Quantities of Yersinia pestis in Fleas (Siphonaptera: Pulicidae, Ceratophyllidae, and Hystrichopsyllidae) Collected from Areas of Known or Suspected Plague Activity

We used a quantitative competitive polymerase chain reaction (PCR) (QC-PCR) to determine bacterial loads in 669 fleas collected in areas of confirmed and suspected plague epizootics. Fleas were collected out of rodent burrows (67.9%) and off of captured animals (24.1%) and rodent carcasses (8.1%). An initial PCR screening assay indicated that 12.1% (81/669) of all fleas were positive for Yersinia pestis.</it> Fleas collected from burrows had significantly lower (?</it>2 = 264.9, P</it> < 0.0001) infection rates (6.8%) but significantly higher (Student t</it>-test, P</it> < 0.0001) bacterial loads (mean = 105.6 Y. pestis</it> per flea) than fleas collected off of rodent carcasses (infection rate = 92.6%; mean bacterial load = 104.8 Y. pestis</it> per flea). None of the fleas collected off of captured animals were positive for Y. pestis</it> by PCR, although seven of the 176 captured animals were serologically positive for Y. pestis.</it>