Ebola
2014 Is Mutating As Fast As Seasonal Flu
21
October, 2014
Yesterday we
reported that
according to Peter Jahrling of the National Institute of Allergy and
Infectious Disease - one of the top authorities in the world on Ebola
- and who is on the front lines fighting Ebola disease in Liberia,
there is something different about the current Ebola outbreak in that
not only does it spread more easily than it did before, but the viral
loads in Ebola patients are much higher than they are used to seeing.
"I have a field team in Monrovia. They are running [tests]. They
are telling me that viral loads are coming up very quickly and really
high, higher than they are used to seeing.... It may be that the
virus burns hotter and quicker."
That
is one observation on how different the current Ebola outbreak may be
from the traditional fare. Another one comes courtesy of Operon
Labs,
which as cited in detail below, notes that "the current Ebola
2014 virus is mutating at a similar rate to seasonal flu (Influenza
A). This means the current Ebola outbreak has a very high
intrinsic rate of viral mutation. The
bottom line is that the Ebola virus is changing rapidly, and in the
intermediate to long term (3 months to 24 months), Ebola has the
potential to evolve."
The
question is evolve into what?
Ebola
2014 is Mutating as Fast as Seasonal Flu
Background:
The
current Ebola 2014 virus is mutating at a similar rate to seasonal
flu (Influenza A). This means the current Ebola outbreak has a
very high intrinsic rate of viral mutation. The bottom line is
that the Ebola virus is changing rapidly, and in the intermediate to
long term (3 months to 24 months), Ebola has the potential to evolve.
We
cannot predict exactly what the Ebola virus will look like in 24
months. There is an inherent stochastic randomness to viral
evolution which makes predictions on future viral strains difficult,
if not impossible. One basic tenet we can rely on is this:
Viruses tend to maximize their infectivity (basic reproduction
number) within their biological constraints (Nowak, 2006).
These
evolutionary constraints can be extremely complex, and can include
trade-offs between virulence and infectivity, conditions of
superinfection, host population dynamics, and even outbreak control
measures.
One
of the few statements we can make with confidence that the Ebola
genome is changing at a specific rate, which is explained below.
Ebola
Mutation Rate:
Analysis
of the available research suggests that the Ebola 2014 virus is
currently mutating at a rate 200% to 300% higher than historically
observed (Gire, 2014).
Ebola
Genome Substitution Rates (Gire, 2014)
Furthermore,
the Ebola-2014 virus's mutation rate of 2.0 x 10−³ subs/site/year
is nearly identical to Influenza A's mutation rate of 1.8 x
10−³ subs/site/year
(Jenkins, 2002). This
means Ebola 2014 is mutating as fast as seasonal flu.
Disclaimer: This
paper contains no evidence (for or against) alternate modes of
transmission for Ebola, nor is this paper postulating that genetic
changes have impacted EVD clinical presentation (although evidence
for this has started to emerge). This paper is simply demonstrating
what appears to be a rapid rate of evolution in the Ebola 2014 Virus.
Many recent Ebola viral mutations have been synonymous mutations,
some have been in intergenic regions, while others are non-synonymous
substitutions in protein-coding regions. All have unknown impact at
the present time. Such questions should be the subject of future
scientific research. This article simply points out that Ebola in
2014 is undergoing rapid mutation and adaptation. The future
implications of Ebola's rapid evolution are unclear.
We
chose to compare Ebola-2014 to Influenza A (Seasonal Flu) because
Influenza is one of the fastest-mutating viruses (Jenkins,
2002). Unlike chickenpox (VZV), which people usually only
contract once per lifetime, Influenza can infect a single individual
many times repeatedly over the years. One of the reasons
Influenza is able to re-infect humans each year is because the
Influenza's high mutation rate allows the virus to generate 'escape
mutants'.
Escape mutants are Influenza viruses which are no
longer recognized by human immune systems. Each winter presents
us with a new mutated strain of the Influenza virus. Rapid mutation
is beneficial to Influenza genetic fitness (in regards to antigenic
regions), because it allows a 'new' Influenza virus to circulate year
after year.
The
benefit of a high mutation rate in Ebola 2014 is different -- the
genetic changes in Ebola-2014 allow for rapid exploration of the
entire fitness landscape in a brand new host -- humans. We need
to be aware that the Ebola-2014 virus is undergoing rapid adaptation.
Ebola
in Zoonotic Reservoir: Viral Genome adapted to Fruit
Bats.
(Green)
Ebola in Human Hosts: Viral Genome adapted to Humans. (Red)
Ebola Genotype will move Green -> Red during serial passage through Humans.
Ebola in Human Hosts: Viral Genome adapted to Humans. (Red)
Ebola Genotype will move Green -> Red during serial passage through Humans.
