Ticks are the vectors for a number of bacterial and viral infections that can affect humans. The US Centers for Disease Control and Prevention (CDC) lists 16 potential tick-borne diseases within the US (CDC, 2019a), and the European Centre for Disease Prevention and Control (ECDC) provide factsheets for three diseases that occur in Europe (ECDC, 2020a). There are various others such as the ‘tick-borne spotted fevers’ that the International Association for Medical Assistance to Travellers (IAMAT) list, which are associated with South America, Africa and Asia (IAMAT, 2017). Practice nurses offering pre-travel health advice should refer to country specific information and other resources available to learn more about diseases they are unfamiliar with (National Travel Health Network and Centre [NaTHNaC], 2020).
With limited space to discuss all tick-borne diseases, this article will focus briefly on the those that ECDC (2020a) provide factsheets for: Crimean Congo Haemorrhagic Fever (CCHF), Lyme disease and tick-borne encephalitis (TBE). The preventive vaccinations available in the UK will be discussed, and bite prevention measures which are applicable to any tick-borne disease.
CDC (2019b) surveillance data on reported tick-borne disease in the US for 2018 identifies six different diseases, with Lyme disease responsible for three quarters of the 47 743 cases. ECDC reported 3092 confirmed cases of TBE (ECDC, 2019a), eight of CCHF (EDCD, 2019b), and there was no data for Lyme disease as it was only in 2018 that the ECDC included it in their surveillance programme (ECDC, 2018). Public Health England (PHE) do not have comparable data for 2018, but their 2017 zoonosis report stated 1750 serologically confirmed Lyme disease cases had occurred in the UK (PHE, 2017a).
Geographic distribution
Tick-borne encephalitis
The author personally recalls attending a talk about travel health and disease from over 30 years ago when TBE was mentioned with a map that had a patch of ‘red’ in what was then Czechoslovakia, and the borders it had with Germany and Austria. There was what looked like a cavernous gap to the east before the next ‘red’ patch in what was USSR. The colours may have changed but the most recent map available on NaTHNaC (2017) (Figure 1) demonstrates how the risk for TBE transmission has spread in Europe.
Figure 1. NaTHNaC Tick-borne encephalitis country risk map April 2017. https://travelhealthpro.org.uk/factsheet/22/tick-borne-encephalitis
What this map does not reflect is the PHE announcement of October 2019 that TBE virus had been detected in ticks for the first time in UK. The virus has been detected in a small number of ticks in Thetford Forest and an area on the border between Hampshire and Dorset in the UK. This comes alongside one highly probable case of TBE in a European visitor who reported having been bitten by a tick in the New Forest and later becoming ill (PHE, 2019).
In light of this information, it is timely for health care providers working with pre- and post-travel populations, primary care and urgent/emergency service providers to look again at this disease and refresh their knowledge.
Crimean Congo Haemorrhagic Fever
The World Health Organization (WHO) (2020a) states that CCHF is endemic in all of Africa, the Balkans, the Middle East and Asia.
ECDC (2020c) report that human infections have been reported from the following countries: Albania, Armenia, Bulgaria, Kazakhstan, Kosovo, Russia, Serbia, Tajikstan, Turkey, Turkmenistan, Ukraine and Uzbekistan, with locally acquired cases diagnosed in Greece and Spain in 2016. This suggests that CCHF is a disease that is widening its spread.
In response to the 2016 infections in Spain, PHE (2017b) acknowledged that CCHF is not present in the UK and nor are there any established populations of Hyalomma ticks, the vector of CCHF virus (CCHFV). They concluded that the risk of infection in the UK was low.
Lyme disease
WHO (2020b) state that Asia, north-western, central and eastern Europe and the USA all have forested areas where Lyme borreliosis is present in tick populations and therefore pose a risk for human transmission of Lyme disease. ECDC (2016) report that Central Europe is the region with the highest infection rate, specifically Austria, Czech Republic, southern Germany, Switzerland, Slovakia and Slovenia.
From a UK perspective, the National Institute for Health and Care Excellence (NICE) report that Lyme disease can occur anywhere in the UK, but 50% of diagnosed cases are from the South East and South West of England. There is also a high incidence reported in Scotland (NICE, 2018).
Transmission of tick-borne diseases
The method of spread for tick-borne infections may vary depending on the tick species and habitat. Ticks can feed on a number of different mammals, birds, reptiles and amphibians, with most preferring a different host at different stages of their life cycle (CDC, 2019c).
