Aeromonas hydrophila as an environmental indicator to detect TiLV-infected tilapia under coinfection threat

As an emerging infectious agent threatening freshwater ecosystems and tilapia aquaculture, tilapia lake virus (TiLV) has expanded its geographical range over last five years. Seeking a way to alleviate loss of tilapia production caused by TiLV is an urgent need for commercial aquaculture. Recently, Aeromonas hydrophila (AH) was found to be concurrent with TiLV causing serious issues. However, our understanding of how coinfection of AH and TiLV impact on disease transmission dynamics remains limited, particularly in real farming ecosystems, where difficulty of direct experimentation makes inference challenging. Here we applied epidemiological models to fit mortality data of tilapia single- or co-infected with TiLV and AH to estimate key transmission parameters that govern virus-bacteria interactions among infection states. Dose–response analysis was performed to assess the effects of AH concentration on TiLV disease transmissibility and mortality. Results showed that basic reproduction number (R0) for TiLV transmission in population that infected with TiLV followed by higher load of AH could be reached ~11. Our dose-response model reveals that AH concentration in fish pond can be a key environmental indicator to drive epidemiology-based measure as well as to assess exacerbating mortality risk of TiLV-infected tilapia under coinfection. The model may therefore be useful for guiding the future development of control measures from an epidemiological perspective to mitigate the impact of TiLV disease on tilapia.