Molecular identification of new picornaviruses and characterization of a proposed enterovirus 73 serotype

Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Mailstop G-17, Atlanta, GA 30333, USA 1 Viral and Rickettsial Diseases Laboratory, California Department of Health Services, Berkeley, CA 94704, USA 2 Department of Laboratories, Directorate General of Health Affairs, Ministry of Health, 113 Muscat, Oman 3 Author for correspondence: Steven Oberste. Fax +1 404 639 4011. e-mail soberste{at}cdc.gov Enteroviruses (EV) have traditionally been identified by using serotype-specific antisera in a virus-neutralization test. Three EV strains isolated in California, USA, in 1955, 1964 and 1978, and a 1995 Oman isolate, were found to be antigenically related to one another; however, the strains were not neutralized by standard EV typing antisera, suggesting that they may represent a new EV serotype. The isolates were characterized genetically by RT–PCR coupled with amplicon sequencing and comparison to a database of enterovirus nucleotide sequences. The strains were 75·3 to 87·2% identical to one another in complete VP1 nucleotide sequence, but no more than 68% identical in sequence to the prototype strain of any EV serotype. Their complete capsid sequences were closely related to one another, but only distantly related to those of any EV prototype strain. The California and Oman isolates were most closely related to members of EV cluster B, suggesting that they are unclassified members (i.e. a new serotype) of cluster B. The complete genome sequence was determined for one isolate, CA55-1988, and the predicted polyprotein sequence was 86·5 to 89·2% identical to those of other cluster B EV and 56·7 to 61·9% identical to the polyprotein sequences of EV belonging to other clusters. Isolation of this new EV serotype from samples obtained on two continents and over a period of 40 years suggests continued circulation over a wide geographical area. In keeping with standard picornavirus nomenclature, we propose that this new serotype be named ‘enterovirus 73’ (EV73).