<i>Y</i>. <i>pestis</i> frequently localizes to the esophagus of <i>X</i>. <i>cheopis</i> following an infectious blood meal of rat or guinea pig blood.

<p>(A) 11–29 mixed-sex <i>X</i>. <i>cheopis</i> fleas (with or without PIER) were dissected 24 hours after ingesting infected blood from 1 of the 4 rodent sources. Digestive tracts were scored for the presence or absence of GFP+ bacteria in the esophagus and partially digested red blood in the proventriculus that obscured visualization of the proventricular spines. Representative bright field (left) and fluorescence (right) microscopy images of dissected <i>X</i>. <i>cheopis</i> foreguts are shown. (B) Percentage of fleas with <i>Y</i>. <i>pestis</i> (GFP+) in the esophagus; (C) Percentage of fleas with incompletely digested blood meal material in the proventriculus that obscured visualization of the proventricular spines. Proventricular spines autofluoresce yellow-orange. Numbers below the x-axis indicate the number of fleas positive/the total number of infected fleas dissected. The cumulative mean of 2–4 independent experiments are shown. *p < 0.001 compared to infectious mouse blood group by chi-square test with Bonferonni post-test. Scale bar = 50 μm.