August • 2002   EHRLICHIA UPDATE   Ehrlichiosis Species Ehrlichia canis was the first species known to infect dogs, and infection results in a variety of acute and chronic clinical and subclinical syndromes. Ehrlichiosis platys also infects dogs and may cause cyclic thrombocytopenia but minimal clinical illness. Several other Ehrlichia spp. infect dogs, the most common being E. ewingii, E. chaffeensis, E. risticii, and E. equi. Most regions of the world have Ehrlichia spp. In cats, E. canis and E. equi can cause natural infections, although other species of Ehrlichia can experimentally infect cats. Vectors Tick transmission vectors for Ehrlichia spp. are usually Ixodes ticks with the granulocytic forms of ehrlichiosis and Rhipicephalus, Amblyomna or Dermacentor ticks with the monocytic Ehrlichia spp. In horses, E. risticii can be transmitted by ingestion of the trematode stages found in intermediate hosts such as aquatic insects and snails. Clinical Manifestations A multisystemic disorder, ehrlichiosis is characterized by depression, lethargy, mild weight loss, and anorexia, both with and without hemorrlogic signs. If present, bleeding usually manifests petechiae, ecchymoses, gastrointestinal bleeding and/or epistaxis. Other less common signs include uveitis, polymyositis, polyarthritis, and central nervous system signs such as seizures, ataxia, vestibular deficits, and cerebellar dysfunction. Adult respiratory distress syndrome and acute renal failure also may occur in dogs as seen in humans. Many dogs are apparently exposed and seroconvert but never show clinical signs of the disease. Some animals harbor the agent for months or even years without developing illness. German Shepherd dogs may be predisposed to clinical ehrlichiosis. Most clinical manifestations of canine ehrlichiosis also have been described in cats. Laboratory Findings Most consistently, the CBC will reveal thrombocytopenia and mild nonregenerative anemia in dogs and cats. Some infected dogs have normal platelet counts. Pancytopenia occurs in severe chronic phase disease from bone marrow hypoplasia. Granular lymphocytosis can occur and mimic well-differentiated lymphocytic leukemia. In about 1/3 of affected dogs, hyperproteinemia is reported. A polyclonal gamnopathy is most common, but monoclonal or biclonal gamnopathies have been seen in both dogs and cats.       Please send comments to the webmaster. ©1997-2008 Antech Diagnostics, Inc. Site design and maintenance by amesDesign.