الفهرس 
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Abstract
Rhodococcus equi, a Gram-positive facultative intracellular pathogen, is among the most widely recognized causes of pneumonia in foals. Several antimicrobial drugs are effective against R. equi in vitro; however, many of these agents are ineffective in vivo because of the capability of R. equi to survive and replicates in macrophages. The present study aimed to prepare R. equi-specific hyperimmune horse antiserum and to evaluate its therapeutic and prophylactic efficacy against R. equi infection. Four horses were immunized with a locally prepared formalin inactivated R. equi vaccine adjuvanted with mineral oil. Each of these horses was immunized with 3 doses of the prepared vaccine (3ml/ dose) at 2 weeks intervals. One week after the last vaccination dose, serum from immunized horses was collected by plasmapheresis. The measured titer of R. equi specific antibodies reached to 104 ELISA units/ml after 2 weeks from the primary immunization and up to 105 ELISA units/ml one week after the third immunization dose. The therapeutic and prophylactic efficacy of the prepared R. equi-specific antibodies was evaluated in a mice model. 87.5% of mice challenged with virulent R. equi bacteria (0.2 ml/mice of 107 CFU/ml) were successfully treated, just after appearance of clinical signs of the infection, by intravenous injection of 0.5 ml of R. equi-specific polyclonal antibodies. Also the efficacy of the prepared R. equi-specific antibodies for induction of immediate protection was insured where 100% of passively immunized mice could resist challenge with virulent R. equi bacteria. The R. equi-specific polyclonal antibodies titer used for evaluation of its protective and prophylactic was 105 ELISA units/ ml.