Veterinary Medicine - October 2007 - (Page S8)

COMMON TICK-BORNE PATHOGENS IN DOGS distribution in the United States. Because of this, co-infections with these two organisms commonly occur and may result in more severe clinical manifestations than infections with a single agent. Laboratory findings include a mild to moderate nonregenerative anemia, thrombocytopenia, and lymphopenia with or without neutropenia. The most common hematologic abnormality is a mild to severe thrombocytopenia, seen in more than 80% of acutely infected dogs. DIAGNOSIS Diagnosis can often be made by microscopic identification of Ehrlichia or Anaplasma morulae in neutrophils in the peripheral blood or synovial fluid. These are most often found during the acute phase of the disease (one to 10 weeks post-infection), and they may be seen in between 1% to 15% of circulating neutrophils.At this point we have no serologic assay available for E. ewingii, although some animals infected with E. ewingii may have a positive reaction on assays that detect E. canis. IFA tests are available for the serologic diagnosis of infection with A. phagocytophilum and PCR assays have been designed to specifically amplify portions of the 16S rRNA gene of this organism.An in-house ELISA assay (SNAP® 4Dx® Test—IDEXX Laboratories, Westbrook, Maine), is now available for in-clinic use.This test identifies animals infected with A. phagocytophilum but will not cross react with animals infected with E. ewingii. It is also important to note that animals infected with A. phagocytophilum will not test positive on assays designed to diagnose E. canis infections (SNAP 3Dx Test). TREATMENT AND PROGNOSIS The treatment for the granulocytic forms of ehrlichiosis and anaplasmosis is oral doxycycline at 10 mg/kg twice a day for 30 days. Clinical signs typically resolve shortly after institution of therapy. However, evidence in both people and dogs shows that some infections with A. phagocytophilum will not be cleared and that carrier states can occur even with appropriate antimicrobial therapy. TABLE 1: EHRLICHIA AND ANAPLASMA SPECIES KNOWN TO INFECT DOGS • E. canis, E. ewingii, and E. chaffeensis • Anaplasma phagocytophilum (formerly E. equi and the human granulocytic ehrlichiosis agent) • Anaplasma platys (formerly E. platys) • Neorickettsia risticii (formerly E. risticii) Infectious cyclic thrombocytopenia Anaplasma platys (formerly Ehrlichia platys) causes infectious cyclic thrombocytopenia in dogs.This agent is unique in that it is the only intracellular infectious agent described in people or animals to specifically infect platelets.The prepatent period is one to two weeks following experimental injection with infected blood. Cyclic parasitemias and concomitant thrombocytopenia occur at one- to two-week intervals. Parasitized platelets are easily found during the initial parasitemia, but subsequent parasitemias have decreasing percentages of parasitized platelets. Platelet counts usually remain below 20,000/µl for only one or two days before rapidly increasing. Infected dogs usually do not exhibit evidence of illness, but mild fever may occur at the time of the initial parasitemia. Minimal or no evidence of hemorrhage is present in most cases, but epistaxis, petechia, and ecchymosis of mucous membranes have been reported.The infection can be diagnosed by observing organisms within platelets. An IFA test for antibodies against A. platys has been developed. Cross-reaction with other Ehrlichia species is not likely. However, animals infected with A. platys will test positive on the SNAP 4Dx. A. platys can be identified using PCR technology, but this is not commercially available. Doxycycline at the dose described previously is effective in treating this infection. Summary Canine ehrlichiosis and anaplasmosis are emerging tick-borne diseases in dogs, endemic to several areas of the United States and expanding in distribution. In addition to causing clinical disease, dogs may be subclinical carriers of persistent infection, causing a positive serology result in healthy dogs.These dogs should be monitored closely because there may be potential for clinical manifestations, particularly after events of stress or immunosuppression. Finally, doxycycline is effective in treating the clinical disease but may not clear the organisms from all infected animals. Zoonosis Of the tick-borne diseases discussed, A. phagocytophilum most commonly affects both dogs and people.To the author’s knowledge, direct transmission from dogs to people has never been documented. Ticks serve as a biological vector and amplifier for the organism. However, infected pets should signal to owners the presence of infected ticks in the environment with due caution for tick control. 8 To view this publication online, visit www.advanstarvhc.com/c16. http://www.advanstarvhc.com/c16

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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