We have never been individuals. Humans as a species have evolved through millions of years. Our bodies have adapted to the diverse microbial life all around us.
They are harmful beneficial and neutral. Bacterial, viral, - and eukaryotic microbes, which can make their homes in our bodies. They can stay on our skin, colonise our guts, - or in annoying cases, get inside our bodies.
For example, in our bloodstream, and cause disease. Our lives, on the genuine physiology has been shaped - for the presence of these microscopic companions. Human history is a continuous change in our microscopic companions.
Before agriculture, the human societies were small and nomadic, - and also infectious diseases were very different to modern pathogens. During the modern times, humans have tried to get rid - of their harmful microbes. Much of the increase in our life expectancy is new - to continuously reduced mortality to infectious diseases.
Better quality of life, improved hygiene and sanitation, - antibiotic and other modern advancements have reduced the disease burden. Surprisingly, though, humans might nowadays have more pathogen - than at any other point in our history. For example, the huge populations of modern cities - and international travel can sustain vast number of respiratory viruses.
Conversely, a bacterial microbe in cities is impoverished in contrast to countryside. The built environment has a lower diversity of beneficial bacteria. And the microbiota of urban dwellers is less diverse - than that of peers in countryside.
The reduction in bacterial diversity in our bodies have been linked - to a number of immune related ailments, such as allergies, asthma, - and autoimmune disorders. The environmental changes and urban environment - does lead to a difficult situation, where environment is more likely - to be conducive of the spread of harmful microbes, - and hinders the spread of beneficial bacteria. Over half of all the species are parasites, that is organisms that benefit - from the host individuals while causing harm to the host.
Every species on the planet have parasites. Humans have the highest known number of parasite species, - as we are large size, long lived popular species, and thus a perfect host - for anyone wanting to profit from our bodies. loss of biodiversity leads to an increase of human parasites through a number of mechanisms.
First one is that when nature is lost or fragmented, - the contacts between humans and other species become much more common, - and thus, create much more opportunities for zoonotics. A spread of pathogens from other species to humans, that is. We know, for example, that the emergence of Ebola in West Africa - occurred in the area of high deforestation.
Second mechanism is the invasive species. Invasive species are sometimes better at spreading parasites, - and they can be new exotic parasites for the areas where they are invading. Usually they are also synanthropic species, - so leaving and surviving near humans, for example, - brown and black rats have spread across the world.
They live near humans, and they are linked - to a spread of many different pathogens, such as Leptospira and plague. Third mechanism is that when host species, the biodiversity goes down, - also the specialist parasites dependent on this species go extinct. This situation in turn, favors generalist parasites, - which can then become more common.
Generalist parasites are obviously more likely to also spread to humans, - because the reduction in parasite numbers - leads to higher prevalence of zoonotic pathogens. Fourth mechanism is the dilution effect. The more there are host species in the environment, - the more likely the parasite is to encountered a species - that is not a suitable host.
Thus, the biodiversity keeps the prevalence of parasites in check. For example, Borreliosis causing borrelia bacteria is spread by ticks. If tick is likely to have a blood meal from a host, - which is not competent host of Borrelia, - the bacteria dies out in tick, and if not transmitted forward.
Fifth mechanism is the loss of genetic diversity. The more similar the host individuals are, - the more likely it is that this parasite, - which is adapted to one host individual, - is also well adapted to all the individuals. This is also the reason why monocultures whether it is farm plants - or in livestock are more vulnerable for parasite spread.
The loss of biodiversity then leads to a difficult situation - where we are more likely to get harmful microbes - as the biodiversity is lost across the globe. Whereas we will get less beneficial bacteria, - if we live in biodiversity impoverished areas. This poses a distinct concern for public health.
If pandemics and other zoonotic epidemics are becoming more and more common, - together with autoimmune related disorders. The humans have not been evolutionarily adapted to nature loss. There are some clear guidelines, what individuals can do - to maintain the nature contact and reduce the spread of parasites.
One of those are targeted hygiene, which calls for balancing - the individual behavior depending on the risks. Working in nature helps to keep to get the good microbes - whereas a personal hygiene, such as hand washing and cleanliness - while cooking, prevent epidemics in urban environment. Nevertheless, public health is also a societal issue, where there - is a societal duty to plan and build a safe and health promoting environment.
Land use and zoning are of highest importance - when we are trying to keep harmful microbes away from us. And to get more beneficial microbes. Biodiversity science is a key to also sustainable public health.
