When bacteria infect parasites that infect humans

Meet the viruses and bacteria that infect parasites, which infect people. It's like a Russian nesting doll of microbial pests. As a human, I'm not sure whether to feel a bit of schadenfreude at parasites getting what's coming to them, or be deeply disturbed.

Many parasites or endosymbionts can be infected with viruses. A classic example is Paramecium, which can harbor an endosymbiotic bacterium, Caedibacter, which in turn carries phages involved in making a toxin. But from the human point of view, things start to get particularly interesting when we consider the viruses that infect parasites of humans and how those viral infections may modulate the parasite's interaction with its human host.

Image: Russian Dolls, a Creative Commons Attribution (2.0) image from aussiegall's photostream