Ehrlichiosis in Dogs: Symptoms, Diagnosis, Treatment, and Prevention Guide
This article is reviewed for clinical accuracy. Always consult your veterinarian for diagnosis and treatment.
Key Takeaways
- Ehrlichiosis is a tick-transmitted rickettsial disease caused by obligate intracellular bacteria of the genus Ehrlichia that invade and multiply within white blood cells; the two species of greatest clinical importance in dogs in the United States are Ehrlichia canis, which infects monocytes and macrophages (canine monocytic ehrlichiosis, CME), and Ehrlichia ewingii, which infects granulocytes (canine granulocytic ehrlichiosis, CGE); a third species, Ehrlichia chaffeensis, primarily infects humans but can occasionally infect dogs; Ehrlichia canis is by far the more severe of the two common canine species and is responsible for the classic severe presentation of ehrlichiosis, while E. ewingii tends to cause a milder disease characterized primarily by polyarthritis and fever.
- Ehrlichia canis is transmitted by the brown dog tick Rhipicephalus sanguineus, which is the most widely distributed tick in the world and can survive indoors in kennels, homes, and shelters; this indoor survival capability makes R. sanguineus and E. canis a year-round threat in warm climates and an indoor threat in any climate; Ehrlichia ewingii is transmitted by the lone star tick Amblyomma americanum, which is prevalent in the south-central and southeastern United States; transmission requires tick attachment and feeding for a minimum of several hours (the exact minimum transmission time is not as precisely established as for Borrelia burgdorferi, but transmission is generally considered possible after several hours of feeding rather than the 24 to 48 hours required for Lyme disease); a single tick can be infected with multiple Ehrlichia species simultaneously, as well as other co-infecting pathogens such as Anaplasma platys, Babesia species, and Bartonella henselae.
- Canine monocytic ehrlichiosis (E. canis) has three recognized clinical phases: the acute phase (1 to 4 weeks after tick bite), characterized by fever of 103 to 106 degrees Fahrenheit, lethargy, anorexia, weight loss, lymphadenopathy, splenomegaly, and thrombocytopenia (low platelet count, typically 50,000 to 100,000 per microliter); the subclinical phase (may last months to years), during which the dog appears outwardly healthy but harbors persistent intracellular infection and thrombocytopenia continues; and the chronic phase, characterized by severe pancytopenia (low red blood cells, white blood cells, AND platelets due to bone marrow suppression), spontaneous bleeding (petechiae, ecchymoses, epistaxis, melena), uveitis, polyarthritis, peripheral edema, and profound weight loss; the chronic phase carries a guarded to grave prognosis, particularly in German Shepherds, which are predisposed to chronic severe disease.
- Thrombocytopenia (low platelet count) is the most consistent and characteristic laboratory finding of ehrlichiosis at all phases; it results from a combination of immune-mediated platelet destruction (antiplatelet antibodies), platelet sequestration in the spleen, and in chronic severe cases, reduced platelet production due to bone marrow suppression; a CBC showing thrombocytopenia in a dog from a tick-endemic area should always prompt evaluation for ehrlichiosis and other tick-borne diseases; other common CBC findings include a mild non-regenerative anemia and lymphocytosis in the acute phase, progressing to severe pancytopenia in the chronic phase; in contrast to E. canis, E. ewingii most commonly causes fever and polyarthritis with a less severe thrombocytopenia and is less likely to cause pancytopenia or life-threatening complications.
- Diagnosis is most commonly confirmed with the SNAP 4Dx Plus (IDEXX Laboratories) in-clinic serology test, which detects antibodies to Ehrlichia canis and Ehrlichia ewingii simultaneously alongside Lyme disease, Anaplasma, and heartworm; a positive SNAP 4Dx Plus result for Ehrlichia confirms antibody exposure but does not distinguish between current active infection and past resolved infection; PCR (polymerase chain reaction) testing of whole blood detects Ehrlichia DNA directly and is most sensitive in the acute phase before the antibody response has fully developed; PCR is the test of choice when clinical signs are strongly consistent with ehrlichiosis but the SNAP test is negative (early acute disease before seroconversion) or when distinguishing active from past infection matters clinically; morulae (intracellular bacterial inclusion bodies visible inside white blood cells on blood smear examination) are pathognomonic when found but are identified in only a minority of cases.
