Freeze-drying foot-and-mouth disease virus antigens. II. For use in the ELISA.

Live and inactivated preparations of foot-and-mouth disease virus strains 01 BFS 1860 and A22 IRQ 24/64 were freeze-dried in the presence or absence of additive solutions and assessed for their reactivity by ELISA at intervals over a six month storage period at various temperatures and also after reconstitution and subsequent storage with or without glycerination. The type specificity of all antigen preparations was maintained throughout the study period and the potency of antigens, judged by titration in ELISA, remained constant during the freeze-drying procedure and throughout subsequent storage at -20 degrees C and 4 degrees C with or without additives having been made to virus suspensions prior to freeze-drying. This was also the case with antigens reconstituted and stored at either -20 degrees C with glycerol or at 4 degrees C without glycerol. Certain additive solutions were necessary, however, to preserve the activity of antigens stored at the elevated temperature of 37 degrees C. The reactivity of all freeze-dried antigens was not unduly affected in the liquid-phase blocking ELISA using bovine convalescent antisera of each of the seven serotypes of foot-and-mouth disease virus and known negative, non-immune bovine sera. The results suggest that shipment and long-term storage of freeze-dried foot-and-mouth disease virus antigens is possible for use in the ELISA in the absence of refrigeration. This has attractive advantages for reducing both shipment and storage costs of antigens and for the development of ELISA kits for the diagnosis of foot-and-mouth disease virus.