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Increased reporting of Lyme borreliosis in England and Wales

Recent media reports have highlighted current interest in the United Kingdom (UK) over ticks and Lyme disease. In particular one recent report describes a case of Lyme disease contracted in the Mendip Hills in Somerset, south west England, although this is an area from which cases have previously been reported. There have also been several articles in both the medical, and the mass media that have raised awareness amongst doctors and their patients.

Anecdotal reports indicate that in the UK, as anticipated, the number of ticks has continued to increase this year following last year’s wet summer and mild winter, which has allowed greater numbers of ticks to survive. European colleagues also report that tick numbers have increased throughout northern Europe. In England and Wales, laboratory confirmed case reports are currently running at slightly higher levels than seen at the same time in previous years, these include infections acquired in the UK, from northern European countries, and from the eastern United States. Most of the overseas cases have occurred primarily in holiday-makers. A provisional total of three hundred and fifty-five reports, up to the end of August 2005, have been received, compared with an annual average of 215 reports during the same period from 2001 to 2004. As in previous years over half the reports of indigenously acquired infection have been from patients resident in southern counties of England, especially the south east and south west health regions The major foci of Lyme borreliosis in England and Wales are around the New Forest, Salisbury Plain, Exmoor, and Thetford Forest. Other endemic areas include the Lake District, the Yorkshire moors, and the Scottish Highlands and Islands, but any area in which ticks are present should be regarded as having a potential risk for infection.

Lyme borreliosis occurs only in people who have been bitten by infected ixodid (hard bodied) ticks, the vector hosts. Infection is caused by the presence of a spiral bacterium, Borrelia burgdorferi and cannot be transmitted from person-to-person, or directly from other animals. Peak times for tick blood meals are late spring, early summer, and autumn, although there may also be a low level of tick feeding activity in mild winter periods. This also coincides with peak leisure activity periods when people visit the countryside during the summer months. The main feeding hosts for larval and nymphal ticks are small mammals such as field mice and voles, and birds including blackbirds and pheasants. These hosts may also be reservoirs of B. burgdorferi, and the tick feeding patterns ensure the organism’s continuing cycle between generations of reservoir and vector hosts. Humans are incidental hosts for tick feeds. Fortunately only a minority of ticks carry borreliae, and borrelial transmission usually occurs late in the feed, after 48 to 72 hours. It is less likely to occur in the first 24 hours of attachment.

As Lyme borreliosis occurs only in people who have been bitten by an infected tick, it is important that a patient’s risk of exposure to tick is properly assessed and the clinical history evaluated for features compatible with Lyme borreliosis before diagnostic tests are requested. The most commonly available tests look for the presence of antibodies to Borrelia burgdorferi although antibodies may not be detectable in the first few weeks after infection. Specific immunoblot (Western blot) tests should be performed on all specimens reacting in preliminary tests and the significance of the results carefully assessed in the light of the patient’s clinical and tick exposure history.

Preventing infection

Risk of human infection can be minimised by:

• Tick-awareness;
• Wearing appropriate clothing in tick-infested areas (long sleeved shirt and long trousers tucked into socks). Light coloured fabrics are useful, as it is easier to see ticks against a light background. Check that unfed ticks are not brought home on clothes;
• Considering use of insect repellents, (eg, N,N-Diethyle-m-toluamide [DEET]-containing preparations;
• Inspecting skin frequently, and removing any attached ticks;
• Checking again for ticks, especially in skin folds, at the end of the day;
• Making sure that children’s head and neck areas, including scalps, are properly checked;
• Checking that pets do not bring unfed ticks into the home on their fur.

Remove ticks by gently gripping them as close to the skin as possible, preferably using fine-toothed tweezers or similar implements, and pulling steadily away from the skin. Some veterinary surgeries and pet supply shops sell tick removal devices, which are inexpensive and very useful, especially for people frequently exposed to ticks. Lighted cigarette ends or match heads are not recommended. Some researchers consider that application of creams or volatile oils to cover an attached tick and force it to detach may increase risk of borrelial transmission, as it can stimulate the tick to regurgitate potentially infected material early.

Further information on Lyme disease can be found on the Health Protection Agency website at: <http://www.hpa.org.uk/infections/topics_az/zoonoses/lyme_borreliosis/menu.htm>.