Borreliosis (Lyme disease) is a bacterial infection transmitted via the bite of an infected tick. In the UK and Ireland, the most common tick species to transmit Borreliosis is Ixodes ricinus (commonly known as the wood tick, sheep tick, deer tick or castor bean tick). If left untreated, an infection can lead to damage of the nervous system, joints and heart, and can be seriously debilitating for both people and certain animals such as dogs and horses.
Borreliosis is often described as rare in the UK and Ireland and it is, in comparison with other infections such as Salmonella. However, on hearing that something is rare, many people tend to assume that it is not a risk to them personally.
In comparing Borreliosis with Leptospirosis (Weil's disease), which often seems to be given significant consideration in regard to health and safety during outdoor activities, there is a vast visible difference in the number of confirmed cases.
New research from the School of Biological Sciences, University of Bristol, published in January 2012 (Smith et al.) demonstrated that ticks carrying Borreliosis in the UK were much more numerous and widespread than previously thought.
So now that we have established that Borreliosis is a potential risk to take seriously, whilst not worrying unduly about, what other difficulties does this disease present us with?
Borreliosis is not easy to diagnose because it produces a bewildering variety of signs and symptoms which are not specific to this disease, and which could be attributed to many other conditions. This means that there is the potential for misdiagnosis.
The only diagnostic sign of Borreliosis is an Erythema Migrans (EM) lesion or rash, which occurs in 40-80 per cent of patients (reports vary). In an analysis of the 813 laboratory-confirmed cases of Borreliosis in England and Wales in 2008, only 32% had a documented EM (similar to the previous year).
An EM may go undetected if appearing in an inaccessible place or if hidden under thick body hair or hair on the scalp. It might also not be as apparent when appearing on darker skin. An EM may present in an atypical form, rather than the classic "bull's-eye" which is so often depicted in medical journals. Evidence suggests that different genospecies of the causative bacteria (Borrelia burgdorferi sensu lato) may influence the appearance of the lesion.
Another diagnostic difficulty that doctors face is the fact that often a patient may not recall a tick bite. Of the 813 laboratory-confirmed cases of Borreliosis in England and Wales in 2008, only 40% had a documented tick bite (similar to the previous year).
In addition to these difficulties, there is no single 100% reliable test for Borreliosis. In Ireland, physicians have access to the National Virus Reference Laboratory which performs serological tests for Borreliosis. The NHS in the UK currently uses a two-tier testing procedure; firstly an ELISA (Enzyme-Linked Immunosorbent Assay), which is followed (but only if equivocal or positive) by a Western blot or 'immunoblot'. However, both in the UK and Ireland, these tests rely on the presence of antibodies which may take some weeks to develop after the patient has become infected. In certain cases, a patient with a more established infection may be sero-negative (infected without the presence of antibodies). This is more likely to occur in patients who have received insufficient antibiotic treatment early in the course of the disease, or if they are on certain other types of medication, such as steroids, both of which can interrupt the antibody response. In such cases, the patient's blood sample can return a false-negative result, and further testing may (but not always) show sero-conversion (the appearance of antibodies where previously there had been none) when they are re-tested at a later date.
Conversely, a patient's blood sample may return a false-positive result if they have previously had an unrecognised or asymptomatic infection but are not currently infected. This can occur in people who are occupationally or recreationally exposed to regular tick bites. False reactions during testing can also occur in people who have been affected by other conditions, such as glandular fever, syphilis, rheumatoid arthritis, other autoimmune conditions and some neurological conditions.
The significance of any test result, negative or positive, should be interpreted carefully by clinicians in the overall context of the patient's clinical, and tick-exposure risk, history.
As of 1st June 2012, the HPA's diagnostic service for Borreliosis became provided by the Rare and Imported Pathogens Laboratory (RIPL), HPA Porton Down.
In England and Wales, there were 959 laboratory-confirmed cases of Borreliosis in 2011 (latest available data), a 2.8% increase in reports compared with 2010. However, the Health Protection Agency states that, "Reporting levels have improved, but the data remain incomplete because they do not include cases diagnosed and treated on the basis of clinical features such as erythema migrans (the early rash of Lyme borreliosis), without laboratory tests. It is estimated that between 1,000 and 2,000 additional cases of LB occur each year in England and Wales".
