Oyster diseases Bonamia ostreae, Bonamia exitiosa och Marteilia refringens
Marteilia refringens, Bonamia ostreae and Bonamia exitiosa are parasites that causes disease to European oyster (Ostrea edulis). Infection with M. refringens, B. ostreae and B. exitiosa are listed as category C disease. The diseases have never been detected on oysters in Sweden.
Recognition of disease-free status in Sweden
The 17th of June 2025 the EU commission decided to recognise disease-free status for infection with Bonamia exitiosa, Bonamia ostreae and Marteilia refringens for the entire territory in Sweden. The disease-free status will be official through the amendment of regulation (EU) 2021/620 when it is published in Official Journal of the European Union.
The application was sent to the Commission the 5th September 2024. For the west coastal part of the territory the application for recognition of disease-free status was based on historical and surveillance data. For other parts of the territory the application for recognition of disease-free status was based on the absence of listed species.
Sweden has a unique coastline. Along the coast around Sweden there is a clear salinity gradient, from almost completely fresh water in the northern Gulf of Bothnia via brackish water in the Baltic Sea to close to oceanic water with high salinity in the Skagerrak. Due to the variation in salinity European oysters can only be found on the west coast. The European oyster is the only susceptible species in Sweden to M. refringens, B. ostreae and B. exitiosa.
There are no imports of oysters from other countries for release in Swedish waters. Sampling of oysters takes place in accordance with the national monitoring plan.
Aquaculture establishments in Sweden receive regular animal health visits. Results from sampling are reported further down this page.
Infection with M. refringens, B. ostreae and B. exitiosa is notifiable. More information about notification obligations and the EU's listed diseases can be found at:
Infection with Bonamia ostreae and Bonamia exitiosa
Infection with B. ostreae and B. exitiosa has never been detected in Sweden.
European oyster (Ostrea edulis) is the only susceptible species in Sweden.
For more information:
- Bonamios hos ostron (sva.se) – in Swedish
- Bonamia sp. – EURL for Molluscs Diseases (eurl-mollusc.eu)
- Bonamia exitiosa: Appendix IX (woah.org)
- Bonamia ostreae: Appendix IX (woah.org)
Infection with Marteilia refringens
There are two types of Marteilia refringens: type M which is most often found in mussels and type O which is most often found in oysters. In the past, these two types have been seen as one species. However, research has recently concluded that these two types of M. refringens are two different species. Type M is in some contexts called Marteilia pararefringens.
European oyster (Ostrea edulis) is the only susceptible species in Sweden. M. refringens has never been detected on oysters in Sweden. M. refringens has been detected on blue mussel. The last time M. refringens was detected on blue mussel was in 2015. Blue mussel (Mytilus edulis) is not listed as a susceptible species for M. refringens.
Legislation
Söker efter grundforeskrifter:
2021:10
- Commission implementing regulation (EU) 2021/620 laying down rules for the application of Regulation (EU) 2016/429 of the European Parliament and of the Council as regards the approval of the disease-free and non-vaccination status of certain Member States or zones or compartments thereof as regards certain listed diseases and the approval of eradication programmes for those listed diseases (eur‑lex.europa.eu)
- Commission implementing regulation (EU) 2018/1882 on the application of certain disease prevention and control rules to categories of listed diseases and establishing a list of species and groups of species posing a considerable risk for the spread of those listed diseases (eur‑lex.europa.eu)
