Giardiasis Organisms in Man Organisms in External Environment

Interest in the intestinal parasitic protozoa that comprise the genus Giardia has increased considerably in the last quarter century. One reason for this has been the gradual recognition that Giardia organisms in humans are potentially pathogenic: while most frequently they occur in the absence of symptoms, they are sometimes capable of causing a mild, self-limiting intestinal syndrome, and even more rarely are responsible for serious disease. In the past the prevailing medical opinion was that Giardia were commensal parasites of humans and that their ability to cause disease was questionable (1). Giardia currently are the intestinal parasites most frequently identified in public health laboratories in this country (2) and in the United Kingdom (3).