Why are parasite eggs bile stained?

Parasite eggs are often bile stained due to their passage through the host's digestive system, particularly in the liver and intestines where bile is produced. Bile, which contains bile salts and pigments like bilirubin, can adhere to the eggs as they are excreted in feces. This staining can aid in the identification of certain parasite species during microscopic examination, as the color difference helps differentiate them from non-parasitic material.