Table 1.
Proportion X. cheopis infected with Y. pestis and bacterial loads in fleas after feeding on artificial feeders containing defibrinated rat blood spiked with 1.4 × 109−7.4 × 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 | 97.5% (39/40) | 5.80 × 104 (6.15 × 102 to 2.37 × 106); n = 35 |
| 2 | 1:256 | 88.5% (23/26) | 2.18 × 105 (1.50 × 103 to 1.83 × 106); n = 22 |
| 3 | 1:512 | 82.4% (14/17) | 1.70 × 105 (1.33 × 103 to 1.44 × 106); n = 14 |
| 4 | 1:512 | 87.5% (14/16) | 4.05 × 105 (1.47 × 103 to 1.89 × 106); n = 13 |
| 5 | 1:512 | 90.5% (19/21) | 3.65 × 105 (4.86 × 102 to 1.76 × 106); n = 19 |
| 6 | 1:1024 | 73.3% (11/15) | 2.17 × 105 (1.02 × 104 to 1.87 × 106); n = 11 |
| 7 | 1:1024 | 100% (19/19) | 1.54 × 106 (9.05 × 104 to 3.86 × 106); n = 19 |
| 8 | 1:1024 | 84.6% (33/39) | 5.05 × 104 (6.70 × 102 to 1.34 × 106); n = 30 |
| 9 | 1:1024 | 92.9% (39/42) | 1.89 × 105 (4.75 × 102 to 1.48 × 106); n = 39 |
| 10 | 1:1024 | 83.8% (31/37) | 2.75 × 104 (3.55 × 102 to 1.68 × 106); n = 27 |
| 11 | 1:2048 | 96.2% (25/26) | 1.08 × 106 (1.16 × 104 to 3.01 × 106); n = 24 |
| Naive mice | |||
| 1 | 0 | 83.3% (10/12) | 5.58 × 105 (1.45 × 104 to 1.28 × 106); n = 10 |
| 2 | 0 | 94.4% (17/18) | 2.70 × 105 (3.90 × 102 to 1.58 × 106); n = 17 |
| 3 | 0 | 87.5% (14/16) | 4.28 × 105 (7.05 × 103 to 1.28 × 106); n = 14 |
| 4 | 0 | 100% (25/25) | 6.10 × 105 (4.45 × 104 to 2.07 × 106); n = 25 |
| 5 | 0 | 100% (22/22) | 4.60 × 105 (8.55 × 102 to 1.95 × 106); n = 22 |
| 6 | 0 | 94.4% (17/18) | 1.00 × 106 (1.77 × 105 to 1.63 × 106); n = 17 |
| 7 | 0 | 90.0% (18/20) | 7.60 × 105 (1.66 × 104 to 3.05 × 106); n = 18 |
| 8 | 0 | 100% (17/17) | 6.50 × 105 (1.09 × 103 to 2.43 × 106); n = 17 |
| 9 | 0 | 92.9% (39/42) | 5.60 × 104 (3.90 × 102 to 2.68 × 106); n = 37 |
| 10 | 0 | 85.7% (30/35) | 7.45 × 104 (3.50 × 102 to 1.22 × 106); n = 28 |
| 11 | 0 | 82.2% (37/45) | 8.30 × 104 (1.46 × 103 to 1.20 × 106); n = 35 |
| 12 | 0 | 83.3% (35/42) | 3.80 × 104 (4.05 × 102 to 6.95 × 105); n = 29 |