Old Friends Hypothesis: A New Theory About Helminths?
The Old Friends Hypothesis (OFH) was first proposed in a paper published in Science magazine in 2009. Since then it has been widely discussed in various forums, blogs and news sites.
Helen E. Fisher, Ph.D., Professor Emerita of Medicine at Harvard Medical School, wrote the original paper “A Natural History of Interpersonal Violence” in which she speculates that many of our “modern” social ills, including mass shootings and school bullying, are actually signs of “a sick society.”
The Old Friends Hypothesis suggests that the rise in some modern diseases is related to our lack of exposure to “old friends” such as parasites and commensal bacteria (also known as probiotics).
The OFH speculates that our Western lifestyle, with its emphasis on cleanliness, sanitation and a disinfectant-heavy medical model is contributing to an epidemic of autoimmune and inflammatory conditions.
The OFH states that we evolved over millions of years living with a variety of microorganisms. These organisms actually had beneficial effects on our immune system, training it not to attack our own bodies.
Over several thousand years of living in large groups with poor sanitation, some of these organisms became virulent, causing diseases like the Black Death. However, humans continued to live in large groups. Over many generations, natural selection favored people with a stronger immune response. The weaker died, and over time this response became stronger and stronger.
In more recent times, with the advent of cleanliness and improved sanitation, our exposure to these Old Friends declined. The OFH is a hypothesis that suggests our immune system still expects to encounter these Old Friends, and when it doesn’t it misfires, causing autoimmune diseases like asthma, allergies, and inflammatory bowel disease.
One important Old Friend is the parasitic worm (helminth). In areas of the developing world with poor sanitation, people are frequently infected with worms.
These worms have a beneficial effect on the host. They suppress the host’s immune system, but do not cause serious disease. In fact, they prevent the host from developing serious autoimmune diseases. In these areas, autoimmune diseases are rare.
In areas of the world with good sanitation and hygiene, helminth infections are rare. Thus, helminth infections are being treated as a “vaccine” against autoimmune diseases.
There is already evidence that hookworm can prevent allergy disease and asthma in genetically susceptible people.
Another Old Friend is our own flora. The human body is host to trillions of bacteria, commonly known as “flora,” on the skin and in the gut.
The gut flora in particular has a significant effect on immune system development. Changes in the types of bacteria and their quantities can have profound effects on the immune system. In mice, changing the gut flora can change the immune system’s response from one of tolerance to one of aggression.
Just as in the developing world, our ancestors had a certain amount of “dirty living.” They were frequently exposed to dirt, animal feces, and so on.
This exposed them to a wide range of bacteria, strengthening their immune systems and preventing the development of autoimmune disease.
In addition, animal bodily fluids and waste were commonly used as medicines in the past. These included blood products like “essence of beef,” and even raw animal organs.
This provided a source of exposure to a wide range of microbiota.
Finally, the OFH suggests that psychological factors also play a part in the development of autoimmune disease. Our immune systems and our stress responses are closely linked.
In stressful situations, our bodies prepare for injury and disease by suppressing the immune system. This is protective if we’re injured, but it leaves us open to disease.
This is particularly true during childhood, when our immune system is still developing. In the case of autoimmune disease, this suppression of the immune system allows it to attack the body instead of external threats.
The OFH notes that in the past, children frequently helped with household chores. This was a form of “dirty work” that exposed them to minor cuts and abrasions. Children with autoimmune diseases are far less common today.
The OFH also suggests some preventative measures to reduce the chances of autoimmune disease. The first is simply to expose yourself to the sort of “dirt” and foreign substances that our ancestors were regularly exposed to.
Get a pet and spend time outdoors. Eat raw vegetables and fruits. Don’t wash your fruit, and try to get it from unsprayed gardens if possible.
Scrapes, cuts, and bruises will help stimulate the immune system. For older children, make a game out of it.
Get your child to do some gardening or minor handyman jobs. They might not enjoy it now, but they’ll thank you when they’re older.
Most importantly, spend some time with your children. Make a game out of everyday tasks.
Teach them about the world around them. And above all, love them. They’ll need it to overcome the many obstacles they will face in the world.
If children have a strong foundation and a healthy psychological state, they’ll be able to overcome the challenges of autoimmune disease. In the future, medicine may be able to treat and cure autoimmune disease.
But for now, we can only do our best to prepare our children for a dangerous new world.
Omnis Ex Oriente
With the severe economic downturn in the east, many trade caravans have stopped travelling to the east. This has had a devastating effect on the economy in Kisharge.
Caravans from Kisharge have been ambushed and destroyed on several occasions, and many goods that used to be imported are now grown locally.
Given that the war in the east isn’t likely to end any time soon, trade is unlikely to resume with the east. The trade with the south is still in a state of equilibrium, with neither over-taking the other.
Given that Kisharge’s main strengths are no longer as attractive to travellers, many have turned to piracy. These pirates take the trade of the caravans for themselves, then sell the loot at inflated prices in Kisharge.
The pirates are hard to contain, as they range far out at sea. A few attempts have been made to stop them, but the pirates always manage to escape back to Kisharge’s long coastline.
Finally, this has given rise to a new profession – privateering.
Sources & references used in this article:
- 99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: Darwinian medicine and the ‘hygiene’or ‘old friends’ hypothesis (GAW Rook – Clinical & Experimental Immunology, 2010 – Wiley Online Library)
- A Darwinian view of the hygiene or “old friends” hypothesis (GAW Rook – Microbe, 2012 – researchgate.net)
- Chronic inflammatory disorders, the gut and “Old Friends” hypothesis (GAW Rook, LR Brunet – … translation from basic research to clinical …, 2004 – books.google.com)
- Antibodies against phosphorylcholine among New Guineans compared to Swedes: an aspect of the hygiene/missing old friends hypothesis (J Frostegård, WJ Tao, L Råstam… – Immunological …, 2017 – Taylor & Francis)
- Microbial ‘Old Friends’, immunoregulation and stress resilience (GAW Rook, CA Lowry, CL Raison – Evolution, medicine, and …, 2013 – academic.oup.com)
- Microbiota, immunoregulatory old friends and psychiatric disorders (GAW Rook, CL Raison, CA Lowry – … : The Microbiota-Gut-Brain Axis in …, 2014 – Springer)