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Production Flow Chart
Inactivation of FMD by BEI
Virus Containment
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Commercially available FMD vaccines are based upon inactivated whole virus
particles, usually grown in either BHK-21 cells or the hamster embryo
cell line NIL-2 (Favre et al.,
1975). Attenuated strains of FMDV have been used as live vaccines
in the past (Mowat, 1964),
but these vaccines have now fallen into disuse due to their inadequate
attenuation and propensity to revert to virulence. During antigen production
temperature and pH have to be closely controlled because of thermal instability
and the low tolerance of the virus to pH conditions outside the range
7.0-8.0. Whole virus particle (146S) content is critical to the potency
of the final product (Pay and
Hingley, 1992), and measurement of 146S is used for vaccine formulation
calculations. VP1 is sensitive to protease degradation (Cavanagh
et al., 1977), which can result in a loss of immunogenicity of the
inactivated antigen (Wild and
Brown, 1967). This is an important consideration during virus production
when the uncontrolled release of cellular proteases can damage the antigenicity
of the virion.
Raw materials of biological origin used in the manufacture of vaccines should be shown to be free of extraneous agents. Vaccines are prepared in closed, sterile production systems based on large stainless steel fermenter-type tanks. Suspension cultures are infected with the virus and the culture maintained until all of the cells are dead. After this, the virus is harvested, filtered to remove debris and held for inactivation. Because of the economic importance of FMD, all work is carried out in officially approved special containment facilities which prevent the possibility of live virus escaping to the atmosphere.
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