Recent successes with monoclonal antibody cocktails ZMapp(TM) and MIL77 against 
Ebola virus (EBOV) infections have reignited interest in antibody-based 
therapeutics. Since the production process for monoclonal antibodies can be 
prolonged and costly, alternative treatments should be investigated. We produced 
purified equine antisera from horses hyperimmunized with EBOV virus-like 
particles, and tested the post-exposure efficacy of the antisera in a mouse 
model of infection. BALB/c mice were given up to 2 mg of purified equine 
antisera per animal, at 30 minutes, 1 or 2 days post-infection (dpi), in which 
all animals survived. To decrease the possibility of serum sickness, the equine 
antisera was digested with pepsin to generate F(ab')2 fragments, with in vitro 
neutralizing activity comparable to whole immunoglobulin. Full protection was 
achieved with when treatment was initiated at 1 dpi, but the suboptimal 
protection observed with the 30 minute and 2 dpi groups demonstrate that in 
addition to virus neutralization, other Fc-dependent antibody mechanisms may 
also contribute to survival. Guinea pigs given 20 mg of antisera or F(ab')2 at 
or starting at 1 or 2 dpi were also fully protected from EBOV infection. These 
results justify future efficacy studies for purified equine products in NHPs.