...I turned to Dr. Elke Muhlberger, an Ebola expert long intimate with the virus — through more than 20 years of Ebola research that included two pregnancies....
Dr. Muhlberger is an associate professor of micriobiology at Boston University and director of the Biomolecule Production Core at the National Emerging Infectious Diseases Laboratories (widely referred to as the NEIDL, pronounced “needle”) at Boston University....
Could you please lay out a brief primer on the biology of how Ebola is transmitted?
We know from previous outbreaks, and also from the current outbreak, that Ebola is transmitted by having very close contact to infected patients. So we know that it is transmitted by bodily fluids, which include blood, first of all — because the amount of virus in the blood is very, very high, especially at late stages of infection — but it’s also spread by vomit, by sputum, by feces, by urine and by other bodily fluids.
The reason for that is that at late stages of infection, the Ebola virus affects almost all our organs — it causes a systemic infection. One main organ targeted by Ebola virus is the liver, and that could be one of the reasons that we see these very high concentrations of viral particles in the blood. But I would like to emphasize that that occurs late in infection.
Early infection is the other way around. The primary targets — the first cells that come in contact with Ebola virus and get infected — are cells that are part of our immune system. And these cells most likely spread the virus throughout our body. But there are not so many cells infected at the very beginning of the infection, which might be the reason why Ebola virus patients do not spread virus at the very beginning of infection. And that’s why it’s safe to have contact with these patients, because the viral titers in their blood are so low that we cannot even detect them with methods like PCR, which is one of the methods we use to diagnose Ebola virus.
Is a virus only contagious when it reaches a certain level of “titer” or load?
That’s very difficult to answer because we know that for some viral infections most likely one viral particle is enough to infect somebody. So then the answer would be no. But we also know that some viruses are not really good spreaders, so you do need a certain amount of viruses to transmit this virus to another person.
Is that true for Ebola?
For Ebola virus, it seems to be true, because from experience, we know that this virus is not transmitted early in infection. If the viral titers are very low, if you’re not able to detect free viruses in the blood, then it seems Ebola virus is not transmitted to other people. Which is very good because, theoretically, that makes it really easy to control Ebola virus infection. And the reason why we have such a disaster right now, with almost 10,000 infected in West Africa and more than 4,000 already dead, is not so much the transmissibility of Ebola but rather the lack of infrastructure in these countries....
...Ebola virus does not begin an infection by infecting our upper respiratory tract. The route of infection starts with little lesions in our skin, and then the virus gets in our skin, and then in our blood system, and then in these immune cells I mentioned before, which are the primary target cells. It’s also able to get into our eyes and mucosal membranes, but it does not infect the cells which we need to get infected to have an infection be airborne. Late in the infection, when the Ebola virus patients have very high viral loads, they are really really ill, way too ill to get on a train and sit there.
So you’re saying that when they’re so ill that it could be in the respiratory system, they’re super-ill, not able to go anywhere?
Exactly. The cells in the lung can be infected by Ebola virus but really late in the infection. That’s very important. As far as we know, the infection starts with the immune cells — for those who know a little more about the immune system, it’s dendritic cells and macrophages. Then it goes to lymph nodes. Then very quickly to the liver, and there it goes crazy. The liver is very crucial in Ebola virus infections because it is so heavily affected. Ebola virus also spreads to the spleen, to other organs, and then later in infection it tends to infect the cells that coat the blood vessels, and of course we have these cells in the lung as well....