Susceptibility of Indian major carp Labeo rohita to tilapia lake virus

Abstract

Infection with tilapia lake virus (TiLV) has been reported to cause large-scale mortalities in tilapines, the second most cultured species in the world. Interestingly, in polyculture system, although tilapia is reported to suffer high mortalities due to infection with TiLV, the disease has not been reported in co-cultured species. Nevertheless, natural host switch is a frequent phenomenon among viruses of lower vertebrates, especially fish viruses. To analyse the risk of spread of virus to new host species, it is essential to study the susceptibility of other fish species to the virus. In India, tilapia is generally cultured along with Indian major carps (IMC) in polyculture systems. Keeping this in consideration, in the present study, the susceptibility of rohu Labeo rohita, an important major carp, to TiLV was evaluated following experimental infection and it was compared with a susceptible host, i.e. Nile tilapia Oreochromis niloticus. The results revealed that the experimentally-infected rohu did not exhibit any clinical signs and mortality. On the other hand, in tilapia, a cumulative mortality of 80% was observed during the experimental period of 12 days with clinical signs typical of TiLV disease. In histopathological examination of liver, one of the main target organ of TiLV, typical syncytial cells were observed in tilapia whereas, no alterations were observed in rohu. Importantly, in rohu, the virus copy numbers in liver and intestine were almost negligible (<3 virus copies) and did not increase with time course, and the virus was not detected in brain at any time point by qRT-PCR. However, in tilapia, there was significant increase in virus copy numbers in liver, brain as well as intestine up to 6 days post-infection (dpi), and thereafter, a marginal decrease was observed up to 12 dpi. Therefore, based on lack of clinical signs and mortality pattern, histopathological findings and results of qRT-PCR, it can be concluded that TiLV did not replicate in rohu, and it is not susceptible to infection with TiLV.