Combined nucleic acid assays for diagnosis of A19 vaccine-caused human brucellosis.

Brucellosis is a common zoonotic disease caused by Brucella and is an epidemic worldwide. Currently, the most effective way to prevent and control the disease in animals is to use live, attenuated vaccines A19 strain. In China, the live attenuated Brucella abortus vaccine is widely used in animal immunization. To detect and confirm which vaccine strain caused the infection, we developed a new method to distinguish A19 strain from non-A19 strains. By comparing the genomic sequences of A19 and wild strain 2,308, we identified signature sequences that are unique to A19. A PCR assay for specific A19 identification was developed based on the genetic marker ABC transporter permease gene. Samples from the outbreak patients were then analysed using the universal quantitative PCR and A19-specific PCR assay, and the A19 strain was successfully identified in them, providing pathogenic evidence of the vaccine-derived infection outbreak. This combined A19-specific differential diagnosis method can provide a means to distinguish between animal vaccine immunization, natural infection and human infection by the vaccine strain. This strategy also has applications in diagnosis, epidemiology and surveillance of A19-related immunizations or infections.