Intracytoplasmic Granulocytic Morulae Counts on Confirmed Cases of Human Granulocytic Ehrlichiosis/Anaplasmosis in the Northeastern United States
Janne V Rand, Ashley Tarasen, Suzanne Homan, Jessica Kumar, Ellis Tobin. Albany Medical Center, Albany, NY
Background: Human Granulocytic Ehrlichiosis (HGE), due to Anaplasma phagocytophilum, is an intracellular gram negative coccobacillus, transmitted by the Ixodes tick. The organism replicates in the cytoplasmic vacuoles of granulocytes to form microcolonies called morulae. PCR is the gold standard of early diagnosis, but can be time consuming and is not routinely available outside of specialty laboratories. Serologic tests are frequently negative during the first week of illness onset and often require both acute and convalescent titers to confirm a diagnosis. The peripheral smear can be prepared and examined quickly for intracytoplasmic granulocytic morulae, and provides prompt diagnosis so that appropriate therapy can be administered in a timely manner. However, the percentage of cells that contain morula is reportedly low and there are no recommendations to help guide a strategy of examining peripheral smears in an effort to maximize the sensitivity of this simple and commonly available test.
Design: Peripheral smears were examined in 14 confirmed cases of HGE/Anaplasmosis. The cases were confirmed by various methods including PCR (50%), serology (35.7%), and examination of peripheral smear with treatment response (14.3%). All 14 patients had relatively severe non-specific symptoms and required hospitalization. The granulocytes were counted until a morula was identified and the number of granulocytes containing morulae per 100 granulocytes was recorded. The average counts of three pathologists were calculated to determine how many cells should be counted to find a positive result.
Results: Morulae were identified before a count of 100 granulocytes in 11 (78.6%) cases, and between 100-200 granulocytes in 3 (21.4%) cases. All 14 cases (100%) had morulae identified before counting 200 granulocytes. The average number of morulae found in cases with morulae identified before a count of 100 was 3.5, and the average number of morulae in cases identified between 100-200 was 0.37.
Conclusions: Peripheral smears are a useful, cost and time effective tool for diagnosing HGE/Anaplasmosis. In positive cases it is very likely that a morulae will be identified in a count of 100 granulocytes. However, it is recommended that a count of 200 granulocytes be performed to increase sensitivity. This is the first study to provide a quantitative analysis for a recommendation to perform peripheral smear testing in an effort to rapidly and routinely confirm a diagnosis of HGE/Anaplasmosis.
Wednesday, March 6, 2013 9:30 AM
Poster Session V # 247, Wednesday Morning