TBE virus is carried inside the tick and is maintained in nature through the cycle of an infected tick biting and infecting small animals (voles and mice), domestic livestock, foxes, bats, hares, deer, wild boar, dogs and some bird species. These act as reservoirs of the virus until the next tick bites and ingests blood containing the virus to transmit to the next host, and so the cycle perpetuates.
Humans occasionally become part of the cycle of tick-borne infection if encroaching into areas where the virus or bacteria is present (NaTHNac, 2017; ECDC, 2020b). NICE (2018), in relation to Lyme disease, comments that ticks live in grassy and wooded areas, both in rural and urban locations, and that people who spend time in these areas for work or recreation are at increased risk of tick exposure.
TBE is a disease caused by a virus transmitted to a human primarily from the bite of an infected tick of the Ixodes species, although it can also be transmitted through consumption of unpasteurised milk or dairy products from infected animals.
Pfeffer and Dobler (2010) have produced infographic cycles for a number of different tick species. Figure 2 relates to the Ixodes species responsible for the transmission of TBE.
Figure 2. Schematic drawing of the transmission cycle of tick-borne encephalitis virus.
Tick-borne encephalitits: signs and symptoms
TBE is one of the flaviviruses, others of which include yellow fever, Japanese encephalitis and dengue (NaTHNaC, 2017). TBE affects the central nervous system and can cause a spectrum of disease—from a mild short-lived illness to a more severe life-threatening illness with the potential for severe neurological complications.
The majority of people who are infected with TBE virus do not develop symptoms. Approximately 2–30% develop a temperature after an incubation period of around 8 days (range of 2–28 days) (NaTHNaC, 2017). TBE tends to follows two stages, with the first stage of the disease lasting up to a week. The symptoms of this are non-specific and flu-like with fever, fatigue, headache and muscle pains. An interval of 1–20 days follows, during which time patients usually have no symptoms. Around one-third of those with initial symptoms progress to the second stage of disease. The second stage of TBE occurs with a sudden rise in temperature and clinical features of:
- Meningitis (inflammation affecting brain lining only)
- Meningoencephalitis (affecting the brain and its lining)
- Meningoencephalomyelitis (the most severe form also affecting the spinal cord).
Cases that progress to the second stage tend to develop long-term neurological complications. The second phase of illness in children is usually limited to meningitis whereas adults over the age of 40 years are at increased risk of developing meningoencephalitis or meningoencephalomyelitis, with higher mortality rates in those over the age of 60 years (NaTHNac, 2017).
Crimean Congo Haemorrhagic Fever: signs and symptoms
CCHF is a viral infection caused by CCHF virus, which belongs to the genus Nairovirus of the Bunyaviridae family. In humans it causes severe disease with a risk of nosocomial transmission and a high fatality rate. The occurrence of the disease is linked to the geographical distribution of hard tick vectors, mostly from the Hyalomma genus (ECDC, 2020c).
The incubation period is usually 3–7 days (ranging from 1 to 13 days) (ECDC, 2020c). Onset of CCHF is sudden, with early signs and symptoms including headache, high fever, back pain, joint pain, stomach pain and vomiting. Red eyes, a flushed face, a red throat, and petechiae (red spots) on the palate are common. In addition, symptoms may also include jaundice, and, in severe cases, changes in mood and sensory perception. Progressively large areas of severe bruising, severe nosebleeds, and uncontrolled bleeding at injection sites can be seen, beginning on about the fourth day of illness and lasting for around 2 weeks. In documented outbreaks of CCHF, fatality rates in hospitalised patients have ranged from 9% to as high as 50% (CDC, 2013).
The length of the incubation period varies depending on several factors, including the viral dose and the route of exposure, and is often shorter following nosocomial infection (ECDC, 2020c). The convalescent period begins about 10–20 days after the onset of illness. The long-term effects of CCHF infection have not been studied well enough in survivors to determine whether or not specific complications exist, and recovery is slow (CDC, 2013).
In endemic areas, those most at risk are farmers, veterinarians and abattoir workers (ie people who deal with agricultural and/or domestic animal husbandry or slaughter activities—meat itself is not an infection source). In addition, anyone exposed to ticks undertaking outdoor activities in endemic areas is also at risk (ECDC, 2020c). Healthcare workers are also at risk when nursing CCHF patients and application of strict personal protection measures is essential.
PHE (2014) have identified that infections pass to humans by not only the bite from an infected tick but also by contamination with tick body contents (for example, if you squash a tick between your fingers).
