors that facilitate the emergence of infectious diseases. Careful and critical analysis will help design future forecasts and prevention strategies.
Raúl Rivas González, Head of Microbiology, University of Salamanca
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