Piscine orthoreovirus genotype 3b (PRV-3b) in rainbow trout Oncorhynchus mykiss farmed in Peru

Piscine orthoreovirus (PRV) infection is widespread in the global salmonid aquaculture industry. This study aimed to investigate the presence or absence of PRV genotypes in rainbow trout Oncorhynchus mykiss farmed in Peru. The Peruvian National Authority for Fisheries and Aquaculture Health and Safety (SANIPES) carried out a disease surveillance plan between October and December 2023. In this context, 48 fish exhibiting clinical signs of circulatory disorders were screened for PRV genotypes. Quantitative PCR analysis showed that 12.5% of pools (2 out of 16) were positive for PRV-3 but negative for PRV-1 and PRV-2. The CT value was 23.48 for tissue pool no. 14 and 27.03 for tissue pool no. 15, but both pools contained tissues from fish farmed in Lake Titicaca. Concurrently, Weissella ceti was isolated from these fish. PRV-3-positive fish showed mild mononuclear myocarditis in the ventricular spongy layer (2 out of 6). The sequences of the S1 and M2 segments of the Peruvian isolates belonged to the PRV-3 gene group, subgroup PRV-3b. These sequences showed 100% identity with the Danish PRV-3b isolates, suggesting possible European origin. Overall, the results of this study confirm, for the first time, the presence of PRV-3b in the Peruvian rainbow trout farming industry and highlight the need to implement biosecurity measures for the import of embryonic eggs to minimize the risk of pathogen entry and dissemination in the industry, as well as a permanent epidemiological surveillance plan for all PRV genotypes.