Classification Cryptosporidium is a unicellular parasite, that infects epithelial cells of the gastroenteric and respiratory tract. In young calves it mainly appears between the first and third week of life. It is a protozoa of the phylum of apicomplexa and the class of sporozoea. Due to its similarity in life cycle, it was formally classified as part of the Coccidea. Currently it has the stat...