The parasite, Schistosoma mansoni, is a remarkably cunning and efficient worm. It spends the first part of its life infecting freshwater snails, where it vigorously multiplies to bulk up numbers. This parasite army then marches out of the snail and into the river, encounters an unsuspecting human, latches on to their skin and burrows its way inside, more often than not through a hair follicle. Schistosomes infect more than 200 million people a year, in many parts of the world, and since most worms live for more than 10 years, infection with this pathogen is a long-term health problem.
In the human body, the parasite lives most of its life in the bloodstream, but when it comes time to produce tiny parasite offspring, this is a bad neighbourhood to bring up the kids. A much more nurturing location is the human gut, a stable, moist and nutrient-rich environment. Eggs are first laid in the veins carrying blood from the gut, and from there, they hop into the intestines, finally being pooped out from the host to continue their life cycle back in the freshwater snail. Exactly how the eggs migrate from the vein to the gut has been a vaguely grey area, but now a team of researcher’s at the University of York have shown that a big part of this journey involves the eggs accumulating in Peyer’s Patches. These are small pockets of immune tissue in the gut wall that maintain immune surveillance, and are particularly well supplied with extra energy and nutrients. Once the eggs are settled in these cosy patches, they secrete factors that force the area to undergo an extensive biological remodelling, making it easier for the eggs to slip out of the host once they’ve reached full maturity.
Thus, the dastardly schistosome is an excellent example of a human pathogen that can commandeer our natural anatomical and biological features, manipulating them to its own advantage to improve the chances of reproductive success.
Turner JD, Narang P, Coles MC, & Mountford AP (2012). Blood Flukes Exploit Peyer's Patch Lymphoid Tissue to Facilitate Transmission from the Mammalian Host. PLoS pathogens, 8 (12) PMID: 23308064