Cryptosporidium tyzzeri and Cryptosporidium pestis: which name is valid?

The dispute on the validity of Cryptosporidium pestis and Cryptosporidium tyzzeri origins from the uncertainty on the identity of Cryptosporidium parvum described by Tyzzer in 1912 and the interpretation of the Principal of Priority of the International Code of Zoological Nomenclature (ICZN). Using a rigid interpretation of the Principal of Priority, one researcher proposed to rename C. parvum as C. pestis and retain C. parvum for Cryptosporidium mouse genotype I on the basis that Tyzzer was probably describing mouse genotype I. However, the ICZN clearly states that the Principle of Priority is to be used to promote stability and is not intended to upset a long-accepted name. Because mice are known to be naturally infected with C. parvum, and the 1985 taxonomic re-description of C. parvum for bovine and human isolates is accepted by almost all Cryptosporidium researchers, the prevailing name C. parvum for the species infective to calves and humans must be retained to avoid confusion. The designation of C. tyzzeri for the mouse genotype I brings further clarity to the taxonomy of Cryptosporidium spp. in humans, cattle, and domestic mice.