Watch out, ticks about!
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Many, if not most, of those working in the countryside will have come across ticks, but it is worth emphasising the need for awareness as tick-borne human disease is spreading in the UK.
Our island status has protected us to a certain extent, so we have fewer of these pathogens in our wildlife than most of Europe where they have known about Lyme disease for more than a century. The UK’s first confirmed case was not recognised until 1985.
What diseases do UK ticks carry?
Lyme disease, or Lyme borreliosis, is by far the most common human pathogen carried by UK ticks and the reservoir of these bacteria is mainly small rodents and birds. Another borreliosis, caused by Borrelia miyamotoi, has also recently been confirmed in UK ticks.
Other diseases include Q Fever, Rickettsia Spotted Fevers, Anaplasmosis and Babesiosis. In 2019-2022 there has been increasing confirmation of the presence of tick-borne encephalitis in Thetford Forest and the New Forest – evidence that, as with Ash Dieback, inevitably other diseases will continue to cross from mainland Europe. Pets can now travel freely throughout Europe and there is no mandatory requirement for tick treatment on imported dogs.
How is Lyme disease passed?
A larval tick hatching from the egg may pick up bacteria from a mouse, moult into the nymph stage and pass the bacteria onto its next host. The nymph is small enough to miss – nothing like as large as the next, adult, stage you may have seen on a dog or other larger mammal. It is the nymph that is most commonly found on humans.
The bacteria and tick have a complex, highly evolved, relationship. The bacteria stay dormant in the cold blooded tick, but when it starts to feed on warm mammalian blood, the bacteria are mobilised, change their structure slightly and are expelled by the tick in a form ready to cause disease. This doesn’t happen immediately as, unlike a mosquito, the tick spends some hours preparing a feeding pit to ensure it can access a good blood supply. As well as injecting an anticoagulant, to ensure the blood flows, it also injects immunosuppressive compounds and an anaesthetic and so your body does not immediately react. Only after this do the bacteria start to be released into your blood stream. Clever stuff!
How common are infected ticks?
UK research has analysed ticks carried by dogs and deer as well as ticks collected in the field. Not every UK tick carries an infection, by any means. Surveys in different parts of the UK have shown that the percentage of ticks carrying disease ranges from zero to about 20%. This varies from place to place, seasonally and also from year to year.
If you find any ticks, either on yourself or on animals, you could help research by submitting them to the Public Health England Tick Surveillance Scheme.
Where and when should you be wary?
Not just in the countryside! Ticks require a microclimate with a relative humidity above 80% for most of the time. They are therefore ground-based and complete each moult in the protection of decaying vegetation. The tick will then climb a nearby piece of vegetation, extending its hooked front legs which will be caught on the fur or clothing of a moving animal. This behaviour is known as questing and potentially exposes the tick to desiccation so ticks are much less likely to be questing in very dry conditions.
A suitable habitat for ticks is vegetation that provides shade, humidity and a layer of leaf litter, abundant small animals on which the larvae and nymphs can feed and sufficient large animals to maintain a high enough adult population for reproduction. Deciduous woodland with good understory vegetation is ideal, but ticks can also abound in coniferous forest, rough pasture and managed gardens, particularly those bordering woodland with a strong wildlife population. Large town parks with wilder areas, also harbour a tick population.
Because colder temperatures and dry conditions reduce tick activity, ticks are most active between March and October, with a lull during a dry summer period. Although ticks tend to remain dormant through a cold winter, they will be active in temperatures exceeding 7oC. Warmer winters mean that in many areas of the UK ticks can be active throughout the year.
What prevention methods should you use?
Itching from a tick doesn’t usually start for about 12 hours or so after the tick attaches, so you need to go looking for the ticks to find them. The key to avoidance of tick-borne disease is awareness.
It is sensible to brush off work clothes before going inside and the easiest way to find an attached tick is to run your hands over your skin in the bath or shower. Something that might be a small scab, that you can rock back and forth, needs investigation. Use a tick remover to extract the tick, which has barbed mouthparts embedded in your skin. If you leave a small part of the tick in your skin, don’t worry unduly. You can introduce more infection by digging around with a needle, and your body will get rid of the small bit left.
You have removed a tick – what now?
Just be aware of symptoms starting in the next couple of weeks. A plain red, non-itchy spreading rash, sometimes with a clear centre, is indicative of Lyme disease. Show your GP who should treat you without a blood test. Also consult your GP if you experience any ‘flu like symptoms after a bite, even if you haven’t noticed a rash. The difficult-to-see spot behind your knee is a very common place for ticks to attach.
There is a range of other symptoms which could occur, so if you fall ill in any way following a tick bite, consult your GP.
Testing for Lyme disease
As Lyme disease is the most common tick-borne infection, you are likely to be offered a blood test if the rash wasn’t noticed. The blood test detects antibodies which take some weeks to develop, so early tests are likely to be negative. Once the antibodies have developed, they last for years, even in people treated. This will cause difficulties as more and more UK residents contract Lyme disease, because “positive test result” could mean “past disease” and it is then down to you and your GP to consider the likelihood of Lyme disease and other possibilities.
Treatment is with antibiotics and is extremely effective in the first few months of infection. Symptoms can sometimes persist if the disease is treated late, but the cause of these symptoms (and how to treat them) is not yet known. They could be due to residual infection, an auto-immune reaction or damage to nerves which take a long time to heal.
Tick-borne disease is not something to panic about, but is definitely something that every countryside worker should be aware off.
More details about ticks, diseases, symptoms and testing is available on the Lyme Disease Action website, with links to the NICE Guidance.
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