There's Something In The Woods....
Ticks, Lyme Disease and the implications for Mountain Bikers

They are out there. Eight-legged, blood drinking, disease-ridden and hiding in the woods waiting for you! A job for agents Mulder and Scully? Well, perhaps not, but certainly something that frequenters of the great outdoors should be aware of.

The Problem
The problem with ticks is that they are the transmission-vector for a potentially serious bacterial disease. The infection was named Lyme disease after an unusual outbreak of arthritis near Lyme, Connecticut, USA, in 1975. It was found to be caused by Borrelia burgdorferi, a member of the family of spirochetes, which also includes the syphilis agent, and is spread by the bite of infected ticks of the genus Ixodes. Since 1975 reports of Lyme disease have increased dramatically in the United States, and the disease has become an important public health problem in some areas.

Unfortunately this is not just a problem to be considered by those planning a trip state-side. It is a worrying fact that infected ticks have been found at multiple sites around the UK including the New forest (Hampshire; not so much a problem for cyclists as it used to be!), Thetford forest (Norfolk), Richmond and Bushey deer parks (London), north Wales and Scotland (2,10-12). In one study, some 30% of ticks were found to be infected (11).

Confirmed cases of Lyme disease in the UK have increased from 68 in 1986 (10) to around 200 per year in the early 1990s (4) although some of these infections were probably acquired overseas. However, the figures may underestimate the true incidence of the disease in the UK through misdiagnosis. Studies drawing on patients from hospital clinics who displayed one or more Lyme disease-like symptoms found that some 3% had antibodies to the bacterium, raising the possibility that this was the root-cause of their disease(13).

Although the national incidence of Lyme disease may still be low, people who spend large amounts of time in tick infested areas face a much higher risk of infection. In such sub-groups e.g. farmers, park keepers, forestry workers, deer-stalkers etc. some 14-25% of those studied had antibodies to the bacterium indicating a higher level of exposure to the disease agent(1,3,8,14). Whilst many with antibodies were symptom free, some 65% of one study described Lyme-like problems(3). Mountain bikers who regularly ride woodland or grassland singletrack should consider themselves as part of such a high risk group.

Lyme disease is not a problem that is likely to go away. The experience of other countries suggests the number of cases will continue to rise. In Czechoslovakia, where, as in the UK, the first confirmed cases were reported in the 1980s, the current annual rate of infection is 3 patients per 20 000 inhabitants (5). In a population the size of the UK that would equate to some 8000 new cases each year, notwithstanding differences in geography and climate. A recent World Health Organisation report also suggested that vector-borne diseases may become more prevalent as global warming increases the range of suitable habitats (15).

Ticks have a complex 2-year life cycle involving larval, nymph and adult stages. It seems that the Borrelia infection is picked up from small rodents during the larval or nymph stage. Nymphs, which are thought to be largely responsible for infecting humans, are very active, particularly in the spring and summer and often go unnoticed because of their size (less than 2 mm) leaving ample time to transmit the infection. This is thought to require 2 or more days of feeding (7). Adult ticks can also transmit the disease, but since they are larger and more easily spotted, they are less likely to have sufficient feeding time for transmission to occur.

The Disease
In most people, the first symptom of Lyme disease is a red rash known as erythema migrans (EM) which appears within a few weeks of an infected tick bite. This rash starts as a small red spot at the site of a bite, and expands over a period of days or weeks. As the infection spreads, several rashes can appear at different sites on the body. EM is often accompanied by flu-like symptoms (7).

After several weeks, months or even years of infection, a variety of secondary symptoms may occur. More than half of untreated cases develop recurrent attacks of arthritis which can shift from one joint to another, although the knee is most commonly affected. Lyme disease can also affect the nervous system, causing symptoms such as stiff neck and severe headache (meningitis), temporary paralysis of facial muscles (Bell's palsy), numbness, pain or weakness in the limbs, or poor motor coordination. More subtle changes such as concentration or memory loss, and unusual mood swings may also occur. Occasionally Lyme disease patients develop an irregular heartbeat, though permanent heart damage is very rare (7).

Happily, nearly all Lyme disease patients can be effectively treated with antibiotic therapy. In general, the sooner such therapy is begun following infection, the quicker and more complete the recovery. In the past, since the risk of developing Lyme disease from a tick bite is small, physicians preferred not to treat patients bitten by ticks with antibiotics unless they developed symptoms of the disease. In the USA, there is now a move to provide preventative treatment to people bitten by ticks in regions where the disease is endemic (6).
One of the major problems with Lyme disease is that of diagnosis, since the symptoms may resemble a wide variety of other diseases. The EM rash, though absent in a quarter of patients, is one of the few things unique to Lyme disease. In many patients, there is no memory of a tick bite (7). It seems that immunity may never be achieved so reinfection with the disease is a real risk (6).

