ETIOPATOGENIA DE LA NEUROCISTICERCOSIS

Cysticercosis is the most common parasitic disease of the central nervous system. Cysticercosis occurs when humans become the intermediate host in the life cycle of Taenia solium by ingesting its eggs form contaminated food. Eggs hatch into oncospheres in the human intestinal tract; oncospheres enter the bloodstream and are carried into the tissues of the host, particularly the brain, where the larvae (cysticerci) develop. Cysticercus consists of two main parts, the vesicular wall and the scolex which has a similar structure than the adult Taenia: body, neck, and head armed with suckers and hooks. As the result of a complex immunological attack form the host, most cysticerci enter in a process of degeneration that ends with the dead of the parasite. This process include four stages of development called: vesicular stage, colloidal stage, nodular stage, and calcified stage. Together with the changes observed within the parasites, the surrounding brain parenchyma also shows tissue changes, including: brain edema, gliosis, inflammatory infiltrates, and neuronal degeneration. In addition, the wall of blood vessels in the vicinity of parasites are invaded by inflammatory cells, leading to endarteritis with thickening of the adventitia, fibrosis of the media, and endothelial hyperplasia. There are cases in which the immune response develops slowly and the parasites may live almost unchanged for several years; the mechanisms by which cysticerci evade the immune surveillance may include: antigenic variation, molecular mimicry, and immunosupression. On the other hand, a state of hypersensitivity occurs in some patients in whom cysticerci are acutely rejected after entering the central nervous system; in those cases, the infection is overcome but the tissues of the host are also damaged as the result of this enhanced state of responsiveness. In between the extremes of immune tolerance and hypersensitivity, there is a wide range of inflammatory response induced by this host parasite relationship. Probably, the gender of the host and the HLA system play a role in the susceptibility and resistance to cysticercosis.