Ehrlichiosis and anaplasmosis are infectious diseases caused by rickettsial organisms of the genera Ehrlichia and Anaplasma, transmitted primarily through tick bites [1][2]. The two major bacterial pathogens are Anaplasma marginale and Anaplasma phagocytophilum, which are Gram-negative bacteria that infect red blood cells [5]. Human granulocytic anaplasmosis is specifically caused by Anaplasma phagocytophilum and transmitted by the black-legged tick (Ixodes scapularis) in North America [3].
Disease overview
BacterialEhrlichiosis and Anaplasmosis
埃立克体病和无形体病
Evidence-backed informationEN 5/7 applicable sections · ZH 5/7 applicable sectionsUpdated Sep 3, 2026
Ehrlichiosis and anaplasmosis are zoonotic tick-borne rickettsial diseases affecting dogs, cats, humans, and other animals with a broad geographic distribution [1][2]. Human granulocytic anaplasmosis (HGA), caused by Anaplasma phagocytophilum, is an emerging infection with increasing incidence in North America [3][4]. Advances in diagnostics have improved understanding of the expanding geographic range and health impacts of these organisms across species [1]. While clinical remission can be achieved with appropriate antimicrobial therapy, no approved vaccines are currently available for prevention [1][5].
Read the full clinical and epidemiological profile6
Human infection presents with fever, chills, headache, and myalgia, with an incubation period of 5 to 14 days following a tick bite [3]. Complications include shock, organ dysfunction, and death, though mortality is less than 1% with appropriate treatment [3]. In animals, particularly ruminants and dogs, signs include weight loss, diarrhea, paleness of mucous membranes, jaundice (sometimes called 'yellow bag' or 'yellow fever'), aggressive behavior, and high fever [5]. The immune response targets and destroys infected red blood cells along with healthy ones [5].
Ehrlichiosis and anaplasmosis have a worldwide distribution with high prevalence rates reported in dogs from multiple European countries, and publications have increased substantially in recent years [1][2]. Human granulocytic anaplasmosis incidence is increasing in North America [3]. The diseases affect multiple species including dogs, cats, horses, and ruminants, with documented zoonotic transmission to humans [1].
Transmission occurs primarily through tick bites, with biological vector transmission by Ixodes scapularis (black-legged or deer tick) requiring 24 to 48 hours of attachment for infection [3][4]. Mechanical transmission can also occur through blood-contaminated surgical equipment such as needles, dehorners, ear taggers, castrating knives, and tattoo instruments, as well as through biting flies carrying the parasite [5]. The black-legged tick is the most common vector for anaplasmosis in North America [5].
No live or inactivated vaccines effective against all strains have received approval for use in humans or animals [1][5]. Tick control remains the primary prevention strategy, including chemical methods and environmental management, though this approach can be labor-intensive [5]. In veterinary settings, vector control measures are widely used in some regions, while testing and eliminating infected animals from herds can help achieve disease-free status [5]. For humans, standard tick-bite prevention measures including repellent use and prompt tick removal are recommended [4].
- 1Diniz PPVP et al. Ehrlichiosis and Anaplasmosis: An Update. Vet Clin North Am Small Anim Pract. 2022 Nov. PMID: 36336419. doi: 10.1016/j.cvsm.2022.07.002.PubMed: https://pubmed.ncbi.nlm.nih.gov/36336419/
- 2Sainz Á et al. Guideline for veterinary practitioners on canine ehrlichiosis and anaplasmosis in Europe. Parasit Vectors. 2015 Feb 4. PMID: 25649069. doi: 10.1186/s13071-015-0649-0.PubMed: https://pubmed.ncbi.nlm.nih.gov/25649069/
- 3MacQueen D et al. Human Granulocytic Anaplasmosis. Infect Dis Clin North Am. 2022 Sep. PMID: 36116840. doi: 10.1016/j.idc.2022.02.008.PubMed: https://pubmed.ncbi.nlm.nih.gov/36116840/
- 4Sanchez E et al. Diagnosis, Treatment, and Prevention of Lyme Disease, Human Granulocytic Anaplasmosis, and Babesiosis: A Review. JAMA. 2016 Apr 26. PMID: 27115378. doi: 10.1001/jama.2016.2884.PubMed: https://pubmed.ncbi.nlm.nih.gov/27115378/
- 5Wikipedia contributors. Anaplasmosis - Wikipedia [Internet]. Wikipedia. cited 3 Sept 2026.Available from: https://en.wikipedia.org/wiki/Anaplasmosis
Data access
Page dataset index with source links and update metadata.
Official sourcesAuthority, cadence, notes1
Public Health Ontario IDTO Monthly
Ontario, Canada
Ontario-level current-year preliminary monthly case counts from Public Health Ontario's IDTO report.