Table 1.
Bacterial load and transmission efficiency for O. montanainfected in artificial feeders containing defibrinated rat blood infected with Y. pestis at a concentration of 1.495 to 4.7 × 109 cfu/ml
| Time point (hours after infectious feed) and mouse number | No. of infected fleas fed on naive mouse (total no. fed of total no. exposed to mouse) | Median (range) bacterial load per infected flea fed on sentinel mouse (cfu per flea) | Transmission from flea to mouse | Estimated transmission efficiency range, %‡ |
|---|---|---|---|---|
| 3 h | ND†§ | |||
| 1 | 14 (ND* of 14) | 2.38 × 105 (5.15 × 104 to 1.12 × 106) | No | ND† |
| 2 | 12 (ND* of 12) | 3.45 × 105 (1.12 × 105 to 6.50 × 105) | No | ND† |
| 3 | 13 (ND* of 13) | 3.10 × 105 (5.60 × 104 to 6.10 × 105) | No | ND† |
| 4 | 9 (ND* of 9) | 2.50 × 105 (1.40 × 104 to 1.60 × 106) | No | ND† |
| 5 | 10 (ND* of 10) | 2.78 × 105 (6.95 × 104 to 8.30 × 105) | No | ND† |
| 24 h | 10.0 (9.3–10.6) | |||
| 1 | 11 (12 of 12) | 1.69 × 106 (2.65 × 105 to 3.91 × 106) | Yes | 9.1–100.0 |
| 2 | 9 (10 of 11) | 4.45 × 105 (2.44 × 105 to 2.86 × 106) | Yes | 11.1–100.0 |
| 3 | 10 (10 of 11) | 1.11 × 106 (5.04 × 104 to 2.44 × 106) | Yes | 11.1–100.0 |
| 4 | 10 (10 of 11) | 1.63 × 106 (3.25 × 105 to 3.12 × 106) | Yes | 11.1–100.0 |
| 5 | 10 (10 of 10) | 4.95 × 105 (4.25 × 102 to 3.67 × 106) | Yes | 10.0–100.0 |
| 6 | 10 (10 of 10) | 1.31 × 106 (1.15 × 104 to 5.13 × 106) | Yes¶ | 10.0–100.0 |
| 48 h | 8.7 (7.7–9.6) | |||
| 1 | 11 (11 of 13) | 5.80 × 105 (8.75 × 102 to 3.26 × 106) | Yes | 9.1–100.0 |
| 2 | 13 (13 of 13) | 8.85 × 105 (1.15 × 104 to 1.61 × 106) | Yes | 7.1–100.0 |
| 3 | 13 (13 of 13) | 1.10 × 106 (1.00 × 103 to 2.64 × 106) | Yes | 7.1–100.0 |
| 4 | 10 (10 of 11) | 1.95 × 105 (9.25 × 102 to 3.05 × 106) | Yes | 10.0–100.0 |
| 5 | 11 (11 of 12) | 3.85 × 105 (1.75 × 104 to 4.47 × 106) | Yes | 9.1–100.0 |
| 6 | 12 (12 of 12) | 3.75 × 105 (1.00 × 103 to 4.96 × 106) | Yes | 8.3–100.0 |
| 72 h | 9.2 (8.0–10.4) | |||
| 1 | 9 (10 of 12) | 1.85 × 104 (3.00 × 102 to 4.20 × 105) | Yes | 11.1–100.0 |
| 2 | 11 (11 of 12) | 1.55 × 105 (2.80 × 104 to 1.76 × 106) | Yes | 9.1–100.0 |
| 3 | 12 (12 of 12) | 8.20 × 105 (2.60 × 104 to 1.19 × 106) | Yes | 8.3–100.0 |
| 4 | 12 (12 of 12) | 6.78 × 104 (7.5 × 101 to 1.76 × 106) | Yes | 8.3–100.0 |
| 5 | 12 (13 of 13) | 3.90 × 105 (3.00 × 103 to 8.70 × 105) | Yes | 8.3–100.0 |
| 6 | 10 (11 of 12) | 5.95 × 104 (4.00 × 103 to 1.41 × 106) | Yes | 10.0–100.0 |
| 96 h | 7.7 (3.5–11.8) | |||
| 1 | 12 (12 of 12) | 1.64 × 105 (4.30 × 104 to 5.25 × 105) | Yes | 8.3–100.0 |
| 2 | 11 (12 of 12) | 4.05 × 104 (1.00 × 103 to 5.65 × 105) | Yes | 9.1–100.0 |
| 3 | 12 (12 of 12) | 4.20 × 104 (2.50 × 103 to 2.50 × 105) | Yes | 8.3–100.0 |
| 4 | 10 (11 of 11) | 2.33 × 104 (2.50 × 101 to 1.07 × 105) | Yes | 10.0–100.0 |
| 5 | 9 (11 of 11) | 2.20 × 104 (5.00 × 101 to 1.90 × 105) | Yes¶ | 11.1–10.0 |
| 6 | 9 (9 of 10) | 3.65 × 104 (1.00 × 102 to 3.15 × 105) | No | 0.0–0.0 |
For each time point, the mean minimum transmission efficiency is shown in boldface. ND*, feeding success could not be determined for this time point because the bloodmeal from the mouse could not be differentiated from the previous infectious bloodmeal. ND†, number of fleas that fed could not be determined.
‡Mean minimum transmission efficiency (95% confidence interval) for each time point.
§Transmission observed previously in two of four mice exposed during pilot study. During a pilot study following methods explained within this report, two naïve mice were exposed to potentially infectious fleas 3 h after feeding on artificial feeders containing rabbit blood infected with CO96-3188 (7.6 × 108 and 3.63 × 108 cfu/ml) or infected rat blood (4.14 × 108 and 5.8 × 109 cfu/ml). Transmission was not observed for either of the mice exposed to fleas fed on infected rabbit blood, but both mice exposed to infected fleas fed on rat blood became infected.
¶Day 21 titers by passive hemagglutination and inhibition tests: 1:2,048 for 24 h mouse 6 and 1:512 for 96 h mouse 5.