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Table 1 Infection, dissemination, and transmission rates of mosquitoes infected with the German USUV Africa 2 strain

From: German Culex pipiens biotype molestus and Culex torrentium are vector-competent for Usutu virus

Blood meal virus titer (TCID50/ml)

Mosquito species

Dpi

Infection rate (%)

(95% CI)

Mean viral load bodies (viral copies/µl of total RNA)

Dissemination rate (%)

(95% CI)

Mean viral load legs plus wings (viral copies/µl of total RNA)

Transmission rate (%)

(95% CI)

High titer

107.4

Culex pipiens biotype molestusa

14

8/10 (80.0)

(44.4–97.5)

6.9 × 105

3/8 (37.5)

(8.5–75.5)

9.0 × 103

3/3 (100)

(29.2–100)

21

4/6 (66.7)

(22.3–95.7)

5.6 × 105

4/4 (100)

(39.7–100)

1.5 × 104

3/4 (75.0)

(19.4–99.4)

Cx. pipiens biotype molestusb

16

13/16 (81.3)

(54.4–96.0)

1.9 × 106

13/13 (100)

(75.3–100)

7.8 × 104

2/13 (15.4)

(1.9–45.4)

21

8/10 (80.0)

(44.4–97.5)

8.1 × 105

8/8 (100)

(63.1–100)

7.8 × 104

4/8 (50.0)

(15.7–84.3)

Aedes aegyptid

14

0/53 (0)

(0–6.7)

NA

NA

NA

NA

21

4/22 (18.2)

(5.2–40.3)

2.3 × 105

1/4 (25.0)

(0.6–80.6)

5.5 × 103

0/1 (0)

(0–97.5)

Low titer

105.1

Cx. pipiens biotype molestusa

14

2/36 (5.6)

(0.7–18.7)

1.2 × 102

0/2 (0)

(0–84.2)

NA

NA

21

1/19 (5.3)

(0.7–18.7)

5.4 × 101

0/1 (0)

(0–84.2)

NA

NA

Cx. torrentiumc

14

1/8 (12.5)

(0.3–52.7)

2.8 × 101

0/1 (0)

(0–97.5)

NA

NA

21

1/8 (12.5)

(0.3–52.7)

3.9 × 106

1/1 (100)

(2.5–100)

4.7 × 104

1/1 (100)

(2.5–100)

  1. Transmission rates include results from the saliva inoculation on Vero cells and from the RT-qPCRs of cell culture supernatants. All mosquitoes were incubated for 14/16 or 21 days. Absolute quantification of virus copies/µl of total RNA was performed via an RT-qPCR-based calibration curve
  2. CI confidence interval, dpi days post infection, NA not applicable
  3. aCx. pipiens biotype molestus laboratory colony from “Wendland,” Lower Saxony, Germany
  4. bCx. pipiens biotype molestus laboratory colony from Novi Sad, the Republic of Serbia
  5. cCx. torrentium field-collected colony near Berlin and Bonn, North Rhine-Westphalia, Germany
  6. dAe. aegypti laboratory colony from Malaysia (Bayer CropScience, Langenfeld, Germany)