Next time you fight off an infection, you can thank your parasites. Often you get infected or cured not because of your immune system - but because of parasites who live in your body.

In a paper published today in Science, we get some compelling examples of how "co-infections" work in small mammals. Essentially, one kind of microscopic parasite can defend you from another. This suggests that probiotic treatments of the future could involve infecting yourself with a parasite to boost your immunity. So tomorrow's therapies will look a lot like quackery of the past: We'll be using leeches, but at the microscopic level.

In a release about the study, the Science reports on how the research was done:


Sandra Telfer and colleagues show that co-infecting parasites may influence how vulnerable we are to other parasites. In a study of wild voles-small mousey rodents-the researchers found that co-infection with different parasites had a larger effect on disease than any other factor. The authors spent five years tracking infections of four different parasites by taking blood samples from nearly 6,000 wild voles. The results indicate that interactions between parasites can have both positive and negative effects on co-infecting parasites. For example, infection with cowpox virus in the voles increased susceptibility to other parasites and prolonged bacterial co-infections. On the other hand, an ongoing infection with the bacterium Anaplasma reduced the rodents' susceptibility to another parasite, Babesia. In turn, chronic infection with Babesia limited susceptibility to the bacterium Bartonella-possibly because they are both competing for the same host red-blood cells.

So basically your immune system is just one line of defense against infection. The other line of defense may be a bunch of parasites. Of course the opposite is true as well, as Telfer and colleagues demonstrate: One infection makes you more vulnerable to others.

Here's what you see in this image:


Vole parasite interactions. Four microparasites–-cowpox virus (CV), the protozoan B. microti (Bm), and two bacteria, A. phagocytophilum (Ap) and Bartonella spp. (Bs)-can have positive effects (red lines) and negative effects (blue lines) on each other (2). Solid lines are proposed direct effects on the host vole (M. agrestis) and thin lines are proposed indirect effects among parasites. Im represents the immune system, and the inset photo represents a limited pool of red blood cells. Image by P. Huey.

Read the full scientific article via Science