Investigation of Tilapia (Oreochromis niloticus) Mortality Events Targeting Tilapia Lake Virus Disease (TiLVD) in Bangladesh.

Background: Tilapia lake virus (TiLV) is an emerging threat to the global tilapia industry. In early 2017, FAO declared that Bangladesh was in a high-risk zone of TiLV disease (TiLVD) spread.

Objective: Considering the current scenario, the present work was designed to investigate the occurrence of TiLV in cultured Nile tilapia (Oreochromis niloticus) causing TiLVD in Bangladesh.

Methods: In this study, several unusual tilapia mortality incidences were investigated. A total of 102 pooled organ samples of 102 tilapia fish were collected from 34 ponds of 25 farms in the regions of 12 Upazilas in Bangladesh from May to October 2019. As a part of the classical approach, histopathological analysis was performed. For molecular identification, both conventional and real-time PCR were used as diagnostic tools to identify TiLV in farm-raised Nile tilapia.

Results: A total of 12 representative organ samples did not show any pathognomonic lesions related to TiLV infection in histopathological analysis. Conventional and real-time PCR assays yielded negative results for TiLV.

Conclusions: In our investigation, no trace of TiLV was detected in the studied samples. A large-scale study involving a broader range of samples collected across Bangladesh, along with the application of a viral metagenomics approach, could provide valuable insights into the unusual mortalities of tilapia in the country.