Anaplasmosis and Lyme disease are two of the most commonly reported tick-borne illnesses in the United States. Both are transmitted by ticks and share similar initial flu-like symptoms, which can make early diagnosis challenging. Distinguishing between the two is important because the long-term health consequences and required medical responses differ significantly. Understanding the specific characteristics of each infection, from the pathogen to the treatment, is necessary for effective diagnosis and patient care.
Shared Vector, Distinct Bacteria
Both Anaplasmosis and Lyme disease are transmitted to humans through the bite of the blacklegged tick (Ixodes scapularis) in the Eastern U.S. and the Western blacklegged tick (Ixodes pacificus) on the West Coast. Ticks acquire these pathogens by feeding on infected reservoir hosts, such as white-footed mice, and transmit them to humans during a subsequent blood meal.
The infections are caused by entirely different bacterial species. Lyme disease is caused by the spirochete bacterium Borrelia burgdorferi, a spiral-shaped organism that lives outside of the host’s cells. Anaplasmosis is caused by the bacterium Anaplasma phagocytophilum, a smaller, intracellular organism that specifically targets and infects granulocytes, a type of white blood cell. This difference in the bacterial target—extracellular tissue versus white blood cells—drives many of the clinical differences between the diseases.
Key Differences in Clinical Presentation
The initial symptoms of both diseases involve fever, headache, and muscle aches, typically beginning days to weeks after a tick bite. Anaplasmosis is characterized by a rapid onset of high fever, severe headache, chills, and intense muscle pain. A distinguishing feature of Anaplasmosis is the rarity of a rash, reported in less than 10% of cases.
Lyme disease, however, is frequently identified by erythema migrans, a unique skin lesion that slowly expands outward from the bite site, sometimes resembling a bullseye pattern. This rash occurs in 70% to 80% of infected people and is often the defining symptom of early localized Lyme disease. If untreated, Lyme disease can progress to cause complications like nerve damage, facial palsy, inflammation of the brain and spinal cord, and arthritis, particularly in large joints.
Anaplasmosis often causes noticeable changes in blood cell counts. Laboratory tests frequently reveal a low white blood cell count (leukopenia) and a low platelet count (thrombocytopenia), as the Anaplasma bacteria infect and reduce these cell populations. If left untreated, Anaplasmosis can lead to severe issues like respiratory distress or kidney failure, with hospitalization rates being higher than for early Lyme disease.
Diagnostic Testing and Treatment Regimens
Diagnostic Testing
The unique biological characteristics of the two pathogens require different laboratory approaches for diagnosis. Lyme disease diagnosis relies on a two-tiered protocol that looks for the body’s immune response to Borrelia burgdorferi, not the bacteria itself. The first step is an enzyme immunoassay (EIA) or immunofluorescence assay (IFA), followed by a Western blot to confirm specific antibodies. This antibody-based testing can be negative in the very early stages before the immune system generates a detectable response.
In contrast, Anaplasmosis diagnosis focuses on detecting the organism directly, especially during the first week when the bacterial load is highest. This is often achieved through Polymerase Chain Reaction (PCR) testing of whole blood, which detects the DNA of Anaplasma phagocytophilum. Another method involves examining a blood smear to visualize characteristic clusters of bacteria, called morulae, within infected white blood cells. Serology is also used for Anaplasmosis, but a definitive diagnosis often requires comparing two samples taken weeks apart to observe a four-fold rise in antibody levels.
Treatment Regimens
The antibiotic Doxycycline is highly effective and is the first-line treatment for both Anaplasmosis and early Lyme disease. For Anaplasmosis, Doxycycline typically leads to rapid improvement within 24 to 48 hours, with a course generally lasting around ten days. The treatment duration for Lyme disease varies, but early localized disease typically requires a 10 to 21-day course of Doxycycline. Alternative antibiotics, such as amoxicillin or cefuroxime axetil, are available for Lyme disease, particularly for pregnant women or young children. Doxycycline remains the preferred choice due to its effectiveness against both infections and its benefit in covering potential co-infections.
Managing the Risk of Co-Infection
Because a single tick can carry multiple pathogens, a person bitten by an Ixodes tick can contract Anaplasmosis and Lyme disease simultaneously, known as co-infection. Having both infections can complicate diagnosis and potentially worsen the severity of symptoms. Patients with Lyme disease who have a high fever lasting more than 48 hours while on Doxycycline should be evaluated for possible Anaplasmosis co-infection.
The best defense against both diseases involves proactive measures to reduce tick bites. These include performing a thorough full-body tick check after spending time outdoors, using insect repellents, and wearing protective clothing. Prompt and proper removal of any attached ticks is also effective, as transmission usually requires the tick to be attached for a specific amount of time.