Concurrent babesiosis and Lyme disease diagnosed in Ontario.

Human babesiosis (caused by Babesia microti) and Lyme disease (caused by Borrelia burgdorferi) are among the most common tick-transmitted zoonoses. Recent evidence indicates that both diseases are emerging in the northeastern and Great Lakes regions of the United States as the deer tick (Ixodes scapularis), which transmits both infections, increases in geographic distribution. Because B. microti and B. burgdorferi reside in the same rodent reservoir (Peromyscus leucopus) and are transmitted by the same tick vector, human co-infection may be relatively common in endemic areas. In support of this contention, up to two-thirds of Long Island residents with Lyme disease have antibodies to Babesia species. However, until recently, only three episodes of co-infection had been described and, in each case, a particularly severe illness was experienced and one individual died. A recent report from New England found that the severity of symptoms and duration of illness in patients with concurrent babesiosis and Lyme disease was greater than for either infection alone.