Liz Szabo

USA TODAY

The unusual nature of the Ebola virus can make it a grave threat to those who have the most intimate contact with patients' bodies — health care workers in intensive care units, family caregivers and mortuary workers — even though the disease doesn't spread readily through casual contact in the general population.

Nurses and others caring for Ebola patients at the end of their lives are at high risk of infection, because the virus replicates wildly as the disease becomes more advanced, says Peter Hotez, dean of the National School of Tropical Medicine in Houston and a professor at the Baylor College of Medicine.

That puts nurses such as 26-year-old Nina Pham, who cared for Ebola patient Thomas Eric Duncan at Texas Health Presbyterian Hospital in Dallas, at high risk of infection. Pham contracted the virus and is now being treated for Ebola. A Spanish nurse in Madrid also tested positive for the virus after treating a priest with Ebola who died.

"When you are first infected, you are actually not contagious," because levels of the virus in blood are too low to spread the infection, Hotez says. "Even in the early days of an infection, the virus is not easily transmitted from person to person because it requires direct contact. Ebola is not associated with respiratory transmission. So you don't get Ebola just from sitting in the same room with someone."

Even doctors and nurses who treat Ebola patients in an emergency room would be at a lower risk, because patients at this early stage are not shedding huge amounts of virus. While the Ebola virus can live on surfaces, those surfaces would have to be covered in blood. The virus doesn't usually spread from coughing or touching objects in public places, such as doorknobs.

The risk goes up exponentially as the virus gains ground in the body, however, because Ebola has a "unique ability" not seen with other viruses, Hotez says.

Unlike other dangerous viruses, such as SARS (Severe Acute Respiratory Syndrome), Ebola shuts down the body's production of a virus-fighting substance called interferon, "the body's first defense against viruses," Hotez says. The substance jumps into action to fight viruses even before antibodies begin to shut them down.

Ebola begins to block interferon production within four to five days after infection.

Without those chemical policemen to stop it, Ebola "has the ability to just replicate and replicate and replicate," Hotez says. "So by the time you are in the end stages of your illness, your liver and your spleen and your kidneys are just teeming with billions of viral particles."

Because the virus attacks the liver, it interferes with the liver's ability to make clotting factors that help stop bleeding, Hotez sais. Patients infected with Ebola can bleed profusely, both internally and externally, and vomit blood.

So Ebola patients treated in intensive care units, such as Duncan, are far more infectious than those at earlier stages of illness. "When you are working with Ebola in an ICU, there can be no margin of error," he says.

Because even a small amount of blood is teeming with the Ebola virus, the disease can spread very easily at this point to caregivers, Hotez says.

Few if any other patients had received the sort of intensive intervention — such as help from a breathing machine and kidney dialysis — given to Duncan at the end of his life, Hotez says. Doctors don't know whether those interventions, which involve inserting tubes into Duncan's airway and cleaning his blood with a machine, increase the risk of spreading Ebola. Hospitals in West Africa don't have the capacity to routinely provide that kind of care to people with Ebola.

Health officials may need to revise how they treat patients with Ebola, Hotez says. While every hospital should be able to screen and isolate Ebola patients who go to an emergency room, every hospital may not be able to provide the sort of meticulous care required in an ICU.

For that reason, Hotez says, it's not yet possible for doctors to know how Pham was infected — whether she or a co-worker committed a "breach of protocol," as the Centers for Disease Control and Prevention initially suggested — or whether something about the nature of providing intensive care allowed her to contract the virus.

In West Africa, each Ebola patient is spreading the disease to an average of one to two people, according to the World Health Organization. In many cases, those people are family members trying to take care of them or health care workers in hospitals who often lack basic ways to protect themselves, such as plastic gloves.

In hard-hit countries of West Africa, many Ebola patients are being cared for at home. In Liberia, there are hospital beds for only one in five of those with Ebola, according to WHO. Many homes in poverty-stricken areas of Guinea, Sierra Leone and Liberia have no running water or modern toilets.



According to WHO, 8,914 Ebola cases, including 4,447 deaths, have been reported, although WHO says those figures sharply underestimate the total effect of the disease. Many health workers are too overwhelmed to take time to file case reports.

Among the afflicted have been 416 health workers, according to WHO. About half have died.

Grave diggers and those handling the bodies of Ebola victims are at especially high risk, Hotez says. "You're basically burying a bag of virus."