The relationship between serum antibody titres and protection from foot and mouth disease in pigs after oil emulsion vaccination.

In trials performed in Brazil, England and Germany, 765 pigs were challenged at one, three to four or 17 weeks after vaccination and their sera were titrated by macrocolour, microcolour or microcytopathic effects neutralization tests. Using O1 virus strains and challenge intervals of three to four weeks, significant correlations (P less than 0.01) were demonstrated between protection and serum neutralizing titres although the titres corresponding to given levels of protection varied with the titration method employed. The protective capacity of antiserum was confirmed by passive antibody transfer experiments. Retrospective analysis of 49 challenge tests showed that when the macrocolour test was employed, a group mean (n = 8) serum titre of 1.74 log10 SN50 corresponded with five out of eight (or more) protected from challenge in 92% of cases. The possibility of using serum titres as an alternative to challenge for oil emulsion vaccine potency tests is discussed.