Quantification of spirochete burden in Borrelia burgdorferi infected ticks fed on OspA immunized mice by 16S rRNA RT real-time PCR

Katharina Ornstein (1, 2), Alan G. Barbour (2)

(1) Department of Medical Microbiology, Dermatology and Infectious Diseases, Lund University, Lund, Sweden.
(2) Department of Microbiology and Molecular Genetics and Medicine, University of California, Irvine College of Medicine, Irvine, CA, USA.

Email: katharina.ornstein@infek.lu.se

We have designed a sensitive method for detection and quantification of Lyme disease and relapsing fever Borrelia spirochetes by 16S rRNA RT real-time PCR using a specific probe (TaqMan). The available Lyme disease OspA vaccine protects mice from Borrelia burgdorferi infection by OspA antibodies killing off the spirochetes in the tick gut. Our aim was to study and monitor the change in spirochete burden in borrelia infected ticks after feeding on mice immunized with a single dose OspA two month earlier. Borrelia infected ticks fed on OspA immunized mice had either cleared off their spirochetes or a very small amount of borrelia 16S rRNA (approximately less than 10 spirochetes per tick) could be detected in the tick by 16S rRNA RT real-time PCR. Infected ticks fed on none immunized mice had an estimated spirochete burden of 100 times higher than infected unfed ticks (103 and 105, respectively). Borrelia RNA could be detected in none immunized mice but not in OspA immunized mice after challenge with borrelia infected ticks. This result show that the spirochete burden in B. burdgdorferi infected ticks fed on single dose OspA immunized mice is remarkably reduced and that a single dose OspA can protect mice from contracting B. burdgdorferi from infected ticks 2 month after vaccination. Monitoring of changes in spirochete burden in B. burgdorferi ticks can successfully be done by 16S rRNA RT real-time PCR.

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