The disease is reported worldwide and throughout the United States. The states of New York, Massachusetts, Connecticut, Rhode Island and New Jersey account for the majority of cases in the United States. However, cases are reported from all geographic regions of the country. Different ticks are carriers in the different regions. Ixodes dammini (the deer tick) in the Northeast and midwest, Ixodes scapularis (the black-legged tick) in the South, Ixodes pacificus (the western black-legged tick) in the West and Amblyomma americanum (the lone star tick) found in several regions are all considered vectors. The is growing concern that Dermacentor variabilis (the American dog tick) may also be capable of transmitting the disease. Transmission by biting insects (flies, fleas, mosquitos) is speculated but appears to be quite rare.