How Ebola kills -- and what it takes to stop it

Health workers carry the coffin of a person suspected of having died from Ebola in the Democratic Republic on Congo. Glody Murhabazi/AFP/via Getty Images hide caption

After jumping to a new person through the bridge of bodily fluids, it goes straight for key immune cells. In typical infections, these immune cells help mount a targeted response to the virus with the goal of clearing it out. But the virus that causes Ebola somehow disables this response.

"That adaptive immune response that we hope for in terms of getting full clearance is often very strongly delayed," says John Connor , a virologist at Boston University.

That gives the virus a head start in rapidly spreading throughout the body . It goes first to the lymph nodes, then to the spleen, liver and kidneys, replicating and damaging these tissues as it goes.

"The cleaning and garbage disposal units of the body are backing up, and that backs up into the blood system, [and] that has a lot of negative consequences," says Connor.

By this point, the immune system still isn't creating antibodies that flag the invader for clearance by other cells. But the immune system has sensed that something is wrong, and spurs a more brute force reaction. In many Ebola patients, this response can go overboard, causing a frenzy of immunological activity known as a cytokine storm – named for the proteins that stoke an inflammatory response.

"That can lead to a lot of essentially collateral damage rather than focused removal of virus from infected cells," says Connor, contributing to multiple organ failure. Later symptoms include vomiting and diarrhea, which can cause patients to lose over 2.5 gallons of fluids a day. In some cases, blood vessels become so damaged they leak. Losing all this fluid is often what kills roughly half of patients who get infected.

But this high mortality rate isn't inevitable, even in the absence of approved treatments targeting the virus.