Lyme Disease: A clear and present danger
Thanks for this article go to WENDY FOX, Chair of Borreliosis and Associated Diseases Awareness UK (BADA-UK), a charity promoting understanding and prevention of Lyme disease.
Before embarking on a trip, travellers obviously should take health protection into account. Many opt for vaccination against diseases, generally associated with travel abroad, but few realise there is an increasing threat within the British Isles, and one that is not vaccine preventable.
Tick-borne disease is increasing in the UK and Ireland. Ticks are the most common arthropod vector of disease and a hard tick (Ixodes species) usually causes infection in the UK. Ticks are most abundant in forested, heathland and moorland areas, but also in suburban parklands. Owing to several factors, including land management and climate changes, parasite numbers have increased and so has their distribution.
Borreliosis (also referred to as Lyme borreliosis or Lyme disease) is most prevalent tick-borne disease. Cases reported via a voluntary surveillance system have trebled in England and Wales since 2001. In Scotland (where the disease is notifiable) they have increased by a factor of eight.
The Health Protection Agency admits that data for reported cases are incomplete because information doesn't include cases diagnosed and treated on the basis of clinical features, without laboratory tests. They estimate an additional 1,000-2,000 cases each year, with an annual total of approximately 3,000.
Cases in England and Wales are most frequently reported in Exmoor, the New Forest, the South Downs, parts of Wiltshire and Berkshire, Thetford Forest, the Lake District and the North York Moors. However, they have been reported from most counties and the HPA states that any area harbouring ticks may have the potential for borreliosis transmission.
Dr Darrel Ho-Yen, head of the national Lyme Disease Testing Service in Scotland, believes that the known number of proven cases should be multiplied by 10 "to take account of wrongly-diagnosed cases, tests giving false results, sufferers who weren't tested, people who are infected but not showing symptoms, failures to notify and infected individuals who don't consult a doctor".
Borreliosis is caused by a spirochaetal bacterium of the Borrelia genus. Lyme disease is generally associated with Old Lyme, Connecticut, in the United States, acquiring its name after a cluster of cases of Borrelia burgdorferi infection was identified in 1974. Since then, other strains of Borrelia which can have different clinical presentations have been discovered in Europe.
Identifying an infection presents a problem for health care practitioners. There is only one sign specific to Borreliosis - an expanding rash (Erythema Migrans), generally occurring three-to-30 days after a tick bite. This rash doesn't always occur and can vary in presentation (sometimes misdiagnosed as ringworm, cellulitis or allergic reaction). Of cases reported to the HPA in 2007, only one third had documented Erythema Migrans.
Early symptoms are non-specific and flu-like (tiredness, headaches, arthralgia and myalgia). In the following weeks or months more serious symptoms may appear in untreated patients, affecting the nervous system, joints and the heart or other tissues. Neuroborreliosis (infection of the nervous system) can cause facial palsy, viral-like meningitis, pain, weakness or altered sensation of limbs or trunk.
Lyme arthritis, usually affecting the knee, is more common with disease acquired in North America or some parts of Europe.
Too tiny to detect
Another diagnostic problem occurs when patients don't recall a tick bite. Of the cases reported to the HPA in 2007, only 43 per cent reported a bite. Because of anaesthetic and anti-inflammatory properties in their saliva, ticks can bite and feed without discovery.
Nymphal ticks (the second stage in a tick's life-cycle) are the most common cause of infection as they resemble a poppy seed and are seldom seen. Ticks prefer attaching to inaccessible places, like skin folds, armpits, groin, or under hair on the scalp. Body hair will often hide small ticks.
A two-tier system is employed in the UK. First, antibody screening tests are performed, followed by immunoblotting (western blotting) of reactive or equivocal samples. Such tests have limitations. Because an antibody response takes several weeks to develop, antibodies may be undetectable in the few weeks after infection. A second sample may then show sero-conversion. Sometimes those with more established infection can be seronegative.
Conversely, people may have antibodies to Borrelia bacteria without having a current infection (regular occupational or recreational exposure to tick bites) and other conditions (for example, glandular fever, syphilis, rheumatoid arthritis) can result in false positive reactions.
A cocktail of infection
Ticks in the UK can carry multiple infections including anaplasmosis, Q-fever, babesiosis and bartonellosis. Clinicians should be aware of the possibility of co-infections, which may cause cases of borreliosis to present atypically and influence treatment choice.
The threat to travellers abroad
Tick-borne diseases are a worldwide concern, with many diseases specific to certain areas. Lyme borreliosis is the most prevalent, being endemic to North America and Eurasia. Tick-borne relapsing fever is also caused by a species of Borrelia bacteria and found primarily in Africa, Spain, Saudi Arabia, Asia and certain areas in the western USA and Canada.
Other risks to travellers include:
- tick-borne encephalitis virus (TBE) - endemic in temperate regions of Europe and Asia
- tularemia (bacterial) - reported from all European countries except Great Britain, Iceland and Portugal. Endemic to the south east, south central and western USA
- Colorado tick fever (virus) - endemic to the western USA
- Crimean-Congo hemorrhagic fever (virus) - endemic in Asia, eastern Europe and the Middle East, but especially common in east and west Africa
- Anaplasmosis (rickettsial) - endemic in the USA and Europe, but recently identified in China
- Rocky Mountain spotted fever (rickettsial) - diagnosed throughout the Americas. Some synonyms in other countries include "tick typhus", "tobia fever" in Columbia, "São Paulo fever" or "febre maculosa" in Brazil and "fiebre manchada" in Mexico.
- Babesiosis (protozoal) - endemic in many regions of Europe and the USA
- Tick paralysis (toxins) - cases occur in the USA and Canada, Australia and Africa. Cases in Eurasia are sporadic.
Apart from vaccination (where applicable) the best defence is tick awareness. Using repellents and dressing to deter ticks getting under clothing is good policy. Regular body checks will identify ticks before or soon after they attach, minimising the risk of disease transmission which increases the longer the tick remains attached.
Correct removal of ticks is vitally important and should be performed using a tick-removal tool or fine-tipped tweezers, easily carried (with antiseptic wipes) in pockets or rucksacks. Freezing, burning or smothering a tick with any substances is likely to result in regurgitation of infective fluids. Detailed instructions on tick-removal techniques are available at: www.bada-uk.org ("Defence" section).
When evaluating a patient it is important for health care practitioners to be aware of places people have visited or intend visiting.