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INTRODUCTION

Lyme disease (also called Lyme borreliosis) is the most common illness resulting from infection with spirochetes of the Borrelia genus.1,2 Lyme disease predominantly occurs in North America and Europe following the bite of infected Ixodes spp. (hard-bodied) ticks. B. miyamotoi is a recently recognized pathogen that causes a relapsing fever illness and is also transmitted by Ixodes ticks.3 Given the common vector, disease resulting from this infection likely occurs in the same geographic regions as Lyme disease.4 Tick-borne relapsing fever (TBRF) and louse-borne relapsing fever (LBRF) are caused by infection with several species from the relapsing fever group of Borrelia. Whereas TBRF is endemic on most continents and most often follows the bite of infected Ornithodoros spp. (soft-bodied) ticks, LBRF occurs only in the Horn of Africa and is transmitted by lice (Pediculus humanus).5 Patients who are ill due to these Borrelia infections most often present with acute fever (without typical symptoms of viral respiratory infection or gastroenteritis), and possibly skin rash. Southern Tick-Associated Rash Illness (STARI) is clinically similar to early Lyme disease, but occurs after the bite of a lone star tick.6 Knowledge regarding geographic location and possibility of exposure to potential vectors, as well as certain risk factors, can inform the differential diagnosis. Methods for prevention of these diseases vary according to the vector of transmission.

LYME DISEASE

Lyme disease is the most commonly reported vector-borne disease in the United States and Europe and is caused by specific genospecies in the B. burgdorferi sensu lato complex.1,2,7 In the United States, it is a considerable public health problem in the upper Midwest, northeast, and mid-Atlantic regions. The distribution of reported cases has expanded significantly in these geographic regions and the incidence of human cases continues to rise in both new and established foci of infection.8,9 It is transmitted throughout the northern hemisphere by Ixodes spp. ticks. The ecology and epidemiology of Lyme disease are complex, and practical methods for prevention and control on a large scale are currently lacking.

AGENT

Borreliae are flexible helical cells comprised of a protoplasmic cylinder surrounded by a cell membrane, periplasmic flagella, and an outer membrane that is loosely associated with the underlying structures.10 A number of genospecies have been described among the B. burgdorferi sensu lato complex. The primary genospecies infecting humans and causing Lyme disease in the United States is B. burgdorferi sensu stricto (hereafter referred to as B. burgdorferi). Recently, the genetically distinct B. mayonii has also been found to cause Lyme disease, with a small number of people affected in the upper Midwestern United States.11 The dominant genospecies in Europe and Asia are B. garinii and B. afzelii; although, B. burgdorferi also contributes to the overall incidence of Lyme borreliosis.11,12 While all four species typically cause the same initial disease ...

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