Let’s face it, people do not imagine anything attractive when they think of parasites. A wiggly protozoan or worm inside our own GI tract? The knee-jerk reaction is “Gross! Kill it…NOW!” There is good reasoning behind this opinion.
Parasites, by definition, live at the expense of their host and can wreak havoc to many body systems. Just as commonly, intestinal parasites may leave no clues that they are present. Even if it’s silent and “harmless,” it does nothing for your social capital to be associated with a parasite.
When one is asymptomatic, another reflex reaction to a positive parasite finding is disbelief—feeling that the test results just have to be wrong. How and where could we pick up parasites? It must be a false positive! Newsflash: DNA-based methods of detecting microbes and helminths are essentially fool-proof in this regard, similar to police forensics.
In any of our stool tests on parasites, we have the means (a universal probe) to detect the presence of parasite DNA, even when the taxonomic classification is unknown. This kind of finding happens in more than 65% of people we test! Why? Because even after the usual 20 or so suspects are ruled out, there are clearly more parasites than we think there are in our collective GI tracts!
Most of these organisms are missed on the customary “ova and parasites” microscopy method of examining stool specimens. So clinicians who haven’t seen very many parasites when using the “o and p” test are understandably questioning the validity of a DNA test that uncovers them more often.
Re-thinking the ecosystem within us
Now, let’s turn this horror of parasite awareness on its head. We just have to think a bit differently about our GI tract’s microbiome—that invaluable mass of bacteria, fungi, parasites and viruses we consider so rarely. These “bugs” live interdependently in various regions of the gut, particularly populating the colon. Research is shedding much light on the many services they perform to our benefit. Resisting infection by “pathogens” is high on that list, by the way!
Our GI “inner tube” is open to the outside world. Microbes (this includes parasite eggs) are everywhere! We swallow them and inhale them. IT HAS ALWAYS BEEN THAT WAY—FOR MILLENNIA! Evolving together, species adapt.
For example, a miniscule, early stage juvenile parasite makes its way into a mammal’s mouth, is swallowed, moves on down to a home in the intestine, grows up, finds a job and makes a living. All on our dime, unbeknownst to us, if we are the mammal in question! Whether said parasite announces its presence by causing severe cramping OR stays serenely quiet for months can depend on many factors, such as who the parasite is, what it feasts on and even which specific bacteria are flourishing nearby in the intestine.
Enter the so-called “hygiene hypothesis.” Its gist is that “too sterile is not healthy for the immune system.” According to this hypothesis, and there is a lot of intellectual ammo behind it now, our immune system (>75% of which is GI-associated) relies on microbes to “instruct” it on how to react and behave properly in the face of constant and innumerable “non-self” microbes and substances.
Since immune systems are designed to protect and defend, and surfaces like the GI tract are so vulnerable to assault by all manner of invading substances and microbes, then logically there must have always been some means in place to keep the body from attacking its own tissues (autoimmune/auto-inflammatory disease). There is very little autoimmune pathology in underdeveloped countries!
In fact, Martin Blaser of NYU cites several studies in his argument to “Stop the killing of beneficial bacteria.” Some citations were Blaser’s work, but all demonstrate negative effects of lowered levels of beneficial bacteria. His fear is that antibiotics can cause permanent detrimental changes to gut bug populations, with serious immunological consequences.
So do parasites have a role in adapting immune function?
Whipworm (Trichuris) is a widespread helminth. There are more than 50 known species of whipworm. Trichuris trichiura, for example, infects the colon of an estimated 1 billion people, according to the World Health Organization. One billion colons is no small matter.
In a 2005 study, twenty-nine patients with Crohn’s disease swallowed live Trichuris ova every three weeks for 24 weeks [2]. At week 24, 72.4 % had remission, with no adverse events! Parasite therapy?
In 2010, Hayes and colleagues [3] in the UK found that in mice, whipworm eggs need the presence of E. coli or other specific bacteria in order to hatch. If antibiotics were given, significantly fewer worms hatched. Many immune changes were evidenced in the antibiotic-treated mice, such as higher interleukins 4 and 13 and lower interleukins 6 and 17.
There is a growing opinion that early exposure to both harmless microbes found in untreated water and soil and to parasitic worms (helminths) is necessary for proper immunoregulatory pathways to develop in humans. So, running barefoot in the dirt as toddlers may have had a health-promoting role after all. This is pretty radical thinking, by conventional medical standards!
The ultra-basic explanation is that these organisms help in the “training and specialization” of dendritic cells that are important for T cell differentiation, a process which is in turn necessary for appropriate inflammatory responses. As one probiotics expert said, “Microbes mentor T regulatory cells.” T reg cells allow the immune system to tolerate microbes (and helminths) that do not pose a threat and keep T cell activation from getting out of hand, as happens in inflammatory bowel disease, for instance.
The Hayes group contends that our adaptive immune system is controlled by microorganisms, including parasites. They are not alone in this thinking.
So how do we popularize parasites? If they and their microbial companions are truly as important to proper immune responses as it seems, we will hear a lot more about them in the coming years. But who will want to listen or see photos? Like poop and bacteria (they’re all bad “germs” to most people), parasites need an image makeover, or the public will never catch on that we actually need them in our lives.
~ Terry Pollock, MS
References:
- Blaser, M. Nature 25 August 2011 vol 476, p 393.
- Summers RW et al, Gut 2005 Jan; Vol 54, p. 87
- Hayes KS, et al, Science 11 June 2010 Vol 328, p. 1391
Further fun reading:
Cass Nelson-Dooley, MS (18)