Innocuity testing of foot-and-mouth disease vaccines. II. Aziridine-inactivated antigen produced in baby hamster kidney cells

Formaldehyde inactivation of foot-and-mouth disease virus. Conditions for the preparation of safe vaccine

The inactivation of foot-and-mouth disease virus by formaldehyde was studied under different conditions, both as free virus and (as in routine vaccine production) after adsorption of the virus to aluminium hydroxide gel (alhydrogel). In the latter case infectivity was monitored after elution of the virus from the gel by isopycnic ultracentrifugation of the virus-alhydrogel mixture in CsCl. By this method good virus recoveries were obtained. Adsorption of the virus to alhydrogel (without formaldehyde) did not reduce infectivity significantly. Both adsorbed and non-absorbed virus lost infectivity at a rate of about one log10 per day (at pH 8.5, 25 degrees C--no formaldehyde). Kinetics of formaldehyde inactivation of adsorbed and non-adsorbed virus were also identical, with a fast reduction in the initial phase (in case of O1 and A10-virus approximately one log10/hour). After this initial phase inactivation became linear and rather slow (for O1 and A10-virus 0.2 log10/hour). No "tailing-off" was observed. Under standard conditions (0.04 per cent formaldehyde, pH 8.5, 25 degrees C) CD-virus was inactivated approximately 1.5 times faster than O1 and A10-virus. At 4 degrees C the inactivation of the three strains continued at about one log10/day. Increased lactalbumin hydrolysate concentrations reduced the inactivation rate, especially at the formaldehyde concentration of 0.02 per cent, which was originally applied. Quaternary amines like Tris strongly inhibited formaldehyde activity. These findings might explain some data of others who observed "tailing off". Analysis of formaldehyde inactivated antigen by SDS-PAGE and electrofocusing showed that extensive cross-linking occurs especially of VP1, probably with other virus proteins but also with non-virus proteins from the medium. VP2 and VP3 are less affected. Cross-linking was enhanced when the virus had been adsorbed to alhydrogel during inactivation. Progressive cross-linking was observed during storage of the vaccine at 4 degrees C, which also indicated that inactivation continued at this temperature. These data show that formaldehyde inactivated adsorbate vaccines can be safe.

Innocuity testing of foot-and-mouth disease vaccines. I. Formaldehyde-inactivated alhydrogel vaccines

Conditions that contribute to efficient innocuity testing of formaldehyde (FA)-inactivated alhydrogel vaccines were investigated. Under our conditions good yields of 146S antigen were obtained if the antigen was eluted by potassium phosphate buffer (pH 7.4) and concentrated by ultrafiltration. Non-inactivated virus added to the vaccine and adsorbed overnight could be recovered if residual FA was removed from the vaccine by washing the gel thoroughly with Frenkel culture medium before the addition of the virus. It was shown that the presence of high concentrations of inactivated virus in the concentrated eluate could prevent the detection of small amounts infectious virus in intradermolingual tests in cattle. This interference phenomenon was not found if (more susceptible) monolayers of foetal calf thyroid cells were used for the detection of virus. Intensive pre-washing of the gel with Frenkel culture medium, elution with potassium phosphate, concentration by ultrafiltration and the use of thyroid cells for the final detection of surviving virus is therefore advised for safety testing.