Characterisation of Recent Human-Like H1 (δ-Cluster) Swine Influenza Virus Isolates

23 December 2011, at 12:00am

There is considerable genetic and antigenic heterogeneity among δ-cluster H1 swine influenza virus (SIV) isolates, according to researchers at Newport Laboratories in the US.

Genetic and antigenic properties of contemporary human-like H1 (δ-cluster) SIV isolates circulating in US swine herds were investigated by Ben M. Hause, MS, and colleagues at Newport Laboratories in Worthington, Minnesota, and reported in a paper published in the Journal of Swine Health and Production.

The haemagglutinin genes from 37 δ-cluster SIV isolates were fully sequenced. The isolates were antigenically categorised using a high throughput serum neutralisation (HTSN) assay incorporating antisera generated against the four currently circulating clusters of H1 SIV and a commercial vaccine containing a δ-cluster SIV isolate. A subset of the isolates were further characterised with the haemagglutination inhibition (HI) assay using H1 SIV antisera.

Genetic analysis of the haemagglutinin gene of 2009-2010 δ-cluster isolates identified five distinct sub-clusters with 97 per cent to 100 per cent sequence similarity within sub-clusters and 95 per cent to 97 per cent similarity between sub-clusters.

Antisera generated against SIV representing α, β and γ clusters failed to neutralise any of 37 δ-cluster viruses in an HTSN assay. Only 46 per cent of the δ-cluster isolates were neutralised by at least one δ-cluster antiserum.

Haemagglutination inhibition assay results on a sub-set of 13 2010 isolates were in good agreement with the HTSN assay, with 38 per cent of the isolates positive (HI titre >40) to at least one δ-cluster antiserum. There was no measurable antibody titre to antiserum generated from the commercial vaccine or the 13 isolates.

Significant genetic and antigenic heterogeneity exists among δ-cluster H1 SIV isolates, conclude Hause and co-authors, suggesting that either multiple representatives of this cluster may be required in commercial vaccines or that herd-specific vaccines may be required to protect swine from influenza virus infection.


Hause B.M., T.A. Oleson, D.L. Stine, R.F. Bey and R.R. Simonson. 2011. Genetic and antigenic characterization of recent human-like H1 (δ-cluster) swine influenza virus isolates. J Swine Health Prod. 19(5):268–276.

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December 2011