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Essential Science: Are parasitic worms good for the gut?

By Tim Sandle     Apr 25, 2016 in Science
Horrible as it may seem, there are biological advantages to having parasitic worms in terms of warding off various diseases. This is because parasites trigger an immune reaction that calms inflammation. The benefit has been explored in a new study.
Parasites and humans have existed together for thousands of years. Examples of parasitic diseases, for example, have been traced back to Ancient Egypt. The process of mummification has preserved some clear examples of how the wealthy members of Egyptian society co-existed with parasites. This preservation in these cases was enhanced through specialist methods the preparation and treatment of cadavers for mummification.
According to one study, humans have acquired an amazing number of parasites, about 300 species of helminth worms and over 70 species of protozoa. Moreover, most parasitologists recognize that they have not found all human parasites.
Most of these parasites are harmless, although a few species are responsible for some of the most unpleasant diseases on the planet. Such is the extent of the association that one leading parasitologist wrote: “our understanding of parasites and parasitic infections cannot be separated from our knowledge of the history of the human race.”
The more deadly human parasites are protozoa. These are single-celled organisms, and include well known deadly parasitic protozoa like plasmodium, which causes malaria. No human disease has killed more people than malaria.
Glass representation of the parasite that causes malaria
Glass representation of the parasite that causes malaria
Luke Jerram
There are three main types of parasites:
Ectoparasites: These live on the outside of their host, either in or on the skin. Fleas and lice are well known examples of ectoparasites.
Endoparasites: These live within the bodies of their hosts. Tapeworms are the largest endoparasites.
Temporary parasites: These live apart from their host most of the time, visiting them only to feed. Ticks, leeches, and bedbugs are examples of temporary parasites.
Given the long association, and the established division of parasites into those that cause harm and those than appear to exert no effects whatsoever, it has taken some time for research to emerge that some parasites may, in actual fact, be beneficial.
In a new study, it has been found that parasitic worms can alter the balance of bacteria in the intestines and lower the rate of inflammation. This tallies with medical data that indicates cases of inflammatory bowel diseases also less prevalent in regions of the world where higher proportions of people are infected with parasitic worms.
Ancylostoma caninum  a type of hookworm  attached to the intestinal mucosa.
Ancylostoma caninum, a type of hookworm, attached to the intestinal mucosa.
Joel Mills
The study was carried out by Dr. P’ng Loke, who works at New York University School of Medicine. Dr. Locke explored how worms in the human gut provide protection against Crohn’s disease. This was shown by studies on mice genetically mutated to experience anm equivalent disease.
Crohn's disease is caused by a combination of environmental, immune and bacterial factors in genetically susceptible individuals. The symptoms of the disease vary. Symptoms include: abdominal pain and diarrhoea, tiredness and fatigue, fever, ulcers and weight loss.
The mutated mice were infected with one of two parasites: whipworm (Trichuris muris) or a corkscrew-shaped worm (Heligmosomoides polygyrus). It was found that the worm-infected mice produced more mucus than uninfected mutant mice did. The parasite infected mice had fewer bacteria of the species Bacteriodales vulgatus, which is associated with some ill-health effects, and more beneficial bacteria from the Clostridiales family, which have been shown to protect the body from inflammation. In medical terms, a type 2 immune response took palace.
With studies on people, where fecal samples have been examined, a similar microbial shift can be seen in association with parasitic worms. The study was an examination of people from parts of Malaysia.
Speaking with Science News, Dr. Aaron Blackwell, who is a leading parasitologist, explained that having some data from humans is useful since results in mice do not always match the effects that occur in people. Here he states: “It’s nice to show that it’s consistent in humans.”
It is hoped that by understanding how parasitic worms alter microbial behaviors could lead to a therapeutic product that allows medics to trigger the same response without the need to deliberately infect a person with parasites.
An earlier study found an associated benefit. This was that parasitic worm infections can lower susceptibility to certain allergies. The new research is published in the journal Science. The research is titled “Helminth infection promotes colonization resistance via type 2 immunity.”
This article is one of Digital Journal's regular Essential Science columns. Each week we explore a topical and important scientific issue. Last week we examined the use of herbs as natural antimicrobials. The previous week we discussed the connection between gum disease and heart problems.
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