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The Executive Committee of the International Committee on Taxonomy of Viruses (ICTV) has recently decided to modify the current definition of virus species (Code of Virus Classification and Nomenclature Rule 3.21) and will soon ask the full ICTV membership (189 voting members) to ratify the proposed controversial change. In this discussion paper, 14 senior virologists, including six Life members of the ICTV, compare the present and proposed new definition and recommend that the existing definition of virus species should be retained. Since the pros and cons of the proposal posted on the ICTV website are not widely consulted, the arguments are summarized here in order to reach a wider audience.

A proposal has been posted on the ICTV website (2011.001aG.N.v1.binomial_sp_names) to replace virus species names by non-Latinized binomial names consisting of the current italicized species name with the terminal word "virus" replaced by the italicized and non-capitalized genus name to which the species belongs. If implemented, the current italicized species name Measles virus, for instance, would become Measles morbillivirus while the current virus name measles virus and its abbreviation MeV would remain unchanged. The rationale for the proposed change is presented.

The fatty acid acylation of the cell-associated virus-specific proteins of mouse hepatitis virus (A 59-strain) was studied. 3H-palmitate label was associated with E2, one of the two virion glycoproteins and its intracellular precursor gp 150. A 110 K protein, the unglycosylated apoprotein of gp 150, accumulated by tunicamycin treatment, also incorporated radiolabeled palmitic acid. The addition of fatty acid to the MHV-A 59 E 2 protein is therefore not dependent on glycosylation.

Using gut sections from pigs infected with porcine epidemic diarrhea virus (strain CV 777) and ascitic fluid from cats which had succumbed to feline infectious peritonitis (FIP), a weak cross reaction was found by immunofluorescence. Its specificity was confirmed when detergent-treated purified CV 777 showed a prominent reaction with FIPV antibodies in ELISA; no reaction was obtained with intact virions, which indicated common determinants on an internal component of the particle. Antigenic cross-reactions at the nucleocapsid level were found in Western blot ELISA performed both ways (CV 777/FIPV antibodies; FIPV/CV 777 antibodies). In immunoprecipitation using [35S]methionine labelled FIPV, anti-CV 777 sera recognized exclusively the nucleocapsid protein. The significance of these findings for the classification of coronaviruses is discussed.