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Tick-borne disease diagnosis: moving from 3Dx to 4Dx (Proceedings)

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Oct 01, 2008

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, "emerging infectious diseases" recently described, in fact, 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 will soon have the ability to test for Anaplasma phagocytophilum antibody, in addition to Borrelia burgdorferi C6 antibody, Ehrlichia canis antibody, and canine heartworm antigen. This advancement in testing capability comes with a new learning curve for clinicians since most, in fact, are not immediately familiar with the clinical presentation of dogs infected with A. phagocytophilum (formerly, Ehrlichia equi).

Specifically, the introduction of a 4Dx Snap 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, as well as the 'healthy' patient.

For any dog presented with fever, decreased appetite, lethargy, and petechia over the oral mucous membranes, testing for the presence of tick-borne disease is clearly indicated...it's become the standard of care in veterinary medicine. However, indications for testing patients that do not have overt clinical signs can be equally important. It's called Surveillance Testing...and is part of a health or "wellness" testing profile for dogs with any risk of tick exposure.

Surveillance Testing for antibody associated with tick-exposure may, in fact, be the best, earliest test of infection or impending illness. Rather than wait for clinical signs to become so obvious that the owner is compelled to have the dog examined...Surveillance Testing provides immediate insight on tick-borne disease exposure in an individual patient...at a reasonable cost to the client.

The implications of a POSITIVE test in a patient with clinical signs consistent with tick-borne disease are obvious...the test drives treatment decisions as well the need to perform follow-up examination of the patient. But the POSITIVE test in a seemingly healthy patient, what some will call 'confusing', actually isn't. In fact, the POSITIVE test in a healthy patient drives the need for further patient assessment and justifies, at the least, a thorough physical examination and a laboratory profile that includes hematology and biochemistry. Antibody POSITIVE patients without physical signs can have significant laboratory abnormalities, such as hypoalbuminemia with hyperglobulinemia, leukocytosis, thrombocytopenia, and anemia, that not only support infection but also warrant immediate therapeutic intervention.

Also...the patient with a POSITIVE test result that has a normal laboratory profile reveals whether or not the patient has been adequately or appropriately treated with a tick preventative. While it is well known that infection with a tick-borne pathogen may never cause clinical illness in some dogs, the ability to define 'exposure' through antibody detection is an important opportunity to educate the client on the use of tick preventatives...over and above what they might purchase at a pet store!

Knowledge that the patient is NEGATIVE, and is therefore unlikely to have had tick exposure, at least in part, denotes adequate tick prevention and reduced risk of exposure. The NEGATIVE test in the sick patient has a high degree of "negative" predictive value...ie, it is highly unlikely that the patient with a NEGATIVE test has the infection it was tested for. The NEGATIVE test result in a sick patient, therefore, drives additional diagnostic testing...but with the knowledge that, exposure to the agents tested is unlikely to be an issue for that patient.