Evidence of TiLV infection in tilapia hatcheries from 2012 to 2017 reveals probable global spread of the disease

Recent outbreaks of tilapia lake virus (TiLV) in farmed tilapia in Thailand were the first indication of spread of the virus to the Southeast Asia region. Here we further investigate TiLV infection of archived and newly collected fish samples obtained from Thai hatcheries from 2012 to 2017. Fertilized eggs, yolk-sac larvae, fries, and fingerlings were tested for the TiLV using an established semi-nested RT-PCR assay. The results revealed that the majority of the tested samples were TiLV positive, including our earliest preserved samples collected in year 2012. DNA sequence analysis of representative amplified products also confirmed the presence of TiLV. Since the discovery of TiLV in 2012, over 40 countries worldwide have imported tilapia fry and fingerlings, and some may have been unaware of risk that they might be infected with TiLV. Thus, if they have not already done so, we recommend that countries that have imported tilapia for aquaculture carry out surveillance studies for its presence and also add TiLV to their import quarantine inspection list.