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Induction of Antibody and Mechanisms
of Neutralisation
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Following infection, it has been demonstrated that neutralising antibody and protection against the original challenge virus may persist for the effective lifetime of some cattle (e.g., 5.5 years). The duration of immunity under these circumstances may owe something to the development of the carrier state in cattle (up to 30 months), in which trace amounts of virus perhaps continue to stimulate the immune response well after recovery from the initial infection. These observations and the success of vaccines such as live poliomyelitis stimulated considerable work in the 1950s and 1960s on the development of attenuated FMD vaccines. However, clinical disease was occasionally observed in animals vaccinated during laboratory and field trials and the programmes were eventually abandoned.
Very little is known about the immune response of sheep and goats to infection and the duration of immunity.
The duration of immunity of pigs following infection is considerably shorter than with cattle and appears to be between 3 and 6 months at best. It is perhaps significant that the carrier state has not been reported with domestic pigs.
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