Ehrlichiosis
Ehrlichia canis
Also known as: Canine monocytotropic ehrlichiosis, Canine granulocytotropic ehrlichiosis, Canine ehrlichiosis
CatDogUrgency: Moderate
Ehrlichia canis
Also known as: Canine monocytotropic ehrlichiosis, Canine granulocytotropic ehrlichiosis, Canine ehrlichiosis
In short
Ehrlichiosis is a common tick-borne bacterial infection in dogs and cats that attacks blood cells, causing symptoms like fever, abnormal bleeding, and lethargy across acute, subclinical, and chronic phases.
TL;DR. Ehrlichiosis is a serious, tick-borne bacterial infection that targets a pet's blood cells, leading to symptoms ranging from fever and swollen lymph nodes to life-threatening bleeding and bone marrow failure.
Ticks are the primary vector for transmitting Ehrlichia bacteria to pets.
Ehrlichiosis is a common and potentially severe infectious disease caused by intracellular bacteria belonging to the genus Ehrlichia. The most notable species affecting companion animals is Ehrlichia canis, which is primarily transmitted by the brown dog tick (Rhipicephalus sanguineus). Unlike many other bacteria that multiply in the bloodstream or tissues, Ehrlichia organisms are obligate intracellular parasites. This means they must invade the host's own blood cells—specifically white blood cells like monocytes and granulocytes—to survive and replicate. Once inside, they form clusters called morulae, effectively hiding from the body's immune system while disrupting normal cellular functions.
While ehrlichiosis is most frequently diagnosed and studied in dogs, cats can also contract the infection. Feline ehrlichiosis is less commonly documented in veterinary literature, and much of our clinical understanding and treatment protocols for cats are extrapolated from canine medicine. In both species, the disease is characterized by its ability to damage the hematopoietic (blood-producing) and immune systems, leading to widespread inflammation of the blood vessels (vasculitis), abnormal clotting, and potential bone marrow failure.
The disease typically progresses through three distinct clinical phases:
The primary cause of ehrlichiosis is the transmission of Ehrlichia bacteria via the bite of an infected tick. The brown dog tick is the most common vector, but other tick species can also transmit the disease. Consequently, any dog or cat that spends time outdoors in areas with active tick populations is at risk. Warm, humid climates where ticks thrive year-round present the highest geographic risk.
According to a study cited in a leading veterinary internal medicine reference:
"In one study of 8662 dogssamplessubmitted from 14 veterinary colleges, 6 private veterinary practices, and 4 diagnostic laboratories across the south and central regions of the United States, antibody prevalence rates for E. canis and E. chaffeensis were 0. 8% and 2. 8%, respectively (Beal et al, 2012)." — Internal Medicine 5th p.1364
There are no specific breed predispositions listed for ehrlichiosis; any dog or cat exposed to vector ticks can contract the infection. However, lifestyle factors greatly influence risk. Hunting dogs, outdoor cats, and pets living in heavily wooded or tall-grass environments face significantly higher exposure rates. Additionally, pets that do not receive consistent, year-round tick preventative medications are highly susceptible.
The symptoms of ehrlichiosis can vary dramatically depending on whether the pet is in the acute or chronic phase of the disease. Because the bacteria target blood cells and blood vessels, many signs relate to abnormal bleeding, anemia, and immune system overactivity.
Petechiae on the gums are a common sign of low platelet counts associated with ehrlichiosis.
Diagnosing ehrlichiosis requires a combination of clinical history, physical examination findings, and specific laboratory tests. Because the symptoms can mimic other diseases, such as autoimmune disorders or other tick-borne infections, your vet will perform a comprehensive diagnostic workup.
