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Marteilia-free Areas in Denmark

The Limfjord, the southwestern Kattegat, the Belt sea and the Isefjord has been declared free for Marteilia refringens according to the EU legislation.

The Limfjord - an area free of marteiliosis
The Limfjord is a coastal area of approximately 1,500 km2 separating northern Jutland from the rest of the peninsular and connecting the North Sea and Kattegat. The Limfjord has narrow openings at both ends allowing water from the North Sea to flow to Kattegat through the fjord and vice versa. The water in the Limfjord is a mixture of seawater from Kattegat and the North Sea and freshwater from the river systems that flow into the Limfjord.

The Limfjord is the only Danish habitat for natural stock of European flat oyster (Oestrea edulis).

The official EU status of the Limfjord as an approved zone with regard to bonamiosis and marteiliosis was obtained in 2005 (Commissions Decision 2005/104/EC). In accordance with Council Directive 2006/88/EC, Denmark has declared the continuation of its disease-free status for bonamiosis and marteiliosis - see the Declaration of bonamiosis and marteiliosis free status.


Infection with Bonamia ostreae has been confirmed in oysters collected in Venø Sund and Salling Sund on March 3rd, 2015. Therefore, The Limfjord is no longer considered to be free of bonamiosis.

The surveillance programme for bonamiosis and marteiliosis in the Limfjord
From 1996 to 2000, an unofficial disease surveillance programme on wild oyster populations for bonamiosis and marteiliosis was conducted in the western Limfjord. The investigations were initiated in order to examine, if there was a basis for a future commercial production. Only oysters of the wild population was sampled and examined during the years 1996-2000, because no aquaculture activities were present in the fjord until 2000. The investigations of the wild oyster stocks revealed neither Bonamia ostreae nor Marteilia refringens.

Since autumn 2000, an official disease surveillance programme for bonamiosis and marteiliosis has been in place in Denmark in respect of both cultivated and wild stocks of oysters. In the first two years, the surveillance programme comprised biannual sampling of 150 oysters at each of three different sites. Since autumn 2002, the sampling has been reduced to the collection of 30 oysters samples from each of the three sites twice a year. Marteilia refringens has never been detected in Denmark.


Bonamia ostreae was detected in surveillance samples from two locations, Venø Sund and Salling Sund, on March 3rd, 2015.  

Southwestern Kattegat, the Belt Sea and the Isefjord - an area free of Marteilia refringens
In 2012, the Danish Veterinary and Food Administration initiated the surveillance programme for Marteilia refringens in southwestern Kattegat, the Belt Sea and the Isefjord. The surveillance programme aimed at declaring freedom from Marteilia refringens in the natural mussel (Mytilus edulis) stocks in those sea areas and in the few aquaculture facilities situated in the areas. Initially, the programme has to run for two years to obtain the disease-free status. After the initial two years of intensive surveillance, the sampling will continue, although with a reduced sample size to provide the documentation required to maintain the disease-free status.

The surveillance area has been separated into four subareas from which samples have been collected. During the first two years, 150 samples of mussels have been collected at three different localities in each of the four subareas. All samples are collected under the supervision of the Danish Veterinary and Food Administration. Histological examinations have been performed at the National Veterinary Institute at the Technical University of Denmark, which is the Danish national reference laboratory for mollusc diseases.

In accordance with Council Directive 2006/88/EC, Denmark has declared the Danish disease-free status for Marteilia refringens in the southwestern Kattegat, the Belt Sea and the Isefjord area.


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Last Modified 14. October 2015