The South Essex Wildlife Hospital, based in Orsett, said it was forced to put down a dying bird who had been taken home by a witness “who couldn't bear to watch the bird suffering and being eaten alive by rats”.
Official advice is to “not touch or pick up any dead or visibly sick birds”.
The injured bird later tested positive for avian influenza, the hospital said. It said that eight dead swans had been found in Hullbridge, Essex, and two more in Canvey.
Sharing pictures of the animals, the hospital said: “The photos show the dead and dying swans suffering from avian influenza at Hullbridge Essex.
“We are powerless to help them due to the risk of transmitting the virus to our hospital and causing an outbreak in our animals.”
It added that “the situation has been repeatedly reported to the authorities and we await further instruction”.
According to an assessment from the Department for Environment, Food and Rural Affairs (Defra) dated December 13, 320 wild birds have tested positive for the “highly pathogenic avian influenza” to date.
Many of those cases were identified in mute swans in England, with 143 confirmed cases. The analysis stated the risk level to wild birds was “very high”.
New housing requirements were introduced on November 29 for bird keepers across the UK to keep their poultry and captive birds indoors to limit the spread of the disease.
The risk to human health from the virus is very low, states official guidance.
Wild birds are thought to spread the disease to captive birds, and the new measures were brought into force after bird flu was uncovered In a number of poultry locations.
When bird flu is confirmed or suspected in poultry or other captive birds, ‘lockdown’ control zones are put in place around the infected premises to prevent the spread of the disease.
Dead wild waterfowl can be reported to the Defra helpline on 03459 33557.