Your vet will start with baseline blood work, including a Complete Blood Count (CBC) and a chemistry profile. A low platelet count (thrombocytopenia) combined with elevated blood proteins (hyperglobulinemia) strongly points toward ehrlichiosis. To confirm the diagnosis, your vet will utilize one or more of the following specific tests:
As noted in a leading veterinary internal medicine reference:
"Changes in bone marrow cell lines associated with ehrlichiosis vary from hypercellular (acute phase) to hypocellular (chronic phase). Bone marrow plasmacytosis is common in dogs with subclinical and chronic ehrlichiosis, and the disease can be confused with multiple myeloma, particularly in dogs with monoclonal gammopathies." — Internal Medicine 5th p.1365
Additionally, evaluating specific proteins in the blood can help categorize the severity of the chronic phase:
"The positive acute phase proteins (APP) C-reactive protein (CRP), serum amyloid A (SAA), and haptoglobin (Hp) and the negative APP albumin concentrations were measured in 27 dogs with nonmyelosuppressive chronic monocytotropic ehrlichiosis, 29 dogs with myelosuppressive chronic monocytotropic ehrlichiosis, and 7 healthy dogs. The acute phase protein levels correlated to type of clinical syndrome..." — Internal Medicine 5th p.1366
Blood smears allow veterinarians to look for Ehrlichia organisms directly inside white blood cells.
Treatment for ehrlichiosis is highly effective when initiated early, particularly during the acute phase. The primary goal is to eliminate the intracellular bacteria and support the pet's body as it recovers.
The primary treatment for ehrlichiosis is a prolonged course of tetracycline-class antibiotics. The consensus among veterinary specialists is to use doxycycline. According to veterinary guidelines:
"Several different tetracycline, doxycycline, chloramphenicol, and imidocarb diproprionate protocols have been used. The ACVIM Infectious Disease Study Group currently recommends doxycycline (10 mg/kg PO q24h for at least 28 days)." — Internal Medicine 5th p.1367
It is vital to complete the entire 28-day course of antibiotics, even if your pet appears completely recovered within the first few days. Stopping treatment early can allow the bacteria to survive in a dormant state, leading to a relapse or progression to the dangerous chronic phase.
Veterinarians sometimes face a dilemma when a healthy dog tests positive for Ehrlichia antibodies during routine screening but shows no clinical signs of illness. As noted in veterinary literature:
"Whether to treat seropositive healthy dogs is controversial. Arguments for and against testing or treating healthy dogs were reviewed by the ACVIM Infectious Disease Study Group (Neer et al, 2002). The primary reason to treat a seropositive healthy dog is to try to eliminate infection before development of chronic-phase disease." — Internal Medicine 5th p.1367
Your vet will weigh the risks and benefits of treating a healthy, antibody-positive pet based on their specific lifestyle, geographic location, and baseline blood work.
The prognosis for pets diagnosed with ehrlichiosis depends heavily on the stage of the disease at which treatment begins.
For pets diagnosed during the acute phase, the prognosis is excellent. Most dogs and cats show noticeable improvement within 24 to 48 hours of starting doxycycline, and complete clearance of the bacteria is highly achievable.
For pets that have progressed to the chronic phase, the prognosis is variable to guarded. If the bacteria have caused severe, irreversible bone marrow suppression (hypocellularity), the body may no longer be able to produce red blood cells, white blood cells, or platelets. Despite aggressive treatment and blood transfusions, these cases can be fatal.
Because feline ehrlichiosis is less common, long-term prognosis data in this species is limited. However, when identified early and treated with appropriate antibiotic courses, cats generally experience a favorable outcome similar to dogs.
Because there is currently no vaccine available for ehrlichiosis in either dogs or cats, prevention relies entirely on minimizing exposure to ticks.
Chronic ehrlichiosis can suppress the bone marrow, halting the production of vital blood cells.
You should contact your veterinarian if your pet has been exposed to ticks and begins showing signs of lethargy, fever, or joint stiffness.
Seek immediate emergency veterinary care if you observe any of the following red-flag signs:
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
Ehrlichiosis is a common tick-borne bacterial infection in dogs and cats that attacks blood cells, causing symptoms like fever, abnormal bleeding, and lethargy across acute, subclinical, and chronic phases.
Fever、Hyperglobulinemia、Hypoalbuminemia、Monocytosis、Nonregenerative anemia、Petechiae、Splenomegaly、Thrombocytopenia
Bone marrow aspirate、Buffy coat smear or blood smear、ELISA (SNAP 3Dx)、IFA (Immunofluorescence assay)、PCR (Polymerase chain reaction)
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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