In just the past 3 to 5 years, advanced diagnostic capabilities have enhanced our ability to detect infectious pathogens in
the dog and have given credence to the term "emerging" infections. However, the ever-expanding list of "emerging infectious
diseases", in fact, may not be emerging at all…as it appears; many of these infections have, quite likely, existed in dogs for several years. It's the emerging
technology that has enabled our ability to detect these infections.
AND…it's MUCH more than Blue Dots! As we move from the 3Dx test to the 4Dx testing platform, veterinarians now have the ability
to test for Anaplasma phagocytophilum antibody, in addition to Borrelia burgdorferi C6 antibody, Ehrlichia canis antibody,
and canine heartworm antigen. Specifically, the introduction of the 4Dx SANP Test emphasizes the importance of understanding
not only the indications for performing the test, but, most importantly, the implications of a POSITIVE vs. NEGATIVE test
result in the sick, versus healthy, patient.
What is the spectrum of clinical signs associated with ehrlichiosis?
The standard answer goes like this:Incubation is 8 to 20 days.
• ACUTE (2-4 weeks): signs may be mild to absent (at least to the owner) or may include lethargy, anorexia and possibly
epistaxis. IF…the owner seeks medical attention, fever may be detected evidence of spontaneous bleeding. A laboratory profile
may reveal thrombocytopenia, low albumin with elevated globulin (total protein may be elevated). THEN…they get better…whether
or not they receive treatment.
• SUB-CLINICAL (months to years [life?]): any clinical signs that manifested in the ACUTE STAGE resolve…this is analogous
to a "latent infection". Any treatment administered will appear to have worked well…THEN…months to more than a year later,
clinical signs associated with infection may redevelop…(we don't know why some dogs never progress into the chronic stage
• CHRONIC (months): This is where infections become complicated. Serious clinical signs may develop months to years
following exposure and infection. Signs are highly variable. Usually, weight loss, decreased appetite, petechiation or ecchymoses,
and epistaxis may develop. Peripheral edema (hypo-albuminemia) and even neurological signs (head tilt, paresis, seizures)
• LABORATORY CHANGES: Thrombocytopenia and/or anemia appear in about 80% of dogs with ehrlichiosis. NOTE: platelet
counts are only modestly reduced (ranges of 150,000 to 50,000 cells/μL are typical)l and distinct from dogs with immune-mediated
platelet destruction (3,000 to 5,000 cells/μL). Hyperglobulinemia/hypoalbuminemia may be present (hence the peripheral edema).
Pancytopenia seems less common today.
The variation in physical signs and laboratory values is significant. For example…the absence of thrombocytopenia does NOT exclude a diagnosis of ehrlichiosis. As such, it is not feasible to rely exclusively on clinical or laboratory findings
to establish a diagnosis. Testing is important. The message here is not to limit testing to only those patients that have
obvious physical signs that are distinctively associated with ehrlichiosis…"test outside the box"!
Is co-infection with other tick-borne agents significant with ehrlichiosis?
With increasing significance…YES. The more we look, the more we discover oc-infected dogs…and this is true in humans who
are infected with tick-borne disease. AND…it's the co-infected patient that makes it difficult to establish a diagnosis on
the basis of clinical signs.
What's still needed in veterinary medicine is a testing platform that will allow screening of individual patients for multiple
tick-borne pathogens, simultaneously! And work is currently underway to achieve that.