Human Monocytic Ehrlichiosis

Ehrlichiosis- Case-fatality rates are highest among children aged <10 years and adults aged ≥70 years, and an increased risk for death has been documented among persons who are immunosuppressed. In areas where ehrlichiosis is endemic, the actual disease incidence is likely underrepresented in estimates that are based on passive surveillance.

E. chaffeensis, the pathogen that causes human monocytic ehrlichiosis, predominantly infects monocytes and tissue macrophages.

E. chaffeensis ehrlichiosis can cause severe disease or death. Approximately 3% of patients with symptoms severe enough to seek medical attention die from the infection. Many cases of severe or fatal ehrlichiosis have been described in previously healthy children and young adults. Receiving a sulfonamide antimicrobial agent might also predispose to severe ehrlichial illness.

In patients with fatal E. chaffeensis ehrlichiosis, systemic, multiorgan involvement has been described with the greatest distribution of bacteria in the spleen, lymph nodes, and bone marrow. Direct vasculitis and endothelial injury are rare in ehrlichiosis.

Fever (96%), headache (72%), malaise (77%), and myalgia (68%) are common signs and symptoms.

Gastrointestinal manifestations can be prominent, including nausea (57%), vomiting (47%), and diarrhea (25%).

Abdominal pain, vomiting, and diarrhea can occur.

Approximately one-third of patients may develop a skin rash during the course of illness; rash occurs more frequently in children than in adults.

Rash patterns vary in character from petechial or maculopapular to diffuse erythema and typically occur a median of 5 days after illness onset. The rash typically involves the extremities and trunk but can affect the palms, soles, or face.

Cough or respiratory symptoms are reported in approximately 28% of patients. Central nervous system involvement, such as meningitis or meningoencephalitis, is present in approximately 20% of patients.

Other severe manifestations include ARDS, toxic shock-like or septic shock-like syndromes, renal failure, hepatic failure, coagulopathies, and occasionally, hemorrhagic manifestations (133).

E. chaffeensis infection might trigger hemophagocytic lymphohistiocytosis.

Severe cases have been mistaken for TTP, appendicitis, or fulminant viral hepatitis. Heartland virus disease, a recently identified tickborne viral infection transmitted by ticks, can closely resemble ehrlichiosis.

Lab Findings

Laboratory findings in the first week of E. chaffeensis ehrlichiosis can include leukopenia (nadir usually 1,300–4,000 cells/µL) (129), thrombocytopenia (nadir usually 50,000–140,000 platelets/µL, although occasionally <20,000 platelets/µL), and mildly or moderately elevated levels of hepatic transaminases.

Anemia can occur later in clinical illness.. Mild-to-moderate hyponatremia might also be present.

During the recovery period, a relative and absolute lymphocytosis is seen in some patients. In some cases, pancytopenia due to ehrlichiosis has prompted bone marrow aspirate and biopsy, which typically reveals normocellular or hyper cellular marrow.

In some patients, morulae might be observed in monocytes in peripheral blood and occasionally in CSF or bone marrow. In this context, a routine blood smear can provide a presumptive clue for early diagnosis.

When CSF is evaluated, a lymphocytic pleocytosis can be observed, although neutrophilic pleocytosis also can occur. CSF white blood cell counts are typically <250 cells/µL but can be higher in children. Elevated CSF protein levels have been noted.

Last Updated- April 2019

Lucy Barnes