Volume 18, Number 10—October 2012
Letter
Rickettsia parkeri and Candidatus Rickettsia andeanae in Gulf Coast Ticks, Mississippi, USA
Table
PCR results for adult Rickettsia parkeri– and Candidatus Rickettsia andeanae–infected Gulf Coast ticks (Amblyomma maculatum) collected from 10 sites in Mississippi, USA, 2008–2010*
| Location (no. collection sites) | No. ticks | No. (%; 95% CI) SFG rompA | No. (%; 95% CI) R. parkeri only | No. (%; 95% CI) Candidatus R. andeanae only | Expected no. (%) co-infected ticks | No. (%; 95% CI) co-infected ticks |
|---|---|---|---|---|---|---|
| North (4) | 257 | 49 (19.1; 14.5–24.4)† | 48 (18.7; 14.1–24)‡ | 0§ | 0.19 (0.07) | 1 (0.4; 0–2.1)¶ |
| Central (1) | 38 | 4 (10.5; NA) | 1 (2.6; NA) | 2 (5.3; NA) | 0.16 (0.42) | 1 (2.6; NA) |
| South (5) | 403 | 75 (18.6; 14.9–22.8)† | 57 (14.1; 10.9–17.9)‡ | 8 (2.0; 0.9–3.9)§ | 2.99 (0.74) | 10 (2.5; 1.2–4.5)¶ |
| Total (10) | 698 | 128 (18.3; NA) | 106 (15.2; NA) | 10 (1.4; NA) | 3.65 (0.52) | 12 (1.7; NA) |
*The estimated value of co-infection caused by chance alone (E) was calculated by using the formula E = (a + b)(a + c) / (a + b + c + d) (5), where a = no. ticks infected with both Rickettsia species, b = no. ticks infected only with R. parkeri, c = no. ticks infected only with Candidatus R. andeanae, and d = no. ticks not infected with either Rickettsia species. SFG rompA, spotted fever group rickettsial outer membrane protein A gene. NA, not applicable.
†p = 0.9187.
‡p = 0.1275.
§p = 0.0257.
¶p = 0.0578 (comparison of prevalence from northern and southern sites only).