- Doxycycline is the treatment of choice for all forms of canine ehrlichiosis; the standard protocol is doxycycline 10 mg/kg once daily (or 5 mg/kg twice daily) for a minimum of 28 days; clinical improvement is typically dramatic and occurs within 24 to 72 hours of starting treatment in acute-phase and subclinical-phase disease; failure to improve within 48 to 72 hours should prompt reconsideration of the diagnosis or consideration of a co-infecting pathogen (such as Babesia or Bartonella) that does not respond to doxycycline; corticosteroids (prednisone 1 to 2 mg/kg per day) are added only when there is evidence of severe immune-mediated thrombocytopenia with active hemorrhage, and they are tapered and discontinued as the platelet count normalizes; platelet transfusion may be necessary in life-threatening hemorrhagic presentations; chronic-phase dogs with pancytopenia and severe bone marrow suppression have the most guarded prognosis and may require weeks of treatment before bone marrow recovery is confirmed.
The 4-year-old German Shepherd mix had been “not himself” for about two weeks: he was eating less, sleeping more, and had developed a nosebleed that his owner initially attributed to sniffing something rough. On physical examination he had a temperature of 104.8 degrees Fahrenheit, mild lymphadenopathy, and scattered petechiae (small pinpoint hemorrhages) on the inner surface of his pinna and on his gum line. A complete blood count showed a platelet count of 32,000 per microliter (reference range 170,000 to 400,000), mild non-regenerative anemia, and a mild lymphocytosis. A SNAP 4Dx Plus run in the clinic was positive for Ehrlichia antibody. His veterinarian explained that E. canis was a strong suspect and that the nosebleed was not trauma but rather spontaneous bleeding from his severely low platelet count. Doxycycline was started the same day. Within 48 hours his owner reported that he was more alert and eating. By day 10 his platelet count had climbed to 95,000 per microliter, and by day 28 it had normalized to 220,000 per microliter.
Ehrlichia Species and Their Tick Vectors
| Species | Cell Type Infected | Primary Tick Vector | Geographic Distribution (US) | Disease Name |
|---|---|---|---|---|
| Ehrlichia canis | Monocytes and macrophages | Rhipicephalus sanguineus (brown dog tick) | Southeastern and south-central US; worldwide in tropical and subtropical regions; can occur in any state where R. sanguineus is established | Canine monocytic ehrlichiosis (CME); historically called “tropical canine pancytopenia” |
| Ehrlichia ewingii | Granulocytes (neutrophils) | Amblyomma americanum (lone star tick) | South-central and southeastern US (Oklahoma, Missouri, Arkansas, Texas, Tennessee, southeastern Atlantic states) | Canine granulocytic ehrlichiosis (CGE) |
| Ehrlichia chaffeensis | Monocytes | Amblyomma americanum | South-central and southeastern US | Primarily a human pathogen (human monocytic ehrlichiosis); occasional dog infection reported; dogs may be asymptomatic reservoir hosts |
The Three Phases of Canine Monocytic Ehrlichiosis (E. canis)
Acute Phase
The acute phase begins 1 to 3 weeks after the infectious tick bite and lasts approximately 2 to 4 weeks. During this phase the Ehrlichia organisms are actively replicating within circulating monocytes and macrophages, triggering a systemic inflammatory response. Clinical signs include:
- Fever (103 to 106 degrees Fahrenheit; typically in the 104 to 105 range)
- Lethargy and depression
- Anorexia and weight loss
- Generalized lymphadenopathy (enlarged lymph nodes throughout the body)
- Splenomegaly (enlarged spleen)
- Thrombocytopenia (low platelets, often 50,000 to 100,000 per microliter)
- Serous or mucopurulent ocular or nasal discharge
- Mild non-regenerative anemia
Many dogs recover spontaneously from the acute phase without treatment, or recover rapidly with doxycycline; however, dogs that do not receive treatment or that are immunocompromised may fail to clear the infection and transition into the subclinical phase.
