A measles-like virus is responsible for the death of 40 dolphins found washed up on Tuscan beaches so far this year, scientists have said.

Tests on some of the dolphins carried out by scientists at the University of Siena and the Experimental Zooprophylactic Institute of Lazio and Tuscany in Rome, show the dolphins were killed by cetacean morbillivirus (CeMV), the Tuscan regional authority announced on Tuesday.

The virus, from the same family as measles, generally causes pneumonia and encephalitis — inflammation in the brain — caused by pronounced immunosuppression.

As dolphins live in pods transmission is highly effective — in 2013-2014, almost 1,500 bottlenose dolphins died along the eastern coast of the United States because of the virus.

"We are powerless in the face of this virus," Federica Fratoni, environment commissioner for the Tuscany region, said in a statement.

"But we could do a lot about another problem highlighted by the analysis of tissues and organs taken during the autopsies," she added, flagging that "high levels" of DDTs and PCBs — both chemical compounds — were found.

"These products can have an immunosuppressive effect and therefore may have contributed to the spread of the disease and its effects," she went on.

Fratoni called on the Italian government to ratify the Stockholm Convention. Agreed in 2001, the convention bans persistent organic pollutants which are resistant to environmental degradation and has so far been signed by 189 countries.

"Ours is the only European country that has not signed up to that pact and the time has come to remedy this error," Fratoni said.