Organisms, vectors and dogs at risk
The ACVIM panel reports that canine Lyme borreliosis in North America has been linked only to Borrelia burgdorferi sensu stricto [1]. Its main vectors are Ixodes scapularis in the Northeast, Mid-Atlantic and upper Midwest, I. pacificus in the Pacific states, and I. ricinus in Europe [1]. CAPC puts regional canine seroprevalence in endemic areas between 1.4% in the West and 13.3% in the Northeast. CAPC adds that infection is rarely documented in southern US pets that have not traveled to an endemic area [2]. The ACVIM panel lists travel history as an important question for any sick or seropositive dog [1].
For the rickettsial agents, CAPC describes several separate cycles [3]:
- E. canis circulates mainly between dogs and Rhipicephalus sanguineus, the brown dog tick.
- E. ewingii and E. chaffeensis circulate between white-tailed deer and Amblyomma americanum, the lone star tick, and are more common in the southern US.
- A. phagocytophilum is carried by the same Ixodes ticks that transmit Lyme disease.
- A. platys is thought to spread through R. sanguineus.
In Europe, the guideline authors describe E. canis as endemic in every European country bordering the Mediterranean, while A. phagocytophilum occurs mainly in northern and central Europe [4]. Because Borrelia and A. phagocytophilum share Ixodes vectors, the European authors report that coinfection with the two is frequently detected [4].
Breed patterns differ by infection. The European guideline names German Shepherds and Siberian Huskies as predisposed to more severe ehrlichiosis, and it reports no confirmed breed predisposition for A. phagocytophilum [4]. The ACVIM panel notes that retrievers are over-represented among dogs with suspected Lyme nephritis [1]. The panel also describes a study of Bernese Mountain Dogs in central Europe in which 58% of 160 healthy dogs were seropositive, compared with 15% of other large long-haired breeds from the same region. The panel says no reason for the difference was found and that the seropositivity was not associated with illness [1].
Clinical presentation
The ACVIM panel describes the classical Lyme presentation as "acute monoarticular or polyarticular lameness with joint swelling, fever, lethargy, and mild local lymphadenopathy," most often in young, active, large-breed dogs [1]. Lyme nephritis is a putative immune-complex glomerulonephritis, meaning kidney inflammation driven by antibody-antigen deposits. The panel reports that proteinuria occurs in fewer than 2% of seropositive dogs and that fewer than 30% of dogs with Lyme nephritis have a history of past or concurrent Lyme arthritis [1]. CAPC adds edema, weight loss, vomiting and diarrhea as signs seen with protein-losing nephropathy [2]. According to the panel, neurologic and cardiac forms of Lyme disease are not well documented in dogs [1].
The European guideline describes three phases of E. canis infection following a 1 to 3 week incubation [4]:
- An acute phase lasting 2 to 4 weeks.
- A subclinical phase in which the dog looks normal but may have a low platelet count.
- In some dogs, a chronic phase with bone marrow hypoplasia and severe pancytopenia (low counts across all blood cell lines).
The authors list fever, lethargy, anorexia, enlarged lymph nodes, bleeding such as epistaxis and petechiae, and ocular lesions including anterior uveitis among the signs [4]. They say lameness in a dog infected with E. canis should prompt a search for coinfection [4].
The European authors describe anaplasmosis caused by A. phagocytophilum as mostly an acute, nonspecific febrile illness. Lameness can result from immune-mediated neutrophilic polyarthritis [4]. CAPC also reports polyarthritis with E. ewingii [3]. A. platys causes episodes of fever and thrombocytopenia that recur every 1 to 2 weeks, according to the European guideline [4].
Screening and diagnosis
Lyme borreliosis
The ACVIM panel considers serology the only recommended way to assess exposure in dogs [1]. Antibodies to C6, VlsE and OspF indicate natural infection because none of these antigens is present in any Lyme vaccine. Some vaccines induce OspC antibodies, which interfere with OspC as a marker of natural exposure [1]. The panel advises against whole-cell ELISA, IFA and Western blot because of possible cross-reactions with other spirochetes [1]. CAPC notes separately that whole-cell vaccines can produce positive whole-cell IFA or ELISA results [2].
The panel's position is that a positive result "is not proof of cause of clinical signs, nor can it be used as a predictor for development of future clinical signs" [1]. All five panelists who voted (5/5) support adding a qualitative antibody test to annual wellness care for dogs that live in or near endemic areas in North America, and the panel recommends screening every seropositive dog for proteinuria [1].
The quantitative C6 test divided the panel. In its discussion of nonclinical, nonproteinuric seropositive dogs, the panel's text states "The magnitude of Quant C6 is not predictive of illness" [1]. CAPC describes PCR as limited by low spirochete numbers and says whole blood is not a useful specimen [2].
Ehrlichiosis and anaplasmosis
The European guideline reports that E. canis morulae appear on blood smears in about 4-6% of clinical cases. A. phagocytophilum morulae are seen in neutrophils in up to 60% of cases, but they cannot be distinguished from those of E. ewingii without PCR [4]. Dogs may still be seronegative early in infection; E. canis antibodies typically do not appear before 12 to 14 days [4].
