Tilapia lake virus disease (TiLVD) (also known as syncytial hepatitis of tilapia-SHT) is a newly emerging viral disease of tilapia caused by tilapia lake virus (TiLV), a novel Orthomyxo-like virus (Ferguson et al. 2014; Eyngor et al. 2014; Bacharach et al. 2016; DelPozo et al. 2017; NACA, 2017; OIE, 2017). Occurrence of the disease was officially documented earliest in Ecuador and Israel in 2013 and 2014, respectively (Ferguson et al. 2014; Eyngor et al. 2014). The virus, however, is believed to have been responsible for massive mortalities in farmed tilapia in Israel since 2009 (Eyngor et al. 2014). Infection of TiLV was later reported from Colombia (Kembou Tsofack et al. 2017) and Egypt (Fathi et al. 2017) and most recently from Thailand (Dong et al. 2017a; Surachetpong et al. 2017). Natural disease outbreaks result in variable mortalities ranging from 9.2 to 90%, with tilapia fingerlings and juveniles being more vulnerable than larger fish (Ferguson et al. 2014; Fathi et al. 2017; Dong et al. 2017a; Surachetpong et al. 2017). Unlike other viral diseases of tilapia, TiLV appears to be widely spread and so may be present in many countries where it is not yet recognized.

Recently, we released a warning of TiLV in Thailand including an improved semi-nested RT-PCR method for rapid detection. The Fish Health Platform in Centex, BIOTEC/Mahidol University has obtained positive test results for TiLV from other countries in Asia where it has not yet been reported. Further, the majority of our archived samples collected from previous disease outbreaks in several tilapia hatcheries in Thailand during 2012-2017 have tested positive for TiLV, indicating the presence of TiLV in Thailand even before the virus became known to science in 2013.

The origin of the disease is currently unknown, but many countries have been translocating tilapia fry/fingerlings prior to and even after the description of TiLV. Based on records we could obtain about such translocations, we have prepared a map that contains a list of 5 countries with confirmed reports of TiLV infections and a list of 43 other countries that we believe have imported tilapia that may have been infected with TiLV. We hope that widespread surveillance for TiLV in the Tilapia industry and in translocated fish will help reduce the impact and spread of this disease.