Norwegian researchers have found that nine types of Listeria monocytogenes identified in three salmon-processing companies in Norway are of a genetic variant which are also found in patients suffering from listeriosis.
In a press release issued on Tuesday, Norway's National Institute of Nutrition and Seafood Research (NIFES) said that a study of three companies producing farmed salmon in different parts of Norway have identified 15 types of Listeria monocytogenes.
Of the 15 types, nine are of a genetic variant that scientists have also found in patients with listeriosis, a disease that can be triggered by the bacterium known as Listeria monocytogenes.
Emphasizing that no link has ever been established between any cases of listeriosis and the salmon products from Norway, the researchers cautioned that salmon can not be discarded as a possible source of the disease, which mainly affect human foetuses, neonates and persons with conditions weakening their immune systems.
This is the first time for the researchers in the institute to conduct a study comparing the samples with Listeria monocytogenes obtained from Norwegian salmon factories and the human cases of the disease, Bjoern Tore Lunestad, a senior scientist with NIFES, told Xinhua in a telephone interview from Bergen, a Norwegian city on the western coast.
"This background in not sufficient for us to claim that fish are the sources of the cases of listeriosis in our study. But on the other hand, we cannot ignore this possibility. Salmon are one of several potential sources of L. monocytogenes," said Lunestad.
However, there is no ground for any panic as the bacterium, which is quite common in cold environment, can be killed through heat treatment such as boiling.
Scientists in Norway have been unable to identify which item of food is responsible for nearly all cases of food-borne listeriosis in the country over the past 10 years.
Three outbreaks whose sources are known have been registered in Norway, but none of them are found to have any link with Norwegian seafood, said Lunestad.
A total of 21 people in Norway were diagnosed in 2007 with listeriosis, where the bacteria could be traced back to cheese produced in a dairy farm. In 1992 processed meat was the source of an outbreak in the Northern Norwegian county of Troendelag, in which eight cases of listeriosis were registered.
Their findings is published in the October issue of the Epidemiology and Infection journal.