Anaplasmosis is a disease caused by the bacterium Anaplasma phagocytophilum. This pathogen is transmitted to humans by the black-legged tick (Ixodes scapularis), found in the northeast and upper midwestern United States. The western black-legged tick (Ixodes pacificus) is the primary vector in Northern California. The first symptoms of anaplasmosis typically begin within 1-2 weeks after the bite of an infected tick. 

Signs and Symptoms​

  • Fever
  • Headache
  • Muscle pain
  • Malaise
  • Chills
  • Nausea / Abdominal pain
  • Cough
  • Confusion
  • Rash (rare with anaplasmosis)
Microscopic tick testing sample of Anaplasma phagocytophilum cells. Anaplasmosis, a tick borne disease, is caused by this bacterium.
Morula detected in a granulocyte
Image courtesy of CDC

Severe clinical presentations may include difficulty breathing, hemorrhage, renal failure or neurological problems. Rash is rarely reported in patients with anaplasmosis and the presence of a rash may signify that the patient has a coinfection with the pathogen that causes Lyme disease or another tickborne disease, such as Rocky Mountain Spotted Fever.​

Laboratory Detection​

A sample of whole blood taken from a tick can be tested by polymerase chain reaction (PCR) assay to determine if it carries A. phagocytophilum. Although a positive PCR result is helpful, a negative result does not completely rule out the diagnosis, and medical consultation and treatment should not be withheld due to a negative result.