Environmental surveillance of vectorborne ...

Background: Arboviral diseases pose significant economic and social threats, especially in less economically developed countries (LEDCs) where monitoring disease circulation is often challenging. Moreover, many cities in LEDCs are experiencing rapid growth with predominantly unplanned informal settlement, which can facilitate the spread of these diseases. In this study, we aimed to explore environmental surveillance (ES) in a non-sewered setting as a complement to syndromic surveillance in Mozambique.

Methods: Water samples were collected from nine points along the Infulene River (n = 66) in the Maputo region of Mozambique over an eight-month period, from February to September 2023. Samples were concentrated using polyethylene glycol, and the presence of arboviruses (Dengue (DENV), Chikungunya (CHIKV), West Nile (WNV), and Usutu (USUV) virus) was determined by RT-qPCR.

Findings: DENV was detected in 82% (54/66) of the samples, with a median concentration of 2·2 x 105 copies/L (cp/L) [5·2 x 104 - 5·5 x 105]. CHIKV was detectable in 98% (65/66) of the samples, with a median concentration of 3·5 x 105 cp/L (Nsp1 gene [5·8 x 104 - 6·5 x 105], and E1 gene [1·5 x 105 - 1·2 x 106]), whereas USUV was detected in 6% (4/66) of the samples at a median concentration of 0 cp/L [0 - 0]. WNV was not detected throughout the study. The prevalence and concentration of each virus varied across sampling points and dates.

Interpretation: Our study demonstrated the efficacy of ES as a tool for assessing the epidemiological status of arboviruses in Mozambique, where a sewered system is unavailable. Consequently, ES should be expanded from polio surveillance to include other targets in LEDCs.