OBJECTIVES

Ehrlichiosis is a tick-borne disease of dogs caused by organisms belonging to genera Ehrlichia and Anaplasma. Ehrlichia canis has a worldwide distribution, but the main clinical manifestations of the disease may vary in different locations. We have previously shown that in our hospital population 23% of the dogs have antibodies against E. canis. Bleeding however was not a risk factor for ehrlichiosis in this study. Only dogs simultaneously serorreagent to E. canis and Babesia canis had a higher chance of presenting superficial bleeding than the general hospital population. Dogs experimentally-infected with Brazilian strains of E. canis develop anemia, but not thrombocytopenia. Thus, we attempted to determine the prevalence of ehrlichiosis in dogs with anemia, thrombocytopenia, or ticks presented to the Veterinary Teaching Hospital of Universidade Estadual de Londrina.

MATERIALS

We selected 130 dogs, being 69 with ticks, 61 with thrombocytopenia (platelet count < 150 000/?l), and 19 with anemia (PCV < 22%). Twenty dogs fulfilled more than one inclusion criteria. Of the 69 dogs with ticks, 67 had only the dog brown tick Rhipicephalus sanguineus, one was infested with R. sanguineus and Amblyomma cajennense, whereas the remaining dog was infested only with A. cajennense. Ehrlichiosis was diagnosed by positive amplification of ehrlichial DNA by PCR using primers ECC and ECB that amplify a sequence of the 16S rRNA gene. Presence of E. canis was confirmed by cleavage of the amplified DNA using endonucleases Hae III and Ava I.

RESULTS

Fourteen of the 69 (20%) dogs with ticks had ehrlichiosis. Twelve of the 61 (20%) dogs presented with thrombocytopenia and 4 of the 19 (21%) anemic dogs had ehrlichiosis. Similar results were obtained in dogs with bicytopenia (thrombocytopenia and anemia) where 2 of 9 were positive, and in dogs with thrombocytopenia and ticks (2 of 9 positive). All four dogs with anemia and ticks, and the dog that fulfilled all inclusion criteria yield no amplification of ehrlichial DNA by PCR.

CONCLUSION

Based on our results, ehrlichiosis appears to be an important differential diagnosis in dogs with anemia and thrombocytopenia. Contrary to widespread believe, however, ehrlichiosis was not the main cause for thrombocytopenia in our region. Because most of the thrombocytopenic patients responded to doxycycline, we cannot exclude a non-ehrlichial organism, sensitive to doxycycline as the reason for the thrombocytopenia in the dogs without ehrlichiosis.