Until
the Ebola outbreak is brought under control, the Ebola-2014 virus
will continue to seed and adapt in its growing pool of West African
human hosts. We need to consider that as the weeks and months
go on, the rapidly-changing Ebola-2014 virus will undergo repeated
export from the West African region to countries around the world.
As
new Ebola cases grow in West Africa and elsewhere, we are effectively
conducting 'serial passage' experiments of Ebola-2014 through human
hosts. The repeated passage of Ebola-2014 through humans is exerting
selection pressure on the Ebola-2014 virus to adapt to our species
(instead of fruit bats). The introduction of Ebola-2014 into a
large pool of West African human hosts (coupled with the complex
dynamics of evolutionary selection pressure) may allow the Ebola-2014
virus to become more transmissible as the months go on, particularly
in the absence of effective control interventions.
The
high mutation rate we see in Ebola-2014 reflects its ability to
rapidly explore the fitness landscape. The ability of Ebola to
undergo rapid genome substitutions and SNPs, coupled with genetic
recombination, will allow 'survival of the fittest' in Ebola-2014
genetic variants (on both the intra-host and inter-host levels). New
Ebola sub-clades are created with each passing month (there are
already four sub-clades as of August 2014). New Ebola genetic
variants are created with each new infection, though most are
selected against. Rapid adaptation emerges from the high intrinsic
Ebola-2014 mutation rate, coupled with the virus's ability to undergo
RNA recombination during superinfection.
Molecular
dating of the Ebola-2014 outbreak (Gire, 2014).
Probability distributions for both 2014 divergence events are overlaid above.
This
phylogenetic tree is based on 99 Ebola viral genomes deep-sequenced
from 78 distinct patients in Sierra Leone (Gire, 2014). We can
see in the figure above that there are at
least four Ebola genetic clusters (or
sub-clades) based on phylogenetic analysis: These Ebola clusters are
called GN, SL1, SL2, and SL3 by Gire et al. The key takeaway is that
even prior to July 2014, the current Ebola outbreak had already
accumulated significant genetic diversity. Furthermore,
the dominant circulating Ebola variants have changed over time.
Up to four different Ebola-2014 viral sub-clades (groups of
genetically related Ebola isolates) have circulated between humans
since the onset of the 2014 Ebola outbreak.
As
the number of people affected by the 2014 Ebola outbreak has grown,
so has the number of Ebola unique viral mutations and unique viral
genetic lineages. We can expect Ebola 2014 viral lineages to
grow as some function f(i) proportional to the number of people
infected with Ebola.
Ebola-2014: Acquisition of genetic variation over time (Gire, 2014).
Fifty mutational events (short dashes) and 29 new viral
lineages (long dashes) were observed.
The
diagram above suggests that as the Ebola-infected host pool grows, so
does the number of unique Ebola viral lineages (Gire, 2014). This
implies that Ebola acquires genetic diversity as it infects more
people, particularly if the virus undergoes recombination during
superinfection (Niman, 2007). The
growing number of new Ebola viral lineages will undergo natural
selection for some 'optimum' balance of virulence, infectivity,
tissue tropism, immune suppression, and other parameters which
maximize the reproductive fitness of the Ebola virus in humans.
What that final virus might eventually look like 2 years from
now is anyone's guess. But the explosion of genetic variation
suggests that the Ebola virus will become more difficult to contain
as time goes on, which is why early action is important.
The
idea that the Ebola-2014 Virus jumped species, but is now somehow
'static' or 'frozen in time' is a mistake. The Ebola-2014 virus is
undergoing a period of rapid adaptation in human hosts, as evidenced
by the Ebola RNA sequences deposited in Genbank, and the studies
referenced with this article. Hopefully, interventions (like
contact tracing) will be able to stop Ebola-2014 before the virus
optimizes its genotype.
These
are two scenarios to outline what may happen in the future. The
critical variable determining the global outcome of Ebola is the
response in West Africa, not the response in the United States.
Best
Case Scenario:
WHO
immediately deploys contact-tracing teams on the ground in West
Africa. The US Military is deployed as well, and constructs
hospitals sufficient to care for the sick. The hospitals are staffed
by qualified (read: well trained) caregivers. Teams on the ground
track down and care for Ebola-infected patients across West
Africa, distributing self-treatment kits, food, medicine, and
expertise. An effort is made to involve local authorities and
community leaders. These efforts cause measurable reductions in
the basic reproduction number of the virus by the end of 2014.
Within
3 months to 9 months, the outbreak in West Africa peaks, levels-off,
and begins to fade. The Ebola virus never has the opportunity
to acquire any significant mutations, due to its limited host pool.
Ebola is fully under control by early 2015. Sporadic cases in
other countries are dealt with by treatment and contact tracing. By
Q4 2015, multiple Ebola vaccines and drugs are in the pipeline
limiting the overall threat Ebola poses.
