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A virus affecting garden birds is spreading to new parts of the UK, researchers are warning.

This form of avian pox causes lesions, often around the eyes and beak.

The virus, affecting great tits, is believed to be a new and more severe strain of a disease that has affected other bird species for several decades.

When it was first found in the UK in 2006 it seemed to be confined to south-east England, but has now spread further north and west.

The findings come from a team at the Zoological Society of London (ZSL).

Researchers now want help from the public to help track any further spread of the disease.

Avian pox can be spread through contaminated bird feeders, via biting insects and through direct contact between birds.

It has been known in species including dunnock, woodpigeons and house sparrows for many years.

The form now affecting great tits may be the same strain as one discovered in central Europe.

Vulnerable to predators

Dr Becki Lawson, from ZSL, said: "What's different about this avian pox in this species is that the lesions can be very severe.

"It's not unusual for several birds to be affected at one site.

"Initially the reports were restricted to south-east England, chiefly in Surrey, Sussex and Kent.

"Over the last year we've seen the geographical range of this disease spread quite significantly, as far west as Wiltshire and as far north as Staffordshire."

In the most severe cases the lesions caused by the virus in great tits can prevent the birds from feeding or flying and makes them more vulnerable to predators.

ZSL has been working with Oxford University, the British Trust for Ornithology and the RSPB. Researchers now want help from the public to monitor suspected cases of the disease:

Dr Lawson said: "We're very keen to track further spread of the disease this year as we progress into the months where we'd expect to see a peak in the numbers of reports, in the late summer and early autumn."