Lyme disease: signs and symptoms
NICE (2018) states that Lyme disease (Lyme borreliosis) is a tick-borne bacterial disease caused by different genospecies of Borrelia and comments that the risk of infections is greater the longer a tick is attached to the skin. ECDC (2016) comment that the subspecies B. burgdorferi comprises at least 15 genospecies that exist worldwide. PHE specify the tick Ixodes ricinus as the source in the UK (PHE, 2018).
ECDC (2016) differentiate the clinical presentation into early and late manifestations, while also stating that those with the infection can also be asymptomatic. NICE (2018a) states that the diagnosis of Lyme disease is made in people presenting with erythema migrans (a red rash) that:
- Increases in size and may have a central clearing (often known as the ‘bulls-eye rash’)
- Is not usually itchy, hot or painful
- Becomes visible from 1–4 weeks (but can be 3 days to 3 months) after a tick bite and can last for several weeks.
- Is usually at the site of a tick bite.
NICE (2018b) have produced an image resource with photographs of various presentations of the rash associated with Lyme disease. They further advise health professionals to consider Lyme disease in people presenting with the symptoms listed below and a history of tick bite or potential exposure to ticks:
- Fever and sweats
- Swollen glands
- Malaise
- Fatigue
- Neck pain or stiffness
- Migratory joint or muscle aches and pain
- Cognitive impairment, such as memory problems and difficulty concentrating (sometimes described as ‘brain fog’)
- Headache
- Paraesthesia.
ECDC (2016) identifies that late presentations—neuroborreliosis (a central nervous system disorder)— may be seen in about 10% of cases. Symptoms include facial palsy and lymphatic meningitis and occur about 6–12 weeks post-infection.
Late-presenting symptoms in those people who have not previously been treated can include persistent skin infection, skin inflammation and eventually thinning of the skin leading to neuropathy—symptoms that resemble multiple sclerosis and Lyme arthritis.
All persons exposed to tick bites are at risk of becoming infected (ECDC, 2016).
Tick avoidance and personal protection measures
The preventive measures for the individual are generic, not disease-specific. The key message is to avoid being bitten and to check and remove any ticks as soon as possible (NICE, 2018a; NaTHNaC, 2018a; CDC, 2019d; ECDC, 2020d). As Lyme disease and TBE are widely spread, total avoidance of risk areas is difficult to achieve. As CCHF is more localised, avoiding an area where it is known to be present can be achieved more easily.
Recommendations for avoiding tick bites include wearing suitable protective clothing, for example long sleeved tops and long trousers tucked into socks, which reduces skin exposure. In addition clothing that is impregnated with insect repellent—either purchased or self-treated—works quite effectively (though can be expensive) when used as an adjunct to other measures. It would be wise to check clothing, including shoes and bags, before entering buildings (NICE, 2018a; NaTHNaC, 2018; CDC, 2019d; ECDC, 2020d).
Skin should be checked after potential exposure. Ticks crawl onto skin or clothing in order to find a suitable place to attach themselves and feed. Places to be aware of are skin folds, the groin, under arms, the scalp line and at the edges of underclothing. Regular and careful examination of skin for the small black ticks—often no bigger than a speck of dust before they have fed, after which they become engorged and can be the size of a coffee bean—and careful removal as soon as possible is essential (NICE, 2018; NaTHNaC, 2018a; CDC, 2019d; ECDC, 2020d). Getting someone else to look at areas you cannot see yourself is also a good idea. CDC (2019d) even suggests showering as soon as possible after being outdoors.
Tick removal should be undertaken as quickly as possible after identification of the tick. An attached tick should be removed using tweezers or fine-pointed forceps, grasping the tick as closely as possible to where it is attached to the skin and pulling it gently upwards, trying not to break off the mouth parts. It is possible to purchase tick removers—a hook like tool or card—in pet stores in UK or online from a number of sources (Figure 3). Once removed from the skin, disinfectant should be applied to the area of the tick bite to prevent infection (NICE, 2018a; NaTHNaC; 2018a; CDC, 2019d; ECDC, 2020d).
Figure 3. It is possible to purchase tick removers—a hook-like tool or card—in pet stores in the UK or online from a number of sources
Although rare, travellers should be aware that TBE can be transmitted through unpasteurised dairy products in risk areas and advised to avoid them (NaTHNaC, 2017).
