OMAHA, Neb. — A surgeon who contracted Ebola in his native Sierra Leone received aggressive treatment at a Nebraska hospital over the weekend but died Monday morning.Dr. Martin Salia’s death is a reminder of how deadly the Ebola virus is and how important it is to receive treatment early, said Dr. Jeff Gold, chancellor of the University of Nebraska Medical Center in Omaha.“In the very advanced stages, even the modern techniques we have at our disposal are not enough to help these patients once they reach a critical threshold,” Gold said at a news conference.Salia, 44, was diagnosed with the virus Nov. 6. By the time he arrived at the Omaha hospital on Saturday, he was in extremely critical condition with no kidney function and severe respiratory problems.He was placed on kidney dialysis and a ventilator, and was given several medications to support his organ systems, the hospital said in a statement. He was given the experimental Ebola drug ZMapp on Saturday and received a plasma transfusion from an Ebola survivor — a treatment that is believed to provide antibodies to fight the virus.