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| Deer slaughter may not stem rise in Lyme disease, experts warn | |
| (about 7 hours later) | |
| Britain’s deer are being unfairly singled out as the chief culprits in spreading Lyme disease, experts claim. By contrast, they say the role played by other factors – and animals – should also be examined. | Britain’s deer are being unfairly singled out as the chief culprits in spreading Lyme disease, experts claim. By contrast, they say the role played by other factors – and animals – should also be examined. |
| Open season on deer commenced last week when the BMJ reported that UK cases of the disease, a bacterial infection passed to humans by an infected tick bite, may be three times higher than previously estimated. | Open season on deer commenced last week when the BMJ reported that UK cases of the disease, a bacterial infection passed to humans by an infected tick bite, may be three times higher than previously estimated. |
| This triggered calls for a cull of deer – a major host of adult ticks – with one writer suggesting that the nation should develop a taste for “Bambiburgers”. | This triggered calls for a cull of deer – a major host of adult ticks – with one writer suggesting that the nation should develop a taste for “Bambiburgers”. |
| Professor Lucy Gilbert, an animal ecologist at the University of Glasgow and an expert on pests and parasites, said it was widely accepted that recorded incidents of Lyme disease have been increasing and that it was “definitely accepted” that the number of ticks in the environment has risen in recent decades. | Professor Lucy Gilbert, an animal ecologist at the University of Glasgow and an expert on pests and parasites, said it was widely accepted that recorded incidents of Lyme disease have been increasing and that it was “definitely accepted” that the number of ticks in the environment has risen in recent decades. |
| “It is highly likely that the increase and abundance of deer is one of the causes of the increase of ticks in the environment,” said Gilbert, who pointed out that the number of red deer in Scotland has increased by “something like four times since the 1960s” and, that they are now spreading south to the north of England and into Wales. | “It is highly likely that the increase and abundance of deer is one of the causes of the increase of ticks in the environment,” said Gilbert, who pointed out that the number of red deer in Scotland has increased by “something like four times since the 1960s” and, that they are now spreading south to the north of England and into Wales. |
| She added that studies also suggested roe deer have been spreading over the past 50 years, and that muntjac, once only found in the south of England, are now encroaching on the Scottish border. | She added that studies also suggested roe deer have been spreading over the past 50 years, and that muntjac, once only found in the south of England, are now encroaching on the Scottish border. |
| But Gilbert counselled against drawing a correlation between greater deer numbers and an increase in reported cases of Lyme disease. | But Gilbert counselled against drawing a correlation between greater deer numbers and an increase in reported cases of Lyme disease. |
| “Lyme disease risk is determined by the density of infected ticks, not the density of ticks,” she said. “And deer do not infect ticks.” | “Lyme disease risk is determined by the density of infected ticks, not the density of ticks,” she said. “And deer do not infect ticks.” |
| These big hosts, such as deer, sheep or hares, feed the adult female ticks so they can lay their eggs | These big hosts, such as deer, sheep or hares, feed the adult female ticks so they can lay their eggs |
| Professor Rory Putman, a research biologist and chair of the British Deer Society, explains that this is because deer are “non-competent hosts” for Borrelia burgdorferi, the Lyme disease organism carried by infected ticks. | Professor Rory Putman, a research biologist and chair of the British Deer Society, explains that this is because deer are “non-competent hosts” for Borrelia burgdorferi, the Lyme disease organism carried by infected ticks. |
| “Once they have reacted to their first infected bite, they produce antibodies which not only prevent infection of the deer themselves but carry on circulating in the bloodstream and may have an active role in cleansing any subsequent ticks which feed on them, removing the Borrelia from its system and thus preventing it infecting anything else.” | “Once they have reacted to their first infected bite, they produce antibodies which not only prevent infection of the deer themselves but carry on circulating in the bloodstream and may have an active role in cleansing any subsequent ticks which feed on them, removing the Borrelia from its system and thus preventing it infecting anything else.” |
| Rather, the infection of ticks takes place when, as larvae, they feed on smaller hosts such as mice, voles, squirrels, hedgehogs and almost all bird species, especially those that forage on the ground such as blackbirds, thrushes and robins. | Rather, the infection of ticks takes place when, as larvae, they feed on smaller hosts such as mice, voles, squirrels, hedgehogs and almost all bird species, especially those that forage on the ground such as blackbirds, thrushes and robins. |
| “If you want a big population of juvenile ticks, then you do need these big hosts, such as deer, sheep or hares, that feed the adult females so 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 data in the field, is likely to be widely studied. | “If you want a big population of juvenile ticks, then you do need these big hosts, such as deer, sheep or hares, that feed the adult females so 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 data in the field, is likely to be widely studied. |
| Putman said he believed a warmer, wetter climate, which has made it easier for ticks to survive winters, was a significant factor in the increase in reported cases of the disease, which can lead to paralysis and, in rare examples, death. A lack of mandatory sheep-dipping, allowing a spread of ticks on sheep, is also blamed by some experts. | Putman said he believed a warmer, wetter climate, which has made it easier for ticks to survive winters, was a significant factor in the increase in reported cases of the disease, which can lead to paralysis and, in rare examples, death. A lack of mandatory sheep-dipping, allowing a spread of ticks on sheep, is also blamed by some experts. |
| So far, one influential study, conducted in Norway and published in the journal Nature Communications in 2016, has found that “managing deer populations will have some effect on disease incidence, but … Lyme disease may nevertheless increase as multiple drivers are involved”. | So far, one influential study, conducted in Norway and published in the journal Nature Communications in 2016, has found that “managing deer populations will have some effect on disease incidence, but … Lyme disease may nevertheless increase as multiple drivers are involved”. |
| “We still don’t know what the impact of deer density is on Lyme disease risk but it’s unlikely to be negative,” Gilbert said. “At best, it could be just neutral.” | “We still don’t know what the impact of deer density is on Lyme disease risk but it’s unlikely to be negative,” Gilbert said. “At best, it could be just neutral.” |
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