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Laboratory Diagnosis of Tick-Borne Infections

Part 1


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Conventional Methods for Diagnosis of Ehrlichiosis and Anaplasmosis

Slide 5

July 2010

So let’s review the conventional laboratory methods that are used for the diagnosis of ehrlichiosis and anaplasmosis. The first method I’d like to discuss is direct examination of peripheral blood smears. This technique has been used for many years in clinical laboratories, and remains one of the most rapid diagnostic methods in cases of suspected ehrlichiosis. In this test, laboratory technologists examine the peripheral smear for the presence of monocytes or granulocytes containing morulae, which is a latin term for “mulberry.”

As you can see in the images on the right-hand side of this slide, the organisms can be seen in characteristic clusters resembling mulberries. While the identification of morulae in peripheral blood smears is relatively specific, it is very insensitive for human monocytic ehrlichiosis, or HME, which is caused by Ehrlichia chaffeensis. We do see a slightly increased sensitivity in cases of human granulocytic anaplasmosis, or HGA, which is caused by Anaplasma phagocytophilum. However, it is still a relatively rare observation, with only 25 to 75% of smears being positive. I should also mention that empiric antimicrobial treatment may further decrease the sensitivity of smear, so ideally, a blood sample should be obtained prior to the initiation of therapy.

Conventional Methods for Diagnosis


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