| Catch-22: Unhygienic living conditions play an important role in strengthening immunity
It all started with a group of genetically-modified mice with a predisposition to Type 1 diabetes that Professor Anne Cooke of Cambridge University, UK, and her colleagues were researching on. Once, some of the mice, while being transported from London, caught bacterial and parasitic infections. This led to an unexpected result — only 50 per cent of the rodents developed diabetes instead of the expected 80 per cent.
Prof. Cooke immediately sensed a correlation between the two incidents. To test the hypothesis, she and her team infected the genetically modified mice with a parasitic worm called schistosome, which causes schistosomiasis (snail fever), a disease found in parts of Africa, Asia and South America. The scientists found the infection reduced the incidence of diabetes.
In fact, when the mice were infected early in life, none of them went on to develop Type 1 diabetes. Further research showed it was some component of the egg rather than the later stages of the parasite’s development that protected the mice from diabetes.
However, in European countries, where schistosomiasis is non-existent, there has been an increase in the occurrence of autoimmune diseases such as Type 1 diabetes, rheumatoid arthritis, Crohn’s disease (also called regional enteritis characterised by diarrhoea, cramps and loss of appetite) and so on.
Autoimmunity is an abnormal function of our immune system, where antibodies are produced against one’s own cells. In Type 1 diabetes, for instance, pancreatic cells are destroyed by the immune system so that the production of insulin is curtailed.
Interestingly, even though schistosomiasis is absent in many Asian countries including India, these nations do not have a very high incidence of autoimmune diseases. The reason, experts say, could be the prevalence of intestinal bacteria and parasitic worms such as hookworm, pinworm, filarial worm and round worm in these countries. According to Prof. B.S. Ramakrishna of the department of gastrointestinal sciences, Christian Medical College, Vellore, intestinal infection with Helecobacter pylori — a bacteria causing certain ulcers — could be the reason for the low incidence of autoimmune diseases in India.
In an article titled “Parasitic worms and inflammatory diseases” in the journal Parasite Immunology (October 2006), Professor Cooke and her colleagues discuss the emerging evidences favouring the “Hygiene hypothesis”, which states that better hygiene and lack of parasites are related to the high incidence of autoimmune diseases.
The researchers say that early human civilisations were exposed to a host of pathogens because of unhygienic living conditions, unclean drinking water, improper sanitation and so on. In due course, the immune system adapted itself to these pathogens and the accompanying parasites and bacteria. In other words, parasites and microbes have played an important part in strengthening one’s immunity.
Most autoimmune diseases are genetic disorders. How, then, does aschistosomal infection help' Studies conducted on twins having the same genes but living in different environments showed that environment played a key role in the expression of the genes. It was found that in hygienic environments, the immunological responses triggered by the immune system were diverted to a different target. In the event of aschistosomal attack, the immune system, instead of targeting the pancreatic cells (that lead to Type 1 diabetes), attacks the infection. This mechanism explains the role of infections in reducing autoimmune disorders.
Worms for health
So what would we prefer: autoimmune diseases or diseases caused by parasitic worms' Since autoimmune diseases are genetic disorders, curing them completely requires gene therapy, a costly and less successful process. On the other hand, parasitic worms can be effectively managed with cheap medication.
However, unhygienic conditions could lead to more serious problems such as cholera. A better option would be to take cues from the “Hygiene hypothesis” and develop better strategies to combat autoimmune diseases.
We may use genetically modified worms, which can elicit the required immune responses from our immune system without triggering any harmful effects. A better option would be to develop a drug based on the chemicals present in the worms that stimulate immune response. It will be interesting to see a reversal in worm related practice, a change from de-worming to artificial worming!
(The author is a lecturer of zoology at a Kerala government college.)