More ticks carry Lyme disease bacteria in pheasant-release areas

Ticks are more likely to carry the bacteria that can cause Lyme disease in areas where pheasants are released, new research shows.

Pheasants are not native to the UK, but about 47 million are released here each year for recreational shooting.

Researchers studied ticks in 25 woodland areas in South West England where pheasants are released – and 25 nearby control sites where no pheasants are released.

They found that Borrelia spp. – the bacteria that can cause Lyme disease – was almost 2.5 times more common in ticks in the pheasant-release areas.

The research was carried out by the University of Exeter and the UK Health Security Agency.

“Borrelia bacteria can live in a wide range of hosts, including pheasants, wild birds and mammals – and humans,” said Emile Michels, from the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall.

“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.”

Researchers tested ticks at different life stages (nymphs and adults) and found that, overall, the proportion containing Borrelia was 7.8% in pheasant-release woodlands, and 3.2% where pheasants were not released.

Dr Barbara Tschirren, also from the University of Exeter, said: “Our findings are evidence of ‘spillback’ – where non-native species increase the prevalence of native pathogens.

“This can be an important route for the emergence of zoonoses (diseases that animals can give to humans).”

Dr Jolyon Medlock, head of the Medical Entomology and Zoonoses Ecology team at UKHSA, said: “While we have observed an increase in the bacteria that can cause Lyme disease in ticks, we do not have data on the resulting impact on human health, including evidence of Lyme infection.

“Following these findings, we continue to work with academic partners to better understand what drives Borrelia transmission, including the roles of climate and environmental change.”

The control sites in the study were one to two kilometres from the pheasant-release sites, so more research would be required to see if Borrelia in ticks declines further at greater distances.

Emile Michels’ PhD is funded by the NERC GW4+ DTP scheme.

The paper, published in the journal Ecology Letters, is entitled: “The release of non-native gamebirds is associated with amplified zoonotic disease risk.”