Neospora caninum is an invalid species name: an evaluation of facts and statements.

An evaluation of both the formal requirements of the International Rules of Zoological Nomenclature and the scientific reasons for the description of new genera and species shows that the name Neospora caninum is a nomen nudum. The only characteristic criteria for discriminating between the previously described species Hammondia heydorni and the proposed new species N. caninum (i.e. the lack of a parasitophorous vacuole) has been shown to be wrong in many publications. Furthermore, absolutely no criteria were presented as to why a new genus (i.e. Neospora) should be established besides the already existing genera Hammondia, Toxoplasma and Isospora. In addition, recent transmission experiments show that an oocyst isolate (from the faeces of dogs) is morphologically indistinguishable from H. heydorni [synonymous with Isospora bigemina - small form, Isospora heydorni (Tadros and Laarman 1976) and H. heydorni (Tadros and Laarman 1976) Dubey 1977] and is almost identical with respect to molecular biological features with the NC-1 strain of N. caninum.