How susceptible are rainbow trout and brown trout to infection with tilapia lake virus at increased water temperature – Is there any potential for climate change driven host jump?

Abstract

In poikilothermic animals like fish, outbreaks of pathogen-related diseases are closely related with the temperature of the surrounding environment. Many salmonid fish species are thermally sensitive and therefore are especially endangered by thermal stress and habitat loss caused by increasing temperatures during summer heat waves. We hypothesized that combining thermal stress and the presence of a novel viral pathogen from for example aquaculture effluents may result in a potential host jump of the pathogen. This could be one of the mechanisms leading to an increased vulnerability of salmonids to a novel disease. Tilapia lake virus (TiLV) could be considered as one of the most dangerous emerging viruses affecting warm water aquaculture of Nile tilapia. This pathogen has a global reach with a yet to be defined host range. The aim of this study was to assess the potential for TiLV to infect salmonid hosts in a range of water temperatures which can be reached during summer heatwaves in Continental Europe. For this, it was established that TiLV can replicate in vitro in salmonid cells over the wide temperature range of 15 °C to 25 °C. The susceptibility of rainbow trout and brown trout juveniles to infection with TiLV was investigated in infection trials based on cohabitation and on intraperitoneal injection of the virus in elevated water temperatures of 20 °C and 25 °C. These experiments showed that if the ability of the virus to enter the organism is considered, the susceptibility of rainbow and brown trout to the virus is low. The exposure of these salmonids to the virus by cohabitation did not lead to high virus loads in the liver and brain. However, the permissivity, i.e. the ability of the virus to replicate in the fish body, is high, because IP-injections of TiLV led to a high virus replication in internal organs. Therefore, TiLV could have some pathogenic potential in salmonids which might be exacerbated by climate change and anthropogenic activities.