Viral diseases in aquaculture

Infectious diseases pose one of the most significant threats to successful aquaculture. A number of serious viral diseases in fish are notifiable diseases listed in EU legislation as non-exotic diseases.

No efficient treatment or vaccines exist for these diseases and their control is thus by prevention of introduction and eradication by stamping-out in case of diseases outbreak. Due to close contact with surrounding water the inter-dependence between wild and farmed fish and between individual fish farms the epidemiology in aquaculture is challenging.  The vast majority of fish diseases are restricted to fish and pose no risk to handlers or consumers.

Koi Herpesvirus of the family Herpesviridae

Koi Herpesvirus Disease is a viral disease of common carpCyprinus carpio, including all its ornamental varieties such as koi, ghost koi etc. The virus is highly contagious and may cause up to 100% mortality. KHV has already caused severe fish losses to ornamental wholesalers, retailers and carp fishery owners and continues to pose a significant threat to anyone dealing with or keeping common carp.

As a notifiable disease there is a legal obligation to report any suspicion of a clinical outbreak of Koi Herpesvirus Disease to the Fish Health Inspectorate (FHI). If the disease is found to be present the FHI will advise on the most appropriate methods of control.

Koi Herpes Virus Disease information (FHI)

Viral haemorrhagic septicaemia virus (VHSV)

Viral Haemorrhagic Septicaemia Virus (VHSV) is an important fish virus that has caused several large scale fish kills in both fresh and saltwater fish in farmed and wild fish. Viral haemorrhagic septicaemia (VHS) is a highly infectious virus disease predominantly affecting rainbow trout (Oncorhynchus mykiss) in aquaculture.

The virus is an enveloped negative-stranded RNA virus belonging to the family Rhabdoviridae and the genus Novirhabdovirus. The virus can be divided into 4 distinct genotypes and 10 subtypes with different geographical occurrence, host range and infectivity patterns. VHSV have been isolated in the tempered Northern hemisphere, e.g. North America, Asia and Europe. The disease occurs endemically in the continental part of Europe, in Turkeyand in part of Finland. Occasionally outbreaks in farmed rainbow trout and turbot have occurred in Scandinavia and the British Isles. The North sea, Kattegat and the Baltic Seahouses endemically infected populations of wild fish. VHSV have been isolated from more than 82 different fish species. 

Information on Viral Haemorrhagic septicaemia virus (OIE)

Infectious haematopoietic necrosis virus(IHNV)

Infectious haematopoietic necrosis (IHN) is a viral disease affecting most species of salmonid fish. Caused by the rhabdovirus, infectious haematopoietic necrosis virus (IHNV), the principal clinical and economic consequences of IHN occur on farms rearing fry or juvenile rainbow trout in freshwater where acute outbreaks can result in very high mortality. However, both Pacific and Atlantic salmon reared in fresh water or sea water can be severely affected.

Infectious hematopoietic necrosis virus (IHNV), is a negative-sense single-stranded RNA virus that is a member of the familyRhabdoviridaeand the genusNovirhabdovirus,like VHSV. IHNV is present inUSAandCanada, inJapanandKoreaand in the continental part ofEurope.

Both VHS and IHN are listed as non-exotic diseases in the EU and are therefore watched closely by the European Community Reference Laboratory for Fish Diseases, and by National Reference Laboratories.

Information on Infectious Haematopoietic Necrosis Virus (OIE).

Results of global Koi Herpes Virus questionnaire 2009

EPIZONE and viral diseases in aquaculture

Diagnostics and Epidemiology

  • Quantitative data on the de facto occurrence of VHS and IHN in Europeare collated, and linked with geographical coordinates of findings and the implementation of GIS in European aquaculture
  • A database, , have been established for collecting data on pathogen pathogens (VHSV and IHNV) to be used for viral characterization and molecular epidemiology
  • More than 100 VHSV and IHNV isolates have been collected from all over Europeand their full length glycoprotein gene of 1500 BP sequenced according to standard operating procedures delivered by EPIZONE partners
  • Know-how on implementation of GIS for aquaculture have been gathered by several EPIZONE partners and the system implemented in some of the laboratories.
  • Molecular diagnostics methods for identification of KHV have been distributed and discussed. Final recommendations on diagnostic methods (PCR and Real time PCR) will be given for international use
  • Two training courses on serological techniques for detection of antibodies against VHSV and IHNV in fish were conducted
  • An inter-laboratory proficiency test on serological techniques for detection of antibodies in trout against VHS and IHN was organized. Result have been compiled and reported.
  • Serological techniques for detection of antibodies against VHSV and IHNV in fish have been validated. Final recommendation for use internationally await data on how to interpret data collected from natural outbreaks in fish farms
  • VHSV, IHNV and KHV outbreak cases have been and are currently traced.
  • KHV inEuropeand abroad: epidemiology, molecular characteristics, and clinical pathology have been collated and reported, published.