The Answer?
The best way to avoid Lyme disease is to avoid tick bites. Assuming that you are not going to be happy spending the summer months indoors, here are some guidelines to help minimise the risks (7):

Ticks are often found in wooded areas and nearby grasslands, especially where the two areas merge. In such areas, avoid overgrown tracks, or try and ride along the center to avoid picking up ticks from overhanging vegetation.

Minimising the amount of exposed skin by, for example, wearing clothes that fit tightly at the ankles and wrists is recommended. My own experience, however, is that clothing offers little protection. Several of the little darlings have successfully negotiated their way into my bib shorts, and you don’t get much tighter fitting than cycling shorts.

Insect repellents that contain a chemical called DEET (N,N-diethyl-M-toluamide) can be applied to clothing or directly onto skin. These are very effective, but can cause serious side effects, so always follow the manufacturers recommendations for use.

Once indoors, clothing should be removed and washed. Showering may wash off ticks which have not yet attached.

Now the fun part: check the body for ticks (you just knew that small mirror would be useful for something). They are particularly fond of the hairy regions of the body, so the groin, armpits and head are prime but not exclusive targets.. Nymphs are only about the size of a poppy seed, so they are easily mistaken for a freckle or a speck of dirt.

If a tick is discovered attached to the skin, it is best to remain calm. Running naked around the house, yelling “GET THAT THING OFF ME” will damage the “wilderness-wise” image you have been carefully cultivating. It should be pulled gently but firmly with blunt tweezers, near the "head", taking care not to squeeze the tick's body, until it releases its hold on the skin. Swab the bite area thoroughly with an antiseptic to prevent bacterial infection.

Other methods of removal, such as the lit end of a cigarette, a burnt match, the application of Vaseline or alcohol while the tick is attached could cause transmission of the bacterium (and burns) and are not recommended (6)

1) Guy E.C., Bateman, D.E., Martyn C.N., Heckels J.E. and Lawton N.F. 1989. Lyme disease: prevalence and clinical importance of Borrelia burgdorferi specific IgG in forestry workers. Lancet 1, 484-486.
2) Guy E.C. and Farquar R.G. 1991. Borrelia burgdorferi in urban parks. Lancet 338, 253-255.
3) Hamlet N., Nathwani D., HoYen D.O. and Walker E. 1989 Borrelia burgdorferi infection in UK workers at risk of tick bites. Lancet 1, 789-790.
4) Haywood G.A., O’Connel S. and Gray H.H. 1993. Lyme Carditis: a UK perspective. Br. Heart J. 70, 15-16.
5) Hercogova J., Tomankova M. and Bartak P. 1992. Contributions to the treatment of dermatologic manifestations of lyme borreliosis. Cutis, 49(6) 409-411.
6) Lyme Disease - An Overview: The National Lyme Disease Network LymeNet Resource Guide. http://www.lehigh.edu/lists/lymenet-l/overview.htm
7) Lyme Disease: The Facts, The Challenge. A brochure issued by U.S. Department of Health and Human Services in conjuntion with Public Health Service and National Institutes of Health. Available from NIAMS/NIH, Box AMS, 9000 Rockville Pike, Bethesda, Maryland 20892.
8) Morgan-Capner P., Cutler S.G. and Wright D.J.M. 1989. Borrelia burgdorferi infection in UK workers at risk of tick bites. Lancet 1(8641), 789.
10) Muhlemann M.F. and Wright D.J.M. 1987. Emerging pattern of Lyme disease in the UK and Irish republic. Lancet 1, 260-262.
11) Nuttall P., Randolph S. Carey D., Craine N. and Livesley A. 1993. The ecology of Lyme borreliosis in the UK. Annals Rheum. Dis. 52, 394-396.
12) O’Connel S. 1993. Lyme disease: a review. Comm. Dis. Rep. 3, 111-115.
13) Rees D.H.E. , O’Connell S., Brown M.M., Robertson J. and Axford J.S. 1995. The value of serological testing for Lyme disease in the UK. Brit. J. Rheumatol. 34(2), 132-136.
14) Rees D.H.E. and Axford J.S. 1994. Evidence for Lyme disease in urban park workers: A potential new health hazard for city inhabitants. Brit. J. Rheumatol 33(2), 123-128.
15) World Health Organisation: Climate change and human health. Press Release WHO/48, 9 July 1996

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