Veterinary Medicine - April 2008 - (Page 216)

Canine anaplasmosis PEER-REVIEWED the SNAP 4Dx. In addition to testing for infection with A. phagocytophilum, the SNAP 4Dx also detects infection with Diro laria immitis, Borrelia burgdorferi, or E. canis. PCR testing. Nucleic acid ampli cation is the most sensitive method for detecting organism DNA in the peripheral blood of an infected animal. Several commercial laboratories offer polymerase chain reaction (PCR) analysis of peripheral blood for detecting A. phagocytophilum and E. ewingii. These assays are speciesspeci c and can distinguish between these two infectious agents. Submit EDTA-anticoagulated peripheral blood to laboratories for PCR analysis. Collect these samples before initiating antimicrobial therapy because recent antibiotic administration, particularly tetracycline or its derivatives, increases the likelihood of a false negative result. Although this technique is more sensitive in detecting circulating organisms than is light microscopy, it has been shown to be only intermittently positive in subclinically infected, persistent carriers of A. phagocytophilum since organisms may circulate intermittently in the peripheral blood of subclinically infected animals.7,15 Therefore, PCR analysis should not be considered a de nitive method for conclusively excluding subclinical infection in clinically normal animals that are seropositive on routine screening. 3. An intracytoplasmic Anaplasma phagocytophilum morula in a neutrophil (above center) in a buffy coat smear prepared from the peripheral blood of a dog. An intracytoplasmic Döhle body is seen in the neutrophil in the upper left corner (Wright’sGiemsa; 100X). Treatment and prognosis The treatment for canine anaplasmosis is the same as that for infection with the closely related Ehrlichia species— doxycycline. The optimal dose and length of therapy have not been rmly established, but an oral dosage of 5 to 10 mg/kg given twice a day for 30 days has been recommended.12,16 In most cases, clinical signs resolve rapidly. Dogs are often markedly improved 24 to 48 hours after therapy is instituted, and the prognosis for clinical recovery is excellent.12 However, persistent infection and subclinical carrier states have been demonstrated in experimentally inoculated dogs treated with doxycycline for 14 days and 28 days at the recommended dose.7,15 Although clinical resolution of disease is usually accomplished, it may be dif cult to ascertain the effectiveness of therapy in completely clearing organisms from naturally infected animals. If an animal no longer produces antibodies to the organism, this may indicate that the organism has been cleared from the body. Since PCR analysis can give false negative results, this assay is unreliable in detecting all subclinical, persistent carriers. In light of these diagnostic challenges, once an animal with clinical anaplasmosis has been treated with the recommended course of doxycycline therapy and is clinically normal, administering a second course of doxycycline therapy or a different antimicrobial agent, in an attempt to obtain a seronegative status, is not recommended at this time. Because tetracyclines may result in tooth discoloration, chloramphenicol (15 to 25 mg/kg every eight hours for 14 to 21 days) has been suggested as an alternative to tetracycline derivatives in dogs under 1 year of age.12 However, it appears that doxycycline, unlike tetracycline, does not result in enamel discoloration in young growing puppies. In vitro testing has shown that rifampin and levo oxacin are also effective against A. phagocytophilum, but their effectiveness in vivo has not been evaluated in dogs.17 Seropositive, clinically healthy dogs Animals from endemic areas are often exposed to A. phagocytophilum, and 40% or more of dogs in these areas may be seropositive.9 However, since the morbidity is low, it appears that many animals may have antibodies to A. phagocytophilum without having any concurrent evidence of clinical disease. Since persistent infection in clinically healthy dogs has been demonstrated,6,7,15 it is likely that a portion of the seropositive animals are chronically infected carriers of the organism. Experimentally, chronically infected carriers did not have any hematologic abnormalities,7 and, thus far, it appears that seropositive animals with no clinical evidence of disease are hematologically normal. Incidents of chronically infected carriers later developing clinical disease have not been clearly documented. 216 April 2008 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - April 2008

Veterinary Medicine - April 2008 Contents Letters Leading Off The Veterinary Medicine Interview: Dr. Barrak Pressler Idea Exchange Help! My Dog Licks Everything An Update on Anaplasmosis in Dogs CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - April 2008

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