Worst
Case Scenario:
The
international response is perpetually behind the curve. Every
response action is 8 to 12 weeks too late. Statistics from the
WHO become volatile and are unreliable as the lack of deployed
personnel make hard numbers impossible to pin down. By 2015 the
number of infections is in the hundreds of thousands in West Africa.
The West African region exports 'asymptomatic infectives' which go
undetected by basic screening. These individuals 'seed'
outbreaks in other countries.
As
more people become infected, a significant mutation arises that
allows for a longer asymptomatic but infectious period, increasing
the R-0. Globally, cases continue to double every 16 days, contact
tracing infrastructure outside the West becomes saturated, and
hospitals are overrun. By early-to-mid 2015, the global pool of
Ebola-infected patients are in the millions, mainly centered in West
Africa and Southeast Asia with multiple strains of varying virulence.
A sudden change in the outbreak epidemiology caused by a recombinant
Ebola strain causes confusion about how to respond. Efforts at
developing treatments/vaccines become logistically complex and
ineffective.
The
implication of the Ebola 2014 mutation rate is this: A single
Ebola mutation doesn't necessarily mean the virus will become
'airborne', or that the virus has altered tissue tropism, or that the
virus spreads more easily. But a high intrinsic rate
of Ebola mutation means that such changes may become possible in the
future. If the number of people infected grows into the
hundreds of thousands, or even low millions, then the probability of
a significant 'constellation' of accumulated Ebola mutations with
phenotypic impact becomes more likely. The problem is that
accumulated Ebola mutations will scale with the size of the
population infected. Conversely, in a small population, such
Ebola mutations are not likely to have a significant impact. It's
a bit like the virus is buying lottery tickets... The more lottery
tickets the Ebola virus 'buys', the more chances it has to 'win'.
Next
Steps:
The
general consensus in the scientific and epidemiological community is
immediate intervention in West Africa is necessary in order to avoid
taking the risky outcomes possible in a 'worst case' scenario. A
suitable response would need to include airlifting self-treatment
kits with thermometers, the distribution of life-saving drugs, the
construction of Ebola treatment centers, hospital staffing, contact
tracing teams, and so forth. A robust international response
must happen soon in order to ensure that the current situation with
the Ebola outbreak remains a 'best case' outcome.
References:
[1]
Genomic surveillance elucidates Ebola virus origin and transmission
during the 2014 outbreak. (Gire et al, 2014).
[2]
Rates of Molecular Evolution in RNA Viruses: A Quantitative
Phylogenetic Analysis. (Jenkins et al, 2002).
[3]
Isolates of Zaire ebolavirus from wild apes reveal genetic lineage
and recombinants. (Wittman et al, 2007).
[4] Ebola
Recombination: Recombinomics Commentary. (Niman, 2007).
[5] Evolutionary
Dynamics: Exploring the Equations of Life. (Nowak, 2006).
Ebola
doctors at breaking point – a major wave of infections is about to
wash everything away
21
October, 2014
October 2014 – AFRICA – At 3:30 a.m. in the world’s biggest Ebola treatment center, Daniel Lucey found the outbreak reduced to its essentials: patients lying on mattresses on the floor and vomiting in the dark, visible only by the wavering flashlight beam of a single volunteer doctor. “I don’t see a light at the end of the tunnel,” said Lucey, a physician and professor from Georgetown University who is halfway through a five-week tour in Liberia with Medecins Sans Frontieres, the medical charity known in English as Doctors Without Borders. “The epidemic is still getting worse,” he said by phone between shifts. That’s an increasingly urgent challenge for MSF and the global health community. As fear spreads in the U.S. over transmission of the virus to two nurses in a modern Dallas hospital, the main fight against the outbreak is still being waged by volunteers like Lucey half a world away.
MSF has been the first — and often only — line of defense against Ebola in West Africa. The group raised the alarm on March 31, months ahead of the World Health Organization. Now, after treating almost a third of the roughly 9,000 confirmed Ebola cases in Africa — and faced with a WHO warning of perhaps 10,000 new infections a week by December — MSF is reaching its limits. “They are at the breaking point,” said Vinh-Kim Nguyen, a professor at the School of Public Health at the University of Montreal who has volunteered for a West African tour with MSF in a few weeks. MSF has already seen 21 workers infected and 12 people die, and “there’s a sense that there’s a major wave of infections that’s about to wash everything away,” Nguyen said. –Bloomberg
South Korean aid workers exposed to Ebola: South Korean aid workers in West Africa have been exposed to the deadly Ebola virus due to a lack of protective wear and medical equipment, a lawmaker claimed Tuesday. A total of 102 South Korean aid workers have been living in West African countries, including Senegal and Cameroon, without proper protection from the epidemic, Rep. Kim Jae-won of the ruling Saenuri Party said, citing data from the government’s official development assistance body, the Korea International Cooperation Agency (KOICA). –Yonhap News
Ebola
health crisis in US
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