Parasitic Diseases; Overview

All the noncommensal (and perhaps commensal) bacteria, fungi, protozoa (or protists), and helminths are parasitic organisms when they colonize their human hosts. However, this article will be limited to the more commonly used, narrow definition that includes only the protozoa and helminths. The parasitic diseases are major causes of morbidity and mortality throughout the world, but strike the populations of the tropical and developing regions disproportionately. Plasmodium falciparum, the species that causes most cases of fatal malaria is a major cause of mortality worldwide. Substantial disease burden also results from numerous other protozoan and helminthic organisms. This article will focus primarily on those parasitic organisms that cause diseases with significant gastrointestinal manifestations.