Previously known as ehrlichiosis or HGE (Human Granulocytic Ehrlichiosis), Anaplasma phagocytophilum infection is now known as HGA (Human Granulocytic Anaplasmosis). HGA is transmitted by the bite of a deer tick (Ixodes scapularis) and is found in the same geographic regions as Lyme and Babesia. The organism is intracellular (inside granulocytes), causes an acute febrile illness with no characteristic rash, and is not known to be associated with a state of chronic infection. Clinically, infection is often asymptomatic and self-limiting, but may be severe and even fatal in immunocompromised persons.
There are several laboratory tests to assist in the diagnosis of HGA. One traditional test is the direct demonstration of the organism intracellularly (in granulocytes) on a thick smear of whole blood. The advantage of this test, in the hands of an experienced pathologist or technician, is that the result is available immediately. One potential disadvantage is that the organisms may not be visible below a certain level of parasitemia, and is in fact negative in most cases of HGA infections.
A more recently developed methodology for the direct demonstration of the organism in a clinical specimen (whole blood) is PCR. This methodology is capable of detecting minute quantities of the Anaplasma phagocytophilum specific DNA, making it a much more sensitive test than visualization on thick smear.
Serologic assays are available to detect the patient antibody response to HGA and include ELISA testing for both IgM and IgG responses. Imugen utilizes a proprietary recombinant protein antigen preparation for this assay. Seropositivity can accurately identify patient exposure, by demonstrating a specific immune response.
There is a window early in the course of an HGA infection when the patient may not yet be symptomatic, or is just beginning to become symptomatic. PCR testing at this stage is frequently positive, prior to a detectable antibody response. In contrast to Babesia infection, the HGA PCR promptly becomes negative after the initiation of antibiotic treatment.
The staff at the laboratory is highly trained in performing and interpreting these assays, has decades of experience in analyzing these test results in the context of various clinical situations, and is available to assist healthcare providers in interpreting tests and answering questions about the detection of tick-borne infections.