Jennie French is our ECS Publications Officer and is studying for a Microbiology BSc. Here she ponders the potential of parasites.
I’d like to talk about the possibility of using parasites, mainly helminths, as treatments against immune disorders such as inflammatory bowel disease (IBD) and Crohn’s disease.
To start off with, what are helminths? They’re a group of worms that love humans so much, they want to live inside us. You may have heard of tapeworms, roundworms and hookworms causing infections in animals such as sheep, but it seems that humans evolved with these parasitic worms too.
Even though developed countries have largely eradicated helminths from their population, these parasites are still a problem because of their prevalence in developing countries. In particular people living in tropical regions have the highest worm burdens.
Way of the worm
Due to the absence of these worms and the subsequent rise in immune disorders and allergies in developed countries, helminths make up part of the hygiene hypothesis. It’s thought that since eradicating helminths and many other diseases from our society, our immune system has been at a loss, become bored and decided to attack us instead.
In my mind, although this is probably wrong, I imagine helminths befriending our immune system, keeping it occupied and steering it off the road that leads to immune disorders.
Obviously, this can’t be said for all helminths, people with roundworm tend to develop all sorts of allergic responses and H. polygyrus is extremely immunosuppressive to the extent that it becomes a chronic infection and has been shown to reduce the effectiveness of the malaria vaccine.
It seems sensible to avoid these helminths in potential treatments for IBD and Crohn’s disease then. Other helminths have been investigated as potential treatments for these immune disorders though. Hookworm has been tested as an asthma preventative but to make a difference you need to give patients quite high numbers of larvae which end up causing damage instead.
Tricuris suis (whipworm) which is a parasite of pigs has been used to treat IBD because once the eggs have developed into worms, they don’t survive long enough in humans to cause disease. They do survive long enough to occupy the immune system and reduce IBD symptoms though and whipworm eggs are now being marketed in Germany (via Ovamed) for $450. This gets you a dose of 25,000 eggs. Tasty!
Although some of these treatments have been shown to work, would people be willing to effectively infect themselves with a parasite? It might take some serious science communication to persuade people this was a good thing but then again, these inflammatory diseases are horribly painful to say the least!
I know that if I had IBD or Crohn’s I’d be willing to take anything to reduce my symptoms! Helminths could also be used for other things too. It’s claimed that Maria Callas gobbled tapeworm larvae and lost 40kg of weight, as they consumed everything she ate and starved her. It’s also been pointed out that her fondness for steak tartare is a possible, and more likely source of infection.
So how do they help with diseases like IBD? All helminths can dampen our immune response to an extent. This is the main reason for their ability to survive in us for so long; the immune response goes down a route that suppresses the formation of inflammatory cytokines like IL-4, IL-5 and other molecules belonging to the T Helper 2 immune response.
In the case of inflammatory diseases like Crohn’s and IBD, this is very beneficial but in the case of getting rid of these parasites from our bodies, inflammation is a key response that has been suggested to help remove helminths from our bodies.
Turning of the worm
Although the hygiene hypothesis paints helminths as a positive presence in our bodies by warding off allergies, they obviously aren’t very pleasant to have inside you if you don’t have a choice!
I think the hygiene hypothesis makes a lot of sense but it doesn’t mean that we shouldn’t try to rid people in developing countries of helminths. They are a large problem for these people and needs to be dealt with regardless of whether allergies increase in these countries!
It seems that the human race has gone full circle; people in developed countries have got rid of helminths only to put them back in again. It’s a confusing vicious cycle that probably won’t end until we discover the root of immune disorders and that could be a long way away.
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