The development of tools for diagnosis of tularemia and typing of Francisella tularensis^†

Rapid development of molecular techniques for the diagnosis of infections and typing of microbes has been seen during the last 10 years. The present review exemplifies this development by presenting the work of the authors and others regarding techniques for the diagnosis of tularemia and typing of Francisella tularensis. The lack of rapid and safe methods for the laboratory diagnosis of tularemia was the rationale behind the development of methods for the direct detection of F. tularensis in clinical specimens. Today, detection by polymerase chain reaction has become an important adjunct to clinical decisions for the early diagnosis of tularemia. The elucidation of the epidemiology and epizootology of the disease has been hampered by the lack of suitable methods. During recent years several DNA-based methods that allow rapid identification of the four F. tularensis subspecies, including differentiation of strains of the two clinically important subspecies, the highly virulent type A strains and less virulent type B strains, have been developed. Since F. tularensis strains of any origin exhibit highly conserved genomic sequences, the availability of extensive genome sequence data was a prerequisite for the development of a typing system that allows discrimination of individual isolates. The most discriminatory method is based on multiple-locus variable-number tandem repeat analysis (MLVA) and uses highly variable parts of the F. tularensis genome. The method will be an important tool in future studies of the molecular epidemiology of tularemia.