How long has giardia been around?

Giardia, a genus of protozoan parasites, has been around for millions of years. Fossil evidence suggests that Giardia-like organisms may have existed as far back as 20 million years ago. It continues to be a significant cause of gastrointestinal illness in humans and animals today. The specific species affecting humans, Giardia intestinalis, has been recognized since the early 19th century.