The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2019

This report describes the results from The surveillance and control programme for bonamiosis and marteiliosis and research activities on Marteilia sp. in 2019. The programme is carried out by the Institute of Marine Research according to a contract with the Norwegian Food Safety Authority. Samples were collected from two oyster farms, one wild oyster population, two mussel farms and four wild beds, two mussel farms and five wild mussel populations. Samples were collected in April/May and in October, in order to be able to detect Bonamia sp. and Marteilia sp. during the periods when the potential prevalence is at the highest. Samples from one of the mussel farms and one wild bed were collected after reports of elevated mortality. Except from these samples, no abnormal mortalities were observed during the surveillance. Bonamia ostreae / B. exitiosa were not detected. There have been several reports on mortality or “disappearance” of mussels along the Norwegian coast. The reason(s) for the mortalities have not been determined. However, the parasite Marteilia sp. was detected for the first time in mussels, Mytilus edulis, collected at Bømlo, western Norway in 2016 and Tysnes in 2019. This has been followed up with an extended survey in several research projects. The results show that Marteilia sp. infecting mussels in Norway, Sweden and England are different from Marteilia refringens infecting flat oysters. The name Marteilia pararefringens has been proposed, and there is strong evidence that Marteilia refringens and Marteilia pararefringens sp. nov. are distinct parasites of bivalves and have different European distributions. The work will be continued in 2020 – 2021, linked to research on the distribution of M. pararefringens in wild mussels. We propose a revision of the surveillance programme combined with the establishment of a new model for health control in mollusk farms, application for disease free status for Norwegian flat oysters and a categorization of zones.publishedVersio

Summarizing the screening for Bonamia ostreae in Norwegian populations of flat oysters, Ostrea edulis

Surveillance and studies performed by The Norwegian Institute of Marine Research and the Norwegian Veterinary Institute has never revealed notifiable diseases in Norwegian populations of European flat oysters, Ostrea edulis. In 2006, microcells resembling the oyster parasite Bonamia sp. were observed during histopathological examination of tissue specimens of flat oysters, Ostrea edulis from the Arendal area, southern Norway. The cells were however not interprated as B. ostreae and PCR-analysis of samples from this oyster population were negative. In 2008, the EU reference laboratory (EURL) received samples from the Norwegian Veterinary Institute and reported one Bonamia sp. in a haemocyte from one oyster, based on microscopy. By real-time PCR, positive results were obtained from two oysters in one triplicate sample. Sequencing of the PCR products gave 100% identity with B. ostreae. After this diagnose, both the Norwegian Veterinary Institute and The Institute of Marine Research have monitored the population. The results are briefly reported here. The observed microcells were found in most samples since the sampling at the site was initiated, always at a low prevalence and intensity. No inflammation, pathology or reductions of the oyster's condition have been associated with the observation. The population appears healthy, with a normal reproductive cycle pattern. Several year classes have been present throughout the study period. Since 2009, more than 3 000 oysters have been examined. Bonamia sp. has never been detected, and all PCR assays have been negative.publishedVersio

First identification of mycobacteriosis in Atlantic mackerel (Scomber scombrus)

Mycobacterium infection in fish is a well-known disease problem globally, mainly in the farming of ornamental fish or fish for food. Less is known about the prevalence, distribution and the effects such infections have on wild fish species. Presumptive mycobacteriosis has previously been observed in Atlantic mackerel (Scomber scombrus). Since 2018, there has been an increase in reports of granulomatous kidney disease in Atlantic mackerel with the suspicion of this being mycobacteriosis. A total of six individuals were sent to the Institute of Marine Research for further examination. They were caught in the Nordic Sea by either commercial fishing vessels or during the International Ecosystem Summer Survey in the Nordic Seas (IESSNS research cruise) between 2018 and 2020. Samples for both histological and molecular analysis were collected. Here, we detect a likely novel Mycobacterium species in tissue samples from Atlantic mackerel with this condition, on the basis of rDNA and protein gene sequences. The same unnamed bacterium seems to have been found in some Pacific marine fishes. The macroscopic and histological manifestation of the disease is described. Over the past years, there has been an increase in reports of mycobacteriosis worldwide and climate change has been suggested as one of the driving forces as these bacteria prefer warm water.publishedVersio

