Veterinary Medicine - April 2008 - (Page 214)

Canine anaplasmosis PEER-REVIEWED 1. An intracytoplasmic Anaplasma phagocytophilum morula in a toxic band neutrophil in the peripheral blood of an infected dog (Wright’s-Giemsa; 100X). 2. An intracytoplasmic Anaplasma phagocytophilum morula in a neutrophil in the synovial ﬂuid of an infected dog (Wright’sGiemsa; 100X). Diagnosis This form of anaplasmosis can be difcult to distinguish from Lyme disease, but new diagnostic capabilities are now available. Light microscopy. Canine anaplasmosis is often diagnosed by microscopic identi cation of morulae in circulating neutrophils in the peripheral blood (Figure 1) and sometimes the synovial uid (Figure 2). These ndings are most often identi ed during the acute phase of the disease. Experimentally, organisms appear in the peripheral blood between four and 14 days after inoculation and usually persist for up to eight days.5 Anaplasma phagocytophilum morulae may be seen in 1% to 27% of circulating neutrophils. The ability to identify morulae in the circulating neutrophils of infected dogs is enhanced by preparing and microscopically evaluating a buffy coat smear (Figure 3). In animals presenting with polyarthritis, synovial uid analysis would reveal decreased viscosity and an increased leukocyte count (> 3,000 cells/µl) with a predominant neutrophil population. Organisms may also be found in a small number ( 1:320.13 For this reason, and because nonspeci c binding of antibodies can occur using this assay when serum samples are at dilutions of 1:40 or less, a titer of > 1:80 is considered positive for antibodies to A. phagocytophilum. In cross-reactivity studies, serum samples from animals or people infected with Neorickettsia risticii, Ehrlichia canis, E. ewingii, Ehrlichia chaffeensis, Ehrlichia sennetsu, Rickettsia rickettsii, Ehrlichia typhi, Bartonella henselae, or Bartonella quintana did not contain antibodies that cross-reacted with A. phagocytophilum.13 Serum samples from animals infected with A. platys were not evaluated in this study. The A. phagocytophilum test spot on the in-house SNAP 4Dx assay uses a synthetic peptide based on the immunodominant p44 protein of A. phagocytophilum as the antigen. Experimentally inoculated dogs had positive test results on the SNAP 4Dx assay as early as eight days after inoculation.7 These animals remained persistently infected for nearly one year and remained seropositive during that entire time even though the animals were clinically healthy and light microscopy did not reveal organisms in circulating neutrophils. In performance trials, the sensitivity and speci city of the SNAP 4Dx test for antibody to A. phagocytophilum was 99.4% and 100%, respectively.14 Dogs infected with Ehrlichia species, including E. ewingii, will not likely crossreact with the A. phagocytophilum test on 214 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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.