Marine Institute

Press Report Regarding Worms in Salmon

October 7, 2005

The Marine Institute is concerned regarding recent newspaper reports on the discovery of the nematode parasitic worm Anisakis in a number of fish from around the coast. The following statement was prepared by our own staff and those of the Veterinary School at University College Dublin.

There have been no reported cases of foodborne illness associated with Anisakis in recent years in Ireland. Nematode worms are common in a wide range of wild fish although only three cases of severely infected salmon have been reported this year. Consumers are advised that such worms are easily killed, and fish made safe to eat, by cooking the flesh above 60 degrees centigrade, or by freezing the fish for a few days. The best advice, as with all meat and fish, is to follow basic hygiene guidelines such as thoroughly cooking the flesh and washing hands after handling raw fish or meat.

If worms are present in the fish, neither refrigeration or marination will kill the worms. It may survive in products such as such as herring roll mops or salmon gravlax which rely on food safety management systems to ensure that the raw material is free from possible contamination.

The presence of this worm does not represent a threat to stocks of salmon and sea trout. There can be no association between falling salmon numbers and the incidence of Anisakis so far described. There is no history of high numbers of Anisakis causing epidemics that might wipe out populations of fish.

While salmon can be intermediate hosts, or occasionally final hosts, other freshwater fish will not become infected unless they actually eat returning salmon or flesh from dead salmon. Therefore horizontal parasite transmission between fish in estuaries does not occur since intermediate hosts need to be eaten for transmission to occur at all.

Reports of fish being "eaten" by Anisakis, or of spreading "to all other fish" are inaccurate and misleading, as are references to eggs infecting the open wounds of anglers. Eggs need to be "incubated" in a crab-like intermediate host before they become active.

The life cycle of these Anisakis starts when worm larvae infect tiny floating crab-like zooplankton, which are then eaten by intermediate hosts such as sardines, mackerel or herring. These intermediate hosts may then eaten by larger intermediate hosts such as salmon, cod, tuna and monkfish or by their final hosts - marine mammals such as dolphins, seals and whales - where they cause severe gastritis and sometimes perforate the stomach wall.

Anisakis does not represent a serious threat to the coarse fish population.

ENDS