To help clarify some of the science about the current Ebola virus outbreak, the American Society for Microbiology has gathered a team of experts to answer frequently answered questions. If you have a question you would like to see answered here, please send it to firstname.lastname@example.org. For additional information about the Ebola virus outbreak from ASM and other organizations, please visit our Ebola Resources page.
How can a person get infected with Ebola virus?
Based on the study of previous outbreaks of Ebolaviruses, it is known that the virus spreads from person to person by direct contact with blood, body fluids, or skin of infected individuals. In the laboratory, animals may be infected with Ebola airborne virus particles, but this mode of transmission has never been observed among humans (http://www.cdc.gov/vhf/ebola/transmission/human-transmission.html).
Recently an epidemiologist suggested that Ebola virus could mutate and become transmitted by the airborne route. When it comes to viruses, it is always difficult to predict what they can or cannot become airborne. It is instructive, however, to see what viruses have done in the past, and use that information to guide our thinking. Therefore we can ask: has any human virus ever changed its mode of transmission? The answer is no. We have been studying viruses for over 100 years, and we’ve never seen a human virus change the way it is transmitted. There is no reason to believe that Ebola virus is any different from any of the viruses that infect humans and have not changed the way that they are spread (http://www.virology.ws/2014/09/18/what-we-are-not-afraid-to-say-about-ebola-virus/)
Ebola virus infection can also be transmitted if an infected person coughs or vomits at close range. In this case large droplets landing on the mucous membranes can initiate infection. Although these droplets are traveling through the air, this mode of transmission is considered a form of contact transmission, not airborne transmission (http://www.virology.ws/2014/09/27/transmission-of-ebola-virus/)
But I heard that Ebola virus can be transmitted in the air from pigs to monkeys. Doesn’t that mean the virus could be transmitted this way among humans?
In a porcine transmission experiment (http://www.ncbi.nlm.nih.gov/pubmed/23155478), animals were infected by dripping virus into the nose, eyes and mouth, and placed in a room with cynomolgous macaques. The pigs were allowed to roam the floor, while the macaques were housed in cages. All of the macaques became infected. However it is not known how the virus was transmitted from pigs to macaques, because the design of the experiment did not make it possible to distinguish whether the transmission was by aerosol, small or large droplets in the air, or droplets created during floor cleaning which landed inside the cages. The authors also say that transmission between macaques in similar housing conditions was never observed.
How stable are Ebola virus particles? Can I get infected by touching a contaminated object?
Ebola virus infectivity is quite stable at room temperature (20°C), especially in the dark, where it can remain for several days. Infectivity is largely inactivated in 30 minutes at 60°C. Infectivity is greatly reduced or destroyed by high doses of ultraviolet light and gamma irradiation, lipid solvents, beta-propiolactone, the photo-inducing alkylating probe 1,5-iodonaphthylazide, guanidiuium isothiocynates, and commercial hypochlorite and phenolic disinfectants (Feldman et al, 2013 32:923, Fields Virology; Lytle & Sagripanti J Virol 79:14244 2014; Sagripanti et al Arch Virol 155:2035, 2010; Sagripanti & Lytle Arch Virol 156:489, 2011; Piercy et al, J Appl Micro 109:1531, 2010).
If an infected person contaminates an environmental surface with body fluids, it might be possible to acquire infection by touching these surfaces and transferring virus to mucous membranes. This type of transmission is more likely to occur in health care settings where ill patients are shedding large amounts of virus particles. However, transmission of the virus from inanimate objects has rarely been observed in previous outbreaks (http://www.cdc.gov/vhf/ebola/transmission/human-transmission.html, http://www.ncbi.nlm.nih.gov/pubmed/17940942)
I’ve heard that Ebola virus is mutating. What does this mean?
Mutations are a way of life for an RNA virus and mutations come and go every time a genome replicates – it is likely that every single genome copy of an RNA virus has a mutation (http://www.virology.ws/2009/05/10/the-error-prone-ways-of-rna-synthesis/). The key is to determine whether these changes affect any of the biological properties of the virus, such as transmission, stability, or virulence.
A recent study determined the genome sequences of 99 Ebola virus isolates from 78 patients in the Sierra Leone outbreak (http://www.ncbi.nlm.nih.gov/pubmed/25214632). This work shows that the viruses are very similar to isolates from recent outbreaks in Central Africa, and a small number of genetic changes were observed. Whether these changes have any effect on the properties of the virus is not known.
Why has the quarantine period for someone infected with Ebola virus set at 21 days?
The quarantine period for an infectious disease is the time that a potentially infected individual should be kept away from others to prevent transmission of infection (http://www.virology.ws/2014/10/16/the-quarantine-period-for-ebola-virus/). The length of the quarantine period is based on the incubation period, the time before symptoms of an infection appear. For Ebola virus, the incubation period is 2-21 days after infection. During this time it is believed that individuals infected with the virus are not contagious, but they do have low levels of virus in the blood (http://www.ncbi.nlm.nih.gov/pubmed/15047846). For Ebola virus, patients are not thought to be contagious during the incubation period. They are only thought to be contagious once they show signs of infection (fever, etc).
