Original: The names for the human parasite Giardia duodenalis, Giardia lamblia and Giardia intestinalis are all in common current use despite the potential for confusion that this has created.
Simplified: Giardia lamblia (synonymous with Lamblia intestinalis and Giardia duodenalis) is a flagellated protozoan parasite that infects the gastrointestinal tract and causes giardiasis. Giardia affects humans, but is also one of the most common parasites infecting cats, dogs and birds.