The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2017

Overvåkingsprogrammet for sykdommene bonamiose og marteiliose i flatøsters og blåskjell utføres av Havforskningsinstituttet på oppdrag fra Mattilsynet. Det ble hentet skjell fra fire ville bestander og ett østersanlegg, basert på utbredelsen av ville skjell og strukturen i østersnæringen. Prøver ble samlet inn i April/Mai og i Oktober, som er de periodene hvor prevalensen av parasittene Bonamia sp. og Marteilia sp. er høyest i smittede bestander. Det ble ikke observert unormal dødelighet verken vår eller høst. Bonamia ostreae / B. exitiosa ble ikke påvist. Det er kommet inn en rekke rapporter om at blåskjell «forsvinner» mange steder langs kysten. Årsakene til dette er ikke kjent. Parasitten Marteilia sp. ble imidlertid for første gang påvist I blåskjell, Mytilus edulis, på Bømlo i 2016. Denne påvisningen er fulgt opp med en utvidet prøvetaking i HI-prosjekt Blåskjelldødelighet (83737-04) i 2017. Det er gjort prøvetaking av blåskjell hver tredje måned og samlet inn fauna fra funnstedet og blåskjell fra områder i nærheten. Østers fra funnstedet ser ikke ut til å bli smittet av Marteilia sp. Genetiske studier av Marteilia spp. Fra England, Sverige og Norge (Bømlo) er inkludert i en studie som er gjort i EU-prosjektet VIVALDI. Marteilia sp. fra disse områdene er ulik Marteilia refringens som forårsaker sykdom hos flatøsters og er foreslått gitt navnet Marteilia pararefringens. Det ser således ut til at Marteilia refringens og Marteilia pararefringens sp. nov. er ulike arter med ulike vertsarter (hhv østers og blåskjell). Studiene videreføres i 2018, som en kombinasjon av overvåkingsprogrammet og forskningsprosjektet.publishedVersio

The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2016

The surveillance programme was carried out in accordance with the model established in 2015, including four wild beds and one oyster farm, based on the present distribution of wild beds, and the structure of the oyster industry. Samples were collected in April/May and in October, in order to be able to detect Bonamia sp. and Marteilia sp. during the periods when the potential prevalence could be at the highest. No abnormal mortalities were observed in oyster populations during the surveillance. Bonamia ostreae / B. exitiosa or microcells resembling Bonamia spp. were not detected during the surveillance programme in 2016. There have been several reports on mortality or “disappearance” of mussels along the Norwegian coast. The reason(s) for the mortalities have not been determined. From one mortality event, at Ytre Hvaler, Østfold, South-eastern Norway, in September 2016, live, presumably moribund mussels were sent to IMR and examined. Affected mussels showed infiltration of bacteria in digestive and connective tissues. Bacteria have been isolated, cultured and frozen for subsequent analysis. No parasites were observed. Marteilia refringens was detected for the first time in mussels, Mytilus sp. collected at Bømlo, western Norway in October. The prevalence was 50% and most infected mussels exhibited a heavy infection with sporulating Marteilia cells in the digestive epithelia, and affected tissues. A plan for extended survey and a study of the Marteilia refringens in affected mussels has been initiated.publishedVersio

The surveillance and control program for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis in 2023

