GWEN IFILL: Finally tonight: Worries, hostility and threats of violence are mounting in West Africa, as the worst Ebola outbreak on record has spread to four countries, Guinea, Liberia, Sierra Leone, and most recently Nigeria. More than 670 people have died.
Among those now infected, two American aid workers and the lead Ebola doctor in Sierra Leone. One of Liberia's top physicians died from the virus on Saturday.

Liberia's president today closed all but three of the country's land border crossings in an effort to contain the disease.

Dr. Estrella Lasry is the tropical medical adviser for Doctors Without Borders, which has workers on the ground throughout West Africa.

Dr. Lasry, thank you for joining us.

DR. ESTRELLA LASRY, Doctors Without Borders: Thank you for having me.

GWEN IFILL: How extensive and surprising is this outbreak?

DR. ESTRELLA LASRY: Well, the fact that it's already extended beyond the numbers, the record numbers of the Uganda outbreak of 2000-2001 and that it has extended to three countries makes it quite — to three countries plus the Nigeria case — makes it quite an unusual outbreak and much more extensive than what we were expecting initially, and much more difficult to manage, of course.

GWEN IFILL: Why do you think this is?

DR. ESTRELLA LASRY: Partly, it's that part of the outbreak happened in urban vs. rural settings, so it is much more difficult to contain, much more difficult to trace the contacts of the people who have been infected.

Also, it's been difficult for to us have access to patients, to areas where we think there are suspect cases. So that is also becoming more difficult to control and control the spread of the infection.

And because the borders in that area are quite permeable in terms of commercial relationships and people moving across — across from one country to the other, that's also making the outbreak spread more than what we would have expected and what we have seen in other areas.

GWEN IFILL: So how do you treat this?

DR. ESTRELLA LASRY: So the treatment is not a specific treatment for Ebola. We treat the symptoms, and we do supportive treatment and palliative treatment for the patients, so fluids, analgesics.

We try to treat them for any other concomitant disease that they might have. We now test patients for malaria, which we didn't used to do in the past, to avoid any invasive procedures. And we're treating patients more invasively than we used to do in the past, because, in the past, we were trying to prevent anything that could put a health care worker in danger.

And now we're still trying to prevent this, but we prevent this at the same time that we're trying to provide more aggressive care for a patient.

GWEN IFILL: So if you are a medical personnel, as Doctors Without Borders is, and you're going into these communities, many of whom are scared about this, how — what are the special challenges for you in tackling this disease?

DR. ESTRELLA LASRY: Well, first of all is trying to gain some kind of acceptance from the community, so that we're actually granted access to the communities where we think the disease is happening.

One of the things that we have to do is, of course, we have to isolate the people who are suspected in probable cases, and also, of course, the confirmed cases, and do contact tracing, which means following the contacts of the people who have been in contact with a suspect probable or a confirmed case in the past 21 days, and follow them up on a daily basis to see if they develop any kind of symptoms, so that if they develop any kind of symptoms, they are brought to an isolation facility and are then tested to assess whether or not they have the disease or whether it's something else.

GWEN IFILL: It seems one of the concerns also for your workers is that they are met with hostility, as well as fear in these communities where they're trying to diagnose and treat. How have you been coping with that?

DR. ESTRELLA LASRY: Well, it's one of the difficult things to cope with.

Part of the intervention, part of the response to an Ebola outbreak or hemorrhagic fever outbreak involves psychosocial support, and a part of educating the communities and reaching out to the communities to explain what the disease is. We usually use survivors, so that they can do advocacy for the disease and explain what it is to be inside an isolation ward, and what it is to come outside to prevent all of this.

So it's actually very — we keep doing what we usually do in an outbreak, but now it's been extremely challenging, because we're having difficulties in accessing the patients. And what that means is that we are also having difficulty in controlling the spread of the disease.

GWEN IFILL: Is there any way to know whether this outbreak has now peaked or whether it's continuing to build?

DR. ESTRELLA LASRY: It's difficult to know.

There were — there was a decrease in cases in the past weeks, and now the cases are starting to spike up again. So it's quite difficult to know. I mean, the outbreak is behaving differently from previous outbreaks. The fact that — again, that it's in multiple countries and in multiple settings in each of these countries is also — makes it also more challenging and also more challenging to predict how it's going to go.

GWEN IFILL: Dr. Estrella Lasry of Doctors Without Borders, thank you for your work.

DR. ESTRELLA LASRY: Thank you for having us. And thank you for your interest.