Lyme Disease

29th September 2016, revised 14th March 2025

Lyme disease is a Tick Borne Infection (TBI) caused by the bacteria Borrelia burgdorferi, spread by the bites of infected ticks.

Ticks find their hosts to feed on by sensing heat, exhalations, vibrations, and odours.  Once a host has been found, ticks burrow their hypostome under the skin using a cutting movement.(1)  Most tick bites are painless.  Once the tick is feeding pathogens from the gut of an infected tick are transmitted to the host.  Prostaglandins in tick saliva inhibit the host’s local immune response, and tick salivary apyrase maintains blood flow into the bite site, stimulates local vasodilation, and prevents platelet aggregation.  Other tick salivary enzymes inhibit the coagulation cascade, enhancing blood flow to the lesion.(2)

Importantly, there is considerable variability in the time it takes to transmit pathogen from tick to human; transmission is believed to take >36hrs (3) in contrast, Rocky Mountain spotted fever can be transmitted in approximately 15 min.(4)

Generally, the risk of Lyme disease transmission is correlated with the duration of tick attachment.  Although the risk of transmission of B burgdorferi after a tick bite in Lyme endemic regions is estimated to be 1 to 3%,(5) the risk increases to 20% when infected Ixodes scapularis ticks are attached longer than 72hrs.(6)  Early animal studies of Ixodes scapularis ticks infected with Borrelia burgdorferi (the pathogenic spirochete responsible for Lyme disease via a tick vector) suggested that at least 48hrs of attachment were necessary for transmission of disease.(7-9)  However, a recent review highlighted that Lyme transmission is possible within 24hrs of attachment and that a definitive study describing a minimum tick attachment time for the transmission of Lyme in humans has not been published.(10)  Until these data are available, the US Centre For Disease Control (CDC) recommends tick removal within 36hrs of attachment to reduce the risk of Lyme disease.(11)

Epidemiology

Ticks can be found in temperate environments, in almost every country in the Northern Hemisphere.  In the UK there are an estimated 2000-3000 cases reported annually.(12)  In the US figures are around 300,000 cases per year.(13)

Ticks cling to branches and latch onto passing animals to feed on their blood.   In the UK deer are the most widely known host but all small mammals and bird can host infected ticks.  It is not currently thought that the infection is actually spread by deer, rather smaller mammals such as mice (14) and birds.

As such any woodland and grassland area is capable of hosting infected ticks.

Although summer has been associated with the highest risk of Lyme disease, transmission

is possible year-round (15) and climate change, with its associated mean average temperature rises, has enabled tick expansion to regions that have previously experienced little TBI.(16-18)

Signs and Symptoms

Finding a tick on your body does not mean that you will have caught Lyme disease;  it is known to take 36-48 hours of attachment for the bacteria to transfer from the tick to the host.(19)  If the tick can be removed within 24 hours, infection is unlikely.(20) 

Lyme disease presents in 3 stages:

1. Early localized

2. Early disseminated

3. Late disseminated.

The most common sign of early localised infection is a red target-like rash called erythema migrans (EM) which begins at the site of a tick bite about a week after it has occurred.  The rash is not usually itchy or painful, however, approximately 20–30% of infected people do not develop a rash (21) and misidentification of EM is relatively common.(22)

Early symptoms within 3-30 days include (11, 23 - 25)

• Fatigue

• Chills

• fever

• Headache

• Muscle and joint aches

• Swollen lymph nodes

Early disseminated Lyme disease is characterized by multiple annular EM distant from the original tick bite, flu-like symptoms, and neurologic or cardiac manifestations such as cranial nerve palsy, meningitis, or conduction abnormalities.  Lyme carditis is rare, but it is an important cause of mortality (26) and may result in complete heart block as early as 4 days after a tick bite. (27)

Days to months after the bite, late symptoms may develop (11, 23 -25)

• Severe headaches and neck stiffness

• Additional EM rashes on other areas of the body

• Arthritis with severe joint pain and swelling, particularly the knees and other large joints.

• Facial palsy (loss of muscle tone or droop on one or both sides of the face)

• Intermittent pain in tendons, muscles, joints, and bones

• Heart palpitations or an irregular heart beat (Lyme carditis)

• Episodes of dizziness or shortness of breath

• Inflammation of the brain and spinal cord

• Nerve pain

• Shooting pains, numbness, or tingling in the hands or feet

• Problems with short-term memory

Late disseminated Lyme disease occurs months or years after the initial tick bite and is characterized by arthralgias (joint pain) in 1 or more major joints or neurologic symptoms such as sleep disturbances, migraines, vertigo, and numbness in the hands, feet, arms, or legs.

Borrelia miyamotoi is an emerging borrelial infection with a distribution similar to Lyme disease. Although the clinical presentation is similar to Lyme disease, rash is uncommon. An early case series described a hospitalization rate of 24%. (28)

Borrelia mayonii, recently discovered by researchers at the Mayo Clinic, also has a similar presentation to Lyme disease but has thus far been confined to the Midwest of the USA. B mayonii infection is associated with higher concentrations of spirochetes in the blood when compared to B burgdorferi.(29)

Treatment

Prophylactic treatment of a single dose of doxycycline may be used to prevent development of infection if the removed tick was full of blood (30, 31) the Infectious Disease Society of America recommends a single dose of doxycycline 200 mg within 72 h of tick removal for adults and children older than 8 years if the following high-risk  criteria are met:

1. The tick bite was from an identified Ixodes vector species, and

2. it occurred in an endemic area, and

3. the tick was attached for more than 36hrs (33)

If signs and symptoms develop, a 2-3 week course of doxycycline, amoxicillin, or cefuroxime may be prescribed.(24)   Early treatment is usually successful.(34)

Late stage treatment typically requires intravenous ceftriaxone or cefotaxime and doxycycline as alternatives.(35)

Some casualties with late stage symptoms can develop long term fatigue, muscle and joint pain and even congestive heart failure.(36)   The lesson here?  

