Freeze-drying foot-and-mouth disease virus antigens. I. Infectivity studies

The ability of foot-and-mouth disease virus strains type O1 BFS 1860 and type A22 IRQ 2464 to retain infectivity after freeze-drying with or without additives being made to virus suspensions was studied. The infectivity titres of freeze-dried antigens was assessed at intervals over a six month storage period at various temperatures and also after reconstitution to the liquid phase and storage with or without glycerination. Certain additive solutions were necessary to prevent degradation of virus during the freeze-drying procedure which reduced any loss of infectivity caused by storage of products at 4°C and 20°C. Additive solutions composed of 10% sucrose and 5% lactalbumin hydrolysate; 10% skimmed milk; 4% peptone and 1% gelatin; and 5% dextran, 1% sodium glutamate and 5% sucrose all prolonged the keeping qualities of virus at the elevated temperature of 37°C. The results indicate that short-term storage and shipment of freeze-dried foot-and-mouth disease virus antigens is possible without the need for refrigeration, thereby reducing transportation and storage costs. Reconstituted antigens survived better after glycerination and storage at −20° C than did non-glycerinated samples stored at 4°C.