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tvpjournal.com | July/August 2015 | TodAy's VeTerinAry PrAcTice PArAsiTology eXPerTise FroM THe ncVP Peer reviewed 57 • Antibodies can be detected in many dogs during both early and established acute disease. • identification of morulae on blood smears can be readily achieved in many patients, particularly during acute infection. Ehrlichiosis Transmission. several different Ehrlichia species can infect dogs in the U.s., including E canis (Figure 1), E ewingii, E chaffeensis, Panola Mountain Ehrlichia species, and E muris. 6,9,10 different tick species are responsible for transmitting these Ehrlichia species, resulting in widespread distribution of infection. Presentation. common clinical abnormalities associated with acute ehrlichiosis include fever, lethargy, myalgia, anorexia, and thrombocytopenia; epistaxis and petechial and ecchymotic hemorrhages may be seen in severe cases of E canis –induced ehrlichiosis, while lameness and polyarthritis are more commonly associated with E ewingii infection. 6,9,10 some animals that become chronically infected with E canis can develop pancytopenia, neurologic disease, bleeding diatheses, or ocular abnormalities, and fatalities are often reported. 6 Many dogs, however, exhibit subclinical Ehrlichia species infections. 6,11 Diagnosis. As with anaplasmosis, diagnosis can be made through Pcr, serologic testing, and examination of blood smears; concurrent use of 2 or more methods improves the likelihood of confrming a diagnosis. 8,11 TAbLE 2. Diagnostic strategies for Tick-Borne Disease agents Diagnostic methoD beneFits Limitations Blood smear evaluation • Rapid, in-clinic assay • Visualization of organisms (if present) confrms presence of Anaplasma species, Ehrlichia species, and protozoal agents • Slide scanning can be time-consuming • Diagnosis to species level may be diffcult • Useful only for identifying infection with Anaplasma species, Ehrlichia species, and protozoal agents Whole blood PC r • Widely available through diagnostic laboratories • Sensitive for acute infections with well- characterized Anaplasma and Ehrlichia species before initiation of antibiotic treatment • Sensitive for identifying infection with Babesia and Hepatozoon species • Depending on assay design, may be more specifc than serologic testing` • Some assays may provide quantitative results • In-clinic testing with same-day results not usually available • Some organisms ( Borrelia burgdorferi , Rickettsia species) unlikely to be present in blood sample, despite presence of infection and clinical disease • Less reliable when very low circulating rickettsemia present (chronic infection) and after initiation of antibiotic treatment • May not identify presence of infection with novel disease agents • May lead to false-positive results due to presence of closely related agents serologic testing • In-clinic assays available for many agents • Depending on design, allows for detection of antibodies to several different agents with one assay • Panel assays often available from diagnostic laboratories • Some assays may provide quantitative results • Paired (acute and convalescent) samples collected 2–4 weeks apart can identify rising or falling titers and, thus, recent infection • May be less useful in acute infections before seroconversion if only a single sample is evaluated • Antibodies persist for months to years after infection, which can confuse interpretation • Cross-reactivity common, particularly with immunofuorescence-based assays, including to nonpathogenic organisms Figure 1. morulae of Ehrlichia canis (arrows) within monocytes. Wright-giemsa stain, magnifcation, 1000×. Courtesy National Center for Veterinary Parasitology