(Science: protozoa) genus of flagellate protozoans which are free swimming parasites that inhabits the gastrointestinal tract of vertebrates and causes gastroenteritis in man (giardia lamblia).
The cells have a large disc or sucker on their anterior ventral surfaces, by which they attach to the intestinal mucosa. The attachment of the disc is very strong and can prevent peristaltic clearing. This can result in acute or chronic diarrhoea especially in children, although infection, which occurs by ingestion of spores, may be asymptomatic. The disease is termed giardiasis or lambliasis.