What We Learned
By Quinn Eastman
Photo by Jack Kearse
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What kinds of research data will be available from the patients with Ebola virus?
Our primary focus was treatment and helping the patients recover. However, now that that goal has been reached with the first two patients, both have expressed interest in improving outcomes for others.
With their permission, we would like to look at their Ebola-specific immune responses. Obtaining this information may support the development of better therapeutics, diagnostics, and hopefully someday, vaccines.
In particular, we want to examine their memory B cells and plasma cells. We would want to know more about the antibodies those cells produce. How much neutralizing antibody is there? What affinity do the antibodies have for the virus? Is there any antibody-dependent cytotoxicity?
This is similar to the research the Emory Vaccine Center was able to perform during the 2009 H1N1 flu outbreak. We learned that some people developed antibodies that are remarkably cross-reactive to different flu strains.
Also, there is little data available on Ebola-specific T cells, even though T cells are thought to be critical for antiviral responses. It has been possible to do some of this research on Ebola survivors in Africa, but to really probe the parts of the immune system responsible, we need fresh cells.
To what extent was Emory involved in providing experimental therapies, such as ZMapp antibodies?
We were not involved in the initial decision to seek out and give ZMapp. However, we obtained enough for the first two patients to be able to finish the course they had started. Beyond that, we simply don't have enough information to judge whether it was effective.
To be honest, I think supportive care, including the ability to provide fluids and nutrition and correct electrolyte problems, had the largest impact on these patients' improvement. We observed that both patients experienced severe diarrhea and vomiting, which led to electrolyte abnormalities, especially low potassium levels. One of the more dangerous consequences of electrolyte imbalances can be irregular heart rhythms, even cardiac arrest.
But replacing their electrolytes wasn't as simple as drinking Gatorade or eating bananas. Careful monitoring and both oral and intravenous electrolyte replacement were necessary.
We also observed significant leakage of fluid into their tissues and low levels of liver-supplied proteins in the blood, probably because of viral damage to the liver. This might lead to problems with blood clotting, for example. In a large well-equipped hospital, it is possible to give separated blood products such as platelets and plasma, which is not possible in smaller rural hospitals. Still, you can get some clot-promoting vitamin K from good nutrition.
What kinds of lab tests were available within the isolation unit?
It was planned to have a small lab inside the unit. But we quickly realized that it would become too crowded, so we and our pathology colleagues established a lab in an office right outside. That made it possible for us to have access to several very useful instruments:
- CBC (complete blood count) measurements
- Instrument that measures blood gases like oxygen, carbon dioxide, pH
- Clinical chemistry analyzer that assesses electrolyte levels and liver and kidney function
- Urinalysis test strip reader
- Bedside PT-INR blood clotting test
- BioFire film array— This gives a quick yes or no answer to the question: Is Ebola virus present? It tests for other sensitive pathogens as well. But the CDC test is still the gold standard.
Helpfully, some of the machines can take a sealed blood tube and puncture it for you, reducing the risk of spills or stray droplets. For others, the instruments needed to fit inside a biosafety cabinet with a laminar flow hood.
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Infectious disease physicians Jay Varkey, Aneesh Mehta, and Marshall Lyon talk with Kent Brantly, the first patient with Ebola to be treated in the US, on the day of his release from Emory Hospital's isolation unit.
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How did doctors decide when it was OK for the first two patients to leave, once they had recovered to the point that they were ready?
Even after our patients' symptoms resolved, they had low but detectable viral levels for several days. Before discharge, the consensus was that a patient had to have levels of Ebola virus that were below the threshold of detection of the CDC-approved test twice in a row.
In Africa and Europe, other tests for Ebola such as tests for viral proteins/antiviral antibodies have been employed, but the CDC's test (RT-PCR) for the virus is more sensitive.
How did the medical team's use of personal protective equipment evolve over time?
We followed the CDC guidelines for treating patients infected with Ebola, which included contact and droplet precautions. That means gloves, gown, eye protection, and facemask.
There is an option to scale up if conditions warrant, such as coughing up blood, vomiting or diarrhea. We decided to start at a higher level of precaution based on the condition of the patients at the time. After the patients were stable, we scaled back to standard contact and droplet precautions.
Many of the staff found that face shields tended to fog up, and the PAPRs (powered air purifying respirators) were more tolerable when they had to work in the unit for hours at a time. It's actually very comfortable. It feels sort of like wearing a bicycle helmet, but with a fan on top blowing in filtered air.