In Scotland, cases are notifiable by diagnostic laboratories. There were 229 laboratory confirmations of Borreliosis in 2011 (latest available data), a 25.6% decline from those reported in 2010. This decline could be attributed to greater awareness about ticks due to campaigns such as Tick Bite Prevention Week. However, some experts consider the yearly statistics to be underestimated, owing to cases that are not reported, patients that are misdiagnosed with other conditions, and asymptomatic carriers of the disease.
In Northern Ireland, voluntary reporting is made to the Public Health Agency. As with other voluntary surveillance systems, the Public Health Agency recognises that cases are likely to be under recorded. There were 13 serologically-confirmed cases of Borreliosis in 2011 (latest available data).
From September 2011, Lyme disease was listed as a notifable disease in the Republic of Ireland, where clinicians should notify cases to the Director of Public Health/Medical Officer of Health for the area of residence of the patient. Prior to it becoming a notifiable illness, there was no voluntary surveillance scheme and therefore the annual number of cases has not been known.
As of the 3rd quarter of 2012 (latest available data), there had been 13 laboratory-confirmed cases of Borreliosis in Ireland; data from the HPSC Ireland, 'Surveillance of Infectious Intestinal (IID), zoonotic and vectorborne disease, and outbreaks of Infectious Disease in Ireland' quarterly reports.
The Health Protection Surveillance Centre (HPSC), Ireland, states that although the true incidence of Lyme disease is not known, it is likely that there are at least 50 - 100 cases in Ireland every year.
Cases of tick-borne disease have increased due to a number of probable factors:
Other potential contributors to the spread of Borreliosis and other tick-borne diseases are:
Ixodes ricinus is an ideal vector for disease as it selects a wide variety of animal species as its hosts (including birds, small to large mammals, reptiles and even amphibians). It can become infected from, and then transmit the disease to, a variety of species including humans.
Because many of the tick's host species are freely mobile, they have the potential to transport infected ticks to new areas (sometimes across oceans), and to act as reservoirs for the disease-causing organisms, ready to pass them on to local ticks, thus spreading the disease.
In the UK and Ireland, Ixodes ricinus can infect livestock (and sometimes humans) with the Louping- ill virus. It can also carry Borreliosis, along with co-infections such as Anaplasmosis, Babesiosis, and possibly Bartonellosis. These co-infections may make the diagnosis and treatment of Borreliosis patients more problematic as co-infection can vary the way in which a disease presents, and the treatment needed.
It is commonly supposed that ticks are only a risk in areas of moorland, heathland or woodland, and then only in acknowledged "hot spots", such as the New Forest or the Highlands of Scotland. However, tick sampling by scientists has demonstrated infected ticks to be present in many areas, including the London parks. A case of urban-acquired Borreliosis may be overlooked by doctors, simply because the patient did not report a countryside visit in an acknowledged "hot spot".
Urban Borreliosis is an issue that is little considered but could have serious implications. There are increasing reports, for example, of homeless individuals spending time and sleeping in parks, cemeteries and on derelict land. Birds, rats, mice, foxes, hedgehogs, squirrels, and domestic dogs and cats, can all help to support local tick populations in more urbanised areas.
Rats and mice too are possible reservoirs for these diseases, infesting buildings as well as parks and gardens. The National Pest Technicians Association's annual survey revealed a marked increase in both rat and mouse problems across the United Kingdom in 2007/8, with over 90% of pest control professionals reporting higher levels of rat activity in recent years, and just under 80% greater mouse activity.
Studies have highlighted pigeon colonies in buildings as harbouring tick species, such as Argas reflexus (a soft tick species which will readily attach to humans and which may have the potential to transmit Borreliosis). The World Health Organisation has highlighted urban sprawl as an increasing contributor to the spread of zoonotic diseases, including Borreliosis.
Whilst the true incidence of tick-borne disease in the UK and Ireland is unknown, it is important for residents to become more aware of the risks that ticks pose, take sensible precautions against tick bites, to learn how to remove an attached tick without increasing the risk of infection, to recognise possible indications of infection in themselves and others, and to access prompt diagnosis and treatment if infection is suspected; all of which can help to protect the health of both people and domestic pets.
Passing on this information to family, friends and colleagues will also dramatically increase the level of awareness which, in turn, will help combat the rise in incidence of tick-borne disease. Simple and informative leaflets are available from BADA-UK.