CDC surges Ebola response, sends 50 more personnel
HIC Q&A with Ebola expert
The ongoing record outbreak of Ebola virus in West Africa is killing six out of every ten people infected. And that, grimly enough, is the good news.
"The mortality rate in some outbreaks can be as high as 90%, but in this outbreak it is currently around 60%, indicating that some of our early treatment efforts may be having an impact," said Stephan Monroe, MD, deputy director of the National Center for Emerging Zoonotic and Infectious Diseases at the Centers for Disease Control and Prevention.
According to the World Health Organization, since the first report of Ebola infection in March there have been approximately 1323 confirmed and suspected cases reported, with 729 deaths in Guinea, Liberia and Sierra Leone as of July 31st.
The CDC recently surged its response to the outbreak, sending 50 additional disease control specialists into the three countries in an effort to stop the epidemic. However, epidemiologists face not only the problems of low functioning health care systems, but hostility and violence by some who think the medical respondents may be part of the Ebola problem.
The first priority is to find the infected patients, isolate them and then trace down their contacts, CDC director Tom Frieden, MD, MPH, said at a press conference. "Finding every single contact of each Ebola patient and following each of the contacts for 21 days, each day checking to see if they have fever," he said. "If they develop fever then they should go to an area where they can be kept apart from other people, tested for Ebola and, if positive, isolated and that whole cycle of identifying their contacts starts again."
Q&A with leading Ebola researcher
As the record outbreak continues we sought further information and insight from a leading Ebola expert, Thomas Geisbert, PhD, Ebola researcher and professor of microbiology and immunology at the University of Texas Medical Branch at Galveston. Geisbert and his team have received a $26 million grant from the National Institutes of Health to develop counter measures against Ebola and Marburg virus. The ongoing research includes both treatments and vaccine development. He fielded the following questions from Hospital Infection Control & Prevention.
HIC. What is it about Ebola biologically that makes it so lethal — 60% to 90% mortality rate — once infection sets in?
Geisbert: "The disease is almost identical in monkeys as man, and through the studies we’ve done in non-human primates, we know that the first cell types that are infected are primary immune cells. So it infects monocytes, macrophages, and dendritic cells. Those are really first-line defense cells in developing an effective immune response to a foreign antigen. And so if you knock out the first line of defense then it’s easier for the virus to replicate and multiply. If you think about it, it’s not really an effective pathogen because an effective pathogen doesn’t kill its host. It has a lot of similarities with septic shock. So there are coagulation disorders, disseminated intravascular coagulation, and multiple organ failures. Typically it starts with flu-like symptoms, fever, vomiting, and diarrhea. Then it goes into a systemic infection and the spleen and liver are big targets. The body just kind of shuts down. It is an acute infection with a very rapid disease course."
HIC: This outbreak has many troubling aspects, including the ability to sustain itself and spread and cause infections in health care workers using full barrier precautions. Is there anything different about this particular strain of Ebola?
Geisbert: "There are five different species of Ebola. Three of them have been associated with human outbreaks and significant mortality in humans. Bundibugyo is one of those species, Sudan is one and Zaire is one. This outbreak is caused by the Zaire species, which is associated with the highest case fatality rates. Strain’ is kind of taking it down defining it even further. It does appear to be a slightly different strain of the Zaire species than some of the outbreaks. I don’t think at this point there’s any evidence that suggests that there’s something different about this strain that’s causing it to be more transmissible. However, I don’t think that we really know for sure. I think the probability is low but I don’t think we are able to rule it out yet. An example would be a small genetic change in the virus that can cause it to be more or less pathogenic. Historically these Ebola outbreaks have really not been transmitted through the air like influenza or something like SARS. There’s really been no evidence that Ebola is transmitted that way and we don’t really see any evidence from this outbreak. I think the only thing that we don’t know that could potentially make it more transmissible — person-to- person through close contact — would be if there’s something about this particular strain that makes it shed higher levels [of virus]. We know that Ebola from this species and all the Ebola can be found in all kinds of body fluids. Obviously blood, but also feces, urine, sweat — things like that. So it’s theoretically possible that for some unknown reason this strain maybe is found at higher levels or higher concentrations in body fluids. So for example, if you had a drop of some kind of body fluid with this strain maybe you had ten thousand particles in there and with another strain maybe you have 10. Your absolute exposure would be higher, but this is all hypothetical. We don’t know that yet.
