Europe has experienced its worst bird flu crisis ever this year with nearly 50 million poultry culled, and the persistence of the virus over the summer has raised the risk of widespread infections next season, the EU's Food Safety Agency has said.

The spread of highly pathogenic avian influenza (HPAI), commonly called bird flu, is a concern for governments and the poultry industry due to the devastation it can cause to flocks, the possibility of trade restrictions and a risk of human transmission.

An unprecedented number of outbreaks were reported in wild and domestic birds this summer, causing massive mortality among sea bird breeding colonies on the north Atlantic coast according to a joint overview by the EFSA, the European Centre for Disease Prevention and Control, and the EU reference laboratory.

In Ireland, the Department of Agriculture confirmed 21 positive cases last month, saying that all but one of the cases were in seabirds.

It said 80 wild birds were submitted to its laboratories for testing since July of this year

Bird flu usually strikes during the autumn and winter months. It is transmitted by infected migrating wild birds' faeces or direct contact with contaminated feed, clothing and equipment.

"As autumn migration begins and the number of wild birds wintering in Europe increases, they are likely at higher risk of HPAI infection than previous years due to the observed persistence of the virus in Europe," Guilhem de Seze, a senior official at the EFSA, said in a statement.

This season's epidemic affected 37 European countries in total, the largest geographical reach on record, and the virus crossed the Atlantic for the first time along migration routes, causing a severe epidemic in poultry in several Canadian provinces and US States, the EFSA said.

Overall, this season's ongoing bird flu crisis is the worst ever seen in Europe with a total of 2,467 outbreaks reported in poultry and 47.7 million birds culled, it said.

In addition, 187 detections were notified in captive birds and 3,573 HPAI events were recorded in wild birds.

The EFSA recommended rapid implementation of risk mitigation and surveillance strategies for an early detection of the virus.