Abstract
Introduction: In recent years, Infectious Hematopoietic Necrosis has spread in Europe, with outbreaks occurring in previously disease-free countries such as Denmark and Finland. The strain of IHNv responsible for outbreaks in Denmark has been isolated from infected fish in follow-up sampling at water temperatures close to 20°C. The IHNv genotypes U and M can replicate in cell culture and induce disease in rainbow trout, Oncorhynchus mykiss, and sockeye salmon, O. nerka, at temperature higher than 14°C. This feature has never been demonstrated for European IHNv strains, which belong to genotype E.
Methodology: A selection of IHNv strains, including the Danish and some Italian isolates, were analysed for their replication fitness at different temperatures of incubation. The panel of isolates was subjected to titration by end-point dilutions assays on EPC cell monolayers at 15°C, 20°C, 22°C and 25°C. Cytopathic effects were monitored daily and titers were calculated according to the Spearman-Karber formula daily up to seven days post inoculation. Based on the results, a subset of IHNv strains was selected to be tested through an in vivo challenge in order to confirm the influence of water temperature on their pathogenicity in rainbow trout. Finally whole genome sequencing was performed to look for genetic markers of temperature adaptations.
Results: The titers yielded in the in vitro testing showed a high degree of variability of IHNv strains in relation to their sensitivity to temperature. Danish isolate and some Italian strains replicated without significant reduction when incubated at 22°C and could replicate even at 25°C that was considered a restrictive condition for this virus. Notably, the temperature tolerance appeared linked to the environment of origin rather than to the year of isolation. The in vivo experiment is on going.
Conclusions: A wider temperature range for IHNv strains belonging to genotype E has been demonstrated in vitro and will be soon confirmed in vivo. Based on results obtained a change of paradigm in the surveillance of IHN should be considered also at the regulatory level.
Funded by the Italian Ministry of Health IZSVe RC 013/19 and by the Aquaexcel 3.0 TNA programme.
Methodology: A selection of IHNv strains, including the Danish and some Italian isolates, were analysed for their replication fitness at different temperatures of incubation. The panel of isolates was subjected to titration by end-point dilutions assays on EPC cell monolayers at 15°C, 20°C, 22°C and 25°C. Cytopathic effects were monitored daily and titers were calculated according to the Spearman-Karber formula daily up to seven days post inoculation. Based on the results, a subset of IHNv strains was selected to be tested through an in vivo challenge in order to confirm the influence of water temperature on their pathogenicity in rainbow trout. Finally whole genome sequencing was performed to look for genetic markers of temperature adaptations.
Results: The titers yielded in the in vitro testing showed a high degree of variability of IHNv strains in relation to their sensitivity to temperature. Danish isolate and some Italian strains replicated without significant reduction when incubated at 22°C and could replicate even at 25°C that was considered a restrictive condition for this virus. Notably, the temperature tolerance appeared linked to the environment of origin rather than to the year of isolation. The in vivo experiment is on going.
Conclusions: A wider temperature range for IHNv strains belonging to genotype E has been demonstrated in vitro and will be soon confirmed in vivo. Based on results obtained a change of paradigm in the surveillance of IHN should be considered also at the regulatory level.
Funded by the Italian Ministry of Health IZSVe RC 013/19 and by the Aquaexcel 3.0 TNA programme.
| Original language | English |
|---|---|
| Title of host publication | 21st International Conference on Diseases of Fish and Shellfish: Abstract Book |
| Number of pages | 1 |
| Publisher | European Association of Fish Pathologists |
| Publication date | 2023 |
| Pages | 64-64 |
| Publication status | Published - 2023 |
| Event | 21st International Conference on Diseases of Fish and Shellfish - P&J Live Aberdeen, Aberdeen, United Kingdom Duration: 11 Sept 2023 → 14 Sept 2023 Conference number: 21 |
Conference
| Conference | 21st International Conference on Diseases of Fish and Shellfish |
|---|---|
| Number | 21 |
| Location | P&J Live Aberdeen |
| Country/Territory | United Kingdom |
| City | Aberdeen |
| Period | 11/09/2023 → 14/09/2023 |