Fieldwork Safety Page 5 of 7 This is the Mandatory Operational Code of Practice for Field Safety produced by the Field Studies Council. FSC OPERATIONAL CODES OF PRACTICE No. 1 : FIELD SAFETY Appendix 3 : Lyme Disease 1. Causes and infection route of the disease 2. Symptoms of the disease 3. Diagnosis and treatment of the disease 4. Incidence of bacteria and of cases of the disease in UK 5. Safety Management Systems for the disease. 6. Acknowledgements 1. Causes and infection route of the disease The disease is caused by the spirochaetae bacteria, Borrelia burgdorferi, which exists in many different strains or [to use a technical term] serovars. The parasite is transmitted to humans predominately by ixodid ticks although biting insects including mosquitoes, horse flies, deer flies and cat fleas have been implicated as transmitters or vectors. Domesticated mammals [eg. dogs, horses, cats, sheep and cattle] as well as wild mammals [eg. yellow-necked field mouse, wood mouse, bank voles, grey squirrel and deer] are known to act as reservoirs of the disease. Pheasants are known hosts, and over 95 species of migratory birds are known carriers [suggesting that they may also act as long-distance dispersal agents]. Tick larvae are rarely infected with the bacteria- The infection is acquired when a tick nymph feeds on a host animal which has been fed on upon by other over-wintering , infected nymphs. [An infected nymph will become an infected adult tick.] Generally, the nymphs are the most important in the disease transmission because of a combination of their small body size [they are not easy to spot] together with high abundance and infection rates [An adult female lays up to 1000 eggs on the ground before dying. This provides a high concentration of larvae to seek out a passing and possibly infected host animal]. Apart from actually handling animals which are carrying ticks, humans pick up the ticks when walking through vegetation on which the tick larvae, nymphs and adults are 'sitting'. Habitats with vegetation suitable for the survival of the ticks therefore present 'risk areas'. They include woods, moorland and long grass. Bracken is a particularly suitable habitat because the constant humidity and temperature of the understorey and litter layer provide an ideal environment for any ticks. It should be noted that dogs and cats may also bring host-seeking ticks into a building. It should be noted that ticks have to bite and fed on their host's blood in order to transmit the disease. It is unlikely that a tick which are still moving about on a human will have bitten the person. Also, it is some time [perhaps 24 -36 hours] after a tick has actually first bitten its host that the bacteria are in fact transmitted to the host. In an unfed tick, the bacteria lie dormant in the tick's gut. It is only when the tick has started to feed that the bacteria become active, then move to the tick's salivary glands and hence into the host. So it is unlikely that a tick, which has only just bitten a person, will have transmitted the disease to the person. 2. Symptoms of the disease The disease caused by the bacteria is borreliosis [usually called Lyme disease after the town of Lyme in Connecticut, USA, where it was first noted]. The disease can affect many organs including the skin. heart, nervous system, joints and muscles [the various serovars, produce different forms of the disease which are characterised by the organs which they affect]. The symptoms usually occur in three phases In 50% or more cases, a rash [erythema chronicurn migrans or ECM1 appears a few days after the tick bite. Usually the rash is at the site of the bite but it can appear elsewhere on the body. The rash may last for 4 weeks or more, and is most frequent during the summer months. It may be accompanied by flu-like symptoms. Weeks or months after the initial infection, patients may experience symptoms such as muscular pain, facial paralysis and meningitis. However the severity of such symptoms is variable and many patients do not display such symptoms or recover without treatment. Such patients often develop a strong immunity to further infections. Some patients, often months or years later, suffer from a chronic stage involving serious fatigue, heart conditions, arthritis [less in Europe than USA] and skin conditions [especially in elderly females]. 3. Diagnosis and treatment of the disease Diagnosis of presented symptoms can be confirmed by blood tests. Treatment of the disease, in the initial phase, with antibiotics is easy and effective, particularly as the UK strains of the disease are relatively weak when compared to those found in the USA. Treatment of the later phases is more difficult because the effects of the disease [eg. arthritis] may have to be dealt with as well as the disease itself. 