(task) Assessing the Science of Ebola Transmission - The Atlantic

GRS, USRS, Africa RSs and RI

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Ebola, transmission

http://www.theatlantic.com/health/archive/2014/10/clarity-in-ebola-transmission-science/382026/2/?utm_medium=referral&utm_source=pulsenews

Assessing the Science of Ebola Transmission

What it boils down to is not only is there no evidence that Ebola virus spreads between primates by an airborne route, there’s actually evidence it does not. If Ebola virus-infected pigs are found in an outbreak zone, which has never happened, they can easily be culled. Hatfill knows about the subsequent study, and that we have never seen airborne transmission in an outbreak; he mentions both. But he still circles back, relying on the pig study, to say that it’s irresponsible to say Ebola virus isn’t airborne. It’s a careful balance of not ignoring the inconvenient data, but emphasizing that which frightens but is far less relevant. It’s misleading without lying, and it leaves the reader, at best, unsure of what to believe.

In reality, there’s nothing equivocal about the data. No biologist would stand before you and absolutely discount the possibility of nearly anything, but based on the excellent experimental data we actually have, we can conclude that Ebola virus simply isn’t transmitted through the air between primates.

The breakdowns in infection control in Dallas have also been in the news, with a focus on the inadequacy of the CDC’s original guidelines on the use of Personal Protective Equipment when treating Ebola patients. Hatfill offered the opinion that the problem here is that “We've taken a BSL-4 disease, and we're treating it in BSL-3 conditions.” BSL-4 though, means positive pressure suits, like those seen in the movies Outbreak and Contagion. In reality, the gold standard for clinical Ebola PPE, recommended by Doctors Without Borders and now the CDC, is something less than that. This entails full skin coverage with an impermeable gown or suit, use of a respirator to protect the worker during procedures like intubation, double gloves, and show covers. This all sounds a lot like what we wear to work with SARS or MERS, two viruses that require BSL-3 containment and procedures.
The specialized facilities we have to treat diseases like Ebola do reflect this. None of the hospitals that have safely treated Ebola patients, Emory, University of Nebraska, the NIH, or Bellevue have BSL-4 medical suites. What they have are contained-isolation rooms and the rigorous and careful use of BSL-3-like PPE by highly trained staff. The BSL-4 medical suite at USAMRIID wasn’t closed for budgetary reasons, it was closed because the NIH isolation facility used to treat Nina Pham is fully sufficient for treating any USAMRIID researchers exposed to Ebola or other dangerous viruses during lab accidents. Ebola is a scary virus, but making it ten feet tall won’t help us save lives. To safely and successfully treat patients we need excellent training and effective PPE that enables nurses and doctors to do their jobs. Not only is medical treatment in a restrictive BSL-4 suit that much more difficult and cumbersome, the recent experience in non-BSL-4 medical facilities shows us that it’s unnecessary for the safe clinical management of infected people.

Another area of concern, mentioned by Steven Hatfill, Darrell Issa, and many riders of the New York City subway, is the possibility of contracting the virus by brushing up against the skin of an infected person. Hatfill talks about Ebola being shed from the skin, and while it’s true that Ebola virus RNA can be found on the skin of infected people, Hatfill’s explanation of how this occurs and the significance of it is scientifically unsound. He goes into a quasi-technical, but inaccurate, explanation of Langerhans cells and their ability to shed virus through the skin. Langerhans cells are skin-resident dendritic cells, a type of cell that ingests a virus or bacteria and goes rapidly to the lymph node, where it activates T-cells specific for that pathogen. Ebola virus infects Langerhans cells and other so-called antigen presenting cells like macrophages, and its trip to the lymph nodes inside them is one of the ways it facilitates its spread throughout the body.

Langerhans cells can’t shed virus onto the outside of your skin, though. The outer layer of skin consists of dead keratinocytes, skin epithelial cells; Langerhans cells are deeper in the tissue. That outer skin cells are dead is a great defense against viruses, because viruses require a living cell to replicate. A virus that lands on unbroken skin is inert; it can’t enter a dead cell and will quickly be destroyed by enzymes on the skin. Likewise, it can’t enter dead cells from inside the tissue and emerge from those cells onto the surface of the skin. Langerhans cells exist so that if a virus gets past that dead outer layer through a break in the skin, it will be quickly recognized and used to activate the immune system. Infected Langerhans cells can certainly produce virus that infects other cells and tissues. They can’t shed virus onto the surface of your skin. Sweat may be able to do that, but very late in infection. Even then, it’s not clear whether virus found on the skin is actually infectious, or dead particles still full of the viral RNA.

Hatfill is right in at least one area, that we need to fight these outbreaks at their source. Ideally we would stamp them out quickly, like the Democratic Republic of the Congo and Nigeria seem to have done with their Ebola outbreaks in the last few months. Sometimes, like in West Africa, that won’t work, or won’t happen. Should we then give up? Whether there’s one case of Ebola in Africa or 10,000, the only way to stop it here is to stop it there. Yet Hatfill undermines his own insistence that we do this by suggesting that the 4,000 troops we are sending to fight this epidemic are at risk of contracting Ebola from bats themselves.

Evidence that fruit bats harbor Ebola virus has mounted in recent years, with the most prominent study finding evidence of infection in three species of bat. The percentage of bats with evidence of infection varied considerably, making it unclear exactly how prevalent the virus is in the bats. It’s certainly not likely that a given bat carries the Ebola virus, and it’s unlikely many American soldiers will be coming into close contact with any bats at all. More importantly, Hatfill’s comment about bats infecting American soldiers through defecation is at odds with everything we know about how Ebola virus cross-species transmission occurs. It’s been hypothesized that bats might drop infected fruit to the forest floor, infecting humans or other animals that subsequently handle or eat it. Overwhelmingly, though, Ebola outbreaks have been linked to the handling of wild-game carcasses, such as bat, gorilla, duiker, or chimpanzee. The current epidemic began with a 2-year-old child, likely infected by touching an infected bat carcass.

American soldiers are unlikely to engage in any of these high-risk behaviors, nor will they be in areas of high bat density. Transmission through bat bodily fluids can’t be entirely ruled out, but why such a rare, theoretical event should threaten 4,000 soldiers to the point that we should reconsider the deployment is a question with an elusive answer.

Ultimately this Ebola outbreak, as even Hatfill acknowledges, will end—though with many more dead than we would have ever imagined. In the aftermath we will learn more about Ebola virus than we know now and use this to ready ourselves for its next appearance. We know that our current knowledge isn’t perfect, but where the data is strong, as it is in the areas I’ve discussed, we can’t ignore it or make it mean something other than what it does. It leaves the public rightfully unsure as to who to trust, and makes the job of those called to fight this epidemic and keep us safe at home that much more difficult.