High throughput estimates of Wolbachia, Zika and chikungunya infection in Aedes aegypti by near-infrared spectroscopy to improve arbovirus surveillance

Abstract

Deployment of Wolbachia to mitigate dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) transmission is ongoing in 12 countries. One way to assess the efficacy of Wolbachia releases is to determine invasion rates within the wild population of Aedes aegypti following their release. Herein we evaluated the accuracy, sensitivity and specificity of the Near Infrared Spectroscopy (NIRS) in estimating the time post death, ZIKV-, CHIKV-, and Wolbachia-infection in trapped dead female Ae. aegypti mosquitoes over a period of 7 days. Regardless of the infection type, time post-death of mosquitoes was accurately predicted into four categories (fresh, 1 day old, 2-4 days old and 5-7 days old). Overall accuracies of 93.2, 97 and 90.3% were observed when NIRS was used to detect ZIKV, CHIKV and Wolbachia in dead Ae. aegypti female mosquitoes indicating NIRS could be potentially applied as a rapid and cost-effective arbovirus surveillance tool. However, field data is required to demonstrate the full capacity of NIRS for detecting these infections under field conditions.

Fig. 1. Death prediction model by days post death and infection status.

Results from training data (a) and results from testing data (b). Monte Carlo simulations were performed using a 75%/25% training/testing split to validate the model. Infection status including CHIKV (red), ZIKV (purple), Wolbachia (blue), and uninfected controls (green) is presented in both panels. Box and whisker plots follow the standard convention where the box represents the range between quartiles 1 and 3, while the whiskers represent maximum and minimum excluding outliers. Outliers are defined as either Q1 − 1.5 × IQR or Q3 + 1.5 × IQR.

Fig. 2. Changes in raw spectra of A. aegypti mosquitoes.

CHIKV-infected and uninfected mosquitoes at day 0 and day 7 post death (a), ZIKV-infected and uninfected mosquitoes at day 0 and day 7 post death (b), and Wolbachia-infected and uninfected mosquitoes at day 0 and day 7 post death (c).

Fig. 3. Prediction accuracy (test set) for detecting infection in A. aegypti mosquitoes.

Mosquitoes infected with CHIKV (a), Wolbachia (b), and ZIKV (c) vs. uninfected mosquitoes. Box and whisker plots follow the standard convention where the box represents the range between quartiles 1 and 3, while the whiskers represent maximum and minimum excluding outliers. Outliers are defined as either Q1 − 1.5*IQR or Q3 + 1.5*IQR.

Fig. 4. Prediction scores of uninfected and uninfected mosquitoes for 0 days post death and 7 days post death.

Infection scores are shown for CHIKV (a), Wolbachia (b), and ZIKV (c), and each dot represents one individual. The Y-axis represents the prediction scores on a continuous scale prior to categorizing into >0.5 (predicted infected) and ≤0.5 (predicted uninfected).