The surveillance program for the molluscan diseases bonamiosis and marteiliosis is carried out by the Institute of Marine Research according to a contract with the Norwegian Food Safety Authority. In 2023, flat oysters were sampled from four locations: A breed poll where oyster spat is produced, an abandoned breed poll where oyster spat was previously produced, and two fjord systems with larger populations of flat oysters. Samples were collected in April – June and September, to be able to detect Bonamia sp. and Marteilia sp. during the periods when the potential prevalence is highest. No abnormal mortalities were observed during the surveillance. Bonamia ostreae / B. exitiosa and Marteilia refringens were not detected. Marteilia refringens Type O and M are now divided into two species; Marteilia refringens in flat oysters and M. pararefringens in blue mussels. Blue mussels are therefore no longer considered susceptible hosts for M. refringens, but our research project shows that the related Marteilia pararefringens is widespread in certain mussel populations along the South and West coasts of Norway. M. pararefringens can have a serious impact on blue mussel populations, and consideration should be given to listing the parasite on a national list. Furthermore, we propose a formal application for disease free status for Bonamia spp. and Marteilia refringens in Norwegian flat oystersThe surveillance and control program for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis in 2023publishedVersio

The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2018

The surveillance programme is carried out by the Institute of Marine Research according to a contract with the Norwegian Food Safety Authority. Samples were collected from four wild beds, two mussel farms and one oyster farm. Samples were collected in April/May and in October, in order to be able to detect Bonamia sp. and Marteilia sp. during the periods when the potential prevalence could be at the highest. No abnormal mortalities were observed in oyster populations during the surveillance. Bonamia ostreae / B. exitiosa were not detected. The results may be used as a background for an application for disease free status for Norwegian flat oysters. There have been several reports on mortality or “disappearance” of mussels along the Norwegian coast. The reason(s) for the mortalities have not been determined. However, the parasite Marteilia sp. was detected for the first time in mussels, Mytilus edulis at Bømlo, western Norway, collected during the surveillance programme in 2016. This has been followed up with an extended survey in the IMR research project Mussel mortalities (83737-04). We have performed transmission experiments that identify the time period of infection and the progress of the infection in mussels. Analyses of samples collected in July 2018 indicate that the parasite may be present in an abandoned oyster lagoon at Espevik, Tysnes. The results from the research project indicate that the Marteilia sp detected is limited to mussels. Flat oysters at the same site do not become infected. This is relevant to the listing of susceptible hosts for Marteilia spp. A genetic study of Marteilia spp. from the UK, Sweden and the present site at Aga has been included in a study in the EU-project VIVALDI. The name Marteilia pararefringens has been proposed, and there is strong evidence that Marteilia refringens and Marteilia pararefringens sp. nov. are distinct parasites of bivalves and have different European distributions. After the detection of M. pararefringens in mussels, it is important to obtain more data from mussels along the Norwegian coast. Mussels from Trøndelag in 2018 represented the first samples from mussels north of Bergen. In order to obtain a better set of data, we propose an extended surveillance that could be obtained through a revised surveillance progamme combined with a new model for health control in mollusk farms.publishedVersio

The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2022

The surveillance programme is carried out by the Institute of Marine Research according to a contract with the Norwegian Food Safety Authority. In 2022, samples were collected from an area in Agder where flat oysters and mussels are harvested from wild beds and farmed, and from one mussel farm in Trøndelag county. Samples were collected in April/May and in October, to be able to detect Bonamia sp. and Marteilia sp. during the periods when the potential prevalence in affected populatioons is highest. No abnormal mortalities were observed during the surveillance. Bonamia ostreae / B. exitiosa and Marteilia refringens were not detected. Marteilia pararefringens has been observed in Norwegian mussels since 2016 and a targeted surveillance was carried out in 2022. M. pararefringens has so far been detected at eight sites. All Marteilia isolates have been sequenced and typed as Marteilia pararefringens, which is presumed specific for mussels. The work will be continued in 2023, linked to research on the distribution of M. pararefringens in wild mussels. We propose a revision of the surveillance programme and application for disease free status for Bonamia exitiosa in Norwegian flat oysters. We also propose an application for lifting the suspension of free status for Bonamia ostreae in Arendal and Marteilia refringens at Bømlo.The surveillance and control programme for bonamiosis and marteiliosis in European flat oysters, Ostrea edulis, and blue mussels, Mytilus sp. in Norway in 2022publishedVersio

Redningsaksjon for Vossolaksen 2010-2020 -status per 2021

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