Free-living amoebae act as a reservoir for rickettsia bug

Due to the high prevalence of Piscirickettsia salmonis in Chilean salmon farming, some researchers have hypothesised that the pathogen may have unknown environmental reservoirs, reports Fish Farming Expert's Chilean sister site, Salmonexpert.cl.

This is coupled with the fact that it is very likely that faced with stressful environmental factors, the bacteria - which causes salmon rickettsial septicaemia (SRS) - will seek refuge in niches that facilitate their survival, replication, and transmission.

Based on the above, Chilean scientists from the Laboratory of Genetics and Molecular Immunology of the Pontifical Catholic University of Valparaíso (PUCV) recently published a study in which they discovered that free-living amoebae could act as reservoirs and vectors.

Two species

Specifically, they evaluated two amoeba species, Acanthamoeba castellanii and Vannella sp., and were able to demonstrate that P. salmonis can be internalised, replicated, and released by both species. Furthermore, the pathogen showed upregulation of its Dot/Icm secretion system, essential for intracellular replication, during this process.

“While Vannella sp. showed pathogen-induced lysis (disintegration of the cell - editor) after 72 hours, A. castellanii maintained the bacteria more stably. Our findings indicate that A. castellanii acts as a reservoir and vector of P. salmonis, which could contribute to the persistence and spread of this pathogen in aquatic environments,” the authors stated.

The authors noted that this better understanding of the pathogen's life cycle has implications for the development of better disease control strategies.

Read the full study titled “Free-living amoebae and their role in Piscirickettsia salmonis transmission in Chilean Salmon aquaculture: insights from in vitro and in vivo studies”, here.