Subclinical Phase
The subclinical phase follows resolution of acute-phase signs and may last from several months to years. The dog appears clinically normal to the owner, but the infection persists intracellularly within bone marrow macrophages. Thrombocytopenia typically persists throughout this phase, and this is often the only abnormality detected on routine bloodwork or screening tests. Dogs in the subclinical phase are still infectious to feeding ticks (which can then transmit the organism to other dogs) and still require treatment; a positive Ehrlichia titer on SNAP 4Dx Plus in an apparently healthy dog should prompt full CBC evaluation and treatment consideration. The subclinical phase is insidious because the dog may appear well while gradual bone marrow suppression progresses silently.
Chronic Phase
The chronic phase represents failure to clear the infection over months to years, leading to progressive bone marrow suppression and multi-organ involvement. This is the most severe and life-threatening stage. Clinical findings include:
- Severe pancytopenia (low red blood cells, white blood cells, and platelets simultaneously) due to hypoplastic or aplastic bone marrow
- Spontaneous hemorrhage: petechiae and ecchymoses on mucous membranes and skin, epistaxis (nosebleeds), melena (digested blood in feces), hematuria, hemoptysis
- Uveitis (anterior or posterior): cloudiness of the eye, hyphema (blood in the anterior chamber), chorioretinitis, retinal detachment in severe cases
- Polyarthritis (more common with E. ewingii but can occur with E. canis): joint swelling, lameness, stiffness
- Peripheral edema (limb swelling due to hypoproteinemia from protein-losing enteropathy or reduced hepatic production)
- Severe weight loss and cachexia
- Neurological signs in some cases: seizures, ataxia, vestibular dysfunction
- Renal involvement: glomerulonephritis from immune complex deposition
German Shepherds are disproportionately affected by the severe chronic form of E. canis infection; the breed appears genetically predisposed to developing pancytopenic chronic ehrlichiosis rather than recovering at the acute or subclinical stage. The prognosis for chronic-phase dogs is guarded to grave, particularly when bone marrow biopsy reveals aplasia; recovery may take weeks to months of doxycycline treatment if bone marrow suppression is reversible, but some dogs never recover adequate marrow function.
Canine Granulocytic Ehrlichiosis (E. ewingii)
Ehrlichia ewingii infection tends to produce a less severe syndrome than E. canis, with fever, lethargy, anorexia, and most distinctively a polyarthritis that causes shifting-leg lameness and joint effusion. E. ewingii infects granulocytes (neutrophils), and morulae may be visible inside neutrophils on blood smear examination in some cases. Thrombocytopenia occurs but is usually less severe than with E. canis. Pancytopenia and bone marrow aplasia are uncommon. Most dogs with E. ewingii infection respond well to doxycycline with rapid clinical improvement. Dogs in the E. ewingii endemic zone (south-central US, particularly Oklahoma, Missouri, Arkansas) that present with acute fever and polyarthritis should be tested for E. ewingii alongside other tick-borne diseases.
Diagnosis
SNAP 4Dx Plus Serology
The SNAP 4Dx Plus (IDEXX Laboratories) is the most widely used point-of-care screening test for ehrlichiosis in dogs; it detects antibodies to Ehrlichia canis and Ehrlichia ewingii simultaneously, alongside Borrelia burgdorferi, Anaplasma phagocytophilum, Anaplasma platys, and heartworm antigen; the test requires only a few drops of blood and produces results within 8 minutes; a positive Ehrlichia result on the SNAP 4Dx Plus indicates the dog has been exposed to Ehrlichia and produced antibodies, but does not by itself distinguish between active infection and resolved past infection; in the appropriate clinical context (thrombocytopenia, fever, tick exposure history), a positive SNAP result is sufficient to initiate doxycycline treatment while confirmatory testing is pending.
