Strains of subsp. small colony (SC) type, the agent of contagious bovine pleuropneumonia (CBPP), were analysed with respect to the polymorphism of distribution of a newly discovered insertion element, IS1296, on the chromosome. Analysis of 64 strains isolated from Europe, Africa and Australia, including four vaccine strains and the type strain PG1, revealed ten different IS patterns, forming two main clusters. The European strains originated from outbreaks of CBPP in different countries, and from various other sources such as semen and preputial washings from cattle, lungs from goats and buffalo, and milk from sheep. They showed identical IS1296 patterns, except one strain which had an additional IS1296 element, but the pattern belonged to the same cluster. This shows that the strains from Europe form a clonal lineage. The strains originating from different geographical parts of the African continent and from Australia showed four closely related IS1296 patterns which belong to a separate cluster. This indicates that strains from Africa and Australia form a clonal lineage different from that of the European strains, suggesting that the sporadic cases of CBPP that have re-emerged in Europe almost 15 years after the last declared endemic case in 1967 arose from an established reservoir within Europe rather than being the result of repeated importation from Africa and Australia. While most strains from Africa and Australia had the same IS1296 pattern, all vaccine strains could be distinguished by an individual pattern. The type strain PG1 also had a particular IS1296 pattern which belongs to the cluster of the strains from Africa and Australia. The molecular definition of clonality of subsp. SC strains with IS1296 represents a rapid and reproducible method for subtyping and differentiation of vaccine strains. It permits at the present time the definition of two main clonal lines, one including the strains from the European continent and a second with strains from Africa and Australia.


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