Infectious pancreatic necrosis virus

Infectious pancreatic necrosis disease virus (IPNV) causes infectious pancreatic necrosis disease (IPN) in fish – most disease has been documented in young, farmed salmonid fish. IPNV's virion has a hexagonal profile without envelopes, and a diameter of approximately 60 nm. To date, only two other Aquabirnavirus are listed by the International Committee on Taxonomy of Viruses (ICTV), the Tellina virus and the Yellowtail ascites virus. Segment A contains the genetic information necessary to produce the polyprotein, consisting of genes pVP2, VP3, VP4, and VP5. Segment A also contains virulence factors. Segment B contains genetic information for creating an RNA-dependent RNA polymerase enzyme made of VP1. == Microbiology ==

Structure Infectious pancreatic necrosis virus is 65-70 nm in diameter, Its buoyant density is 1.33 grams per cm3. The shell is made up of 120 subunits of a coat protein. VP2 (54 kDa) VP4 converts pre-VP2 to capsid protein VP2, while VP5 is likely related to gene expression. Replication A single cycle of replication of IPNV, which takes place in the cytoplasm, takes 16–20 hours at 22 degrees Celsius. This falls within the optimal temperature for replication, which is between 20 and 24 degrees Celsius. Replication is slow or completely halted in cells above 24 degrees Celsius. == History ==

Discovery In 1940, the first pancreatic necrosis symptom was found in Canada's farmed Atlantic salmon, Salvelinus fontinalis, resulting in significant losses of juvenile trout. A study has shown that the strain found in Europe has distinct antigenic properties compared to the VR229 strain. Infectious pancreatic necrosis (IPN) was categorized as a notifiable disease between 1991 and 2008 in Norway. Using Dr Wolf's technique previously mentioned, Dr Sano isolated the virus from fish cells and identified that IPNV caused the fish's symptoms. == Host interactions ==

Transmission Predominantly infecting young salmonids, infectious pancreatic necrosis virus (IPNV) outbreaks occur both in fingerlings and parr (freshwater stage) and later as post-smolts weeks after transfer to seawater. These carriers are typically life-long spreaders, posing a danger to other healthy fish either through recurrence of the disease within the carrier under stress, or as sources of horizontal and vertical transmission. Myh9’s conservation across many of the hosts of IPNV is speculated to contribute to the extensive host range of the virus. This has been observed in Brook trout and Rainbow trout, but has yet to be proven in Atlantic salmon, although it is suspected. Long distance waterborne transmission IPNV may also be possible as the virus remains viable in marine, freshwater and sediments for several months. Once introduced, the virus is stable across a wide range of pH (3-9) and temperature, making it resistant to many disinfectants. Long distance transmission raises risks of farm to wild transmission as has already been observed during the infection of resident fish downstream of a farm experiencing an outbreak. Other sources of transmission of the virus include wild birds, farmed escapes, and transport between farms (infected eggs, feed, equipment, inventory) alongside waterborne and within fish groups (vertical and horizontal transmission) discussed above. In addition to carriers and sources of transfer, the ability of the virus to infect such a wide range of species creates endemic areas for IPNV. Clinical symptoms External Monitoring in farms by visual inspection is often used to identify outbreaks of acute cases of infectious pancreatic necrosis virus. Other changes to appearance also occur, including darkened skin, pale gills, exophthalmia and a distended abdomen. Skin haemorrhages caused by the virus can also be seen on the belly. Differences in virulence (10%-90%) of strains alongside variations in host characteristics and environmental stressors are all influential for mortality rates caused by the virus. == Diagnosis ==

At present, infectious pancreatic necrosis virus has been reported in Europe, North America, South America, South Africa, Asia, and Australia, where it is a major threat to aquaculture due to its wide host range and high mortality. More recent studies have proposed the use of the more efficient and rapid RT-PCR and its variants to test for IPNV. == Treatment and control ==

There have been a variety of attempts to reduce transmission and increase protection against infectious pancreatic necrosis virus (IPNV). Selective breeding, as well as vaccination, have both been shown to be viable ways of at least reducing infection rates. as injection of hundreds of fry is impractical. Selective breeding has been massively successful in reducing mortality and spread of IPNV. In Atlantic salmon, resistance has been shown to be conferred by variations in one singular gene, although since, previously-resistant fish have been infected and killed by a new IPNV strain. == References ==