Compared to classic Lyme disease (LD), Baggio–Yoshinari syndrome (BYS) has the following distinctive characteristics: it is transmitted in the Amazon area and Northeast, Central-West, Southeast, and South regions of Brazil by hard ticks, notably Amblyomma cajannense or Rhipicefalus sp. The absence of Ixodes sp. ticks in areas at risk of BYS in Brazil is probably the main reason for the disease’s differences from LD in the United States, Europe, and Asia. Biodiversity and climate probably favor the formation of atypical pleomorphic Borrelias, which have not yet been cultivated or isolated. Clinically, the first manifestation of BYS is the erythema migrans as in the classic forms of Lyme disease, but BYS is distinguished from LD by its prolonged clinical evolution, with a high frequency of relapses and the appearance of autoimmune manifestations. Prevalent symptoms are headache and erythema nodosum. Five clinical cases of BYS in patients who contracted the disease in the Brazilian Amazon rainforest are described here. This syndrome should be considered among differential diagnoses in patients bitten by ticks in Brazil who present with erythema migrans and/or headache. It is important to pursue an early diagnosis because symptoms respond well to antibiotics in the early stages; if treatment is started late, a chronic course with articular and neurological sequelae can be detected.