PCR (Polymerase Chain Reaction)
PCR testing of whole blood (EDTA tube) detects Ehrlichia DNA directly and is most sensitive during the acute phase of infection, when organisms are actively replicating in circulating white blood cells and before the antibody response has fully developed; PCR is the preferred diagnostic test in two specific situations: when clinical signs strongly suggest ehrlichiosis but the SNAP test is negative (early acute infection before seroconversion occurs, typically the first 7 to 10 days of infection), and when the SNAP is positive but the clinical team wants to confirm active infection versus residual antibody from a resolved past infection; PCR is less sensitive in the subclinical phase, when organisms are sequestered in bone marrow macrophages and circulating parasitemia is low; species-specific PCR can differentiate E. canis, E. ewingii, and E. chaffeensis, which is useful in geographic overlap zones.
Complete Blood Count and Chemistry Panel
The CBC is an essential component of the diagnostic workup; thrombocytopenia is the hallmark finding and is present in the vast majority of dogs with active E. canis infection; the platelet count at presentation correlates roughly with phase and severity: mild thrombocytopenia (100,000 to 150,000 per microliter) suggests acute or subclinical disease; moderate thrombocytopenia (50,000 to 100,000 per microliter) suggests active acute disease with hemorrhagic risk; severe thrombocytopenia (below 20,000 to 30,000 per microliter) with evidence of spontaneous bleeding suggests advanced or chronic disease; pancytopenia (low RBC, WBC, and platelets simultaneously) in a thrombocytopenic dog with tick exposure history is a classic presentation of chronic ehrlichiosis; chemistry panel findings may include hypoproteinemia (low total protein and albumin), elevated BUN and creatinine from renal involvement, and mild hepatic enzyme elevation.
Blood Smear Examination
Microscopic examination of a Wright-Giemsa stained blood smear may reveal morulae: clusters of Ehrlichia organisms visible as small dark intracytoplasmic inclusion bodies within the host white blood cells (within monocytes for E. canis; within neutrophils for E. ewingii); morulae are pathognomonic when identified and confirm active infection without requiring PCR; however, morulae are found in only a minority of infected dogs on blood smear examination (estimates range from 4 to 20 percent of E. canis cases), making their absence non-diagnostic; morulae are more likely to be found during the acute phase when circulating parasitemia is highest.
Bone Marrow Aspiration
Bone marrow aspiration and cytology are indicated in dogs with severe pancytopenia to evaluate the degree of bone marrow suppression: hypoplastic or aplastic bone marrow (reduced cellularity, loss of normal hematopoietic precursors, replacement with fat cells or fibrosis) indicates severe chronic ehrlichiosis with a guarded prognosis; some hypoplastic marrows recover with prolonged doxycycline treatment, while aplastic marrow carries a worse prognosis; bone marrow evaluation also rules out other causes of pancytopenia such as immune-mediated disease or neoplastic infiltration (lymphoma, leukemia, mast cell disease).
Treatment
Doxycycline
Doxycycline is the treatment of choice for all forms and phases of canine ehrlichiosis; the standard protocol is doxycycline at 10 mg/kg orally once daily (or 5 mg/kg orally twice daily) for a minimum of 28 days; doxycycline should be administered with food to reduce the risk of gastrointestinal side effects (nausea, esophageal irritation); doxycycline tablets should always be followed by a small amount of food or water to prevent esophageal lodging, which can cause esophageal stricture; clinical improvement in acute and subclinical disease is typically rapid and dramatic: most dogs show meaningful improvement in fever, appetite, and energy within 24 to 72 hours of starting treatment; platelet count recovery lags behind clinical improvement, typically normalizing within 2 to 4 weeks; a platelet count that fails to normalize by day 28 of treatment, or that re-declines after initial recovery, is a signal for further evaluation.
Corticosteroids
Corticosteroids (prednisone 1 to 2 mg/kg per day) are added to the treatment protocol only when there is evidence of significant immune-mediated thrombocytopenia with active clinical bleeding; this subset of ehrlichiosis patients develops antiplatelet antibodies that destroy platelets faster than they can be produced, and corticosteroids suppress this immune-mediated destruction; prednisone is tapered as the platelet count rises and discontinued once the count normalizes; corticosteroids are not given empirically to all dogs with thrombocytopenia, as immunosuppression in a dog with active bacterial infection carries its own risks; the decision to add prednisone is made case-by-case based on platelet count trend, clinical signs of bleeding, and the treating veterinarian’s assessment.
