Selection of vaccine strains of foot and mouth disease virus for use in southern Africa.

In the countries of Southern Africa, types SAT 1, SAT 2 and SAT 3 (SAT: Southern African Territories) of foot and mouth disease (FMD) virus are the most widely represented, especially the SAT 2 virus. Since 1982, examinations have been conducted on 139 isolates of these virus types. Other viruses, types O and A, have been detected in the north of this area. The typing and sub-typing of viruses with the complement fixation (CF) test can be improved by using panels of monoclonal antibodies (MAbs), which provide an accurate antigenic profile of a new strain. A total of 33 SAT 2 strains have been investigated using MAbs, and the results enable the classification of viruses into groups presenting the same profile. The author presents comparisons of isolates and vaccine viruses using conventional methods of serotyping--CF and virus neutralisation (VN) tests--as well as profiling the isolates using MAbs. Both manners of analysis provide information on the relationships between the viruses. The CF and VN tests give details on how animals responded against a particular isolate and how this antibody response would recognise another isolate; from this, the serological relationships can be proposed with respect to how different isolates might induce a humoral immune response. With MAb profiling, details of antigenic relationships between the isolates are obtained, enabling the identification of individual epitopic variations. These analyses can provide the potential to place different isolates into 'antigenic' groups. When compared with vaccine viruses, one can attempt to identify the vaccine virus with the closest profile to the isolate group. Immunological analysis (e.g. using the CF tests employed in this paper) can provide further information on the relationship between a particular vaccine and an antigenic group identified by MAb profiling. Of course, this MAb profiling can provide essential information in a very short time, which is of particular benefit in an emergency situation. Confirmation of the conclusions from the profiling would then be forthcoming through the serological analyses. Such combined analyses offer a more extensive identification of antigenic and immunogenic relationships between FMD virus isolates, as well as between isolates and vaccine viruses.