Characteristic peripheral blood findings in human ehrlichiosis

Abstract

Human ehrlichiosis is a potentially fatal tick-borne illness if not treated promptly. Ehrlichia infection is difficult to diagnose as the organism does not grow in standard blood culture medium and serological confirmation of infection takes several days to weeks. The most timely way of confirming Ehrlichia infection is identification of characteristic cytoplasmic morulae in peripheral blood leukocytes. A total of 23 patients with clinical and laboratory findings suggesting a rickettsial infection were tested for Ehrlichia using polymerase chain reaction and culture: 16 cases contained Ehrlichia DNA by polymerase chain reaction (15 E. chaffeensis, one E. ewingii), including 14 cases in which the blood culture grew Ehrlichia. The cases that contained Ehrlichia DNA by polymerase chain reaction had lower mean white blood cell and platelet counts and more numerous atypical lymphocytes and pronounced toxic change than cases in which Ehrlichia DNA was not detected. Cytoplasmic morulae were identified on peripheral blood smears in six (five E. chaffeensis, one E. ewingii) of 16 (38%) of the cases that contained Ehrlichia DNA, including 4/4 (100%) immunocompromised and 2/12 (17%) immunocompetent patients. Morulae were present in monocytes in E. chaffeensis-infected cases and granulocytes in the E. ewingii-infected case. In two immunocompromised patients, the number of infected cells was 1-10%, but in four patients it was o0.2%. In conclusion, peripheral blood film examination is diagnostic in a substantial number of Ehrlichia infections, particularly in immunocompromised patients. The number of infected white blood cells may be less than 0.2%, requiring examination of more than 500 white blood cells. Associated changes prompting careful film review include prominent toxic granulation and atypical large granular lymphocytes.

New Findings from an Old Pathogen: Intraerythrocytic Bacteria (Family Anaplasmatacea) in Red-Backed Salamanders Plethodon cinereus

“…In a similar evaluation of hematological response of chickens with, and without, infection by Aegyptianella pullorum, Nazifi et al (2008) found no evidence of an innate immune (i.e., white blood cell) response; however, less than 1% of red blood cells were infected in that study. Humans infected with the bacteria, Ehrlichia chaffeensis, which infects white rather than red blood cells, have fewer white cells than uninfected individuals (Hamilton et al, 2004).…”

Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States

“…In some cases, pancytopenia due to ehrlichiosis has prompted bone marrow aspirate and biopsy, which typically reveals normocellular or hypercellular marrow (128,156). In some patients, morulae might be observed in monocytes in peripheral blood (157) (Figure 28) and occasionally in CSF (158,159) or bone marrow. In this context, a routine blood smear can provide a presumptive clue for early diagnosis; however, the visualization of morulae still requires confirmatory diagnostic testing (see Confirmatory Diagnostic Tests).…”

First Reported Case of Ehrlichia ewingii Involving Human Bone Marrow

“…Patients with ehrlichiosis may present with fever, headache, myalgia, rash, nausea, vomiting, and laboratory findings of thrombocytopenia, leukopenia, anemia, and elevated liver enzyme numbers (4, 6, 9, 10). In peripheral blood, E. chaffeensis generally has tropism for monocytes and E. ewingii tropism for granulocytes (1,4,6). Anaplasmosis has similar symptoms and was formerly referred to as human granulocytic ehrlichiosis (11,12).…”

“…On peripheral smears made using a Wright-Giemsa stain, E. chaffeensis, E. ewingii (Fig. 1), and A. phagocytophilum appear as basophilic clusters of intacytoplasmic bacteria referred to as morulae (1,11,15). E. murislike bacteria have yet to be morphologically described in vivo but infect granulocytic and monocytic cell lineages in cell culture (8).…”

“…Thus, these tick-borne diseases go under-or misreported to public health departments. Obstacles to identification to the species level include the turnaround time for PCR and serology and the fact that morulae are seen on peripheral blood smears in only 22% to 38% of ehrlichiosis cases (1,19). Additionally, serologic studies can be misleading, as cross-reactivity is seen among Ehrlichia spp., A. phagocytophilum, and Rickettsia spp.…”