HIC: Another deep concern of course, is that health care workers have been infected despite wearing elaborate barrier precautions to treat patients. What do you think is happening there?
Geisbert: "I think that’s the $64,000 question. We really don’t know. These are heroes who go into these outbreak situations and put their lives on the line working with something that’s this deadly. So, you certainly don’t want to criticize people that take that risk. At the same time, I mean this outbreak is so large compared to any past Ebola outbreak that the public health folks that really have the expertise in responding to these outbreaks like WHO and the CDC are stretched to the limit. I wish I had an answer for you.
HIC: Have any clear exposure events like a blood splash or a needlestick been reported in the health care worker infections?
Geisbert: "I’ve heard rumors. I don’t have first or second hand information — I have third hand information [that there] may have been a needlestick in one. That’s understandable. No matter how well you’re trained or how good your skill set is, stuff happens. That kind of thing you can understand."
HIC: Is it possible some transmission is occurring from contaminated environmental surfaces and fomites? Can Ebola spread effectively this way and how long can it survive in the environment?
Geisbert: "There’s data that suggests that depending on different environmental conditions it can survive for a fair amount of time. There’s some anecdotal information that during the 1995 outbreak of Ebola in Zaire that someone from the CDC found a syringe in a desk drawer that had dried blood in it. I think this was like 30 something days after the syringe was in there they were still able to isolate virus. But that’s also telling you there’s some kind of a protected serum in blood as it dries down -- kind of almost lyophilized in protecting it. The Russian literature is hard to follow but if you look at that there’s some information that says that Ebola virus in cell cultures in culture fluid — their data says it took 53 days to completely have 100% loss where they were not able to detect the virus. So I think a lot of it depends on the environmental conditions. Is the virus subjected to sunlight? UV and heat can inactivate it. Historically if you look at what’s happened [in outbreaks] there really isn’t any evidence that suggests that it really hangs around for a long time and poses some kind of a problem on a surface.
HIC: The length of this outbreak runs counter to the usual perception of Ebola appearing in explosive short-term outbreaks? What do think are the factors behind this sustained transmission?
Geisbert: I think it’s because of the wide area that it’s scattered across. Historically, if you look at what’s happened in central Africa where these outbreaks have tended to occur sporadically in the Congo or Sudan, there’s identification of a small episode or outbreak and WHO, humanitarian aid organizations like MSF, and the CDC jump in and quarantine the patients. They do a great job of getting in there, talking to people, finding out who is infected and quarantining a village or small area. And it just burns out. It’s sad, but I mean you’re talking about viruses with really high mortality rates. If you stop the chain of transmission you kill the outbreak. What’s been so difficult with what’s going on now in West Africa is it’s sporadic, random, in the way it’s spread out over these different countries. It’s popping up in different places across these three different countries and it’s a huge geographic area. That makes it really challenging to try to contain."
HIC: There’s got to be an epi link there somewhere.
Geisbert: "I couldn’t agree with you more, I’ve told a lot of reporters that I don’t think we know why and how. There’s probably multiple factors, multiple variables. Transportation is easier now, infrastructure better and in Africa it’s easier to go from point to point than maybe it was 20 or 30 years ago.
Their cultural practices are different — the whole burial procedure and touching of the body and things like that. Somebody goes to a funeral or whatever, comes in contact with the virus and then goes a couple hundred miles somewhere else carrying the virus. That could be part of it. I think there is an epi component. We know that fruit bats are a major reservoir, but we don’t know if they are the only reservoir. Did something ecological happen to cause the bats to shed more virus or have more people been in contact with bats than they have before? I think these are all plausible explanations — and it may be not one but a combination, a perfect storm."