The coronavirus pandemic has had a major impact on all our lives. The months of lockdown have taken their toll both on the economy and on mental health. Farming is one of the few industries that continues much the same as ever. But, as I spend another day without leaving my home except to walk my dogs, I have been contemplating pandemics in general.
Covid-19 may be the first major plague to affect humans in this country since the Spanish flu a century ago, but there have been a number to impact plants and animals. It is almost certain that frequency will accelerate, driven by climate change and globalisation, unless we take radical action. With travel and trade throughout the world ever more common, at least until last spring, pests and diseases can spread very quickly as we have seen in recent months.
In farm animals, perhaps the most obvious epidemics have been of Foot and Mouth Disease, particularly those of 1967 and 2001. It is a notifiable disease which means that any suspected outbreak must be reported to the authorities, the Animal and Plant health Agency (APHA), and immediately triggers draconian action, including the slaughter of infected animals and contacts. Such measures have been criticised, not least due to the expense, and future outbreaks may be met with a less robust approach.
There are a large number of notifiable animal diseases including Foot and Mouth Disease, Avian influenza, African and classical swine fever, bovine tuberculosis and bluetongue. There was a significant outbreak of swine fever in East Anglia in 2011 which was thought to be caused by a ham sandwich discarded from a footpath near outdoor pigs. 50,000 animals were destroyed as a consequence. Whether or not that is true, it just shows how easily disease can be spread.
Bluetongue is a disease of cattle, sheep and goats caused by a virus spread by midges that can also infect wild animals such as deer. Originally confined to tropical and subtropical regions, it has spread with global warming and became significant in Europe from 2006. It came across the Channel with midges blown over from France, but there are currently no cases in this country. However, it is still in France and may come again with favourable climatic conditions. Fortunately there is an effective vaccine.
One major concern is African swine fever, another viral disease that causes almost total mortality. There was a major outbreak in China in 2018 resulting in an unconfirmed estimate of 200 million deaths from disease and precautionary culling, perhaps 40% of the entire population. Since then it has spread, creeping closer to these shores. There have been cases in wild boar in Germany and Belgium, so the APHA is extremely concerned to avoid any spread to the UK. There is no vaccine or treatment. Avian influenza, commonly known as bird flu, is currently in this country, thought to be spread by migratory birds. There was an outbreak on Anglesey recently and the whole of England is a Protection Zone with heightened biosecurity measures and an order for the housing of all birds where possible.
But such pandemics are not confined to the animal kingdom, they are widespread amongst plants as well. Perhaps the most catastrophic was Dutch elm disease caused by a fungus spread by elm bark beetles. It was thought to be introduced into this country in the 1960s and swept through the countryside in the 1970s and 1980s, causing the loss of an estimated 25 million elm trees. In France, the loss was put at 97%. There has been research into disease resistant strains but there remain very few elm trees where once it was a common and iconic species in our countryside.
Since then, there has been a succession of pandemics amongst trees. Many have been caused by species of Phytophthora, similar to the microorganism that causes potato blight. P. ramorum caused the loss of millions of larch trees as forests were felled in an attempt to limit the spread. It can also infect oak trees, causing sudden oak death, and sweet chestnut.
Then came ash dieback or Chalara caused by a fungus. It has been known in Europe for around thirty years but was only formally described in 2006 and first recorded in the UK in 2012. Fungal spores can be spread by wind but it is thought that Chalara arrived here in imported ash saplings, thousands of which were coming into the country until the trade was banned in 2012. The Woodland Trust suggests that ‘it will kill 80% of ash trees across the country at a cost of billions. The effects will be staggering; it will change the landscape forever and threaten many species that rely on ash’.
There are numerous other threats to our trees, let alone other plants including farm crops. Horse chestnuts face several, including bleeding canker, leaf-mining moth and leaf blotch fungus. Oaks have acute oak decline, oak wilt and oak processionary moth amongst other threats. The list of current and potential threats is long and one has to wonder which species of tree will remain in a decade or two.
We shall learn lessons from Covid-19 which will reduce the risk of future pandemics, but will they also be applied to plant and animal pests and diseases? Apart from the efforts made to reduce greenhouse gas emissions, there is little we can do to mitigate the threats posed by climate change. New pests and diseases will appear, whether brought in by the wind or migratory species. But we can improve our biosecurity, especially at points of entry, and we can limit the risk of bringing pests and diseases into the country. Why are we importing trees, shrubs and plants that we could be growing in nurseries in this country? No doubt, measures will be introduced to reduce the risk to human health as the result of the current pandemic. They should be applied to plants and animals as well.