Okay, let’s try and bring this down a peg and look at what is really the story behind the sensationalist headline. Whilst it is sometimes amusing to read these stories, the lack of balance with resulting scare-mongering is frustrating.
A study has been performed by Public Health England in association with the National Institute for Health Research Health Protection Research Unit in Emerging and Zoonotic Infections, Liverpool, looking at the presence of Flaviviruses in deer and deer ticks in the UK. Gosh! What a mouthful, even abbreviated that’s NIHRHPRUEZI, yeah! So we’ll just call them “Liverpool” from now on!!!
Anyhow back to the Flaviviruses! Some Flaviviruses cause tick-borne encephalitis (TBE), a condition transmitted by ticks of the Ixodes spp. which usually feed on deer. There are three main types of TBE based upon geographical area:
- European (Scandinavia down to the Adriatic)
- Far-Eastern (Russia, China, Japan)
- Siberian (Siberia and the Baltic)
The surveillance study from PHE and Liverpool looked at the presence of antibodies against Flaviviruses in the serum of deer which had been culled through deer management programs across the UK. They also looked for the presence of viral RNA in ticks taken from the culled deer.
In total, 52 (4%) of 1,309 blood samples from deer showed that the deer had been infected in the past with a Flavivirus. Only 5 of 2,041 (0.25%) ticks tested positive for the TBE virus by viral RNA. So yes this confirms the presence of TBE in ticks and deer in the UK but hang on a minute, the potential for TBE to occur in humans bitten by these infected ticks, although possible, is rare.
So if this rate isn’t very high, why all the concern? Well when the study zoomed in and looked in more detail, the rate of infection in Thetford Forest in Suffolk was actually 47.7% of deer and 2.6% of ticks, and this is as high as ANY other area in the World with on-going transmission of TBE to humans! That’s quite alarming; should I be cancelling my autumn walk in Thetford Forest? Maybe. The Telegraph newspaper is right, it looks like there is a very real possibility of TBE being transmitted to humans, especially following tick bites in Thetford Forest, some areas of Norfolk and the New Forest in Hampshire. These findings add a new breadth to Thetford Forest promoting itself as a “refuge for a rich variety of animal and plant life”.
Where has the TBE virus come from?
Looking at the genetic sequence of the TBE isolates from the ticks in the study showed a similarity to a strain from Norway; which makes sense as Suffolk, in terms of the UK, is geographically close to Norway. It is proposed that infected ticks travel on birds (probably migratory blackbirds and redwings); these infected ticks fall off before attaching to passing deer. The infected ticks feed on the deer which themselves get infected, our native UK Ixodes spp. ticks then feed on the infected deer and become infected. The cycle can then become established.
Humans are actually a dead-end host for TBE as we rarely pass the virus back to uninfected ticks. Fortunately there is no person-to-person transmission although in theory the virus could be transmitted via a needlestick injury from an infected person.
How does TBE present?
The incubation period for TBE is between 3-14 days. Most TBE (66%) is asymptomatic. European TBE usually has a prodrome (early symptoms) of a flu-like illness followed by a seven day asymptomatic phase before neurological symptoms develop such as meningitis, encephalitis, myelitis and spinal paralysis. Symptoms can be mild or severe. There are no specific symptoms or signs associated with TBE although a history of a tick bite can be a useful indicator.
The mortality from European TBE is about 1-2%, whereas it can be as high as 8% with Siberian and 20% with Far-Eastern TBE. Long-term neurological sequelae (resulting from the disease) such as headaches and weakness occur in up to 50% of confirmed cases.
How is TBE diagnosed?
Patients with TBE will have IgM antibodies detectable in their serum. Imaging is non-specific with only 18% of patients having an abnormal MRI scan involving the thalamus, cerebellum, brainstem, and caudate nucleus.
Any patient with suspected encephalitis should have a cerebrospinal fluid (CSF) taken by lumbar puncture. Typically the CSF will have a raised white blood cell count with predominantly lymphocytes. The CSF protein will be normal or slightly raised and the glucose will be normal. TBE is confirmed by detecting viral RNA in the CSF.
How is TBE treated?
There is no specific treatment for TBE. Respiratory compromise due to neurological involvement can require mechanical ventilation in up to 5% of patients.
Can TBE be prevented?
The best way to avoid tick-borne diseases is to avoid being bitten by ticks:
- Use insect repellent
- Wear protective clothing, with long sleeves and long trousers tucked into socks treated with an appropriate insecticide
- Carry out regular tick inspections and remove ticks when found
Vaccination against European TBE is available and effective. The coverage rates vary by country, for example in Austria coverage is 96%. Travellers to high endemic areas who are likely to be exposed to tick bites (camping and hiking in the summer) should be offered vaccination.
So it appears that there is a risk of someone acquiring TBE in the UK, especially in the Thetford Forest area, but this risk is still very low. Not only would they have to be bitten by a tick, but that tick would have to be one of the very few actually carrying the virus. Even then, only 33% will develop any symptoms, and less than 1-2% will actually die.
So let’s put the Telegraph story back into perspective; there is a very low risk of infection. TBE should only be considered if a patient has a good clinical history (e.g. tick bitten dog walker from Thetford Forest), but otherwise we should still think of TBE as an overseas infection.