Virus Research 103 (2004) 79–83A novel means of identifying the neuraminidase type of currentlycirculating human A(H1) influenza virusesAeron C. Hurt∗, Ian G. Barr, Naomi Komadina, Alan W. HampsonWHO Collaborating Centre for Reference and Research on Influenza, 45 Poplar Rd, Parkville, Melbourne, Vic. 3052, AustraliaAvailable online 9 April 2004AbstractWith the recent emergence and spread of influenza A(H1N2) viruses which appear to have arisen by reassortment of circulating A(H1N1)andA(H3N2)strains,thereisaneedinepidemiologicalstudiestodeterminetheneuraminidasetypeinordertodifferentiatebetweeninfluenzaA(H1N2) and A(H1N1) strains. A fluorescence-based neuraminidase enzyme inhibition assay that has been developed to screen influenzaviruses for potential resistance to the neuraminidase inhibitor drugs appears to be suitable for this purpose. When used with the neuraminidaseinhibitor zanamivir the assay was able to provide a positive predictive value of 93.5% for the identification of neuraminidase type N1 or N2.This assay enables a large number of influenza A viruses to be screened at low cost to determine relative levels of A(H1N2) or A(H1N1)viruses circulating in the population.© 2004 Elsevier B.V. All rights reserved.Keywords: Influenza; A(H1N2); A(H1N1); Neuraminidase inhibitors1. IntroductionInfluenza A subtypes A(H3N2) and A(H1N1) have co-circulated in humans worldwide since the reappearance ofA(H1N1) viruses in 1977 (Kendal et al., 1979; Stuart-Harriset al., 1985). Recently, reassortant influenza A viruses withan H1N2 antigenic composition subtype (PHLS, 2002)have been detected by surveillance programs in a numberof countries. Based on haemagglutination-inhibition assaysand sequence analysis these viruses contain an haemagglu-tinin (HA) component closely related to that of recentlycirculating human A(H1N1) viruses, and a neuraminidase(NA) component similar to that of contemporary humanA(H3N2) viruses. While genetic reassortment of influenzacan be readily achieved in the laboratory (Maassab andBryant, 1999) and has been found to occur naturally inanimals and birds (Marozin et al., 2002; Zhou et al., 1999),there have been few reported instances of viruses in whichthere had been genetic reassortment of internal genes (Xuet al., 1993; Couch et al., 1986; Young and Palese, 1979) orof the surface antigen genes (Li et al., 1992; Guo et al., 1992;∗Corresponding author. Tel.: +61-3-9389-1392;fax: +61-3-9389-1881.E-mail address: aeron hurt@csl.com.au (A.C. Hurt).Nishikawa and Sugiyama, 1983) between the A(H1N1) andA(H3N2) viruses infecting humans. One previous occasion,however, where surface antigen gene reassortment of thesesubtypes was detected was in China during 1988/1989where a small number of A(H1N2) viruses were isolatedfrom the human population (Guo et al., 1992; Li et al.,1992). Ongoing surveillance has indicated that the currentlycirculating A(H1N2) reassortant viruses are more numerousand more widespread than the strains reported from Chinain 1988/1989. Recently, viruses of this type have been iden-tified in Europe, USA and south-east Asia, and in the UKthey were more numerous than A(H1N1) strains during the2001/2002 season suggesting that A(H1N2) viruses maybecome established on a continuing basis in the humanpopulation.Prior to the recent identification of A(H1N2) strains, rou-tine laboratory studies of influenza viruses generally classi-fied the known circulating human influenza A subtypes onthe basis of HA type with the NA type usually being as-sumed. However, for epidemiological purposes it may nowbe important to identify NA type to distinguish betweenA(H1N1) and A(H1N2) strains.The haemagglutination-inhibition assay that is routinelyused for subtyping and antigenic characterisation of in-fluenza strains does not distinguish between A(H1N1) and0168-1702/$ – see front matter © 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.virusres.2004.02.017
