Table 1.
Flea infection status, observed transmission events, and estimated transmission efficiency of individual fleas 24 h after feeding on blood containing a target concentration of 103–109 cfu/ml Y. pestis
| Target concentration of Y. pestis | Concentration of Y. pestis (cfu/ml) used in flea feed, range | Median bacterial load (range) of infected fleas that fed on naïve mice (cfu/flea)a | % of infected fleas that fed (no. of infected/no. of fed) | No. of mice infected (total no. of exposed) | Estimated transmission efficiency (%) (95% CI)b |
|---|---|---|---|---|---|
| 1×103 | 1.6×103–3.9×103 | 28 (10–2.5×102), n=20 | 28.0 (23/82) | 0 (9) | 0.0 (0.0, 13.7) |
| 1×104 | 2.0×104–3.3×104 | 2.0×102 (10–3.5×103), n=82 | 91.7 (88/96) | 0 (10) | 0.0 (0.0, 3.6) |
| 1×105 | 2.3×105–3.0×105 | 9.2×102 (15–2.1×104), n=71 | 85.2 (75/88) | 0 (10) | 0.0 (0.0, 4.2) |
| 1×106 | 2.2×106–2.7×106 | 2.0×103 (10–1.8×105), n=84 | 93.7 (89/95) | 0 (10) | 0.0 (0.0, 3.6) |
| 1×107 | 2.0×107–4.1×107 | 1.1×104 (20–1.4×106), n=89 | 96.8 (90/93) | 1 (10) | 1.1 (0.1, 5.4) |
| 1×108 | 2.3×108–3.4×108 | 2.9×105 (40–3.1×106), n=99 | 100.0 (100/100) | 5 (10) | 6.3 (2.4, 14.2) |
| 1×109 | 1.7×109–3.4×109 | 1.0×106 (1.9×103–1.0×107), n=92 | 98.9 (92/93) | 9 (10) | 18.5 (9.6, 41.1) |
a
Calculated from fleas with≥10 cfu. Individual fleas were excluded if nonspecific growth impeded enumeration of plates.
b
Calculated using maximum likelihood estimation (MLE) method. Results expressed as maximum likelihood of transmission per infected flea.