If in doubt – get checked out.

Prevention

Common sense dictates that avoiding wooded or grassy areas, especially during summer months when foliage is dense and animal life is more active is the best way to reduce the likelihood of infection.   If you are to encounter these environments, several strategies can reduce the risk of infection. (37)

• Avoid dense foliage and long grass by sticking to footpaths.

• Cover arms and legs to prevent ticks from latching onto your skin when brushing through long grass and foliage.(38)

  Light clothing may make it easier to spot ticks on your clothes, however, there is some evidence Ixodes ricinus may in fact be attracted to light-colored clothing.(39)   In a subsequent study, the use of light collared clothing did not sown a reduced risk of Lyme disease.(40)

• Permethrin insecticide can be sprayed onto clothing which may kill insects and arachnids, including ticks, on contact and has been thoroughly studied in a number of populations and has been shown to reduce the rate of tick attachment and tick bites in studies of volunteers (41) military personnel (42) and forestry workers (43, 44).

  When used in combination, permethrin-treated clothing and topical DEET were found to be more effective in preventing mosquito bites compared to either used alone. 45

• DEET (N, N-Diethyl-meta-toluamide) based insect repellents can be applied to the skin – especially around collars, cuffs and hems.  DEET, has been in use since 1956 and has been widely shown to be an effective tick repellent.(46-49)

  Seizure and neurotoxicity are possible side effects (50) but with approximately 30% of the Western populations having used DEET at some point (51) in their lives the absolute risk is likely quite low.

  The concentration of DEET is associated with estimated protection time. For example, 30% DEET will protect the user for an estimated 6hrs, whereas 5% DEET offers 2hrs of protection. The American Academy of Pediatrics does not recommend the use of DEET in children 2 months of age or younger, and DEET concentrations of 10% or less should be used in those 12 y of age and younger.(52)

  Additionally, DEET is known to be corrosive to synthetic fabrics.

  Other alternative or traditional repellants such as citronella or eucalyptus oil have either a lower efficacy or significantly shorter duration of action when compared to DEET. (53, 54)

• Inspect your skin for ticks including your head, neck and skin folds, armpits and groin.  You may need a willing accomplice and repay the favour.

  • Remove clothing for overall visual inspection.

  • Systematically scan the body for ticks, paying special attention to warm places (armpits, knees, under underwear, around hairline of neck, ears, and navel).

  • Remove any identified ticks by grasping at the head of the tick with pointed tweezers or tick remover and pulling perpendicular to the skin (Figure 1).

• Wash clothing in a high heat and tumble dry to kill any ticks you have brought home with you.

  In an early study of A americanum and I scapularis survival after exposure to automatic washer and dryer conditions, all nymphs were killed after 1h of drying at 40 to 42oC. (55)

  Although large proportions of nymphs survived hot water washes in this study, a more recent study showed 100% effectiveness of hot water washes at temperatures greater than 54oC (130oF) in killing both nymphal and adult I scapularis.(56)

  These studies did not look specifically at the effect of these interventions on the incidence of TBI, however. Recommendation. Washing clothes at temperatures over 54C/130.F and drying clothing in high heat for 10 min kills ticks and therefore may reduce the risk of TBIs.

• Remove any ticks you find promptly.

Tick Removal

Ticks are small!   Depending upon the stage of life cycle from larva to adult, ticks can be less than a millimeter in size so finding them can be difficult.

No ‘traditional’ method of tick removal is known to be effective (57-73); using oil, petrol or Vaseline etc. can kill the tick, forcing it to vomit while drinking your blood, increasing the likelihood of infection.  Using the flame from a cigarette lighter or the ember of a cigarette itself is more likely to cause a burn to your skin with a dead tick stick in it.

In a case series, simply removing the tick with tweezers was associated with a lower rate of spirochetal and rickettsial infections (74) and is generally accepted as best practice.(75)

A number of dedicated tick removal tools exist which all work equally well.   Tweezers can also be used as long as:

1. The tick is grasped at the head – grasping the body is likely to squeeze the tick’s stomach contents back into and

2. as close to the skin as possible.   The further up the body of the tick you pull, the more you are likely to leave behind.

The Decision to Evacuate?

The decision to evacuate versus expectant monitoring is a constant dilemma for the Remote Medic can be the most important decision the provider can make in resource-limited settings. This decision balance of risks and benefits, including cost, interruption of business continuity, consideration of the possible harms of an inaccurate diagnosis and the potential for delayed care.

No randomized controlled trials exist comparing field management to evacuation for patients with potential systemic TBI.  Available cohort studies from the National Outdoor Leadership School describe a low incidence of TBI in the field, but in nearly all cases those with suspected TBI were evacuated.(76-78)   This is appropriate because management of TBI requires accurate clinical and laboratory diagnosis, prompt treatment, and close follow-up.  Life-threatening complications such as Lyme carditis could also potentially develop within the timeframe of a multiday backcountry trip.  An algorithmic decision tree outlining the field management of tick bites is summarized in Figure 2.

Summary

• Reduce the risk of infection by being aware of your environment and preparing properly with appropriate clothing and chemical agents.

• Check yourself diligently after exposure to these environments.

• If found, remove the tick using a dedicated tool or tweezers.

• Being bitten does not mean you will have caught Lyme disease.   Attachment of 36-48 hours is usually required.

• If you are infected, the flu-like symptoms associated with early development do not show immediately.   If you experience these symptoms up to 30 days after being in a tick-likely environment, see your GP.

• Prevention is better than cure and treatment works best when delivered early.

References

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