Surveillance of fish pathogens during complex disease outbreak in RAS by high-throughput microfluidic qPCR: 21st International Conference on Diseases of Fish and Shellfish

Juliane Sørensen, Giulia Zarantonello, Alejandra Villamil Alonso, Simon Brøndgaard Madsen, Argelia Cuenca, Lone Madsen, Tine Moesgaard Iburg, Niccolò Vendramin

Publikation: KonferencebidragKonferenceabstrakt til konferenceForskningpeer review

Abstract

Introduction: Piscine orthoreovirus genotype 3 (PRV-3) was first reported in Denmark in 2017 in association with disease outbreaks with high mortality in rainbow trout (Oncorhynchus mykiss). In 2017-2019, we conducted a surveillance program for PRV-3 in Danish farms, revealing that PRV-3 is widespread. Importantly, disease outbreaks with mortality were only observed in recirculating aquaculture systems, and primarily during the winter. The effect of water temperature has been confirmed experimentally: When comparing PRV-3 infected fish at different temperatures, it was shown that virus levels increased at low temperatures (5°C) compared to higher temperatures (12° and 18°C) as well as a tendency towards worse heart pathology. Field investigations highlight presence of other pathogens during PRV-3 associated disease outbreaks.In order to deepen the understanding of PRV-3 associated disease, we developed a high-throughput qPCR method (Fluidigm) for simultaneous detection of multiple pathogens. Field samples were collected from a farm with history of PRV-3 associated disease.Methodology: From March to September 2022, monthly sampling was performed from 10 fish from the same batch. Sample collection consisted of 1) heart, spleen and kidney in RNAlater, 2) gills in RNAlater, 3) blood, 4) kidney swab, 5) heart, spleen and kidney in medium, and 6) water. Swabs and tissue were tested by gold standard methods for virology and bacteriology, and tissue collected in RNAlater along with filters from water were tested by standard qPCR and Fluidigm.Additionally, production data was recorded during the seven months, including weight, feeding, disease outbreaks, treatments, and water quality parameters.Results: Bacteriological examination revealed recurrent presence of Yersinia ruckerii and occasionally Flavobacterium psychrophilum. Additionally, PRV-3 was detected by qPCR in connection with significantly increased mortality. The disease outbreak lasted five weeks with an overall mortality yielding more than 2 ton. A comprehensive diagnostic overview combined with the production data will be presented.Conclusions: PRV-3 associated disease outbreaks in RAS are complex, and sustained by co-infections and possibly stressors induced by farm practices. Interestingly, mortality increased significantly after fish transfer, and was not mitigated by water treatment with salt. Additionally, PRV-3 can be detected by qPCR before disease outbreaks in the prodromal phase.
OriginalsprogEngelsk
Publikationsdato2023
Antal sider1
StatusUdgivet - 2023
Udgivet eksterntJa

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