Veterinary Medicine - October 2007 - (Page S7)

SUMMIT VetPharm ECTOPARASITOLOGY SYMPOSIUM 50% to 75% in a six-month period may indicate that therapy has effectively eliminated the organisms. Blood transfusions may be required in severe cases. Clinical improvement in response to therapy precedes the return of hematologic parameters to normal, which may take months in severe cases. With treatment, the prognosis is excellent in acute cases and mildly affected chronic cases but guarded in cases with severe pancytopenia and hypoplastic or aplastic bone marrow. Low dose tetracycline (7 mg/kg/day) has been recommended as a prophylaxis in dogs at high risk for reinfection. the indirect fluorescent antibody (IFA) test, which is available at most commercial laboratories, and the SNAP® 3Dx® Test and SNAP® 4Dx® Test (IDEXX Laboratories,Westbrook, Maine) for inclinic use.The IFA test uses whole E. canis organisms cultured in a canine macrophage cell line as the reacting antigen.The assay is difficult to interpret with many false positives due to crossreactivity and background staining. The SNAP 3Dx and SNAP 4Dx assays use synthetic peptides based on a major outer membrane protein of E. canis.This reduces the number of false positive results seen with IFA, giving the assay a very high positive and negative predictive value.The new SNAP 3Dx and SNAP 4Dx tests have increased specificity and sensitivity over the older SNAP® 3Dx® Canine Combo. Animals infected with E. canis or E. chaffeensis will test positive using any of the currently available serologic assays.The only way to distinguish between these two infectious agents is by in vitro cultivation or polymerase chain reaction (PCR) analysis.Therefore, the role of E. chaffeensis as a cause of canine monocytic ehrlichiosis is poorly defined. PCR analysis can be performed by many commercial laboratories and may be one way to identify a seropositive animal as having an active infection. However, a negative PCR reaction does not rule out infection because many subclinically infected animals have organisms in the peripheral blood at levels below the sensitivity of the PCR test. TREATMENT AND PROGNOSIS During a routine exam, if a clinically normal animal is found to be positive on serology, this indicates the animal has been exposed to ehrlichiosis and could be a carrier in the subclinical stage of the infection.A CBC should be performed to identify any characteristic hematologic abnormalities, such as a mild nonregenerative anemia or thrombocytopenia. If blood abnormalities are found, the patient should be treated appropriately and retested in three to six months. If no abnormalities are found, the need to treat the animal is not clearly established. Minimally, a serologic evaluation should be repeated in three to six months. If persistently positive, a course of therapy should be considered. Tetracycline (20 mg/kg orally three times a day) or doxycycline (5 to 10 mg/kg orally twice a day) treatment for four weeks is generally effective in eliminating clinical signs, but titers (especially high titers) may persist for long periods of time. Animals cleared of infection should have a gradual decline in antibody titer, and a titer reduction of Granulocytic forms of disease The granulocytic forms of these diseases are recognized as such because the organisms have a tropism for circulating granulocytes, particularly neutrophils. There are two main organisms that are known to infect dogs: E. ewingii and A. phagocytophilum (formerly E. equi). Infections with these agents have been reported across the United States, and a particularly virulent strain of A. phagocytophilum has been reported to cause clinical disease in dogs in Sweden. E. ewingii has been reported in dogs in several U.S. states, including Arkansas, Oklahoma, North Carolina, and Virginia. Infections in people have been reported in Missouri, Oklahoma, and Tennessee.The only confirmed tick vector is Amblyomma americanum.The white-tailed deer is suspected to be an important reservoir for infection, similar to E. chaffeensis. Infection with A. phagocytophilum has been recognized in a variety of hosts, including people, dogs, cats, horses, ruminants, and many wildlife species, such as white-tailed deer, dusky-footed wood rats, mountain lions, and bears. Canine infection with A. phagocytophilum was first reported in dogs from Minnesota and Wisconsin in 1996. In the United States, most disease outbreaks are seasonal and coincide with the emergence of the tick vectors in spring and early summer (May and June) and then again in September. CLINICAL SIGNS AND LABORATORY FINDINGS Vague clinical signs, similar to those seen with monocytic ehrlichiosis, occur in dogs with the granulocytic form of the disease as well.These include fever, lethargy, anorexia, and reluctance to move. The predominant and most characteristic clinical sign is lameness due to suppurative polyarthritis, which makes the clinical findings of these diseases indistinguishable from those seen in Lyme disease. A. phagocytophilum and the agent of Lyme disease (Borrelia burgdorferi) share the same tick vector, Ixodes ticks or deer ticks, and have a similar geographic 7

Table of Contents Feed for the Digital Edition of Veterinary Medicine - October 2007

Veterinary Medicine - October 2007 Contents Leading Off The Veterinary Medicine Interview: Dr. Kevin Fitzgerald Toxicology Brief Idea Exchange Animal Sheltering in the United States: Yesterday, Today, and Tomorrow The Euthanasia Problem Offer Basic Behavior Counseling for Every Pet at Every Visit Promote and Perform Early Spaying and Neutering Assist Owners in Selecting the Best Pets for their Lifestyles Champion Animal Welfare in Your Community CE Form Product Review Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - October 2007

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