4. Incidence of bacteria and of cases of the disease in UK There are some 170 - 200 reported cases per annum in the UK. However, in approximately 20% of these cases, infection has occurred outside the UK as a result of the patients having visited places such as the eastern USA, the Black Forest and certain areas of France. Although the bacteria is widespread throughout the UK, relatively high incidences of infected ticks have been recorded in Norfolk and the South East [especially Thetford Forest and the New Forest] and on Dartrnoor and Exmoor. Having said that, it must be noted that the actual 'spirochaete burden' in the ticks is very low. By comparison with ticks from areas in the USA where the disease is endemic and the ticks may be carrying 20 -30,000 spirochaetes per sample, ticks in the UK carry burdens several orders of magnitude less than this [ie. less than 100 spirochaetes per sample]. Even if bitten by a tick, the chances of actually being infected are therefore quite low. To set this in context : Surveys carried out on 'at risk' groups [ Farmworkers in Hereford & Worcestershire and Countryside Rangers in Snowdonia] indicates that, even amongst those people who knew that they had been bitten by ticks, serological tests revealed the presence of antibodies in their blood in only a minority of cases. There have been only two cases of the disease [some 7 or 8 years apart] in people carrying out fieldwork. Both infections occurred in Thetford Forest and one of the people was actually carrying out ecological fieldwork on ticks. 5. Safety Management Systems for the disease. Preliminary advice on the possibility of infection should be provided to group organisers, students and parents by means of appropriate letters circulated prior to the course. [See section 5.3.a. and section 7. of FSC OCoP No.1. : Appendix 2.] Obviously the simplest management is the prevention of actually acquiring the ticks. However, advice to avoid potentially tick-infested areas [such as forest edges, clearings, old fields, heaths and moorland, narrow animal tracks, brushing against vegetation, sitting on the ground or standing in farmyards where ticks may be present and active] may be difficult to adhere to when carrying out fieldwork. Where work in such areas is carried out [particularly in spring and summer when any ticks will be active], students must be advised to wear long trousers tucked into boots or socks. Certainly the wearing of shorts in such circumstance should be avoided. Repellents containing permethrin, or 'Deet' may be applied to clothing or the skin as appropriate and can offer some protection. Wearing light coloured clothing also makes it easier to spot any ticks on the clothing if this is examined on return from the field. It should be noted that the survey carried out in Snowdonia suggested that a contributory factor [to the lack of tick bites amongst the personnel involved] was that clothing was changed and washed on a regular basis. In the case of students, simply changing clothes on return from the field is likely to be of little assistance especially if the clothing is not. then kept separate from 'clean' clothing. Taking a shower or bath on return may also aid the removal of any moving ticks. Careful and thorough examination of the body is also another recommendation. However, given that the ticks will move to warm and humid parts of the body [eg. armpits, back of knee, groin and lower abdomen] and that the ticks can be very small, such an examination can be very difficult for a person to carry out on their own. [A report in the New England Journal of Medicine noted a low incidence of Lyme disease [in an endemic area] amongst nudists, which was attributed to the fact that the people saw the ticks on one another before the ticks had a chance to start feeding.] However, once a tick attaches and starts to feed, it may actually be felt usually as a persistent itch. Students could certainly be advised to carry out a careful examination, perhaps with the assistance of a friend, should they note such an itch. If an attached tick is discovered, it is recommended that no attempt, by either the person themselves, friends or staff, is made to remove it. The person should be taken to a doctor who can remove the tick. Successful removal of a tick is difficult and, if done badly, can lead to continued irritation and possibly septicaemia. Also the tick may be required for later identification and confirmation of any possible infection. As noted above, even. when people have been bitten by ticks, the chances of them becoming infected are low. It is important to stress this fact to students in order to avoid unnecessary alarm. However they must also be advised [during the course] that, if they do feel unwell [particularly with 'flu-like' symptoms] or spot a rash within 4 weeks of returning home, they must consult their own GR They must tell the doctor that they have been on a field course with the possibility that they have contracted a bacterial infection. Failure to give this information has undoubtedly led to incorrect initial diagnoses particularly when patients have been from urban areas and 1 or 'the flu has been going around'. 6. Acknowledgements This appendix was written with the invaluable advice and information provided by Dr. R Smith of the Communicable Diseases Surveillance Unit, Cardiff. The contents of this appendix, particularly its recommendations for safe working procedures to be undertaken by FSC staff, remain the responsibility of the FSC. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | Page 5 of 7