Ehrlichia bovis (Donatien & Lestoquard, 1936) - Diagnóstico, cultivo "in vitro" e aspectos epidemiológicos em bovinos no Brasil

Abstract

The aetiological agent of bovine ehrlichiosis, Ehrlichia bovis (Donatien & Lestoquard, 1936) known in Africa as "Nopi", "Nofel" or Ear Sickness is reported for the first time in Brazil, in the States of Rio de Janeiro and Minas Gerais. The diagnosis of the rickettsial disease was confirmed by finding the parasites in mononuclear cells on blood smears and visceral impressed slides from cattle. Low numbers of parasites were observed even during fever periods of the infection transmitted experimentally. A survey based on blood smears from 296 calves of 12 regions of these two States were stained on Giemsa and a prevalence of 9,8% for E. bovis was found, including single or multiple infections with Anaplasma marginale, Babesia bigemina and Babesia bovis. Calves apparently negative when splenectomized became positive to E. bovis, B. bigemina, B. bovis, A. marginale, Eperythrozoon wenyoni and Eperythrozoon teganodes. Leukocytes cultures obtained from desfibrinated cattle blood performed in Leighton tubes, incubated at 37°C, allowed the demonstration of multiplication of E. bovis in cytoplasm of leukocytes. The viability of microorganisms from "in vitro" cultivation was established by reproducing the infection by experimental inoculation of cattle. E. bovis particulate antigens obtained from cell cultures and inoculated into rabbits induced the production of sera immune specific responses. The conjugation of the sera immune specific with fluorescein isothiocyanate permitted their utilization for diagnosis of E. bovis by the direct immunofluorescence test. This method was more efficient and faster than the conventional blood smears stained on Giemsa. The inoculation of sheep, dog, rabbit and goat with blood and cell cultures did not establish the infection. Nymphal stages of Amblyomma cajennense, fed during larval stage on infected cattle, transmitted the disease. Direct immunofluorescence tests performed with nymphal stages of A. cajennense were also positive. Clinical signs in cattle infected with E. bovis were fever, enlargement of peripheral lymphonodes, apathy, loss of appetite and loss of weight. Hematological studies showed monocytic and lymphocytic leukocytosis, eosinopaenia and large number of vacuolated monocytes. These signs permit a presumptive diagnosis of E. bovis. Laboratory diagnosis, can be performed using blood smears stained on xviii Giemsa and confirmed by direct immunofluorescence test. Under natural conditions E. bovis was found in cattle during the seasons when tick populations were high. Clinical signs were more evident in debilitated cattle.