Unwanted lodgers in the gut can be disgusting. But their presence is also useful in the case of certain diseases: Because the little parasites influence their host's immune system in a very selfish way - with beneficial side effects.
A nematode that burrows into the tissue of the intestinal mucosa with its thin head, feasts on its host's body and produces hundreds of eggs every day, doesn't exactly sound like the most pleasant lodger. A mass infestation with the whipworm Trichuris trichiura, for example, also triggers diarrhoea, pain and anemia. So it's probably no wonder that modern medicine once made the suppression of parasites an important milestone on the way to a he althier - and more hygienic - society.
But new studies are always giving cause for rethinking. As soon as the parasitic plagues were contained in the USA, Europe and Canada, for example, other evils spread: allergies, asthma, multiple sclerosis and other autoimmune diseases have experienced a steady increase in recent decades. The body seems to turn against itself in the absence of its usual enemies.
a: Onchocerca (Filarium, Onchocerca), b: Trichinella (Trichine), c: Enterobius (pinworm), d: Ancylostoma (hookworm), e: Trichuris (whipworm)
The "hygiene hypothesis" has been doing the rounds for a number of years: actually, according to the theory, our body is designed to coexist with the small blackheads. However, due to the decline in parasitic infections due to better hygiene measures, this balance has been upset. Initial tests confirmed the thesis for the inflammatory bowel disease Crohn's disease - but only in animal experiments. Now the first human study shows that, at least in multiple sclerosis, the intestinal parasites can actually be beneficial to he alth.
Jorge Correale and Mauricio Farez from the Raúl Carrea Neurological Research Institute in Buenos Aires accompanied 24 MS patients with regular examinations for four and a half years. All study participants had a similar course of the disease at the beginning of the tests. With one exception: half of the subjects had contracted an intestinal parasite after the onset of the autoimmune disease. Instead of removing it, the researchers left the parasites in their hosts and observed whether and how such an infection affects the nerve disease that causes paralysis, visual difficulties and pain at irregular intervals.
The results were amazing. Because the regular neurological tests showed that the disease progression of multiple sclerosis was significantly weakened in the infected patients: During the four years, the parasite carriers had only three severe flare-ups - while the control group had 56 such deteriorations. Only two patients from the infected group also experienced measurable deterioration in their he alth, and these were also less serious than in the other 12 subjects, all but one of whom had to contend with additional problems. In addition, magnetic resonance images of the brain in the parasite-infested subjects showed fewer foci of inflammation in the brain, which are often the first sign of a deterioration in he alth.
The scientists also found significantly more messenger substances in the blood of MS patients infected with parasites, which render the pro-inflammatory cytokines harmless. And this is exactly where Correale and his colleagues suspect the beneficial effects of the intestinal parasites: To ensure that the roundworms do not experience any unpleasant surprises when they are in the intestine, they influence the immune system of the host body so that it leaves them alone. To do this, they activate certain immune cells, the T-lymphocytes, which regulate the body's immune responses and prevent an aggressive immune response.
Apparently, the nematodes not only save themselves, but also the nerve cells of their host from an attack by the immune system. How exactly they do this is still a mystery to the researchers. So before parasites can be used as biological immune controllers, there is still a lot of research to be done. Nevertheless, at least one thing seems clear: the common enemy image of the little freeloaders has to be revised.