Blue mussels and Marteilia refringens: is it possible to process mussels from non-approved zones in zones with disease-free status with the proper preventive measures? Lone Madsen 1 & Stig Mellergaard 2 1 DTU Vet, Division of Veterinary Diagnostics and Research 2 Danish Veterinary and Food Administration
Danish production/harvest of M. edulis and O. edulis 2010 M. edulis: 19,485 t O. edulis: 1,050 t Cardium spp.: 55 t LIMFJORDEN Approved zone KATTEGAT M. edulis: 1,777 t O. edulis: 0 t North Sea Wadden Sea M. edulis: 0 t O. edulis: 0 t Cardium spp.: 132 t Belt Sea & Baltic Sea M. edulis: 6,600 t O. edulis: 0 t In total Mytilus edulis: 27,862 t Ostrea edulis: 1,050 t Cardium spp.: 187 t Chlamys opercularis: 0 t Spisola solida: 0 t
Blue mussels (Mytilus edulis) Geographical distribution: from North of Spain to Norway, from Carolina, USA to Newfoundland, Canada Densities up to 1000-2000/m 2 Very tolerant against extreme environmental conditions and changes (e.g. temperature, salinity) Predators: starfish, crab, periwinkles 1998: production 1,6 mio. tons (Europe half of the production) 2002: production 112,000 tons in Denmark (80,000 tons from Limfjorden) 2007: production 57,000 tons in Denmark (33,000 tons from Limfjorden) 2008: production 35,000 tons in Denmark (26,000 tons from Limfjorden)
Blue mussel fisheries/production in Denmark 2002 2003 2004 2005 2006 2007 2008 2009 2010 In total 112,271 t 92,523 t 99,500 t 69,155 t 54,699 t 57,000 t 35,000 t 37,427 t 27,862 t Limfjorden 80,000 t 72,781 t 70,336 t 45,043 t 29,520 t 33,000 t 26,000 t 28,846 t 19,485 t
Histological screening of oysters for Bonamia og Marteilia Since 1996 Autumn 2000 until summer 2002: 150 samples per site (in all three sites) twice yearly Autumn 2002- : 30 samples per site (three sites) twice yearly Application sent from the Danish Veterinary and Food Administration to the EU to gain approved zone status for Limfjorden as disease-free zone concerning the parasitic diseases Bonamiosis and Marteiliosis in August 2004 Approved zone status for Limfjorden gained in December 2004 Future: Screening programme for blue mussels sampled in other Danish waters than Limfjorden?
In the EU: Coastal zones with status as approved zones according to the notifiable diseases. Molluscs can be moved between zones with same zone status as well as from approved zones to nonapproved zones
Sampling from blue mussels Technical University of Denmark
Marteiliosis: Both in oysters and other molluscs (blue mussels) Marteilia refringens: Two types (sequencing of rrna) O-type and M-type (co-infections are seen) The effect of Marteilia refringens on oyster production in France Year Ostrea edulis Crassostrea sp. 1960 21.600 t 65.900 t 1969 18.000 t 43.200 t 1970 19.100 t 40.300 t 1971 14.100 t 20.100 t 1972 14.900 t 53.900 t 1973 10.300 t 61.700 t 1974 14.100 t 59.500 t 1975 8.400 t 85.000 t
Life cycle of Marteilia refringens Technical University of Denmark Hovgaard, Mortensen & Strand Skjell biologi og dyrkning 2001 Transmission by sporulation (water temperatures > 16 degrees) Transmission through an intermediate host No new infections at high salinities
Histological slide of Marteilia refringens, x50 Histological slide of Marteilia refringens, x400
Mussel processing plants are situated at Limfjorden Wastewater is lead into Limfjorden What about processing of mussels from outside Limfjorden? Screening programme for Danish waters outside Limfjorden Alternative? Mitigation steps/preventive measures Main contamination risk Effluent water of the processing
Steps preventing the introduction of Marteilia refringens and Bonamia ostreae into Limfjorden The import of mussels from the east coast of Jutland (ECJ) to Limfjorden will only take place when water temperatures at ECJ is lower than 15 degrees (= no sporulation of Marteilia) salinity in Limfjorden is equal or higher than salinities of the waters off ECJ Salinity in the water surface Salinity fluctuations in the water surface Tyge Christensen: Alger i naturen og laboratoriet, KU, 1988
Steps preventing the introduction of Marteilia refringens and Bonamia ostreae into Limfjorden No oysters among the transported blue mussels (= no risk of Bonamia) Rinse truck with marine water from Limfjorden (= increasing the salinity which means lowering the chance of sporulation) Rinse truck with freshwater (= killing micro-organisms due to cell burst because of osmosis) and chlorine Tarra (shell fragments, barnacles etc.) transported to an area with no contact with the water in Limfjorden The processed mussels will be exported to areas outside Limfjorden
Steps preventing the introduction of Marteilia refringens and Bonamia ostreae into Limfjorden Processing plant cleaned with marine water and afterwards freshwater with chlorine Effluent water lead to sedimentation basins final disinfection step = electrochlorination long pipeline before water is redirected to Limfjorden, so the sodium hypochlorite concentration can drop below a detectable level before the water is released to Limfjorden realistic prevention measures? Electrochlorination: an electrical current triggers the production of sodium hypochlorite from sea water
Alternative prevention step Filtration of effluent water at 3 µm would be efficient = the smallest stage of Marteilia is 4 µm Unrealistic? Overall question What is the risk of oysters getting infected by Marteilia from blue mussels?