Coronavirus has been identified in mink on four more fur farms, taking the total where infections have been found so far to 13.

The new cases are on fur farms in Noord-Brabant province and in Limburg, which are the centres of the Dutch fur farming industry.

Three of the new cases came to light through the routine testing of dead animals and one was reported in as a possible case of coroanvirus. The source of the new infections has not yet been traced, farm minister Carola Schouten said in a briefing to MPs.

All animals on the farms will be gassed and the barns and cages cleaned to remove any possible trace of the virus.

Last weekend officials began gassing tens of thousands of mink on the farms where corona virus had already been identified.

The Netherlands is home to some 128 mink farms, making it the third largest producer of mink pelts in the world after Denmark and China.

The use of fur and the conditions the animals were kept had prompted calls to ban the industry since 1989 but didn’t result in a law prohibiting the practice until 2013. At the time, fur farmers were told they would get until the end of 2023 to make good on their investments.