Human Granulocytic Anaplasmosis
What is anaplasmosis?
Anaplasmosis, also known as human granulocytic anaplasmosis (HGA), is a tick-borne disease caused by the bacterium
Anaplasma phagocytophilum. It is usually transmitted to people via the bite of an infected tick. In the Northeast and Midwestern United States,
Anaplasma phagocytophilum is carried by blacklegged ticks (Ixodes scapularis), and on the West Coast it is carried by the Western blacklegged tick (Ixodes pacificus). An infected tick needs to be attached for at least 24-48 hours to transmit the bacteria that causes HGA. Therefore, removing an attached tick promptly can decrease the chances of being infected. In some rare cases, anaplasmosis has also been transmitted by blood transfusion.
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From left to right. Ixodes Scapularis larva, nymph, adult male, adult female.
| Distrobution of Ixodes scapularis and Ixodes pacificus.
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What are some of the risk factors for HGA?
Geography: HGA cases are most frequently reported from the upper Midwestern and Northeastern United States, where blacklegged ticks are most common. The range of the blacklegged tick is expanding along the Hudson River valley, and into Michigan and Virginia.
Seasonality: HGA cases can occur during any month of the year, but the majority of cases (>50%) occur during the summer months with a peak in June and July. There is also a smaller peak in the number of cases during October and November corresponding with the period of adult blacklegged tick activity.
Environment: Blacklegged ticks live on the ground in wooded areas or areas with lots of brush. The ticks search for hosts at or near ground level and grab onto a person or animal as they walk by.
People at Risk: The frequency of reported HGA cases is higher among males, people over 40, people with weakened immune system (due to being on immune suppressant drugs, HIV infection, cancer treatment), and people who live or spend time in tick habitats.
What are the symptoms of HGA?
Early HGA symptoms are similar to a mild viral infection, and usually occur within 1-2 weeks after the bite of an infected tick. They include a fever, chills, a severe headache, muscle aches, and gastrointestinal symptoms (nausea, vomiting, diarrhea, loss of appetite). Rash occurs in less than 10% of cases and might be a sign of co-infection with another tick-borne illness such as Lyme disease. If left untreated, the infection may progress to a late-stage illness. Signs and symptoms of this late-stage illness can include liver damage, kidney failure, bleeding in the gastrointestinal tract, and death (in less than 1% of cases).
How is HGA diagnosed?
Initial diagnosis of anaplasmosis is made by a healthcare provider based on exposure, signs and symptoms, and routine blood test to reveal low white blood cell counts, low platelet counts, and elevated levels of specific liver enzymes. The diagnosis can be confirmed by identifying the presence of
A. phagocytophilum DNA using polymerase chain reaction (PCR), visualization of morulae on a peripheral blood smear, or identification of antibodies specific to
A. phagocytophilum using an indirect immunofluorescence assay (IFA).
How is HGA treated?
It can take days or weeks to confirm the diagnosis using PCR or IFA, but if anaplasmosis is suspected based on routine blood tests, symptoms, and/or a history of outdoor activities, treatment should not be delayed. It has been shown that early treatment of anaplasmosis with doxycycline antibiotic improves outcomes and prevents severe complications. Seek medical attention if you experience the symptoms described above.
How can HGA be prevented?
The best way to prevent anaplasmosis is to avoid tick bites. Use the DoD Insect Repellent System when in tick habitat (tall grass, weeds, scrubby areas, woods, and leaf litter). The system includes using permethrin repellent on the uniform; applying DEET, picaridin, or IR3535 repellent to exposed skin; wearing uniforms properly; and sleeping inside a permethrin-treated bed net in tick habitat. It is also important to routinely check your skin and clothing for ticks while in tick habitat, and to carefully check your whole body once indoors. A friend or a mirror can help you check areas you cannot see. Attached ticks should be removed as soon as they are found by using sharp tweezers to grasp the tick as close to the skin as possible and applying steady upward pressure. Clothes can be put in a dryer on high heat for 10 minutes to kill ticks. Wet clothes may require more time. Ticks that are removed can be folded in a piece of sticky tape and discarded, or saved for identification and testing. Ticks removed from military personnel, their dependents, or DoD Civilians can be submitted for identification and disease testing through the MilTICK program. For more information on MilTICK please click below:
