According to Québec’s public health research centre, the Institut national de santé publique du Québec (INSPQ), the proportion of people suffering from asthma in the province has almost doubled since the early 2000s. It rose from 6.4 per cent to 11 per cent between 2001 and 2017.
The World Health Organization links this increase to urbanization and the lifestyle associated with it.
Pollen allergies are also on the rise, according to the INSPQ, leading to increased health-care costs for governments.
How can these trends be slowed down? The answer might come from farms.
As microbiologists, our goal is to shed light on environmental micro-organisms and the beneficial effects they can have on human health.
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The unexpected benefits of the countryside
Let’s start with a small scenario. Spring has arrived and you are suddenly feeling generous, so you offer to lend a hand to a farmer friend who is harvesting a crop that produces hay. A great idea, right?
The only problem is, you forget about your allergies, so, unfortunately, there’s a good chance that hay fever will take hold of your respiratory tract. Yet surprisingly, your friend, who has lived on a farm all his life, never seems to have this problem.
This difference is no coincidence.
Since the early 2000s, several studies have shown that rates of asthma and allergies are significantly lower in people who grew up on farms than those raised in urban areas. It turns out that growing up near a farm during childhood can significantly reduce the risk of developing these diseases.
What explains this phenomenon? Greater diversity of micro-organisms in the air.
These micro-organisms constitute what is known as the aerobiome. Its composition depends mainly on the environment — for example, weather conditions, vegetation and land use.
And it plays a role in our health.
Bacteria to the rescue for asthma
The first year of life is crucial for children, since this is when the bacteria that make up the microbiome establish themselves in the body.
It’s during this period that bacteria from the farm environment come into play, like true superheroes. Through their interaction with a child’s immune system, they help reduce the risk of developing allergies.
With their incredible bacterial diversity, farms provide a rich environment for these interactions.
First, rural bacteria help establish new bacteria in the digestive systems of babies aged two to 12 months. They do this by colonizing the body via entry points, such as the mouth, or directly on the skin. Once established, they produce anti-inflammatory compounds called short-chain fatty acids.
Then, when the body recognizes the presence of environmental bacteria due to their distinctive genetic material, the immune system produces anti-inflammatory molecules. Over the long term, a certain tolerance to bacteria develops. This anti-inflammatory activity then helps reduce the inflammation caused by asthma.
Other factors besides the aerobiome may play a role in preventing asthma and allergies, including consuming unpasteurized milk directly from the farm.
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Did you say toxins?
But that’s not all. The protective effect of the aerobiome could also be caused by a compound on the outer part of bacteria, called endotoxin.
This inflammatory compound, located in the bacterial membrane, can be found in the air and causes inflammation in the respiratory tract.
Endotoxins are ubiquitous in farming environments. However, when children are exposed to low concentrations of endotoxins at a young age, these operate as “coaches” for their immune systems.
This could be compared to certain types of vaccines, which administer a microbe in a harmless form. For example, the chickenpox vaccine allows the body to develop an effective immune defence without provoking the serious effects of the disease.
Similarly, in the presence of endotoxins, children’s immune systems develop defences in the form of specific cells. Thus, Type 1 helper T cells are present in greater quantities in children who live on farms. Conversely, in children with asthma, Type 2 helper T cells predominate.
Type 1 helper T cells are associated with the recognition, via endotoxins, of infectious bacteria that are harmful to health. Compounds that can cause an allergic reaction are recognized by Type 2 helper T cells, which explains why they are found in greater quantities in children with asthma.
Allergies and tolerance
When it comes to allergies, it is more likely that regular contact with potential sources of allergens will lead to the development of tolerance.
Let’s return to the anecdote about our farmer friend. Since he’s always lived on a farm, he’s been in constant contact with hay since childhood. So his immune system has developed a tolerance to these compounds. Coming from a more urban environment, you will not have developed this tolerance.
However, we don’t yet know all the mechanisms of the protection farm life offers. It is also likely that some people are genetically predisposed to developing certain types of respiratory diseases.
As part of our current research, we’re analyzing the bacteria present in the air of several Canadian cities and their inflammatory effects. The role of different bacterial communities in asthma may vary depending on both the latitudinal gradient of urbanization and vegetation.
While it’s fine to praise the benefits of rural life, we must not forget that the majority of the population lives in cities.
Perhaps we can try to improve the urban environment so we can enjoy the beneficial effects of farms without having to live there. Promoting contact with animals and increasing the number of diverse green spaces in our urban centres could be possible solutions.
