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Økt kunnskap om Hysterothylacium aduncum i torsk, sei og hyse norske farvann med praktiske preventive tiltak

The larvae of parasitic nematodes, particularly Anisakis, Pseudoterranova and Contracaecum species, in Norway collectively known as “kveis”, commonly occur in the viscera and muscle of many commercially important marine fish species, such as cod (Gadus morhua), saithe (Pollachius virens) and haddock (Melanogrammus aegleginus). These parasites may cause human disease (anisakidosis) upon consumption of raw, marinated or lightly processed fishery products contaminated with viable larvae. Kveis are also of socioeconomic concern, since they may reduce the marketability of fishery products and cause rejection of products by sellers and consumers.

Another kveis-type, Hysterothylacium aduncum, is also very common in gadoid whitefish caught in Norway. In contrast to Anisakis which use marine mammals (cetaceans) as final host, Hysterothylacium lives exclusively in cold-blooded organisms (marine invertebrates and fish) and is per definition not adapted to the conditions that prevail in the alimentary tract of mammals. Therefore, H. aduncum is considered non-zoonotic, i.e. in principle, it does not pose any direct consumer health risk. However, H. aduncum can indeed heavily infect some fish species, and the massive presence of larval or adult specimens in or around the visceral organs could contribute to a reduction of the aesthetical appeal of the products, potentially causing socioeconomic problems to the industry. 
• To improve our knowledge in relation to the timely and spatial occurrence and distribution of Hysterothylacium aduncum in cod, saithe and haddock caught in Norwegian waters.
• To study current handling procedures along the fish value chain, as a basis for advice to improve handling/cleaning practices in processing plants.
• ​To assess survival and motility of the parasite by mimicking the temperature conditions during handling and transport of fresh cod to European markets. 
Expected project impact
Based on the results and findings of this project, the industry will be advised with respect to revising their handling practices in order to improve parasite control measures adapted to fish species, fishing ground, catching date and handling, etc. If implemented by the industry, the recommendations could largely eliminate the problems at the marketplaces caused by Hysterothylacium.
Project design and implementation
Fish sampling

30 cods will be sampled freshly on board a fishing vessel by HI (IMR) researchers and visually inspected for Hysterothylacium. Whole catches will be followed throughout the production chain from catch via landing and processing to final packing in the plant, in order to identify critical control points for the detection and subsequent elimination or at least drastic reduction of the Hysterothylacium problem. Additionally, 30 saithe and 30 haddock fished in March 2019, and the same numbers of fish (i.e. 30 cod, 30 saithe and 30 haddock) caught in April/May 2019 in the Barents Sea, need to be frozen as soon as possible after capture (if not possible, cooling conditions must be kept from the boat to IMR facilities), and sent to the IMR for parasite inspection and identification. 

Hysterothylacium survival trials
Hysterothylacium will be collected from cod viscera and placed in petri dishes in physiological saline which will be kept in a fridge at 2–4⁰C for at least 7 days, thus mimicking the temperature conditions during transport to various markets. Hysterothylacium will be also placed in a peptic solution, which mimics the conditions found in the mammalian stomach. Hysterothylacium survival will be assessed in both trials. Results might provide some valuable information to determine if Hysterothylacium would survive long enough in order to eventually be able to cause any damage in a human stomach.

Data analyses and reporting
Parasite data will be analyzed, and descriptive infection data such as prevalence and abundance per infection site/organ will be calculated. The relationship between nematode abundance and fish size and sex will be statistically assessed. Based on the results of the observations and analyses, a set of guidelines will be prepared, e.g. a visual flow chart, so that the industry can implement certain handling and cleaning routines during processing of fresh cod/whitefish in order to cope with the Hysterothylacium problem.​ 
Dissemination of project results
It is planned to publish an article in the IMR's website and in a peer-reviewed international scientific journal.

A workshop on the “kveis”​-problem in the Norwegian whitefish industry will be organized at the IMR in Bergen during autumn 2019. As a synergistic spin-off effect, the results and findings from the currently proposed project on Hysterothylacium, will be also integrated in the workshop.