During her work commute, a pediatrician was listening to a podcast about the European outdoors. One of the segments discussed how Lyme disease was more common in urban areas of Europe than most people realized.
She saw many patients for concerns about tick bites and knew about the epidemiology in her location, but didn’t know as much about it in other locations.
Lyme disease (LD) is caused by several genospecies of Borrelia burgdorferi senu lato that are transmitted by ticks of the Ixodes ricinus complex. In the U.S. and Europe it is the most common vector-borne disease. It is named for Lyme, Connecticut in the 1970s when it was “discovered,” but there are reports of LD-type disease in Europe since 1883. There are 18 distinct genospecies with B. afzelii, B. garinii and B. burgdorferi sensu stricto being the 3 most common ones causing human infection. There are many species of Ixodes ticks but only 4 commonly bite humans. Ixodes ricinus mainly in Europe, I, persultcatus in Asia, I. scapularis in the eastern and central US, and I. pacificus in the western US and Canada. However I. pacificus is rarely infected and accounts for very few human infections.
I. scapularis lives for approximately 2 years and eats blood meals at each of its 3 stages, larval, nymph and adult. Ticks are not infected when they hatch from eggs (a single female can produce > 2000 larvae). They become infected from the blood they feed upon. For I. scapularis, reservoir hosts for larva and nymphs are small mammals (i.e. mice, shrews) and birds. Adults like larger mammals such as deer and dogs. (Dogs are used as sentinels for epidemiological studies of Borrelis sp. in the environment). Humans are dead-end hosts as the spirochetes are not sustainable in human tissues in large numbers. I. scapularis ticks need attachment to transmit LD (usually 36 hours or more). Therefore attachment prevention with long clothing, showering (within 2 hours of being outside) and tick checks have demonstrated decreased risks of ticks bites. Additionally, using insect repellents with 20-30% of DEET is recommended.
Nymph stages are particularly important in LD transmission as they are abundant and small. Nymphs tend to feed in the late spring/early summer seasons or similar time frame depending on the local global latitude. Nymph stages are sensitive to desiccation, therefore they are increased in areas of humidity.
A review of LD clinical symptoms can be found here. Serological testing for disease depends on the geography, especially the expected prevalence of the organism. “In general, serological testing is only considered useful when the prior probability of disease is between 20% and 80%. In circumstances when the risk is lower, positive laboratory tests are more likely to reflect a false-positive result than actual infection.” Therefore management decisions about testing, prophylactic antibiotic use or treatment antibiotic use depends on location.
LD is seen around the northern hemisphere of the world but is particularly common in Northeastern, Mid-atlantic and upper Midwest areas of the US and corresponding Canadian provinces with I. scapularis as the primary vector. Western coastal areas including British Columbia and Northeastern Mexico and the Baja, have I. pacificus ticks but the number of human cases of LD is few. In Europe LD common in all Eastern, Central and Western European countries below 1300 m2 elevation and the primary vector is I. ricinus. B. afzelii is more predominant in Northern and Eastern Europe “(e.g. Scandinavia, Baltic states, Czech Republic, Slovakia, Croatia, Bulgaria).” B. garinii is more predominant in Western Countries “(eg. Austria, Switzerland, United Kingdom).”
LD can also be seen in the northern Africa coast in northern Algeria, Morocco and Tunisia with the common species being B. lusitaniae. LD is seen in Turkey and Russia with extension into the Asian continent including Japan, Korea, Taiwan and China. There are possibly LD cases noted in the southern hemisphere in Australia, Brazil and South Africa.
In the United Kingdom, Scotland has the highest prevalence rate along with South West and Southern England. Birds are a more important vector in Europe and it is thought that this is part of the reason that Scotland and other countries with large coastlines such as Norway may have higher disease rates. Ground feeding birds, especially thrushes, carry the most ticks and therefore potentially Borrelia sp.
Studies have found ticks with I. ricinus in urban areas throughout Europe including 2 South London parks. Urban greenspaces are often not thought of as carrying ticks and other potential environmental hazards, but can. This is especially true for green spaces at the “edge” of the city (periurban) or with increased connectivity between the green spaces which helps to support the birds, mammals and other environments suitable for ticks to survive and migrate between. Even isolated pockets of green space can harbor significant urban tick populations. The green space microclimate is also important with more trees, bushes and leaf-litter supporting a more humid environment which supports tick populations, while increased gravel or paved landscapes are drier and do not support tick populations as well.
Questions for Further Discussion
1. Describe erythema marginatum?
2. What is the local prevalance of Borrelia sp. in your location?
3. What is the treatment for Lyme neuroborreliosis in children?
- Symptom/Presentation: None
- Age: None
To Learn More
To view pediatric review articles on this topic from the past year check PubMed.
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Cairns V, Wallenhorst C, Rietbrock S, Martinez C. Incidence of Lyme disease in the UK: A population-based cohort study. BMJ Open. 2019;9(8):e025916. doi:10.1136/bmjopen-2018-025916
Mead PS. Epidemiology of Lyme disease. Infect Dis Clin North Am. 2015;29(2):187-210. doi:10.1016/j.idc.2015.02.010
Heylen D, Lasters R, Adriaensen F, Fonville M, Sprong H, Matthysen E. Ticks and tick-borne diseases in the city: Role of landscape connectivity and green space characteristics in a metropolitan area. Sci Total Environ. 2019;670:941-949. doi:10.1016/j.scitotenv.2019.03.235
Rizzoli A, Silaghi C, Obiegala A, et al. Ixodes ricinus and Its Transmitted Pathogens in Urban and Peri-Urban Areas in Europe: New Hazards and Relevance for Public Health. Front Public Health. 2014;2:251. doi:10.3389/fpubh.2014.00251
Oechslin CP, Heutschi D, Lenz N, et al. Prevalence of tick-borne pathogens in questing Ixodes ricinus ticks in urban and suburban areas of Switzerland. Parasit Vectors. 2017;10(1):558. doi:10.1186/s13071-017-2500-2
Nelson C, Banks S, Jeffries CL, Walker T, Logan JG. Tick abundances in South London parks and the potential risk for Lyme borreliosis to the general public. Med Vet Entomol. 2015;29(4):448-452. doi:10.1111/mve.12137
Hansford KM, Fonville M, Gillingham EL, et al. Ticks and Borrelia in urban and peri-urban green space habitats in a city in southern England. Ticks Tick-Borne Dis. 2017;8(3):353-361. doi:10.1016/j.ttbdis.2016.12.009
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa