Ehrlicia: acute inflamatory invaders (among dogs) part 2 ;diagnosis and treatment

HOW THE DIAGNOSIS IS MADE

Diagnosis does not rest on a single test but instead on a collection of results. The first step is to find a constellation of typical findings:

• A dog with fever, enlarged lymph nodes, bleeding, or arthritis in multiple joints.
  
• Low platelet numbers, high globulin levels, and mild anemia on blood testing.

When Ehrlichia are suspected, a blood test for antibodies against Ehrlichia organisms can be ordered. A positive test indicates that the dog has been exposed to Ehrlichia and does not imply active current infection necessarily. A negative titer does not fully rule out Ehrlichia, either, as a very sick patient will be too sick to produce antibodies and an early case may not yet have started to produce antibodies. The antibody level or “titer” can be done with an IFA (immunofluorescent antibody) or by ELISA (Enzyme-linked Immunosorbant assay). The IFA test is the traditional test. The ELISA test is included in a new in-house test kit from IDEXX labs (the “snap 3DX” test) that also includes a Lyme Disease test and a Heartworm test. The 3DX test is geared specifically to detect antibodies against Ehrlichia canis. It is not entirely clear if antibodies against other types of Ehrlichia will be similar enough to be detected by either the IFA or ELISA tests reliably. It takes 6-9 months after infection for titers to begin to drop.

Recently PCR testing for the actual presence of Ehrlichia organisms has become available. The disadvantage of this test is that it gives either a positive or negative results rather than an actual quantitative number that can be tracked. A combination of PCR testing as well as antibody titers are currently recommended by the American College of Veterinary Internal Medicine. PCR testing remains positive for several weeks after infection as PCR testing does not distinguish between live and dead organisms. It takes time to clear dead organisms from the body.

If one is lucky one will actually see the organisms on a blood smear, and this, of course, clinches the diagnosis.

TREATMENT

Despite being one of the oldest antibiotics in use, tetracycline is probably the most effective against Ehrlichia (and any other intracellular blood parasite for that matter). Doxycycline, a more modern derivative, has a more convenient dosing schedule and has become more popular. Expect at least a month of treatment to be needed. Response is initially rapid (improvement is notable in the first few days).

If immune-mediated secondary reactions to the Ehrlichia are a problem (such as immune-mediated arthritis, or immune-mediated platelet loss) corticosteroids such as prednisone can be used to palliate the situation while the antibiotics are starting to work.

After infection, it is possible to become re-infected; immunity is not lasting after a previous infection.
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