MADRID (AFP) — About 400 storks have been found dead along a river near Madrid, officials said Tuesday, raising concerns that a highly infectious strain of bird flu may be circulating.

Bird flu, also known as avian influenza, rarely poses a risk to humans but can cause major losses in the agricultural sector and disruptions to food supplies.

The dead storks were discovered on the banks of the Manzanares River in Getafe, a southern Madrid suburb.

Initial tests detected a low-pathogenic strain of avian influenza in the area, but the “large number” of stork deaths has fueled suspicions of a more virulent variant, the Madrid regional government said in a statement.

Samples have been sent to a laboratory operated by the Agriculture Ministry for further analysis, it added.

Strict control measures are already in place, including bans on free-range poultry farming, limits on visits to breeding facilities, restrictions on raising ducks and geese alongside other poultry, and increased oversight of water supplies.

The virus spreads through bird droppings, saliva and contaminated food or water, but it cannot be transmitted through the consumption of poultry products.

More than 200 outbreaks of avian influenza have been reported at poultry farms across Europe this year, higher than in recent years but far below the peak in 2022, when tens of millions of birds were culled.