The Immunological Enigma of Human Giardiasis

Abstract

Giardiasis is a major cause of enteritis in humans worldwide. The disease is caused by two very distinct genetic groups (referred to as assemblages A and B) of the species complex Giardia duodenalis. The trophozoites stage colonizes the duodenum and jejunum of the small intestine and may cause a broad variety of disease outcomes that reach from asymptomatic carriers to patients with acute or chronic severe gastrointestinal complaints. Studies in immunocompromised patients imply that antibody-mediated acquired immune responses and a minimal T cell availability are of major importance for parasite clearance. These mechanisms likely play in concert with natural resistance mechanisms that are present in the intestinal mucosa. In humans no sterile immunity is acquired after infection. Epidemiological studies further suggest passive protection from symptomatic giardiasis in breastfed children. However, there is a fundamental lack of knowledge about the underlying immunological mechanisms of human giardiasis.