Vaccination
TBE is the only tick-borne infection discussed where a vaccination is available for disease prevention in the UK. See Tables 1 and 2 for vaccination details. Vaccination is recommended to anyone living in an area where TBE is endemic (ECDC, 2020a). This at present does not include areas of the UK where TBE has been found.
Table 1. Adult immunisation schedule
| Basic immunisation | Dose | Conventional schedule | Rapid schedule |
|---|---|---|---|
| 1st dose | 0.5 ml | Elected date | Elected date |
| 2nd dose | 0.5 ml | 1–3 months after the 1st vaccination | 14 days after the 1st vaccination |
| 3rd dose | 0.5 ml | 5–12 months after the 2nd vaccination | 5–12 months after the 2nd vaccination |
Booster doses Persons from 16 to 60 years of age:
|
|||
| Booster dose ≥16 to <60 years | Dose | Timing | |
| 1st booster | 0.5 ml | 3 years after the 3rd vaccination | |
| Sequential booster doses | 0.5 ml | Every 5 years | |
| Booster dose ≥60 years | Dose | Timing | |
| All booster doses | 0.5 ml | Every 3 years | |
Table 2. Paediatric immunisation schedule
| Basic immunisation | Dose | Conventional schedule | Rapid schedule |
|---|---|---|---|
| 1st dose | 0.25 ml | Elected date | Elected date |
| 2nd dose | 0.25 ml | 1–3 months after the 1st vaccination | 14 days after the 1st vaccination |
| 3rd dose | 0.25 ml | 5–12 months after the 2nd vaccination | 5–12 months after the 2nd vaccination |
Booster doses
|
|||
| Booster dose | Dose | Timing | |
| 1st booster | 0.25 ml | 3 years after the 3rd vaccination | |
| Sequential booster doses | 0.25 ml | Every 5 years | |
In addition, those at occupational risk would also be recommended vaccination. This includes laboratory workers and those engaged in forestry, farming or military activities who may be at risk of exposure (NaTHNaC undated; ECDC, 2020a).
Vaccination is also available for travellers but this is not an NHS vaccine and is therefore administered as a private arrangement between the traveller and healthcare provider. In the UK there are licensed adult and paediatric vaccines available.
To achieve immunity before the beginning of seasonal tick activity, which is in spring, the first and second doses should preferably be given in the winter months if possible. The vaccination schedule should ideally be completed with the third vaccination within the same tick season or at least before the start of the following tick season. However, this may not always be possible.
As with all vaccines, contraindications include allergy or hypersensitivity to previous TBE vaccination and any constituent of the vaccine. Additionally, severe egg allergy reaction and severe febrile illness applies to the TBE vaccine. Further information about vaccines can be found on the Summary of Product Characteristics (Electronic Medicines Compendium, 2020a; 2020b) and in the Green Book (PHE, 2013). Before vaccination you should refer to this information and be aware of contraindications and precautions.
Conclusion
Ticks that are present across Europe, the USA, Africa and Asia are responsible for a number of tick-borne infections. Lyme disease and TBE are both under surveillance in the UK so awareness among health professionals of the presentation of these diseases is necessary to ensure prompt treatment. TBE is an endemic disease across much of Europe and Asia, and few travellers in the UK seek pre-travel advice to many of these areas but will be at risk of potential exposure. Perhaps the presence of the infection in the UK will change this. An awareness campaign in your practice before the main holiday season for the UK and Europe may be a good way to highlight the issue to those potentially at risk. Being aware of preventive measures and sharing this with travellers may be the difference between a safe, successful holiday and returning with a tick-borne infection. In addition, advising your travellers about TBE vaccination if appropriate could reduce the long-term sequalae of a preventable infection.
CPD reflective practice:
- Which tick-borne diseases can be contracted in the UK?
- What advice could you give to travellers to reduce their risk of tick-borne dieases?
- How could you raise awareness of tick-borne diseases in your practice, particularly among those travellers who are unlikely to access pre-travel consultations?
KEY POINTS:
- Ticks are the vectors for a number of bacterial and viral infections that can affect humans, including Crimean Congo Haemorrhagic fever, Lyme disease and tick-borne encephalitis
- The method of spread for tick-borne infections may vary depending on the tick species and habitat
- Lyme disease and tick-borne encephalitits can both be contracted in the UK
- TBE is the only tick-borne infection discussed where a vaccination is available for disease prevention in the UK
- Avoiding tick bites, and removing ticks as soon as possible in the event of being bitten, are key to the prevention of tick-borne diseases