Table 2.
Proportion O. montana infected with Y. pestis and bacterial loads in fleas after feeding on artificial feeders containing defibrinated rat blood spiked with 1.1 × 109–3.1 × 109 cfu/ml Y. pestis (CO96-3188), taking a second bloodmeal 2 d postinfection from a mouse immunized with an attenuated Y. pestis strain (CO96-3188(Pgm−)) or from an age-matched naive mouse, and subsequently being held alive for 3 d
| Immune status and mouse no. | Mouse titer | Percent fleas infected after feeding on mouse (no. infected/no, fed on mouse) | Median (range) cfu per flea in fleas with a quantifiable bacterial load |
|---|---|---|---|
| Immunized mice | |||
| 1 | 1:128 | 94.7% (18/19) | 1.26 × 105 (3.10 × 103 to 1.95 × 106); n = 18 |
| 2 | 1:512 | 100% (10/10) | 8.93 × 104 (5.45 × 103 to 1.81 × 106); n = 10 |
| 3 | 1:512 | 100% (10/10) | 1.92 × 105 (5.50 × 103 to 1.80 × 106); n = 22 |
| 4 | 1:512 | 96.6% (28/29) | 1.08 × 105 (3.65 × 103 to 6.75 × 105); n = 28 |
| 5 | 1:512 | 100% (33/33) | 6.48 × 104 (1.47 × 103 to 8.05 × 105); n = 32 |
| 6 | 1:1024 | 95.5% (21/22) | 4.75 × 104 (4.20 × 103 to 1.87 × 106); n = 21 |
| 7 | 1:1024 | 100% (30/30) | 9.50 × 104 (6.00 × 102 to 1.05 × 106); n = 30 |
| Naive mice | |||
| 1 | 0 | 100% (21/21) | 5.25 × 104 (4.70 × 102 to 1.95 × 106); n = 21 |
| 2 | 0 | 100% (16/16) | 5.85 × 104 (1.32 × 103 to 1.52 × 106); n = 15 |
| 3 | 0 | 100% (20/20) | 7.20 × 104 (4.45 × 103 to 1.85 × 105); n = 20 |
| 4 | 0 | 100% (22/22) | 5.28 × 104 (2.00 × 103 to 9.25 × 105); n = 22 |
| 5 | 0 | 100% (15/15) | 4.03 × 104 (5.20 × 103 to 5.15 × 105); n = 14 |
| 6 | 0 | 100% (26/26) | 1.01 × 105 (3.45 × 103 to 3.95 × 105); n = 26 |
| 7 | 0 | 100% (31/31) | 3.45 × 104 (1.14 × 103 to 3.95 × 105); n = 30 |