Why such a small percentage is difficult to expel parasites has hindered researchers for some time. However, a new mathematical model developed by the University of Nebraska at Lincoln and the Royal Dutch Institute of Oceanography provides an answer and reinforces the adage that quantity is safe.
Clay Cressler, Anieke van Leeuwen and their colleagues concluded that when a large number of worms occupy a certain position in the host intestine, they usually try to stay there for a long time. In contrast, the model shows that a single worm-or a small part of it-is submerged by the immune system and is quickly washed out of the gastrointestinal tract.
"Anything parasites do to increase their access to resources indirectly deprives them of their owners," kressler said. The more parasites there are, the better they are at manipulating resources. The better they manipulate, the easier it is for parasites to grow. Then they are better at dealing with it. So you get this positive feedback loop, allowing them to establish a chronic infection.