Epidemics and pandemics are unfortunately nothing new. A simple look at human history is enough to show that our species’ struggle against infectious diseases has been constant. Not to mention the recent Covid, the Black Death, cholera, tuberculosis, flu, typhoid or smallpox are just a few examples of those that have left indelible marks…
Each disease requires specific action and the implementation of different prevention, response and treatment mechanisms. Therefore, it is essential to identify the origin and appearance of pathogens.
In this regard, about 60% of emerging infectious diseases reported worldwide are zoonoses (transmitted between animals and humans). It is estimated that approximately one billion people worldwide become ill and millions die each year as a result of zoonotic events. And of the more than 30 new human pathogens discovered in recent decades, 75% come from animals.
The recent emergence of several zoonoses – avian influenza H5N1, avian influenza H7N9, HIV, Zika, West Nile virus, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), Ebola or Covid-19 (SARS-CoV -2) among others – has posed a serious threat to human health and global economic development.
They are generally unpredictable, as many come from animals and are caused by new viruses that are only discovered afterwards. However, there are at least ten factors that we already know for sure are related to the emergence of a future epidemic or pandemic. They are collected and explained below.
1. Wars and Famines
The damage caused by war is clearly many and complex: the dead, wounded and mass displacements of people to flee the fighting are the most obvious. But also the emergence of contagious epidemics is closely related to conflict.
In 2006, cholera outbreaks were reported in 33 African countries, of which 88% were in conflict-affected countries. In recent years, several countries in the Middle East and Africa have faced contagious epidemics as a direct result of 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 change caused directly by human populations. The consequences are very broad.
Indeed, these changes can affect the diversity, abundance and distribution of wildlife and make them more susceptible to infection by pathogens. In addition, by creating new opportunities for contact, they facilitate the circulation and spread of pathogens between species, which can ultimately lead to human infection.
3. Deforestation
Through deforestation and forest fragmentation, we are promoting the extinction of specialized species in these habitats and the development and installation of more common species. Some species in the wild that host pathogens, especially bats and other mammalian species such as rodents, are relatively more prevalent in landscapes so altered, such as agricultural ecosystems and urban areas, than in adjacent undisturbed sites.
The creation of pastures, plantations or intensive livestock activities near forest edges can also increase the flow of pathogens from wildlife to humans.
Deforested area of the Brazilian Amazon.
4. Uncontrolled Urbanization and Population Growth
Changes in population size and density due to urbanization in turn influence the dynamics of infectious diseases. For example, influenza tends to have more persistent epidemics in more populated and densely populated urban areas.
5. Climate Change
Climate change increases the risk of virus transmission between species. Many virus species are still unknown, but probably have the ability to infect our species. Fortunately, the vast majority of them currently circulate silently among wild mammals.
However, the expected temperature increase from climate change will lead to mass migrations of animals in search of milder environmental conditions, facilitating the emergence of “biodiversity hotspots” (threatened biogeographic area with at least 1,500 species of endemic plants and animals). Reaching areas of high human population density, especially in Asia and Africa, will open up new opportunities for zoonotic spread to humans.
According to recent predictions based on climate change scenarios, by 2070, the transmission of viruses between species will increase about 4,000-fold.
6. Globalization
Globalization has facilitated the spread of many infectious agents to all corners of the world.
The transmission of infectious diseases is the best example of the increasing porosity of borders. Globalization and increased connectivity are accelerating the potential emergence of a pandemic and its rapid spread, thanks to the constant movement of microorganisms through international trade and transport.
7. Bushmeat Hunting, Trade and Consumption
Transmission of zoonoses can occur at any point in the bushmeat supply chain, from hunting in the forest to the point of consumption. Pathogens transmitted to humans by bushmeat are numerous and include but are not limited to HIV, Ebola virus, monkey foam virus, and monkey pox virus…
View of the Tomohon market in Indonesia, where wild animals are traded for consumption.
8. Illegal Cash Trade and Wildlife Markets
An ecosystem with a high species richness reduces the encounter rate between susceptible and infectious individuals, reducing the chance of pathogen transmission. Conversely, live animal markets and other hidden abodes for illegal trade 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 disease-carrying ectoparasites and endoparasites. Animals bleed, drool, defecate and urinate on each other: This leads to the exchange of pathogenic microorganisms and parasites, forcing interactions between species that should never have happened.
9. Microbial Evolution
Microorganisms evolve continuously, naturally and in response to direct and indirect selection pressures from their environment. A well-known example is that of the influenza A viruses, whose ancestral reservoir is waterfowl, from which they could 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 quickly.
10. Collapse of Public Health Systems
In recent decades, financial support to public health systems has been gradually withdrawn in many countries.
This decimated the critical infrastructure needed to cope with sudden outbreaks. The recent and rapid emergence of new infectious disease threats, such as Covid-19, coupled with the resurgence 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 emergence of infectious diseases. Careful and critical analysis will help design future forecasting and prevention strategies.
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