Nephrology and Infectious Diseases

parasitic disease, in humans, any sickness that is caused by a parasite, an organism that lives in or on another organism (known as the host). Parasites usually benefit from such relationships, often at the expense of the host organisms. Parasites of humans include protozoans, helminths, and ectoparasites (organisms that live on the external surface of a host). They are responsible for many diseases and are transmitted to their hosts most often through the ingestion of contaminated food or water or through the bite of an arthropod (e.g., a fly or tick), which can act as an intermediate host and as a vector. (For information on parasitic diseases in animals, see animal disease.

Indeed, more than 3 billion people worldwide are infected by intestinal parasites or protozoans, and parasitic diseases are among the leading causes of deaths in humans globally. Epidemiological studies indicate that multiple factors influence a person’s risk of infection and the spread of parasitic disease, including parasite pathogenicity, host health, environment, and social conditions.