July • 2002   EHRLICHIA UPDATE (CONT'D)   Serologic Diagnosis In the dog, diagnosis usually is made by detecting specific antibodies by indirect immuno- florescent antibody (IFA) test. Serum ehrlichial antibodies can be detected as early as 7 days after initial infection but some dogs become seropositive only after 28 days. Thus, clinical signs of disease can occur before the development of serum antibodies in acutely infected dogs. In such cases of strongly suspected infection, the IFA test should be repeated in 2-3 weeks. Cross-reactivity among Ehrlichia spp. is variable, and so E. canis-based antibody tests often fail to detect other Ehrlichia spp. The E. canis IFA test detects only ~40% of dogs infected with E. ewingii, and does not detect any E. risticii- or E. equi-infected dogs. The Idexx Snap 3Dx test does not detect dogs infected with E. ewingii, E. risticii, or E. equi. The IFA test results are usually reported as a quantitative antibody titer. However, titer levels do not correlate with duration of infection or severity of disease. Experts believe that titers >1:80 should be considered positive. It is important to remember that in endemic areas, many healthy dogs have positive IFA titers to E. canis. In the cat, a definitive statement about the utility of diagnostic ehrlichial serology cannot be made. For cats with clinical findings supportive of ehrlichiosis and seropositivity with E. canis or E. risticii reagents, treatment with antiehrlichial drugs is advised. Some cats found positive for E. canis DNA are seronegative by IFA. PCR Testing and Western Immunoblotting Due to the limitations of serological testing, PCR testing may play a more important role in diagnosing canine and feline ehrlichiosis. The PCR method is very sensitive for detection of ehrlichial infections in dogs. It is recommended that PCR testing be used in conjunction with IFA serology, and not instead of it, for the diagnosis of ehrlichiosis. Treatment is recommended for PCR positive dogs, even those that are subclinically infected, as they can decompensate, and develop clinical disease. Treatment Drugs used most frequently today to treat all Ehrlichia spp. are doxycycline and minocycline, although tetracycline and oxytetracycline are still used. Experts currently recommend doxycycline at a dosage of 10 mg/kg P O q 24 hr for 28 days. Dramatic clinical improvement is usually seen within 24-48hrs. Doxycycline and tetracycline have also been used successfully at the same dosage in cats with presumed ehrlichiosis. Another drug that can be used is imidocarb dispropriate at 2 doses of 5 mg/kg IM given 2-3 weeks apart for dogs or cats. Enrofloxacin, used effectively to treat Rocky Mountain Spotted Fever, is ineffective in E. canis infection. As thrombocytopenia occurs in about 82% of dogs infected with E. canis, normalization of the platelet count is usually indicative of good response to therapy. Platelet counts begin to increase after 24-48 hours of therapy and are usually normal within 14 days. If resolution is not seen within 7 days of therapy, consider a diagnosis of immune-mediated platelet destruction or coinfection with Babesia spp. or Bartonella. Hyperglobulinemia will resolve gradually in 6-9 months if the organism has been eliminated. Serologic antibody levels will gradually decline and typically become negative within 6-9 months of therapy, although dogs with high serum titers can maintain them for longer periods, even years. Thus, monitoring IFA titers is probably not a very effective way to assess response to treatment. The PCR test may be more useful in distinguishing successfully treated dogs with persistently high IFA titers from unsuccessfully treated dogs.       Please send comments to the webmaster. ©1997-2008 Antech Diagnostics, Inc. Site design and maintenance by amesDesign.