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.
The following highlights some of the key issues behind diagnosis, treatment, and prevention of the most common tick-borne
diseases seen in dogs.
1. There are many Ehrlichiae capable of infecting dogs...but we currently only test for one (E. canis)...which infections
are most significant for dogs?
E. canis (officially called 'canine monocytotropic ehrlichiosis') is probably the most important. It's certainly the most common infection in dogs in the US. However, infections with E. chaffeensis, E. ewingi (canine granulocytotropic ehrlichiosis), and E. equi are also known to infect dogs living in the US.
What compounds conventional diagnostic strategies is the fact commercial tests are simply not available (yet) for many of
these infections. Furthermore, it's becoming more apparent that individual dogs can be (and are) infected with multiple tick-borne pathogens simultaneously...such as Anaplasma spp and Neorickettsia.
2. What is the spectrum of clinical signs associated with ehrlichiosis?
The standard answer goes like this: Incubation is 8 to 20 days.
ACUTE PHASE (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 PHASE (months to years): 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 of ehrlichiosis.
CHRONIC PHASE (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) may develop.
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/ÁL are typical)l and distinct from dogs with immune-mediated
platelet destruction (3,000 to 5,000 cells/ÁL).
Hyperglobulinemia/hypoalbuminemia may be present (hence the peripheral edema). Granular lymphocytosis (counts between 5,000
and 17,000 lymphocytes/ÁL). Pancytopenia seems less common today. Less common are a variety of multisystemic signs, including
peripheral limb edema, vasculitis (generalized), neurological signs ranging from head tilt (vestibular) to disorientation
to meningitis and seizures. Hyperviscosity syndrome, retinal detachment, and a host of immune-complex disorders affecting
joints and kidney may develop. Death is possible...despite aggressive treatment.
BUT...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"!