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Ehrlichiosis and Anaplasmosis are tick-borne bacterial infections caused by intracellular bacteria belonging to the family Anaplasmataceae, genera Ehrlichia, and Anaplasma. [See table below for more details].
Human Ehrlichiosis is a disease caused by at least three different ehrlichial species in the United States: Ehrlichia chaffeensis (mononuclear), Ehrlichia ewingii (granulocytes), and Ehrlichia muris-like (mononuclear). Human Granulocytic Anaplasmosis is a disease caused by Anaplasma phagocytophilum in the US and Anaplasma capra in China.
Ehrlichia chaffeensis (A and C; Wright stain) and Anaplasma phagocytophilum (B and D; Hema-3 stain) morulae (arrows) in peripheral blood monocytes (A), peripheral blood neutrophils (B), DH82 canine histiocytic cell culture (C), and human HL-60 promyelocytic cell culture (D).
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How Is Ehrlichia and Anaplasma Transmitted? What Are the Infected Regions?
Ehrlichia and Anaplasma are transmitted to humans by the bite of an infected tick. The lone star tick (Amblyomma americanum) is the primary vector of both Ehrlichia chaffeensis and Ehrlichia ewingii in the United States. The disease is transmitted to humans by tick bites primarily from the eastern black-legged tick (I. scapularis), the western black-legged tick (I. pacificus) in the US, and I. persulcatus in China. I. persulcatus, the taiga tick, is a species of hard-bodied tick found in Europe, central and northern Asia to the People’s Republic of China and Japan. The Dermacentor Variabilis (dog tick) has also been suggested in the transmission of both. Of the four distinct phases in the tick life-cycle (egg, larvae, nymph, adult), nymphal and adult ticks are most frequently associated with transmission of anaplasmosis to humans.
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