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Background: Although tick-borne pathogens have been reported as an important cause of imported fever, the incidence of Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis (HGA), in travellers is unknown., Methods: We conducted a prospective cohort study to investigate the aetiologies of fever in returning travellers (November 2017-July 2019). Polymerase chain reaction for msp2 gene amplification and indirect immunofluorescence assay for A. phagocitophilum were performed in all returning travellers with undifferentiated non-malarial fever., Results: Among 141 travellers included, 8 patients were diagnosed with probable or confirmed HGA. The overall incidence rate of HGA was 19.9 cases/1000 person-week of travel. The main destination of travel was Asia, accounting for 62.5% patients with HGA. Co-infections were found in 37.5% of patients with HGA., Conclusions: Diagnosis of HGA and empirical treatment with doxycycline should be considered in travellers with fever., (© International Society of Travel Medicine 2021. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Ehrlichia/Anaplasma, Bartonella, Rickettsia and Tropheryma whipplei (formerly called whippelii) are fastidious bacterial organisms, considered the causative agents of potentially severe emerging and re-emerging diseases with repercussions on public health. The recent availability of advanced molecular biology and cell culture techniques has led to the implication of many of these species in human pathologies. These issues are extensively covered in number 27 of the SEIMC microbiological procedure: Diagnóstico microbiológico de las infecciones por patógenos bacterianos emergentes: Anaplasma, Bartonella, Rickettsia y Tropheryma whippelii (Microbiological diagnosis of Anaplasma, Bartonella, Rickettsia and Tropheryma whippelii infections) (2nd ed., 2007) (www.seimc.org/documentos/protocolos/microbiologia/).

Human ehrlichiosis and anaplasmosis are acute febrile tick-borne diseases caused by various species of the genera Ehrlichia and Anaplasma (Anaplasmataceae). To date, only cases of human granulocytic anaplasmosis (HGA) caused by Anaplasma phagocytophilum (formerly human granulocytic Ehrlichia, Ehrlichia phagocytophila, and E. equi) have been diagnosed in Europe. HGA and Lyme borreliosis are closely related diseases that share vector and reservoirs. In addition to HGA, human monocytic ehrlichiosis caused by E. chaffeensis has been reported in North America, as well as cases of infection due to E. ewingii in immunocompromised hosts. Ehrlichia spp. and A. phagocytophilum have tropism for blood cells, especially leukocytes and platelets, causing a considerable decrease of both components in these patients. HGA should be suspected in tick-bitten patients or those who have visited an endemic area and show symptoms of flu-like fever, leukopenia and thrombocytopenia.