Hypovirus CHV1 is the only hypovirus found in Europe up to 2000. It is known for reducing the virulence of the fungus that causes chestnut blight (i.e. hypovirulence).Cryptonectria parasitica, the ascomycete fungus, originated in Asia and causes the disease chestnut blight in several chestnut species (Castanea sp.). Although symptoms are mild in Asian chestnut species that have co-evolved with the fungus, they are very severe in the North American chestnut species C. dentata and also in the European sweet chestnut, C. sativa. Hypovirus has been used for protection against chestnut blight in Europe since the 1970s.