You have asked… How should we manage subclinical dogs that are seropositive for rickettsial diseases?
The expert says… Popular combined screening tests, such as SNAP 4Dx Plus and AccuPlex4, can help identify healthy subclinical (nonclinical) dogs seropositive for rickettsial agents by assaying for heartworm antigen and for antibodies against Lyme disease (Borrelia burgdorferi), anaplasmosis (Anaplasma phagocytophilum), and ehrlichiosis (Ehrlichia canis). In addition, the SNAP 4Dx Plus test identifies antibodies against E chaffeensis, E ewingii, A platys, and a novel E muris-like agent found in dogs.1,2 Anaplasma and Ehrlichia organisms may also be associated with carrier status both in untreated exposed dogs and in treated dogs. Whether to give antibiotics to dogs with subclinical, nonproteinuric Lyme-seropositivity has been debated3-6; the consensus appears to be no, although such dogs should be monitored for occult proteinuria. Meanwhile, how should subclinical Anaplasma spp and/or Ehrlichia spp seropositive dogs be clinically managed? Might they still be carriers, and might carriers become clinically ill in the future? Can the carrier state be cleared, and can seropositive dogs be used safely as blood donors? Do these dogs remain potential reservoirs for infection of other animals and humans?
Related Article: A Matter of Opinion: Should We Treat Asymptomatic, Nonproteinuric Lyme-Seropositive Dogs with Antibiotics? Clinical Cues Certain rickettsial organisms parasitize granulocytic (A phagocytophilum, E ewingii) or mononuclear (E canis, E chaffeensis) WBCs or platelets (A platys). Signs in infected dogs vary (see Clinical Signs of Rickettsial Infection below),7-11 and infection may result in chronic carrier states with no sign of clinical illness.
Diagnostic tests may reveal cytopenias (eg, thrombocytopenia, possible anemia and/or leukopenia), basophilic cytoplasmic inclusion bodies (morulae) in WBCs or platelets (via synovial fluid cytology or peripheral blood or buffy coat smears), renal proteinuria with negative urine culture, hypoalbuminemia, hyperglobulinemia with polyclonal or monoclonal gammopathy, hypercholesterolemia, and possibly elevated liver enzymes.7-11 To Treat or Not to Treat? For seropositive dogs with illness suggestive of rickettsial disease, treatment with doxycycline at 5 mg/kg q12h or 10 mg/kg q24h for 28 days is recommended; dogs with acute or mild to moderate illness generally respond within 1 or 2 days of antibiotics.7-11 Quantitative IFA or ELISA testing may be used to assess response to therapy and establish baselines for future comparisons at 0 and 6 to 12 months posttreatment, particularly if signs recur or worsen. Decreased titers or normalization of hematologic/urinalysis abnormalities may indicate organism clearance or decreased antigenic burden. But should we routinely treat subclinical seropositive dogs with doxycycline? The author’s answer is no; however, occult clinicopathologic changes such as cytopenias (eg, anemia, leukopenia, thrombocytopenia), proteinuria, hypoalbuminemia, or hyperglobulinemia should be evaluated (see Management Plan for Subclinical Seropositive Dogs on page 3 of this PDF). Abnormalities necessitate antimicrobial treatment, and further investigation may be indicated to rule out other causes of these changes, including coinfection with other infectious diseases, as seropositivity may be a coincidence or a marker for tick and wildlife exposure. Additional testing for heartworm antigen and antibodies against B burgdorferi, Babesia spp, Bartonella spp, Leptospira spp, Hepatozoon spp, Brucella spp, or Leishmania spp may be indicated.