A strain of the disease responsible for killing off nearly two thirds of the UK's greenfinches has been discovered in myna bird populations in Pakistan.

Mynas are native to the Indian subcontinent and are one of the world's most invasive species. Although the disease is not generally fatal to them, experts from the University of East Anglia studying the birds say there is a risk they might pass it on to other species.

Avian trichomonosis, more commonly called canker or frounce, is carried by a parasite that primarily infects pigeons in the UK and the larger birds of prey which feed on them.

But in 2005 scientists found the disease had jumped into Britain's garden songbird populations, predominantly affecting greenfinches and chaffinches.

Since then, the greenfinch population in the UK has fallen from around 4.3 million breeding pairs to fewer than 1.5 million in 2016.

In 2011, the disease was discovered to have reached European finch populations. Now researchers at the University of East Anglia (UEA) have found it in an entirely separate songbird species - the common myna.

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Working in partnership with the University of Agriculture in Pakistan, researchers captured and screened 167 myna birds from eight different sites around the Faisalabad region of Pakistan. They discovered that around 20 per cent of the birds were infected with the disease and that there were infected birds at all of the sites surveyed.

The study, published in the journal Parasitology, also identified that the disease affecting the mynas was a different strain from the one found in the UK songbirds. Few of the infected birds had signs of poor health, suggesting that they can carry the disease without it being fatal.

Because myna birds are so invasive, however, there is a significant risk that they can spread the disease to other species that might not otherwise come into contact with it.

Dr Kevin Tyler, from UEA and a senior author of the study, said: "Mynas are able to roost almost anywhere in warm climates, which is one reason they are so successful, but it could also mean they are likely to spread the disease further.

"Mynas have already been implicated in the spread of bird flu through contact with poultry, so this could be of concern to poultry farmers. However, further research and testing is needed to see whether the disease has yet spread from mynas to other species."

He added: "In the UK, pigeons carry this disease without serious symptoms and it looks like myna birds are able to do the same. This could be due to a natural resilience to the disease, or it could be that this is a less virulent strain - again, we need to carry out further research to investigate."

Although mynas are thought to be native to the Indian subcontinent, populations of the birds have spread around the world, so the team is also keen to test for the disease in other countries.

'Endemic infection of the common mynah Acridotheres tristis with Trichomonas gallinae the agent of avian trichomonosis', by Hassan Ali Farooq, Hammad Ahmad Khan, Abdulwahed Fahad Alrefaei and Kevin Morris Tyler, is published in Parasitology on April 23, 2018.