Real Dictionary

giardiasis in American English
an intestinal infection by a parasitic protozoan (Giardia lamblia) that may cause prolonged pain, diarrhea, etc.
noun: an intestinal disorder characterized by abdominal discomfort and prolonged, intermittent diarrhea, caused by the protozoan Giardia lamblia and contracted by drinking untreated water, as of streams or ponds, contaminated with the feces of infected animals

giardiasis in British English
noun: infection with the parasitic protozoan Giardia lamblia, which can cause severe diarrhoea