The Usutu virus, which is transmitted by mosquitoes, has spread north through Europe, with at least 25,000 dead blackbirds reported in Germany this year.
Magazine Fugle og Natur (Birds and Nature), which is published for members of the Danish Ornithological Society, writes that Usutu has now reached Denmark.
The group’s biologist Henning Heldbjerg said the full effect of the virus would not be felt in Denmark until next summer, given that mosquitoes thrive from May to September.
“We were told by Germany that it starts with individual cases and then spreads,” Heldbjerg said.
“That can be followed by the decline of a population. That might mean there are fewer blackbirds in the population next year,” he added.
With this year’s warm weather a primary reason for the virus reaching so far north, a cold summer next year could yet come to the rescue of blackbirds.
“If we have a cold summer, it won’t be certain that we’ll see anything (of the virus) at all,” Heldbjerg said.
The virus was first detected in Europe around 2000 and has since begun to spread north. It was unknown in Denmark until cases were reported in the Netherlands and Belgium within the last two years.
Most of the recent German cases were located near Hamburg, around 150 kilometres south of the Danish border. As such, people in the southern part of Jutland may already have found blackbirds killed by the virus.
Heldbjerg advised people in the area to be alert to blackbirds behaving unusually or dying suddenly.
“The affected birds become lethargic and drowsy. They don’t fly away, and when they’ve had the virus for a day or two, they fall down dead,” he said.
“We have brought this up because this is a bird everyone knows and likes. It’s often seen in the garden, so you should be aware that if a bird is acting unusually, it may be sick,” he said.
The Danish Ornithological Society has contacted the veterinary department at the Technical University of Denmark for confirmation that the virus is not harmful to humans.
Epidemiologist Rene Bødker told Fugle og Natur that dead blackbirds must be handled with caution.
“Usutu only rarely infects humans, but it can happen, so dead birds must be handled carefully,” Bødker said.