Within the last few centuries, humanity has made great improvements in cleanliness and hygiene. Modern cities, with added infrastructure and sewage systems, are completely unrecognizable from a century ago. The last few decades have also seen an unmatched rise in medical innovation. Because of these improvements in sanitation and medicine, mortality from infectious diseases in the United States has declined by more than 90 percent since 1900 , and the quality of life has drastically improved.
Although mortality rates from infectious diseases have decreased in recent years, a new type of affliction has arisen in its place. Autoimmune diseases are those in which our body’s own immune system attacks normal and healthy cells. This occurs because the immune system cannot tell the difference between foreign objects and normal body tissues. However, the reason why the immune system becomes unable to differentiate between normal tissues and foreign objects is unknown. Some theories include the involvement of microorganisms and drugs, but no studies have shown a conclusive link. The more common autoimmune diseases are rheumatoid arthritis, celiac disease, type I diabetes, multiple sclerosis (MS), and Lupus. Unlike infectious diseases, most autoimmune diseases are currently incurable because we don’t know why they occur; however, the symptoms can be managed to a certain degree using drugs. As such, the drive to find a cure for these diseases has become an objective for modern medicine. To start, scientists have turned to elucidating a trend in the incidence of autoimmune diseases.
As studies have found, the prevalence of these diseases over the past century has increased. For instance, the incidence of Celiac’s disease was found to have increased fourfold over the past fifty years . Scientists have also found that the percentage of acute lymphoblastic leukemia patients has increased threefold in the past eighty years . Though there is evidence that the incidence of diseases involving the immune system has increased over the past century, no definitive explanation has been found .
The most prominent explanation for this phenomenon looks at the basics of the immune system and its symbiotic relationships with other organisms. For the past 200,000 years, humans have lived in coexistence with microorganisms. This close proximity has inevitably fostered a long history of interactions between humans and these microbes. However, in recent history, we have mostly removed these microorganisms from our environment and daily lives by using cleaning agents such as soap in our everyday lives, and also by cleaning or removing previously common sources of microbes. Several examples include the sewage system, water treatment plants, and even public trash collection. Although microorganisms certainly have not completely disappeared from our day-to-day lives, they have been widely eradicated in a crucial moment in the development of the immune system, our infancy.
Our immune system grows and develops the most in childhood. Here, it is drastically different from the adult immune system. This difference is important to consider when developing vaccines, and when tackling issues of autoimmunity. Babies have a much stronger immune response to the proteins of biological organisms such as bacteria, viruses, and parasites , resulting in a large role for these microbes in the development of the early immune system. But in this new world, where hygiene has become of the utmost importance, the presence of bacteria, viruses, and other antigens is frowned upon, and all efforts are made to rigorously eradicate these microbes from the baby’s surrounding. Even though microbes will always persist, their diversity and potency are not as great as they would have been in times past. Thus, the baby’s immune system is denied the potential to fully develop at this crucial age.
Because our immune systems are not properly developed at a young age, they are at risk of malfunctioning later in our lives. One proposed mechanism is that this early lack of development causes regulatory T cell development to develop improperly, which causes the T helper cells that it normally regulates to become hyperactive . This lack of “training” for our immune system in turn causes a higher incidence of autoimmune diseases. In fact, a hypothesis, aptly named the “hygiene hypothesis”, states that good hygiene inadvertently causes autoimmune diseases. Many studies have shown that this hypothesis is likely accurate. For example, one study on the relationship between MS and sanitation found that there is a statistically significant increase in risk for MS later in life if children had been in more sanitary environments . Studies have also linked sanitation with increasing incidences of allergies and type I diabetes .
As such, if the hygiene hypothesis is correct, the cure for autoimmune diseases is simple: expose our bodies to organisms that can help properly develop and control our immune system. Currently, the most promising form of treatment for autoimmune diseases revolves around the use of parasitic worm infection. These worms have evolved parallel to humans for millennia, and so both worms and humans have learned, in some ways, to cooperate with each other. Parasitic worms thrive and reproduce using the nutrients from their host. In addition, they cleverly avoid the host’s immune system by suppressing it. In the past, it was likely that the vast majority of humanity were infected by these worms to some degree, meaning the suppressed immune system was actually a norm. Yet in the modern world, parasitic worm infections have been severely reduced. They are now only prevalent in Africa and third world countries, where shoes and clean drinking water are not always readily available to the populace .
These worms helped regulate the immune system in our ancestors by keeping it in check against itself. But today, without the help of these worms, autoimmune diseases are manifest as an overreaction of our immune system; classifying certain elements as foreign even when they are a part of our body. Nevertheless, worm treatment has shown great promise in curing or at least mitigating the effects of autoimmune diseases. For instance, people with worm infections have lower chances of developing multiple sclerosis than people without infections. In fact, there have been documented cases where worm infection has actually cured multiple sclerosis, a feat that modern medicine has been unable to replicate . The same effects have been seen in studies focusing on worm infection and Crohn’s disease . Although autoimmune diseases may occur more frequently as we become more hygienic, the future also holds some promising potential in worm therapy.
- EA Mortimer, Jr. Immunization against infectious disease. Science. 1978;200 (4344): 902-907.
- Alberto Rubio–Tapia, et al. Increased Prevalence and Mortality in Undiagnosed Celiac Disease. Gastroenterology. 2009; 137(1):88-93
- Smith MA, et al. Evidence that childhood acute lymphoblastic leukemia is associated with an infectious agent linked to hygiene conditions. Cancer Causes Control. 1998 May;9(3):285-98.
- Wilson MS, Maizels RM. Regulation of allergy and autoimmunity in helminth infection. Clin Rev Allergy Immunol. 2004 Feb;26(1):35-50.
- Heather B. Jaspan, Stephen D. Lawn, Jeffrey T. Safrit, Linda-Gail Bekker. The Maturing Immune System: Implications for Development and Testing HIV-1 Vaccines for Children and Adolescents. AIDS. 2006 Feb 28;20(4):483-94.
- Bufford JD, Gern JE. The hygiene hypothesis revisited. Immunol Allergy Clin North Am. 2005 May;25(2):247-62, v-vi.
- Leibowitz U, Antonovsky A, Medalie JM, Smith HA, Halpern L, Alter M. Epidemiological study of multiple sclerosis in Israel. II. Multiple sclerosis and level of sanitation. J Neurol Neurosurg Psychiatry 1966;29:60-68
- Onkamo P, Väänänen S, Karvonen M, Tuomilehto J. Worldwide increase in incidence of Type I diabetes–the analysis of the data on published incidence trends. Diabetologia. 1999 Dec;42(12):1395-403. Erratum in: Diabetologia 2000 May;43(5):685.
- J. Correale and M. Farez. Association between parasite infection and immune responses in multiple sclerosis. Annals of Neurology, 2007;61:97.
- R.W. Summers et al. Trichuris suis therapy in Crohn’s disease. Gut. 2005;54:87.
- Lauke P. [photograph] 2009. Available at: http://www.flickr.com/photos/redux/3418936283/
Allan Zhang is a first-year student at the University of Chicago.