Neurocysticercosis Is the Result of the Interplay between Parasites, Hormones, and Inflammation

Parasitic infections of the central nervous system are still a health problem in low- and middle-income countries and due to international travels and migration can affect even opulent countries. Parasites can modulate host immunity to ensure their long-term survival without inflammatory symptoms; therefore, infection of the brain parenchyma by Taenia solium cysticerci (parenchymal neurocysticercosis) may be asymptomatic, or on the other hand lead to severe inflammation that initiates glial activation with production of pro-inflammatory cytokines, with mild to severe neurological symptoms. Besides, when cysticerci are localized in the ventricles or in the subarachnoid space (extraparenchymal neurocysticercosis) severe symptoms and treatment difficulties occur.

Here we review how the nervous, the immune, and the endocrine systems interact with T. solium and crassiceps cysticerci and influence the course and individualities of the disease that the parasites trigger in humans and animals. For example, a clear sexual dimorphism in cysticercosis has been found in experimental models of the disease, but the influence of gender in human patients needs further investigation. The synthesis of steroids by the brain cells and the cysticerci might influence the local immune response elicited by the presence of the parasites. Remarkably, cultured cysticerci can synthesize sex steroids and deoxycorticosterone, suggesting that these parasites can influence the local brain microenvironment, especially by producing dehydroepiandrosterone, estrogens, and androgens, which could modify the immune response. Treatment of neurocysticercosis includes cysticidal drugs and corticosteroids intended to control the inflammation caused by the parasite; however, these steroids represent a double-edged tool due to their side effects during prolonged administration and also because of some beneficial effects for the parasite itself.

Parasite survival in the host depends on the inflammatory response and the local microenvironment, including steroid hormones that can promote their survival and even their development and proliferation. New strategies should be designed to manage the severe symptoms induced by the chronic presence or the death of parasites and the poor response to treatment that occurs in extraparenchymal neurocysticercosis.