Susceptibility of cattle to infection with Ehrlichia equi and the agent ofhuman granulocytic ehrlichiosis

Objective-To determine susceptibility of cattle to infection with Ehrlichia equi and the agent of human granulocytic ehrlichiosis (HGE). Design-Experimental disease and prevalence survey. Animals-6 cattle, 2 horses, and 2,725 serum samples from healthy cattle. Procedure-2 cattle and 1 horse were inoculated with E equi, 2 cattle and 1 horse were inoculated with the HGE agent, and 2 cattle served as sham-inocu lated controls; inoculated animals were evaluated via clinical, hematologic , serologic, and real-time polymerase chain reaction tests. Prevalence of a ntibodies against E equi in 2,725 healthy cattle was determined by use of a n indirect immunofluorescent technique. Results-No abnormal clinical or hematologic findings or inclusion bodies wi thin granulocytes were observed in the cattle after inoculation, and result s of all polymerase chain reaction tests were negative. Seroconversion in i noculated cattle developed 10 to 12 days after inoculation (reciprocal tite rs, 160). Both horses developed clinical signs of ehrlichiosis. Five of 2,7 25 (0.18%) cattle were seropositive for E equi, with titers ranging from 20 to 80. All seropositive cattle originated from the same tick-rich region i n the Sierra Nevada foothills. Conclusions and Clinical Relevance-Results suggest that cattle are not susc eptible to infection with E equi or the agent of HGE and that prevalence of exposure to E equi in healthy cattle is low. Therefore, E equi and the age nt of HGE are likely of negligible importance for cattle in North America.