The existence of epidemics and pandemics is nothing new. A review of human history is sufficient to confirm that the human struggle with infectious diseases is continuous. Black plague, cholera, tuberculosis, influenza, typhus or smallpox are just a few examples of diseases that leave an indelible mark on us.

Each disease requires a specific action and the application of different prevention, response and treatment mechanisms. Therefore, it is essential to identify the origins and appearance patterns of pathogens.

In this sense, approximately 60% of the emerging infectious diseases reported worldwide are zoonoses (transmitted between animals and humans). Estimates suggest that around one billion people fall ill and millions die as a result of zoonotic events worldwide each year. Of the more than 30 new human pathogens identified in recent years, 75% are from animals.

Recent emergence of various zoonotic diseases – avian influenza H5N1, avian influenza H7N9, HIV, Zika, West Nile virus, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), Ebola virus disease or covid-19 (SARS- CoV2) – posed serious threats to human health and global economic development.

They are often unpredictable, as many originate from animals and are caused by new viruses that are only detected after an outbreak has occurred. However, there are at least ten factors that we already know for certain are linked to the emergence of a future epidemic or pandemic. We list them.

1. Wars and famines

The damage caused by war is many and complex. Death, injury and displacement are the most obvious. However, the emergence of contagious epidemics is also closely related to armed conflicts.

In 2006, cholera outbreaks were reported in 33 African countries, and 88% of the reports came from countries affected by armed conflict. In recent years, different countries in the Middle East and Africa have suffered contagious epidemics as a direct effect of the war, aggravated by food and water shortages, displacement and damage to infrastructure and healthcare.

2. Land use change

Land use change is a human-induced change in the ecosystem. These changes can affect the abundance and distribution of wildlife and make it more susceptible to infection by pathogens. They also create new contact opportunities, facilitating the movement of pathogens between species, ultimately leading to human infection and further spread of pathogens.

3. Deforestation

With deforestation and forest fragmentation, we support the extinction of specialist habitat types and allow generalists to thrive. Wildlife species that host pathogens, particularly other mammalian species such as bats and rodents, have been shown to be relatively abundant in human-manipulated landscapes such as agro-ecosystems and urban areas compared to neighboring undisturbed areas.

Setting up pastures, fields, or dense livestock farms near forest edges can also increase pathogen flow from wildlife to humans.

4. Uncontrolled urbanization and population growth

Demographic changes in population size and density through urbanization affect the dynamics of infectious diseases. For example, influenza tends to exhibit more persistent outbreaks in more populated and denser urban areas.

5. Climate change

Climate change increases the risk of viral transmission between species. Many types of viruses are still unknown, but they are likely to have the ability to infect humans. Fortunately, the vast majority now roam quietly in wild mammals. However, the rise in temperatures will cause mass migrations of animals seeking milder environmental conditions and will facilitate the emergence of critical points of biodiversity. If they reach densely populated areas, particularly in Asia and Africa, new opportunities will arise for zoonotic spread to humans.

Recent estimates under climate change scenarios show that by 2070, the transmission of viruses between species will increase by about 4,000 times.

• Ómicron appears to evade antibodies produced by other variants

6. Globalization

Globalization has facilitated the spread of countless infectious agents to every corner of the planet. The transmission of infectious diseases is a prime example of the increased porosity of borders. Globalization and increased connectivity are accelerating the appearance of a possible pandemic due to the constant movement of microorganisms through international trade and transport.

7. Bush meat hunting, trade and consumption

Zoonotic disease transmission can occur at any point in the bushmeat supply chain, from bushmeat hunting to the point of consumption. Pathogens transmitted to humans from bush meat are numerous and include, but are not limited to, HIV, Ebola virus, monkeypox virus, or monkeypox virus.

8. Illegal species trafficking and wild animal markets

A natural ecosystem with a high degree of species richness reduces the chance of transmission of a pathogen by reducing the rate of encounter between susceptible and infectious individuals. On the contrary, livestock markets and fences dedicated to the containment of illegally traded animals are places where all kinds of animals are caged and overcrowded.

In these conditions, they not only share the same unhealthy and unnatural space, but also ectoparasites and endoparasites, which are disease vectors. Animals bleed, mite, feces and urinate on each other, resulting in the exchange of pathogenic microorganisms and parasites, forcing interspecies interactions that should never have happened.

9. Microbial evolution

Microorganisms continually evolve in response to indirect and direct selection pressures in their environment. A clear example is type A influenza viruses, whose ancestral reservoir was waterfowl and which they managed to infect other animal species.

Another obvious example of the ability of microorganisms to adapt rapidly is the worldwide development of many types of antimicrobial resistance in common human pathogens.

10. The collapse of the public health system

In recent years, financial support for public health systems has been gradually withdrawn in many countries. This has destroyed the necessary and necessary infrastructure to deal with surprise epidemic outbreaks. The recent rapid emergence of new infectious disease threats such as covid-19 and the re-emergence of old conditions such as measles or tuberculosis have important implications for global public health systems.

We must be aware that preparing for possible future epidemics and pandemics requires a thorough and comprehensive examination of the potential factors that facilitate the emergence of infectious diseases. Calm and critical analysis will allow designing future forecasting and prevention strategies.

Raúl Rivas González, Professor of Microbiology, University of Salamanca

This article was originally published on The Conversation. Read the original.