Listen to The Mould Show Podcast on ITunes

The Evolutionary Duel Between Humans and Pathogens - Can We Overcome It?

Uncategorized Nov 20, 2020

Pathogen. Germ. Bug. Infection. Virus. Plague. Today, more than ever, it seems like we are constantly surrounded by an invisible world of hidden dangers. These words are synonymous with our times, but we are not the first generation who have had to contend with a dangerous pathogen. So, what is a pathogen, and how has history shaped the relationship between them and humans?

Pathogens, defined as an organism that causes a disease to its host, are spread across our planet on an unbelievably vast scope. They occupy every known environment, from nuclear waste sites to rocks buried thousands of metres beneath the surface of the Earth. Moreover, they are numerous as well as widespread. Scientists estimate the number of viruses on earth to be about 1031. That’s 10 billion times the number of stars in the universe. 

For over 1.5 billion years, viruses and other microorganisms have been seeking biological hosts in which they can manifest, and humans have been in an evolutionary brawl with pathogens including prions, viruses, bacteria and fungi for as long as we have existed. However, only about 1 in a billion microbes is a human pathogen, meaning we have identified around 1400 unique pathogens that can harm us, but as we’ve discovered with COVID-19, there is a huge amount of undiscovered threat.

Pathogens have, of course, brought havoc and suffering to countless human populations throughout our history. They do this by colonising a host growing and manifesting inside us. They can enter us through our food or drink, and as we’ve seen with COVID-19, some can be airborne in water droplets. Once contaminated by the pathogen, they begin producing toxins which are often waste-products of the microbial cell life cycle. These toxins are often extremely poisonous. Anthrax, for example, has been exploited as a biowarfare agent.  

Our history is littered with the effects of such pathogens and their devastating effects. The Justinian Plague (541-549) claimed the lives of 100 million Europeans and brought about the fall of the Roman Empire. Fast forward 800 years and the Black Death is terrorizing Europe and Asia. One in three people in Europe were killed by the disease. To this day, building projects in London have to conduct investigation work to see if the ground underneath them is littered with the remains of medieval Londoners, tossed into one of the cities many plague pits.

And to this day there are emerging threats. COVID-19 is the third serious coronavirus we’ve had to confront in recent history, succeeding the Spanish Flu and SARS.  On top of this, there is influenza, and it’s ever-mutating strains that cyclically return to claim an estimated 389,000 lives annually, disproportionately affecting those with a lower level of access to basic health care and sanitation.  

Drug-resistant germs can also cause a serious health impact, especially within hospitals and nursing home patients. Candida auris, a drug-resistant infection, was only discovered in 2009 and causes problems for already immunocompromised people. Those who are already unwell face a serious risk from such infections, as treatment options are limited.

infectious diseases beyond COVID-19 have, and will, cause a major burden globally. They are responsible for up to one-third of all deaths and half of all deaths in people under the age of 45. There are steps we take to help, including good hand hygiene and cough etiquette, regular environmental cleaning and disinfection and the use of PPE like masks and gloves. Perhaps the best action we can all take is to be mindful of others and our own environment by cleaning regularly, as it is the number one method of infection control. This is something we must be mindful of in our daily lives.

Improved attention to infection control will benefit society as and should become part of our daily lives as we proceed into 2021.


Balloux, F., van Dorp, L. Q&A: What are pathogens, and what have they done to and for us?. BMC Biol 15, 91 (2017).

Janik, E.; Ceremuga, M.; Niemcewicz, M.; Bijak, M. Dangerous Pathogens as a Potential Problem for Public Health. Medicina 2020, 56, 591.

Candida auris: A Drug-resistant Germ That Spreads in Healthcare Facilities | Candida auris | Fungal Diseases | CDC. (2020). Retrieved 16 November 2020, from

Department of Health | Chapter 8: Infection control. (2020). Retrieved 16 November 2020, from

When Anthrax-Laced Letters Terrorized the Nation. (2020). Retrieved 16 November 2020, from



50% Complete

Get your FREE mould assessment questionnaire

Find out today how your home ranks using our 12-point rating scale and take control of your environmental health.