US researchers said Monday they have identified "weak spots" on the surface of the deadly Ebola virus that are targeted by the antibodies in ZMapp, the experimental drug cocktail administered to several patients during the recent Ebola outbreak.

The study, led by researchers at the Scripps Research Institute and published by the US journal Proceedings of the National Academy of Sciences, provided a 3-D picture of how the ZMapp antibodies bind to the virus.

"The structural images of Ebola virus are like enemy reconnaissance," said coauthor Erica Ollmann Saphire, a Scripps structural biologist. "They tell us exactly where to target antibodies or drugs."

Using an imaging technique called electron microscopy, the new study found that two of the ZMapp antibodies bind near the base of virus, appearing to prevent the virus from entering cells.

A third antibody binds near the top of the virus, possibly acting as a beacon to call the body's immune system to the site of infection, the researchers said.

"Now that we know how ZMapp targets Ebola, we can compare all newly discovered anti-Ebola antibodies as we try to formulate an even better immunotherapeutic cocktail," said coauthor Andrew Ward, another structural biologist at Scripps.

ZMapp, developed by San Diego-based Mapp Biopharmaceutical, was used in August to treat several patients diagnosed positive with Ebola virus infection.

According to Scripps, five of the seven patients who received ZMapp survived and the treatment is expected to go into clinical trials in early 2015.