Supportive Care
Dogs with severe thrombocytopenia and active hemorrhage may require: intravenous fluid therapy to maintain hydration and blood pressure; fresh whole blood or platelet-rich plasma transfusion when platelet counts fall below 10,000 to 20,000 per microliter with active bleeding; packed red blood cell transfusion for severe anemia (PCV below 15 to 20 percent); nutritional support in anorectic or cachectic dogs; and strict exercise restriction to minimize trauma-related hemorrhage while platelet counts are critically low; hospitalization is recommended for dogs with platelet counts below 20,000 to 30,000 per microliter or with active spontaneous hemorrhage.
Geographic Distribution and Tick Prevention
| Region | Primary Risk | Peak Tick Season | Notes |
|---|---|---|---|
| Southeastern US (FL, GA, SC, NC, AL, MS, LA) | E. canis (very high risk); E. ewingii | Year-round; R. sanguineus can survive indoors in any season | Highest E. canis prevalence in the US; R. sanguineus thrives in humid subtropical climate; kennel-acquired E. canis common in this region |
| South-central US (TX, OK, AR, MO, TN) | E. canis; E. ewingii (high risk for both) | Spring through fall for Amblyomma; R. sanguineus year-round in warm areas | Overlap zone for both E. canis and E. ewingii; dogs may be co-infected with both species; also a high-risk zone for Rocky Mountain spotted fever |
| Mid-Atlantic and northeastern US | E. canis (lower but present); Anaplasma (higher relative risk) | Spring through fall | E. canis less common than in southeastern states; Anaplasma phagocytophilum (a related organism causing similar signs) is more prevalent in the Northeast; co-testing for both organisms recommended in this region |
| Western US | E. canis lower prevalence; R. sanguineus present | Variable by location | E. canis cases occur but are less common; dogs that have traveled from or to high-risk southern regions may be seropositive |
Prevention of ehrlichiosis relies on tick prevention with products active against Rhipicephalus sanguineus and Amblyomma americanum:
- Isoxazoline products (afoxolaner/NexGard, sarolaner/Simparica, fluralaner/Bravecto, lotilaner/Credelio): oral or topical products with excellent efficacy against both R. sanguineus and A. americanum; kill ticks rapidly after attachment, reducing transmission risk; monthly or every-3-month dosing depending on product; FDA-issued label warning for potential neurological adverse events (tremors, seizures) in susceptible animals, warranting discussion with the veterinarian for dogs with a history of seizures
- Amitraz collars (Seresto): 8-month collar with both repellent and kill activity; effective against brown dog tick and lone star tick; good choice for dogs in high-tick-burden environments
- Permethrin-based topical products: effective against ticks but toxic to cats; not for use on cats or in households with cats that groom dogs
- Environmental control: because R. sanguineus can survive and breed indoors (in wall crevices, carpet edges, kennels), treatment of the home environment with appropriate acaricides is recommended when an indoor infestation is established; brown dog tick infestations in homes can perpetuate E. canis transmission year-round even in non-endemic climates
US Cost Overview for Ehrlichiosis
| Service | Typical US Cost |
|---|---|
| Veterinary examination | $60 to $150 |
| SNAP 4Dx Plus (in-clinic) | $50 to $90 |
| Complete blood count | $80 to $150 |
| Chemistry panel | $80 to $160 |
| PCR testing for Ehrlichia species | $80 to $180 (reference laboratory) |
| Doxycycline (28-day course, 30 kg dog) | $30 to $80 |
| Follow-up CBC at day 14 and day 28 | $80 to $150 each |
| Hospitalization with IV fluids and supportive care (severe cases) | $500 to $2,500 per day |
| Whole blood or platelet transfusion | $400 to $1,200 per unit |
| Bone marrow aspiration and cytology | $400 to $900 |
| Monthly tick prevention (isoxazoline, large dog) | $20 to $50 per month |
Age-Specific Considerations
Puppies (Under 12 Months)
- Puppies in tick-endemic areas are at risk for ehrlichiosis from their first outdoor exposure; a puppy with fever, lethargy, decreased appetite, and petechiae in a tick-endemic area should be considered for ehrlichiosis testing alongside other diagnoses; the clinical presentation of acute ehrlichiosis in puppies is similar to that in adults, but puppies may have a more exaggerated inflammatory response and more rapid clinical deterioration due to immature immune function; thrombocytopenia in a puppy should always prompt testing for tick-borne diseases even if no tick has been directly observed, as brown dog ticks are small and may not be noticed
