You do not always read about the potential benefits of parasites for health, those small, sometimes microscopic organisms responsible for a large amount of diseases. However, the researchers suggest that there is a strong connection between exposure to parasites and reduced susceptibility to pollen and grass allergies, among others.
Early exposure to external invaders, such as microbes and parasites, helps the immune system to create tolerance to certain allergens, including grass and pollen.
David P. Strachan, scientist and developer of the hygiene hypothesis
The hygiene hypothesis
The hygiene hypothesis is a concept developed by scientist David P. Strachan. Strachan suggests that early exposure to external invaders, such as microbes and parasites, helps the immune system to create tolerance to certain allergens, including grass and pollen. This technique can also reduce incidents of asthma and autoimmune diseases.
Strachan's theory implies that the relative cleanliness of industrialized societies contributes to high rates of these conditions. Ironically, people who live in societies that have managed to eliminate or drastically reduce exposure to many parasites and microbes are much more likely to develop allergies and asthma.
This may be because the consistent use of antibacterial soaps and sanitizers (or avoiding contact with others), combined with the increased use of antibiotics, can weaken the body's defenses. This can make it harder to fight viruses and bacteria. Consequently, the immune system can try to compensate with an exaggerated reaction to harmless invaders such as grass, pollen and pet dander. This overreaction can produce the symptoms of allergy.
Parasites and reduced allergy risk
According to a 2004 study published in the journal Clinical Reviews in Allergy and Immunology, high rates of exposure to specific parasites in different regions of the world are accompanied by lower rates of inflammatory diseases in those regions.
In other words, infection by parasites seems to protect people against the development of allergies, asthma and other inflammatory diseases. The study found that this connection was related to infection by three types of parasites:
The schistosome is a parasitic worm that lives in freshwater snails. Swimming or swimming in contaminated fresh water increases the risk of schistosomiasis or bilharzia.
Although the schistosome does not live in the United States, it infects more than 200 million people around the world and can be found in parts of Africa, South America, the Caribbean, Indonesia and Southeast Asia, according to the Center for Disease Control and Prevention.
Helminths are intestinal worms that humans contract through contact with contaminated soil. Hookworm, Ascaris and whipworms are all examples of helminths. The CDC estimates that between two and three billion people around the world are infected with at least one of these parasites.
Slightly infected individuals often have no apparent health problems. Severely affected individuals may suffer from diarrhea, abdominal pain, loss of blood and protein, and decreased mental and physical growth and development.
Unlike schistosoma and helminths, Toxoplasma gondii is not a worm, but a unicellular parasitic organism. It infects more than 60 million people in the United States. People can become infected by eating contaminated or poorly cooked food, handling their pets' feces or drinking contaminated water.
In most cases, the microbe is quarantined by the immune system and does not cause symptoms. However, it may cause symptoms such as flu in some cases. It presents serious risks for pregnant women and women with weakened immune systems.
According to the medical center at Leiden University in the Netherlands, exposure to these or other parasites during childhood can help the immune system better adjust to the balance between two types of immune system cells called T cells. auxiliary
T helper cells 1 can do a better job of counterbalancing the inflammatory effects of helper T cells 2 in people whose immune systems have been compromised early in their lives. This may be enough to prevent your immune system from overreacting to harmless substances, as in the case of allergies, asthma and other inflammatory diseases.
About the author
Boyan Hadjiev, MD, has been practicing as a doctor for five years. He has been certified twice in internal medicine (2003) and allergy and immunology (2005).
Dr. Hadjiev graduated from the University of Michigan with a BA in biology and an MD from the Cleveland Clinic-Case Western Reserve School of Medicine.