One important thing is that we established procedures to make sure that every time someone was putting on or removing their protective equipment, another team member observed them.
Do people who survive Ebola infection develop protective antibodies?
Generally, we think people who recover from infection develop immunity to the virus. It's important to keep in mind that there are five different strains of Ebola, and if there is protection, it's likely to be only for that strain.
A previous study of an outbreak of Ebola in Gabon showed that people who survived tended to have strong antibody responses and those who died did not, for example. However, another study published last year showed that only about half of the survivors of an outbreak in Uganda have detectable antibodies against viral proteins.
So a lot of survivors may have antibodies, but how protective their antibodies are, that is unknown. T cells may account for some immune protection too. The antibodies and the cells that make them may fade from the blood after a few years go by. That's one of the reasons why we want to bring our patients back—to track their antibodies and immune responses over time.
Could a survivor carry the Ebola virus in the body for several years, as with HIV?
Ebola is not like HIV or other retroviruses. There is no latency. There is no integration. Once you've cleared it, it's gone.
Retroviruses make a DNA copy of their RNA genome, and can insert that DNA into the chromosomal DNA in host cells. Ebola virus has an RNA genome but does not have the enzymes retroviruses have (reverse transcriptase and integrase) that allow them to integrate into host cells.
There is some evidence that the virus can persist in semen for weeks or months, even after it's gone from the blood. A possible explanation is that the prostate is an immune-privileged site, like the eye. But there is no information to say that the virus replicates in the prostate, and there is no epidemiological data that virus present in semen can lead to an infection.
Could Ebola evolve to become even more contagious, becoming more durable in the external environment, for example?
Ebola is a simple envelope virus. Like many other viruses, it grows by budding out of the host cell's membrane and taking some of the membrane with it. So you can make the envelope disintegrate with detergent or alcohol.
Compare this to norovirus, a leading cause of gastrointestinal illnesses, which is notorious for being hard to get rid of. Norovirus is more stable because it's a “non-enveloped” virus. You need stronger disinfectants and more thorough procedures for viruses in this category.
It would be very difficult to transform Ebola, via mutation, into a virus that was significantly more stable in the external environment.
Why is Ebola so dangerous then?
Once infection is achieved, the virus rapidly replicates and overwhelms the body's defenses. Symptoms such as vomiting or diarrhea lead to shedding of virus, so that it is easy to transmit to caregivers or family members when hygienic practices do not prevent it. As we saw, the fluid loss can lead to irregular heart rhythms.
On a cellular level, the virus attacks the linings of blood vessels, which can lead to hemorrhage. The virus infects immune cells such as dendritic cells and macrophages, leading to systemic inflammation, sometimes called a “cytokine storm.” At the same time, it shuts down the interferon pathway, which is important for antiviral responses. The inflammation can bring about a condition resembling septic shock, involving a dangerous loss of blood pressure.
One paper that looked at the evolution of Ebola and its relative, Marburg virus, calculated that they mutate at a rate that is 100 times less than either influenza or HIV. Is that reassuring?
Actually, there's a lot of new information on that question. A Science paper published in August sequenced dozens of Ebola virus samples obtained from patients in Sierra Leone. It's not mutating quite as fast as flu or HIV, but according to this more recent analysis, the virus is collecting mutations about twice as quickly as it did while circulating in animals for the last decade.
I think this is a reflection that Ebola is very well adapted to its natural host—bats. In humans, it just kills them too quickly.
In terms of viral evolution, it looks like each strain stays in its lane. You don't see reassortment like with flu. You don't see so much interaction with the immune system, leading to genetic drift and shift. By this measure, flu is a much more successful virus than Ebola.
It's not yet known if any of the genetic changes that have appeared in the virus involved in the current outbreak have contributed to its virulence. One main explanation for the current outbreak's severity is that this is the first time it has reached such densely populated areas in West Africa.
Where does Ebola come from?
The main hypothesis is that Ebola's reservoir is fruit bats, which can migrate between communities and across international borders. In previous outbreaks, there was a concern about wild game meat, but the latest evidence from Guinea suggests it was not a factor this time. In human-to-human transmission, it appears that close caregivers and relatives are the most vulnerable, and funerals are a particular point of risk.
