Infectious haematopoietic necrosis (IHN)

Infectious haematopoietic necrosis (IHN) is a viral infection that primarily infects fish in the salmon family, but other fish species can also be susceptible to IHN.

The first outbreak of Infectious haematopoietic necrosis (IHN) was reported in Denmark in May 2021. The whole territory of Denmark remained approved as IHN free by the European Union until December 2021, and Denmark handled outbreaks of IHN until December 2021 according to the EU Animal Health Law (2016/429) and Commission Delegated Regulation (EU) 2020/689 to maintain the IHN-free status. As a result, the DVFA imposed restrictions on infected farms and farms under suspicion. The restrictions included movement restrictions, requirements of cleaning, disinfection and fallowing, and restriction zones covering the whole water catchment area around the infected farm.

The Danish fish farm industry bore the entire financial burden of infection controls to prevent the potential spread of IHN. The restrictions had major financial consequences to the industry, and consequently the industry asked the DVFA to abandon the Danish IHN-free status. The IHN-free status was withdrawn on 10 December 2021. Before the IHN-free status was withdrawn, the DVFA declared 28 fish farms IHN-free compartments. These farms are considered IHN-free regardsless of Denmark's IHN status.

In total, infection with IHN was found in eight fish farms and three put-and-take lakes.

In 2022 there were 19 confirmed outbreaks of Infectious haematopoietic necrosis in Denmark. 10 confirmed outbreaks were in saltwater fish farms and 9 confirmed outbreaks were in freshwater fish farms. Most outbreaks were epidemiologically linked by hydrodynamic conditions or by movement of fish, and none of the outbreaks was confirmed in the IHN-free compartments. The DVFA has a national surveillance programme for IHN in accordance with Annex VI, Part III of Regulation (EU) 2020/689. An infected establishment may re-enter the surveillance programme for IHN provided that the DVFA has approved that the establishment has been emptied, cleaned, disinfected and fallowed for 6 weeks.