Examining the vector-host-pathogen interface with quantitative molecular tools.

We developed PCR assays to detect and quantitate Yersinia pestis, the bacterial agent of plague, in flea vector and mammalian host tissues. Bacterial numbers in fleas, fleabite sites, and infected lymph nodes were determined using real-time PCR with primers and probes for a gene target on a multi-copy plasmid specific to Y. pestis. Tissue-matched standard curves used to determine absolute bacterial numbers in unknown samples were linear over at least five orders of magnitude. The methods were applied to studies of transmission of Y. pestis by the rat flea Xenopsylla cheopis, but should be generally useful to investigate the transmission dynamics of any arthropod-borne disease.