The bird shooting industry is responsible for a huge amount of harm. For example it sells vast numbers of birds to be shot dead, traps and kills native predators like foxes and stoats on a huge scale to ‘protect’ its birds, and it is almost entirely responsible for the scourge of raptor persecution. Now various media have been highlighting a University of Exeter study (“The deliberate release of a non-native species amplifies zoonotic disease risk via spillback”) originally released in October last year.
The study concluded that “the release of non-native pheasants for recreational shooting is associated with almost 2.5 times greater odds of ticks carrying Borrelia sp., the causative agent of Lyme Disease.” Why, and – firstly – what is Lyme Disease?
Lyme Disease
Lyme Disease gets its name from a small coastal town in Connecticut where, in 1975, an unusual cluster of more than 51 cases of pediatric arthritis was pointed out to Yale researchers. They later found that infected deer ticks were responsible for the outbreak.
The disease is transmitted to humans through the bite of feeding ticks, typically Ixodes ricinus (the Castor Bean or Deer Tick) in the UK and Europe and Ixodes scapularis (the Blacklegged or Deer Tick) in the US. Ticks usually attach to an animal when they brush against them, often while the animal is walking through tall grass or shrubs. The ticks themselves pick up the causative agent of Lyme Disease, the spirochete bacterium Borrelia burgdorferi, from mice and deer and pass the bacteria to humans through their bites. Not all ticks carry the bacterium and not all tick bites will lead to Lyme, Disease but Borrelia can cause a range of symptoms, including a characteristic ‘bullseye’ shaped rash (erythema migrans), fever, headache, fatigue, and joint or muscle pain. If left untreated with antibiotics, Lyme Disease can spread to the heart, nervous system, and joints. In very rare instances it can cause encephalitis and meningitis.
Who gets it?
Lyme Disease is not a ‘new’ or ‘modern’ disease, of course. Ticks have been feeding on animals for millions of years (a tick was found clinging to a dinosaur feather in amber that’s around 100 million years old), and an autopsy on a 5,300-year-old mummy indicated the presence of the bacteria which cause Lyme Disease.
While still relatively unusual here, Lyme Disease is increasing. The UK Government monitors the disease in England and Wales. Though not notifiable, since October 2010 every microbiology laboratory (including those in the private sector) in England is required to notify all laboratory diagnoses of Lyme disease to the UK Health Security Agency (UKHSA). The data is not current, but mean annual incidence rates for laboratory-confirmed cases have risen from 0.38 per 100,000 population for the period 1997 to 2000, to a peak of 2.77 cases per 100,000 population in 2018. It has been estimated that there are also between 1,000 and 2,000 additional cases of Lyme disease each year in England and Wales that are not laboratory-confirmed.
Lyme Disease is thought to be the most common vector-borne human infection in England and Wales (and the US). Based on laboratory-confirmed Lyme Disease, cases occur in people of all ages and both sexes are equally susceptible. Peaks in cases are seen in those aged between 45 and 64 years (perhaps reflecting the ages of people who work in forestry and on shoots), followed by those aged from 25 to 44 years.
Most of these cases probably acquired infection in late spring and early summer, allowing for the time period between being bitten, developing symptoms, and developing levels of antibodies high enough to give positive results on laboratory tests.
While that may not seem like an ‘epidemic’ (especially when compared with the almost half a million annual cases in the US), increasing awareness of Lyme’s undoubtedly causes genuine anxiety and every case – particularly if in a child – can be deeply concerning.
Could that awareness – along with the ever-increasing numbers of ‘Keep Out’ shoot signs adorning woodlands – mean that more and more of the countryside is effectively being put out of bounds to the general public?
Many people already feel that the countryside is not open to them, catching a potentially serious disease from it is hardly an encouragement to visit…
The link with pheasants
As stated above, the media have been highlighting an October 2024 research paper by the Centre for Ecology and Conservation on the University of Exeter’s Penryn campus in Cornwall and the UK Health Security Agency (UKHSA).
In that study researchers looked at ticks in 25 woodland areas in south-west England where pheasants were released and 25 nearby control sites where no pheasants were released. They found that the bacteria that can cause Lyme Disease was almost 2.5 times more common in ticks in the pheasant-release areas (7.8% in pheasant-release woodlands and 3.2% where pheasants were not released).
They say that their work “provides direct evidence that non-native species [ie pheasants released for shooting] can amplify zoonotic pathogens via spillback [which is usually defined as “where non-native species increase the prevalence of native pathogens”] in an ecologically meaningful context.”
That’s quite a mouthful, but essentially means that releasing millions of non-native pheasants into the countryside for shooting increases the number of organisms (such as a virus, bacterium, fungus, or parasite) which can be transmitted between animals and humans causing an infectious disease.
That wouldn’t seem to us to be all that surprising. Many species carry Ixodes ticks (mice and deer for example), but pheasants are relatively large birds, released in extremely high densities, that spend their time foraging low down in habitats that are ideal for disease-carrying ticks.
Not the only evidence
While it is good news that the media are increasingly looking critically at the shooting industry, the 2024 study is not unique.
In 1998’s ‘Competence of Pheasants as Reservoirs for Lyme Disease Spirochetes’ Kurt Klautenbach et al stated that “Pheasants constitute a major part of the ground-feeding avifauna of England and Wales and are important hosts to immature stages of Ixodes ricinus”.
Their laboratory study injected reared pheasants with cultured Borellia burgdorferi organisms, and a second group of birds was infested with Ixodes ricinus nymphs collected “from a focus of Lyme borreliosis in southern England”. Both groups proved to be “infective for ticks. The birds that were infected by tick bites proved to be significantly more infective for ticks (23% of the xenodiagnostic ticks positive) than those infected by needle.”
The authors concluded that “pheasants are reservoir competent [ie have the ability to maintain and transmit a pathogen to new hosts or vectors] for Lyme borreliosis spirochetes and potentially play an important role in the maintenance of B. burgdorferi in England and Wales.”
More pheasants, more disease
The 1998 study stated that “pheasants are significant hosts for the principal European tick vector, Ixodes ricinus” and “pheasants potentially play a role in sylvatic Lyme borreliosis transmission cycles.” They estimated that “over the past 30 years the number of artificially reared pheasants released into British woodlands in early summer to supplement shooting in winter has increased at 4% per annum and now stands at 20 million.”
The industry hasn’t been standing still in the intervening decades. A staggering number of pheasants – some 40 million – are being released every year. Breaking down how many are released in woodlands vs being released in suboptimal moorland to supplement grouse shoots is not really possible, but there is little doubt that the 1998 figures will be far lower than current figures.
Shooting lobbyists are quick to point out that pheasants – as we have pointed out above – are not the only vectors and rubbished the 1998 findings by providing anecdotal evidence that gamekeepers were not reporting the disease. Why lobbyists would think that a lowland gamekeeper who depends almost entirely on producing pheasants to shoot would point to pheasants spreading disease to them is not explained…
Ticks occur in the wild, that is not in doubt. Other species are bitten by ticks, that is not in doubt either. But anyone who thinks that releasing millions and millions of ‘significant hosts’ into tick habitat won’t have a serious impact is deluded.
It’s been known for decades that an industry that is dumping millions of pheasants into an already stressed countryside has not only been normalising cruelty but has been providing an excellent reservoir for the bacteria that cause Lyme Disease.
