Ehrlichiosis and Anaplasmosis are two distinct but related **bacterial infections** primarily transmitted to humans by **tick bites**. Both diseases can cause flu-like symptoms and are most common in areas where their specific tick vectors reside across the United States. Ehrlichiosis is caused by *Ehrlichia* species, and Anaplasmosis by *Anaplasma phagocytophilum*.
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Human Anaplasmosis (initially called Human Granulocytic Ehrlichiosis) was first recognized in the United States in the early 1990s, while Human Monocytic Ehrlichiosis caused by *Ehrlichia chaffeensis* was identified in the mid-1980s. Their emergence highlighted the increasing public health threat posed by newly recognized tick-borne diseases, leading to significant research efforts.
Both diseases are transmitted through the bite of infected ticks. Anaplasmosis is primarily spread by the **blacklegged tick** (*Ixodes scapularis*) in the Northeast and Upper Midwest US, and the **western blacklegged tick** (*Ixodes pacificus*) in the West. Ehrlichiosis (specifically *E. chaffeensis*) is mainly transmitted by the **lone star tick** (*Amblyomma americanum*) across the South-Central, Southeastern, and Eastern US.
Contagious Period: Varies by disease
Local health department information and state-specific prevention guidance
Our AI-powered surveillance continuously monitors Ehrlichiosis and Anaplasmosis activity across Colorado. We track data from state health departments, local hospitals, CDC reports, and 50+ global health sources to provide early warning of emerging threats.
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For official state health alerts, vaccination locations, and public health guidance specific to Colorado, visit your state health department's website.
Whether you live in Colorado or are traveling there, knowing the symptoms, timeline, and when to seek care helps you act quickly if exposure occurs.
Seek care if you experience severe dehydration, bloody stools, high fever, or symptoms lasting more than 3 days. Children under 5, adults over 65, and immunocompromised individuals should seek care earlier.
Emergency symptoms: Severe dehydration, inability to keep fluids down for 12 or more hours, or neurological symptoms require emergency care.
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Trusted information from leading health organizations
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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