In general terms, infectious agents include bacteria, viruses, fungi, parasites and prions. The severity of these diseases in humans can vary from mild symptoms to life-threatening conditions.
The infection can be acquired directly from contact with animals or through ingestion of contaminated foodstuffs. Most cases of food-borne zoonoses are associated with terrestrial animals, but seafood is also involved.
In Norwegian seafood there are a few potential zoonoses of concern. Zoonotic fungi and prions are of no relevance for seafood. The main challenge is the possible contamination of seafood by Listeria monocytogenes, accumulation of infectious matter by shells and the presence of parasites in wild fish stocks:
Listeriosis is an infection caused by the bacterium Listeria monocytogenes, a common environmental and processing facility contaminating bacterium that may be transferred to seafood products. The bacterium is destroyed by common heat treatment, such as frying, steaming and boiling, but can grow at refrigeration temperatures and survive freezing. Listeriosis is predominantly associated with mildly preserved ready-to-eat foods. The dose of infection is usually very high, and Listeriosis largely affects specific segments of the population who have increased susceptibilities. No cases of Listeriosis in Norway have yet been linked to commercially produced seafood.
Bivalve shells are filter feeders and can thus accumulate infectious matter such as viruses and pathogenic bacteria if present in the rearing water. These may result in infection if contaminated products should reach the market.
Larvae from parasitic nematodes (roundworms) can be found in most wild living marine fish species worldwide. Farmed fish under Norwegian conditions do not harbour nematodes of human health concern. The main nematode found in marine fish in cold-water areas is Anisakis spp. This parasite may cause infection in humans if ingested live. When the fish is boiled, fried, salted or frozen these nematodes, if present, are destroyed.
An overview of ways to ensure seafood safety is given here.