- Doxycycline is the treatment of choice for ehrlichiosis in dogs of all ages including puppies; concerns about doxycycline causing tooth enamel discoloration in young dogs have been raised based on extrapolation from human pediatric data, but veterinary clinical experience and current ACVIM guidelines support doxycycline use in puppies as young as 6 to 8 weeks when the clinical indication warrants it; the risks of untreated ehrlichiosis (severe thrombocytopenia, hemorrhage, disease progression) substantially outweigh the potential cosmetic concern about tooth discoloration; amoxicillin is not effective against Ehrlichia and should not be substituted
- Tick prevention should begin in puppies as soon as they are old enough for the selected product; the minimum age for isoxazoline products varies by product (NexGard and Simparica are labeled for use at 8 weeks; Bravecto at 8 weeks; Credelio at 8 weeks) and minimum body weight (typically 2 to 4 kg); kennels, shelters, and households with known brown dog tick infestations represent high-risk environments for puppies, and tick prevention in these settings should start immediately at the earliest labeled age; the presence of R. sanguineus in an indoor environment can expose a puppy to repeated tick bites even without outdoor access
Adult Dogs (1 to 8 Years)
- Most clinical cases of ehrlichiosis in published veterinary case series are in adult dogs in the 2-to-7-year age range; this likely reflects duration of exposure rather than age-specific susceptibility; adult dogs in tick-endemic areas should be screened annually with the SNAP 4Dx Plus as part of their heartworm and tick-borne disease annual testing, even if they appear clinically healthy; subclinical ehrlichiosis with persistent thrombocytopenia is common, and treatment of subclinical-phase disease prevents progression to the much more serious chronic phase
- German Shepherd owners in ehrlichiosis-endemic areas should be particularly attentive: the breed’s predisposition to severe chronic E. canis disease means that a positive Ehrlichia titer on annual SNAP testing in a German Shepherd warrants a full CBC evaluation and strong consideration of treatment even in the absence of clinical signs, rather than a “watchful waiting” approach; the cost and relatively benign side effect profile of a 28-day doxycycline course is small compared to the risk of progressing to life-threatening pancytopenic chronic disease in this breed
- Dogs with known positive Ehrlichia titers that have been treated with doxycycline may remain antibody-positive on the SNAP 4Dx Plus for months to years after successful treatment; a positive SNAP test in a previously treated dog does not automatically indicate reinfection or treatment failure; PCR testing of whole blood is the appropriate tool in this situation: a positive PCR confirms active infection requiring re-treatment, while a negative PCR in a seropositive dog is consistent with persistent residual antibody from a successfully cleared prior infection
Senior Dogs (9 Years and Older)
- Senior dogs with ehrlichiosis present particular management challenges because concurrent age-related conditions (renal disease, hepatic dysfunction, cardiac disease, immune senescence) complicate treatment decisions; doxycycline is still the treatment of choice, but renal and hepatic monitoring with bloodwork before and during treatment is appropriate in senior dogs with known concurrent organ dysfunction; the standard 28-day doxycycline course is well tolerated in most senior dogs when administered with food, but vomiting or inappetence should prompt a dose reduction or switch to twice-daily dosing (5 mg/kg twice daily) which is sometimes better tolerated
- Senior dogs that develop pancytopenia during annual bloodwork screening in tick-endemic areas require careful evaluation to distinguish chronic ehrlichiosis from other causes of pancytopenia in older dogs including immune-mediated disease, bone marrow neoplasia (leukemia, lymphoma, multiple myeloma), and drug-induced bone marrow suppression; the diagnostic workup should include tick-borne disease serology and PCR, bone marrow aspiration and cytology, and thorough review of the dog’s medication history; chronic ehrlichiosis and lymphoma can occur simultaneously in the same dog, and treatment of one condition may unmask the other
- The prognosis for chronic ehrlichiosis in senior dogs is more guarded than in younger adults, primarily because older dogs have less bone marrow reserve and slower recovery kinetics; a senior dog with aplastic marrow from chronic E. canis has a limited capacity to repopulate its hematopoietic compartment even when the infection is controlled with doxycycline; owner discussions should include realistic timelines for recovery (weeks to months), the possibility of non-recovery, and the quality of life implications of prolonged hospitalization and blood product support
Myths and Facts About Ehrlichiosis in Dogs
My dog tested positive for Ehrlichia on the SNAP test but seems fine, so I do not need to treat it.
