Comparison of Lyme Disease in the United States and Europe

Adriana R. Marques; Franc Strle; Gary P. Wormser


Emerging Infectious Diseases. 2021;27(8):2017-2024. 

In This Article

Abstract and Introduction


Lyme disease, or Lyme borreliosis, is the most common tickborne disease in the United States and Europe. In both locations, Ixodes species ticks transmit the Borrelia burgdorferi sensu lato bacteria species responsible for causing the infection. The diversity of Borrelia species that cause human infection is greater in Europe; the 2 B. burgdorferi s.l. species collectively responsible for most infections in Europe, B. afzelii and B. garinii, are not found in the United States, where most infections are caused by B. burgdorferi sensu stricto. Strain differences seem to explain some of the variation in the clinical manifestations of Lyme disease, which are both minor and substantive, between the United States and Europe. Future studies should attempt to delineate the specific virulence factors of the different species of B. burgdorferi s.l. responsible for these variations in clinical features.


Lyme disease, or Lyme borreliosis, is the most common tickborne disease in both the United States and Europe; an estimated ≈476,000 cases are diagnosed and treated per year in the United States and >200,000 cases per year in western Europe.[1–3] The principal tick vector in the United States is Ixodes scapularis, followed by I. pacificus; in Europe, most cases are transmitted by I. ricinus, followed by I. persulcatus ticks (Table 1). The etiologic agent, Borrelia burgdorferi, was discovered in 1982 in the United States. Later, it became recognized that strains of B. burgdorferi in Europe were more heterogenous than strains in North America. B. burgdorferi sensu lato was then classified into 3 main genospecies. The originally discovered genospecies was named B. burgdorferi sensu stricto. The second genospecies was named Borrelia garinii sp. nov., and the third was named Borrelia afzelii sp. nov. Recently, the taxonomy of the family Borreliaceae (and the genus Borrelia) has been revised into 2 main genera, Borrelia and Borreliella.[4] The spirochetes that cause relapsing fever retained the genus name Borrelia, and spirochetes that cause Lyme disease have been renamed Borreliella (hereafter referred to as Lyme borrelia). However, these changes have been challenged.[5]

Most cases of Lyme disease in the United States occur in the mid-Atlantic, Northeast, and Upper Midwest regions. B. burgdorferi s.s., which also is found in Europe, causes most human infections in the United States;[1,2] the newly recognized species B. mayonii (which is not known to exist in Europe) is an infrequent cause of human illness in the Upper Midwest region of the United States.[6] The incidence of Lyme disease in Europe is highest in the Scandinavian and Baltic states in northern Europe and in Austria, the Czech Republic, Germany, and Slovenia in central Europe. B. afzelii and B. garinii are the genospecies most frequently detected in I. ricinus and I. persulcatus ticks and cause most cases of Lyme disease in Europe.[1,2] Neither genospecies is found in the United States. Transmission of B. burgdorferi s.s. by I. scapularis or by I. pacificus ticks is very infrequent during the first 36 hours after tick attachment; in contrast, transmission of B. afzelii by I. ricinus ticks may occur within 24 hours (Table 1).[7]