Understanding Anaplasma phagocytophilum
Anaplasma phagocytophilum is a microscopic bacterium that lives inside host cells. It has an affinity for white blood cells called neutrophils.
Inside host cells, Anaplasma phagocytophilum multiplies within membrane-bound compartments, forming visible clusters called morulae. This bacterium infects and thrives within neutrophils.
Understanding Anaplasmosis
The disease caused by Anaplasma phagocytophilum is human granulocytic anaplasmosis (HGA), known as anaplasmosis. This bacterial infection targets granulocytes, a type of white blood cell. The bacterium invades and replicates within these cells.
Anaplasmosis is a zoonotic disease, meaning it can transmit from animals to humans. Humans are incidental hosts. The infection can range from mild, flu-like symptoms to serious complications if untreated.
How Infection Spreads
Anaplasmosis primarily spreads through the bite of infected ticks. The blacklegged tick (Ixodes scapularis) is the main carrier in the eastern and upper Midwestern United States. On the West Coast, the western blacklegged tick (Ixodes pacificus) transmits the disease.
These ticks acquire the bacterium by feeding on infected animals like small rodents and deer. When an infected tick bites a human, the bacteria can transfer into the bloodstream. For transmission, the tick typically needs to remain attached for 24 to 48 hours. Transmission can occur at any time of year when ticks are active, but peak periods for human cases align with the activity of young ticks (nymphs) in late spring and summer, and adult ticks in the fall and spring.
Signs of Infection
Symptoms of human granulocytic anaplasmosis typically begin within 5 to 21 days after an infected tick bite. Initial symptoms often resemble the flu, including fever, headache, and muscle aches. Chills are common.
Some individuals may experience nausea, vomiting, diarrhea, or a cough. Joint pain and confusion are less frequently reported. A skin rash is rare, appearing in less than 10% of cases.
Confirming and Treating the Infection
Confirming anaplasmosis involves specific laboratory tests, often initiated when symptoms suggest infection. Polymerase chain reaction (PCR) testing identifies bacterial DNA and is most sensitive during the first week of illness.
Serology, which measures antibodies against the bacterium, typically requires two blood samples taken several weeks apart to show a significant rise in antibody levels. Examining a peripheral blood smear under a microscope can sometimes reveal morulae, the characteristic bacterial clusters, within white blood cells, providing a rapid but less sensitive diagnostic indicator. Early diagnosis is important to prevent complications.
Doxycycline is the standard antibiotic treatment for anaplasmosis, prescribed for individuals of all ages. Patients usually show improvement, with fever often subsiding within 24 to 48 hours of starting treatment. The typical course of treatment lasts for 10 to 14 days, or at least three days after the fever has resolved.
Protecting Yourself
Preventing anaplasmosis primarily involves reducing exposure to tick bites. When spending time outdoors, especially in wooded or grassy areas, wearing light-colored clothing can make it easier to spot ticks. Long-sleeved shirts and long pants tucked into socks can help limit exposed skin.
Using insect repellents containing active ingredients like DEET, picaridin, or IR3535 on exposed skin is effective. Treating clothing and gear with permethrin-based products provides further protection.
After outdoor activities, perform thorough tick checks on yourself, children, and pets. If a tick is found, remove it promptly using fine-tipped tweezers by grasping the tick close to the skin and pulling upward with steady, even pressure.