New emerging tick-borne diseases

The definition of emerging diseases includes infections where the etiologic al agent has been discovered during the past 20 yeats or known infections t hat have either changed character or epidemiology during, the same time per iod. With this definition, tick-borne diseases represent important emerging infections. Lyme borreliosis; which was shown in the early 1980s to be cau sed by a spirochete , Borrelia burgdorferi sensu late, has been found to be the most common bacterial cause of neurological disease in both adults and children. In recent years ehrlichiosis and babesiosis have also emerged or - re-emerged as important human tick-borne diseases. Ehrlichiosis is caused by intracellular bacteria, with a predilection to invade either monocytic or granulocytic cells A new monocytic ehrlichia causing human disease Ehrli chia chaffeensis was isolated in the early 1990s in the southern pairs of t he US. Human granulocytic ehrlichiosis (HGE) was described in the mid-1990s from the northern parts of the US to be caused by an agent which closely r esembles E. equi/E.phagocytophila, well-known pathogens in veterinary medic ine. HGE has recently also been described in Europe. Babesia microti, a pir oplasm related to the malaria parasite, was Sound to cause disease in immun ocompetent individuals in the US. Babesia divergens, the cause of babesiosi s in fur-ope has been long known to cause fulminant disease in immuno-suppr essed individuals ir;while disease caused by B. microti has not been descri bed on our continent. However, the parasite has been isolated from rodents in different parts of Europe and indirect evidence suggests the presence of both babesial infections in immunocompetent individuals Ehrlichiosis and b abesiosis have a wide range of clinical manifestations, from subclinical to fulminant but with a non-specific flu-like illness as the most common symp tom. Both are known to cause immunosuppression and chronic infection, with B. microti also being blood transfusion transmitted. With the exception of E. chaffeensis, all the above mentioned pathogens are transmitted by ticks of the Ixodes genus, which in Europe also transmit the virus causing tick-b onze encephalitis is (TBE). Go-infections with two or more of these pathoge ns has been described and in one study concomitant infection with B. microt i was shown to result in a mor e severe and protracted Lyme borreliosis. Co nsidering the potential importance of these new emerging tick-borne disease s and of co-infections, efforts to improve the diagnostic methods in order to delineate the full clinical spectrum of the diseases and to evaluate new treatment strategies seem to be warranted.