For suspected cases, the authors suggest paired titers taken 2-4 weeks apart. They note that a four-fold rise in IgG has been suggested as evidence of ongoing infection [4]. They also point out that the 4Dx ELISA cannot distinguish A. phagocytophilum from A. platys [4]. In their view, PCR on EDTA blood is evidence of active infection, while a negative PCR should be read as "no detection of the tested pathogen-DNA in the sample" [4]. CAPC advises collecting PCR samples before antimicrobials are started. It also states that antibodies alone do not indicate a need for treatment when there is no evidence of clinical disease [3].
Treatment
For Lyme arthritis, the ACVIM panel agreed on four weeks of antibiotics, with doxycycline preferred [1]. Its table lists doxycycline at 10 mg/kg once or twice daily for 30 days and amoxicillin at 20 mg/kg three times daily for 30 days. For dogs that cannot tolerate tetracyclines, it lists cefovecin at 8 mg/kg SC, given twice, 14 days apart [1]. The panel expects a response within 1 to 3 days if the signs are caused by Lyme disease. It notes that glucocorticoids may be indicated for suspected immune-mediated polyarthropathy in nonresponsive dogs. If relapse occurs, it lists other diagnoses to consider, including other infectious agents, immune-mediated disease, soft tissue trauma, septic arthritis and degenerative joint disease [1].
For seropositive dogs with protein-losing nephropathy, the panel recommends antimicrobials together with the IRIS standard of care. That includes a renin-angiotensin-aldosterone system inhibitor, antithrombotics, diet changes, omega-3 fatty acids and antihypertensives as needed [1]. Immunosuppressive treatment, with mycophenolate favored, is reserved for the following situations [1]:
- Biopsy evidence of an active immune-mediated process.
- Nonresponders or dogs with rapid progression.
- Serum creatinine above 5 mg/dL.
- Serum albumin below 2.0 g/dL.
Panelists did not agree on how long to give antibiotics for nephritis; suggestions ranged from 1 to 3 months [1].
For ehrlichiosis and anaplasmosis, CAPC recommends doxycycline at 10 mg/kg for 28 days [3]. The European guideline gives the following regimens [4]:
| Agent | Doxycycline regimen in the European guideline |
|---|
| E. canis | 5 mg/kg twice daily or 10 mg/kg once daily for 4 weeks |
| A. phagocytophilum | Same dosage, for 2-3 weeks |
| A. platys | 5-10 mg/kg q12-24h for 8-10 days |
The European authors advise against starting glucocorticoids alongside antibiotics. They reserve steroids for immune-mediated complications or a poor response, and they report that imidocarb dipropionate was not effective against E. canis [4].
Monitoring and prognosis
According to the European guideline, dogs treated in the acute phase of ehrlichiosis or anaplasmosis improve within 24-48 hours and have a good prognosis. The chronic severe form of ehrlichiosis carries a grave prognosis [4]. The guideline cites a 2008 study by Shipov and colleagues that found pronounced pancytopenia was a risk factor for death. The guideline does not report that study's design or size [4].
In dogs treated for acute disease, blood counts usually normalize within 10-15 days of starting therapy. E. canis titers generally fall over 6-9 months but can persist for years [4]. The authors say clinicians should aim for a negative PCR rather than seronegativity, with PCR repeated several weeks after treatment ends [4]. CAPC reports that protective immunity does not appear to develop and that reinfection may occur [3]. The European guideline says prior E. canis infection does not confer permanent immunity, but states it is unknown whether natural infection protects against clinical anaplasmosis [4].
For Lyme disease, four of six ACVIM panelists favor measuring quantitative C6 before and after treatment to check for a decline and to set a new baseline. The dissenting panelists state there is no published evidence that quantitative results predict current illness or chronic disease, or differentiate reinfection from reactivation [1]. North American panelists recommend rechecking healthy seropositive dogs for proteinuria at least 2-3 times a year, whether or not they are treated [1].
Prevention and client communication
All six ACVIM panelists support year-round tick control. Their reasoning is that adult Ixodes ticks can be active whenever temperatures rise above 4 degrees C (40 degrees F) [1]. The panel prefers products that prevent attachment or kill ticks quickly over fipronil, which it says does not kill ticks until they have been attached for 24 hours. The panel also cautions that topical permethrins should not be used on or near cats [1].
Lyme vaccination split the ACVIM panel 3 to 3 [1]. CAPC recommends basing vaccination on an individual risk assessment and says routine vaccination is not warranted in non-endemic areas [2]. The panel describes a 15-month duration-of-immunity study completed by the manufacturer, in which 7 of 16 vaccinated dogs and 14 of 16 control dogs seroconverted after tick challenge [1]. The panel does not recommend vaccinating sick or proteinuric dogs [1].
CAPC does not recommend prophylactic antibiotics after a tick bite in dogs [2]. It advises removing ticks with forceps or a removal device, ideally while wearing gloves, and washing hands afterward [2]. CAPC also states that pets are not an immediate source of human infection. It describes dogs instead as sentinels, citing CDC work that linked canine seroprevalence above 5% at the county level with the emergence of human Lyme disease [2]. In highly endemic areas, the European authors recommend PCR screening of canine blood products because these agents can be transmitted by transfusion [4].
For client communication, the ACVIM panel and CAPC take a consistent position: a positive screening test indicates exposure, not proof of disease [1][2]. Their recommended response to that result is follow-up testing (proteinuria screening and blood work or urinalysis) and a review of tick control. CAPC does not recommend antibiotics for seropositive dogs without clinical or pathological abnormalities [1][2].
