Living with animals is thought to have profound effects on our immunity – potentially reducing the risk of allergies, eczema and even autoimmune conditions.

Since they first emigrated from Central Europe to North America in the 18th Century, the Amish have become known for their unique lifestyle. Today they are reliant on the same practices of dairy cattle farming and horse-borne transportation that were followed by their ancestors for centuries.

The Amish have gripped the imaginations of Hollywood scriptwriters, documentary makers and sociologists for decades. But in the past 10 years, their way of life has become of increasing interest to the medical world too, as they seem to defy one particularly concerning modern trend. While rates of immune-related conditions which begin in childhood, such as asthma, eczema and allergies, have soared since the 1960s, this has not been the case for the Amish.

The reason for this is revealing insights into how our immune systems operate – and the profound ways that the animals in our lives are affecting them.

To try and understand why the Amish have lower rates of certain immune conditions, a group of scientists spent time back in 2012 with an Amish community in the state of Indiana, and with another farming community known as the Hutterites, in South Dakota. In both cases, they took blood samples from 30 children and studied their immune systems in detail.

There are many similarities between the two groups. Like the Amish, the Hutterites also live off the land, have European ancestry, have minimal exposure to air pollution and follow a diet which is low in processed foods. However, their rates of asthma and childhood allergies are between four and six times higher than among the Amish.

One difference between the two communities is that while the Hutterites have fully embraced industrialised farming technologies, the Amish have not, meaning that from a young age, they live in close contact with animals and the plethora of microbes that they carry.

"If you look at an aerial drone photographs of Amish settlements, and compare them with Hutterite communities, the Amish are living on the farm with the animals, whereas the Hutterites live in little hamlets, and the farm could be a few miles away," says Fergus Shanahan, professor emeritus of medicine at University College Cork, Ireland.

In 2016, a team of scientists from the US and Germany published a now-landmark study concluding that Amish children have a lower risk of allergies because of the way their environments shape their immune systems. In particular, the researchers found that the Amish children in their study had more finely tuned so-called regulatory T cells than those from Hutterite backgrounds. These cells help to dampen down unusual immune responses.

When the researchers scanned dust samples collected from the homes of Amish and Hutterite children for signs of bacteria, they found clear evidence that Amish children were being exposed to more microbes, likely from the animals that they lived among.

Around the world, other scientists have been making similar findings. A group of immunologists reported that children........

© BBC