Improving heat stability of haemagglutinating antigens for avian influenza

The increasing demand for avian influenza diagnostic reagents worldwide, has included requests for significant supplies of product to developing countries. Difficulties in dispatching to remote areas and tropical countries are a major concern to suppliers, international organisations and donors as delays in forwarding parcels often result in storage at non-optimal or inadequate temperatures results in loss in titre and thus wastage of resources. In this study we demonstrate that the heat stability of avian influenza haemagglutination inhibition antigens of the H5, H7 and H9 subtype following 14 days of exposure to 37°C and 45°C is significantly increased by adding D-(+)-Trehalose to the freshly prepared antigen. Increased stability was detected both for freeze-dried antigens over an extended period of 6 months and also in heat exposed antigens that were then stored at +4C for up to 35 days post reconstitution.