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Experts say that British deer are unfairly chosen as the main culprits for the spread of Lyme disease. On the other hand, they say that the role played by other factors – and animals – should also be examined.
The deer hunting season started last week when BMJ reported that British cases of the disease, a bacterial infection transmitted to humans through an infected tick bite, could be three times higher than previously estimated.
This triggered calls for the killing of deer – a major host of adult ticks – with an author suggesting that the nation should develop the taste of "bambiburgers".
Professor Lucy Gilbert, animal ecologist at the University of Glasgow and pest and parasite specialist, said that it was widely acknowledged that recorded Lyme disease incidents were on the rise and that there was no evidence that they had been infected. it was "definitely accepted" as the number of ticks in the environment. has increased in recent decades.
"It is very likely that the increase and abundance of deer is one of the causes of the increase in the number of ticks in the environment," said Gilbert, pointing out that the number of deer in Scotland was about four times the 1960s "and now spread from south to north England and Wales.
She added that studies had also suggested that deer had spread over the last 50 years and that the muntjac, which was formerly found only in southern England, encroached now on the Scottish border.
But Gilbert advised against correlating a higher number of deer with an increase in reported cases of Lyme disease.
"The risk of Lyme disease is determined by the density of ticks, not the tick density," she said. "And deer do not infect ticks."
Professor Rory Putman, biology researcher and president of the British Deer Society, explains that this is explained by the fact that deer are "unskilled hosts" for Borrelia burgdorferi, the organism responsible for the disease. of Lyme carried by infected ticks.
"Once they have responded to their first infected bite, they produce antibodies that not only prevent the infection of the deer themselves, but continue to circulate in the blood and can play an active role in the cleaning all ticks that feed next, eliminating Borrelia. its system and thus preventing it from infecting anything else. "
Tick infection occurs when, as larvae, they feed on smaller hosts such as mice, voles, squirrels, hedgehogs and almost all species of birds, especially those that feed on the ground, such as blackbirds, thrushes and blackbirds.
"If you want a large population of juvenile ticks, you need those big hosts, like deer, sheep or hares, that feed adult females so that they can lay their eggs," said Gilbert, whose work on the relationship between deer density and Lyme disease will be completed in the next three to five years and, given the lack of field data, will likely be the subject of many studies.
Putman said that in his opinion, a warmer and wetter climate facilitating the survival of ticks, has been an important factor in the increase in the number of reported cases, which can lead to paralysis and, in rare case, death. Some experts have also criticized some experts for not using the technique of quenching sheep, allowing ticks to spread in sheep.
Until now, an influential study, conducted in Norway and published in the journal Nature Communications in 2016, found that 'the management of deer populations will have some effect on the incidence of the disease, but that … Lyme disease could nevertheless increase due to the presence of multiple drivers'.
"We still do not know what is the impact of deer density on the risk of Lyme disease, but it is unlikely to be negative," said Gilbert. "At best, it could be just neutral."
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