Anaplasmosis is a bacterial infection caused by the bacterium Anaplasma phagocytophilum. It is primarily transmitted to humans through tick bites and commonly affects people in the upper Midwest and northeastern United States, as well as parts of Europe and Asia. It can cause a range of flu-like symptoms.
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Human granulocytic anaplasmosis (HGA) was first recognized as a distinct human disease in the United States in 1990 in Wisconsin and Minnesota. It was initially identified as human granulocytic ehrlichiosis before the causative agent was reclassified. Its discovery highlighted the expanding spectrum of tick-borne diseases affecting humans.
Anaplasmosis is primarily transmitted to humans through the bite of an infected tick. In the United States, the **blacklegged tick** (*Ixodes scapularis*) is the main vector in the Northeast and Midwest, and the **western blacklegged tick** (*Ixodes pacificus*) on the Pacific coast. Ticks acquire the bacteria by feeding on infected animals such as white-footed mice and other small mammals, then transmit it during subsequent blood meals.
Contagious Period: Varies by disease
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On his sprawling property in the heart of the Ottawa Valley, Martin Haché has seen deer, wild turkeys and even a mama bear with her cubs. But the 80-year-old retired accountant has never spotted a tick.
So, in July, 2025, ticks were the furthest thing from Mr. Haché's mind when he suddenly became ill and collapsed in the bathroom, too weak to even lift his head. After he fell two more times, his wife, Kathleen, called 911 and Mr. Haché was rushed to a nearby hospital, where he became deliriou
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Trusted information from leading health organizations
Official guidance from the U.S. Centers for Disease Control and Prevention
View CDC Resources →Global disease surveillance and guidelines from the World Health Organization
View WHO Resources →Disease information on Virus Watcher is reviewed by our Chief Epidemiologist, a former CDC lead analyst for FluSight forecasting. Outbreak data is aggregated from verified sources including BEACON, ProMED, WHO, CDC, and 50+ national health agencies. This information is for educational purposes and should not replace professional medical advice.
Last reviewed: 2026-07-18
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