The length of the quarantine period of Ebola virus infection is based on the incubation period observed during previous outbreaks. The incubation period for the first 9 months of the current West African outbreak is similar to those determined from previous outbreaks (http://www.virology.ws/2014/10/16/the-quarantine-period-for-ebola-virus/).
Are there any treatments for Ebola virus infection?
Chances of survival significantly improve when Ebola virus infection is detected early, and patients are given intravenous fluids, maintaining balanced electrolytes, oxygen status, and blood pressure (http://www.cdc.gov/vhf/ebola/treatment/index.html)
Several Ebola virus vaccines and antiviral drugs are being tested for safety in humans, but none have yet been approved by the Food and Drug Administration.
Vincent Racaniello, Columbia University
Lynn Enquist, Princeton University
Ron Atlas, University of Louisville
John Connor, Boston University School of Medicine
Andrea Marzi, National Institutes of Health
Elke Muhlberger, Boston University School of Medicine
Sean Whelan, Harvard Medical School
Should scientific journals publish gain-of-function (GOF) studies, especially those involving pathogens with pandemic potential? While journal editors at the American Society for Microbiology have done so after careful consideration, some scientists expressed concern over that decision. A series of letters to and responses from the editors, and a new editorial on the situation, appear in this week's mBio.
At issue is an April report in the ASM's Journal of Virology of sequence changes in highly pathogenic avian influenza virus A H7N1 associated with airborne transmission in mammals. Authors found that serial inoculation of A/H7N1 into ferrets led to mutations allowing airborne transmission of the virus to other ferrets housed in the same area.
The JV study was accompanied by two editorials from ASM, one detailing a rigorous, multistep evaluation of the paper for the possibility of dual use research of concern (DURC) --- research that could be misapplied to pose a significant threat to public health and safety --- before editors decided it made important contributions toward understanding of influenza virus transmission. A second editorial called for a federal board to assess DURC. DURC evaluations are now conducted by journal editors with occasional consultation from individuals serving on a national science advisory board for biosecurity.
Even so, Simon Wain-Hobson of the Institut Pasteur in Paris wrote that he disagreed with both the decision to publish the paper and the editorial explaining its publication, "for the underlying science is not as strong as it appears." H7N1 is not a threat to humans, his letter said, and because flu lineages come and go, the scientists should have used a currently circulating H7 virus. The number of ferrets used also was "too small to yield statistically robust results," he said.
"We are left with a highly pathogenic H7N1 virus that is transmissible via the airborne route," he said. "This lab-engineered H7N1 strain would constitute a novel danger for humans if it ever escaped."
Editors defended their position in a reply, noting that reviewers "concurred that the results were novel, significant and scientifically sound," that they carefully debated whether the study represents DURC, and that although they could not spell out a concrete risk-benefit analysis they felt the potential risks of the study were low. "The risk of some type of laboratory accident is not zero, but we think that appropriate steps were taken to diminish risk to a minimum degree."
Others responded to a September editorial from mBio editors discussing the epistemological perspective on the value of GOF studies. There, Editor-in-chief Arturo Casadevall and colleagues wrote that GOF experiments, in generating microbes with new functions and new phenotypes, inform experimenters on the possibility of additional outcomes and provide insight into how microbes acquire new functions. With no alternatives to GOF experiments for seeking answers to certain biological questions, "we all think that some risks are reasonable for the gain that comes from scientific progress."
Nicholas Evans of the University of Pennsylvania, and Marc Lipsitch of the Harvard School of Public Health, took issue with the original report and the September editorial. "Arguing that bodies of knowledge are valuable for their own sake says nothing about how we ought to weigh this value against other considerations," Evans wrote. "Even less clear is how we account for the marginal increases in value—of knowledge for its own sake—that we receive from GOF/PPP experiments." Lipsitch argued that in a world of scarce scientific resources, it's essential to judge the epistemic value of GOF/PPP experiments versus other approaches with safer viral genetic backgrounds: "Can a risk to the life and health of large numbers of people ever be balanced by the benefit of pure scientific knowledge?"
In an editorial, mBio editors note that debating the risks and benefits of such experiments will continue. Proponents of GOF emphasize the potential benefits of research and link the work to benefits like the development of better vaccines, improved public health surveillance tools and new basic science knowledge, they said, while opponents cite the risk of these experiments, including nefarious use of the information to lab accidents unleashing new pandemics. Only time will reveal the answer, they said, but meanwhile individuals should not over-rely on apocalyptic scenarios when arguing their position. History has shown that humans are "notoriously bad" at assessing risks and benefits, they noted, and "rhetoric never gave us a single medical advance."