Releasing pheasants into the countryside may boost the risk of humans catching Lyme disease, according to new research from universities and the UK Health Security Agency.

The study, published in the journal Ecology Letters, found the bacteria that can cause Lyme disease was almost 2.5 times more common in ticks located in areas where the gamebirds were released.

Some 35 to 48 million pheasants are released into the UK countryside each year to be shot for sport. Lyme disease-infected ticks can be found right across Scotland, but are most prevalent in the Highlands and Tayside.

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Contracting the disease can be life-changing, causing later-stage symptoms including pain, muscle, heart and memory issues, disturbed sleep and fatigue, as well as anxiety and depression.

The prevalence of ticks in Scotland is set to increase by a quarter in the coming decade under the most "optimistic" climate change scenario, according to a University of Stirling study published last August.

If global temperatures are limited to 1C by 2080, the prevalence of ticks will increase by 26 per cent, but under a 4C temperature rise, the number will almost double, with only the highest peaks in Scotland remaining too cold for the parasites.

In the pheasant study, from the UK Government's Health Security Agency and academics at Cardiff and Exeter universities, researchers studied ticks in 25 woodland areas in South West England where pheasants are released - and 25 nearby sites where no pheasants are released.

'Increased risk' of Lyme disease for humans

"Borrelia bacteria can live in a wide range of hosts, including pheasants, wild birds and mammals - and humans," said Emile Michels, from Exeter's university's centre for ecology and conservation.

"Pheasants are known to be 'competent' hosts of Borrelia - meaning they have a relatively high likelihood of contracting and retransmitting the bacteria.

"More research is needed, but our findings suggest there may be an increased risk of potential exposure to Borrelia-infected ticks for people - such as gamekeepers - who work in woodlands where pheasants are released in numbers."

Dr Jolyon Medlockfrom the Health Security Agency said the government body lacked data on "the resulting impact on human health, including evidence of Lyme infection", but would continue to work with academics to better understand the factors that cause the disease to be transmitted.

A spokesperson for Lyme Disease UK said they welcome "all research that gives a greater understanding of the bacteria that causes Lyme disease". They added: "As ticks now seem to be staying active in some areas throughout the colder months, due to our warming climate, it is essential to know what drives the spread of this bacteria".

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The Scottish Greens' spokesperson for rural affairs, Ariane Burgess MSP pointed out that pheasants' "capacity to spread Lyme disease to humans has been discussed and debated for decades".

It was therefore "not surprising to consider the risks increasing through breeding and releasing more of these beautiful birds for humans to simply murder as a pastime," she claimed.

Burgess added: "Hunting is not only cruel in its practice. The ritualistic mass-killing of species like pheasants for sport is also majorly damaging to our biodiversity and should be completely outlawed in Scotland."

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Pheasant header image thanks to Freek Wolsink. Tick header image thanks to Erik Karits.