A positive Ehrlichia result on the SNAP 4Dx Plus in an apparently healthy dog may indicate subclinical-phase ehrlichiosis, in which the dog harbors active infection but shows no outward signs because the disease has not yet progressed to the chronic phase. Subclinical-phase dogs typically have persistent thrombocytopenia on CBC. Without treatment, subclinical ehrlichiosis can progress to life-threatening chronic ehrlichiosis with bone marrow suppression, spontaneous hemorrhage, and organ failure, particularly in German Shepherds. A positive SNAP in a healthy dog warrants a CBC, PCR, and a conversation with your veterinarian about treatment rather than observation.
Since my dog finished the doxycycline and the SNAP test is still positive, the treatment did not work.
The SNAP 4Dx Plus detects antibodies, which can persist in the bloodstream for months to years after the infection has been successfully cleared with doxycycline. A persistently positive SNAP test after treatment does not indicate treatment failure. The correct way to evaluate treatment success is PCR testing of whole blood: a negative PCR after completing doxycycline, combined with normalization of the platelet count and resolution of clinical signs, indicates successful bacterial clearance. Repeating treatment solely on the basis of a persistently positive SNAP test in a clinically well dog with a normal CBC is generally not warranted without PCR confirmation of active infection.
Ehrlichiosis only affects dogs in the South and my dog in the North is not at risk.
While E. canis prevalence is highest in the southeastern and south-central United States, the brown dog tick (Rhipicephalus sanguineus) can establish year-round indoor infestations in any climate because it is an indoor tick that survives in heated homes, kennels, and shelters. Dogs acquired from southern states (rescue dogs transported northward, dogs with travel history) can be exposed in the South and become infected before arriving in northern states. Additionally, the range of A. americanum (vector for E. ewingii) has been expanding northward. Any dog with tick exposure or exposure to ticks via other dogs or environments can be at risk regardless of geographic location.
Red Flags: Signs That Require Same-Day Veterinary Evaluation
- Spontaneous bleeding from any site without a known injury: nosebleeds (epistaxis) in a dog with no recent facial trauma, blood in urine (hematuria), black tarry stools (melena indicating digested blood in the GI tract), blood in vomit, or visible petechiae (small pinpoint hemorrhages) or ecchymoses (bruises) on the gums or inner ear flap; these signs indicate platelet counts may be critically low and the dog needs emergency evaluation
- Sudden onset of blindness, cloudy eyes, or visible blood pooled in the front of the eye (hyphema): uveitis and hyphema are serious ocular complications of ehrlichiosis that can cause permanent vision loss if not treated promptly; any sudden eye change in a dog from a tick-endemic area should prompt evaluation for tick-borne disease
- High fever (above 104 degrees Fahrenheit) with lethargy and complete anorexia lasting more than 24 to 48 hours in a dog from a tick-endemic area or with recent tick exposure: this is a classic presentation of acute ehrlichiosis and several other tick-borne diseases; early treatment with doxycycline while awaiting test results is appropriate when clinical suspicion is high
- A dog known to have ehrlichiosis that is currently on doxycycline treatment and develops worsening signs rather than improvement within 72 hours of starting treatment: this suggests either a severe case requiring supportive care (hospitalization, blood transfusion), a co-infecting pathogen not covered by doxycycline (Babesia requires additional treatment with imidocarb dipropionate or atovaquone/azithromycin), or an incorrect primary diagnosis
- Extreme weakness, pale gums, rapid breathing, and collapse in a dog with known or suspected ehrlichiosis: this pattern suggests severe anemia or hemorrhagic shock from very low platelet counts and requires emergency veterinary care immediately
Frequently Asked Questions About Ehrlichiosis in Dogs
What is ehrlichiosis in dogs?
