anaplasmosis

Anaplasmosis is a tick-borne infectious disease caused by bacteria of the Anaplasma genus, most commonly Anaplasma phagocytophilum in humans. In humans, it is known as human granulocytic anaplasmosis (HGA). The organisms are obligate intracellular bacteria that infect white blood cells, particularly neutrophils.

Transmission and epidemiology: The disease is primarily transmitted through bites from Ixodes ticks, including Ixodes scapularis and Ixodes pacificus in North America and Ixodes ricinus in Europe (with other Ixodes species in parts of Asia). Wildlife and small mammals often serve as natural reservoirs. Cases cluster in spring and summer in regions where ticks are active. While most infections occur in humans, anaplasmosis also affects livestock and companion animals, sometimes influencing veterinary health and farming.

Clinical features and pathophysiology: After an incubation period of about 5 to 14 days, symptoms typically begin as a nonspecific febrile illness with fever, severe headache, myalgia, malaise, and sometimes nausea or vomiting. Rash is uncommon in HGA. Laboratory findings often include leukopenia (low white blood cell count), thrombocytopenia (low platelets), and elevated liver enzymes; C-reactive protein may be elevated. Morulae (clusters of bacteria) can be seen in neutrophils on blood smear in some cases but are not consistently present. Severe disease can occur, especially in older adults or those with immune compromise, and may include altered mental status, respiratory symptoms, or multi-organ involvement.

Diagnosis and treatment: Diagnosis relies on clinical suspicion with laboratory confirmation by PCR testing of blood during the acute phase, and serology (fluorescent antibody tests) showing rising antibody titers in convalescence. Early treatment improves outcomes. Doxycycline is first-line, typically 100 mg twice daily for 10–14 days; alternative antibiotics such as rifampin may be used when doxycycline is contraindicated. Most patients recover with appropriate therapy.

Prevention: Preventive measures focus on reducing tick exposure and bite risk, including the use of effective repellents, wearing long sleeves and pants, permethrin-treated clothing, prompt and careful tick removal, and performing tick checks after outdoor activity. There is no widely available human vaccine; vaccines exist for certain animal forms of anaplasmosis in veterinary contexts.