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Understanding the risks with rewilding

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Beavers have already been reintroduced to parts of Devon and Scotland

By Josh Loeb

The trend for reintroducing formerly extant mammals such as beavers and wild boar into the British countryside could have an epidemiological downside, according to two disease experts who spoke at the World One Health congress this month.

Rowland Kao, chair of veterinary epidemiology and data science at the University of Edinburgh, and Flavie Vial, a leading scientist at the APHA, were both careful to make clear that they were not advocating halting species reintroduction projects. However, both highlighted potentially negative public health consequences from ‘rewilding’ schemes.

By way of example, Vial highlighted the risk of introducing the Echinococcus multilocularis tapeworm with imported beavers, while Kao pointed to the potential for expanding deer populations to act as reservoirs for bovine TB.

Kao, who sits on Defra’s science advisory council, said the civil service was aware that policies aimed at boosting biodiversity and tackling the effects of climate change could also inadvertently provide pathogens with new opportunities to spread.

He told delegates: ‘We’re trying to respond to climate change by changing the way we do things, and we’re trying to increase the amount of wildlife – and they’re both very, very important things.’

However, he went on to warn: ‘Wildlife may hold certain diseases. Those may always have been out there – but by increasing the amount of contact between wildlife and livestock, or between wildlife and humans, that increases the opportunity for disease to transmit.

We tend not to think about the effect of disruption

‘The other factor we tend not to think about so much is the effect of disruption. Things can reach a stable state where you sort of know what’s happening [epidemiologically] and you know what’s going to happen next. But as soon as you disrupt that, as soon as you change the pattern of what’s going on, that provides diseases that may always have been there with new opportunities to move from one population to another – those are the kinds of changes we’re implementing in response to climate change and in response to trying to create greater biodiversity.’

Such issues must be given due consideration when formulating policy, he added.

Vial, for her part, said the risk of exotic diseases impacting the UK was likely to increase in future – brought about by processes as varied as climate change, post-Brexit trading patterns and the government’s nature recovery plans.

In her talk – titled ‘Beavers, Brexit and birch trees’ – she said: ‘We are not arguing that we should not consider [species] reintroductions as part of the UK’s ecological restoration plans, but we are advocating caution and an increased understanding about what is unknown about the epidemiological consequences of rewilding – in particular when released animals are likely to be immunologically stressed, and when post-release management strategies, such as supplementary feeding, may facilitate pathogen transmission.’

It was important to consider greater health screening and quarantine for animals being imported for reintroduction purposes, she stressed.

She even said that the creation of wildlife corridors comprising newly planted woodland and restored waterways could potentially hasten disease spread.

‘Connecting our best wildlife sites will no doubt provide much-needed opportunities for species conservation and the reintroduction of native species, such as the pine marten, for example,’ she said. ‘But as epidemiologists we have to question the role this growing “green and blue” network throughout the UK will play in wildlife disease spread, control and management.’

On Brexit, she said that, as trade patterns and flows of goods and people evolved outside of the EU, a greater risk of invasive and non-native species entering and establishing themselves in the UK could arise. She cited in particular the risk of wildlife ‘stowaways’ entering the UK via container ships from Asia as the UK moved to do more trade with non-European countries.

‘Species whose native ranges are outside of Europe have an invasiveness potential in the UK that is twice that of species found on the European mainland,’ she said. ‘This has important ramifications when we consider the wider range of trading partners that the UK will be dealing with.’

Enhanced surveillance was needed at key points of import, she said, adding that, in particular, it was vital to enhance surveillance for non-native mosquitoes.

Lockdown may have caused a closer proximity of wildlife to urban areas

Concluding her talk, Vial also said that during the Covid-19 lockdown, as a result of decreased human activity, ‘closer proximity of wildlife to urban areas and farmland is likely to have occurred, potentially increasing the risk of infection spillover’.

In addition, any decline in hunting arising from constraints on non-essential activity during lockdown and beyond ‘could result in...insufficient population control of wildlife reservoir hosts, such as wild boar’.

In terms of improvements, Vial proposed closer working between epidemiologists and ecologists or forestry experts ‘to understand what it is we are trying to do [on agricultural and biodiversity policy]...and to try and anticipate what some of the risks might be and put in place contingency plans’.

Her comments came as Tony Juniper, head of Natural England, this week said proposals to reintroduce lynx into the British countryside could help control deer numbers. Juniper said lynx were a more likely candidate for reintroduction than wolves, which some supporters of rewilding would also like to see reintroduced in the UK. ●

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