Ehrlichiosis is a tick-transmitted bacterial infection caused by Ehrlichia species, primarily Ehrlichia canis (transmitted by the brown dog tick) and Ehrlichia ewingii (transmitted by the lone star tick). The bacteria invade white blood cells and cause disease ranging from mild fever and thrombocytopenia in acute cases to life-threatening bone marrow failure, spontaneous hemorrhage, and organ dysfunction in chronic cases. It is treatable with doxycycline when caught early.
What are the symptoms of ehrlichiosis in dogs?
Acute ehrlichiosis: fever (103 to 106 degrees Fahrenheit), lethargy, decreased appetite, lymph node enlargement, and thrombocytopenia (low platelets). Chronic ehrlichiosis: spontaneous bleeding from the nose or gums, petechiae on the skin or mucous membranes, extreme weight loss, uveitis (eye inflammation and cloudiness), swollen limbs from low protein, and bone marrow suppression producing pancytopenia. E. ewingii most distinctively causes fever and polyarthritis (shifting-leg lameness and joint swelling).
How is ehrlichiosis diagnosed in dogs?
The SNAP 4Dx Plus (IDEXX) is the most common initial test; it detects Ehrlichia antibodies alongside heartworm, Lyme disease, and Anaplasma. PCR testing of whole blood detects Ehrlichia DNA directly and is most useful in early acute disease before antibodies have developed. A complete blood count showing thrombocytopenia (low platelets) is the hallmark laboratory finding. In severe cases, bone marrow aspiration evaluates the degree of bone marrow suppression.
What is the treatment for ehrlichiosis in dogs?
Doxycycline 10 mg/kg once daily for 28 days is the standard treatment. Dramatic clinical improvement typically occurs within 24 to 72 hours in acute and subclinical cases. Corticosteroids (prednisone) are added only when severe immune-mediated thrombocytopenia with active hemorrhage is present. Severely ill dogs may need hospitalization, IV fluids, and blood or platelet transfusions. Chronic-phase dogs with bone marrow suppression require weeks of treatment and close monitoring.
Can ehrlichiosis be prevented in dogs?
Yes. Monthly or every-3-month isoxazoline products (NexGard, Simparica, Bravecto, Credelio) kill ticks rapidly after attachment and are highly effective at preventing ehrlichiosis. Seresto collars provide 8-month protection. Annual SNAP 4Dx Plus testing catches subclinical infection before it progresses to the dangerous chronic phase. Because the brown dog tick (R. sanguineus) can infest indoor environments, tick control in kennels and homes is also important in endemic areas.
Can dogs give ehrlichiosis to humans?
Dogs cannot directly transmit ehrlichiosis to humans; the bacteria are transmitted only through tick bites. However, a dog that brings infected ticks into the home environment increases the risk of human tick exposure. Ehrlichia chaffeensis and Ehrlichia ewingii can infect both dogs and humans via the lone star tick, so a household with an ehrlichiosis-diagnosed dog should inspect family members for tick bites and seek medical attention if any person develops fever, headache, rash, or fatigue after tick exposure.
What is the prognosis for dogs with ehrlichiosis?
Dogs treated in the acute or subclinical phase typically recover fully with a 28-day course of doxycycline; the prognosis is excellent for these cases. Dogs treated in the early chronic phase (before severe bone marrow aplasia) have a good to guarded prognosis depending on the degree of bone marrow suppression. Dogs presenting in the late chronic phase with aplastic bone marrow, severe pancytopenia, and multi-organ involvement have a guarded to grave prognosis; some recover with weeks of intensive support, while others do not survive. German Shepherds have a higher rate of severe chronic disease.
For more guides on keeping your dog healthy, browse all our Dog Health articles.
Explore Dog Health Articles