The important information here is that
the application of a simple one week quarantine can work well enough
to prevent the disease running away. If it does start to get out of
control, then applying that is what will work best. We can live with
a one week pause in travel for example.
During that week we scout out victims
and wait until no more are reporting in. Communities can be declared
free and access opened up for them. This is rough and ready but the
key idea is to halt transmission and to buy time for all victims to
emerge and be isolated. It is a dynamic approach but should actually
work well enough if we have to ever go there.
Right now the Ebola scare remains just
that. It is a scare that will producec a handful of the unlucky but
then fade back down. We may even master the art of working with this
disease and drop the death rate. Unfortunately bad actors are
happily promoting bunkum and extreme fear..
New Math Shows ‘True Scale’
of Ebola Outbreak
By Fabio
Bergamin, ETH Zurich | October 11, 2014
A team of scientists
has made new calculations about how the Ebola epidemic will develop,
its scale, and perhaps how to stop it from spreading.
The researchers used a
statistical program they developed to calculate the viral
reproductive number, which is the average number of infections caused
by a single infected individual.
They also analyzed the
length of incubation and infectious periods. Their calculations are
based on the gene sequence of the virus in various patient samples.
The virus sequences
were obtained by American, British, and Sierra Leonean researchers
from blood samples taken from patients in Sierra Leone in the first
few weeks after the epidemic migrated to the country from neighboring
Guinea in May and June 2014.
Newer sequences are
currently not publicly available, says team leader Tanja Stadler,
professor of computational evolution at ETH Zurich.
From the data, the
researchers calculated a viral reproductive number of 2.18. This
value is in the range of the previous estimated values based on the
incidence and prevalence of the disease, which are between 1.2 and
8.2.
“A major benefit of
our method is that we can use it to calculate unreported cases and
therefore the true scale of the epidemic,” says Stadler.
They report their
findings in PLOS Currents.
Unreported Cases
Official patient
figures only take into account those cases reported to the health
authorities. The actual number of infected persons is generally
significantly higher. Using the data made available to them, the ETH
researchers were able to calculate an unreported case rate of 30
percent.
“However, this
applies only to the situation analyzed in Sierra Leone in May and
June. We do not have any blood samples since June at all,” notes
Stadler.
The researchers
were also able to calculate the incubation period for Ebola—five
days, although this value is subject to significant uncertainty—and
the infectious time. Patients can pass on the virus from 1.2 to 7
days after becoming infected.
To obtain these
values, the researchers created a phylogenetic tree based on the gene
sequences of the virus samples.
“The Ebola virus
changes in the body of the patient from day to day, meaning that the
virus sequence varies slightly from patient to patient,” explains
Stadler.
With the knowledge of
the different sequences, the researchers were able to determine at
what point in the past infection events happened between patients.
From this, they were able to calculate the epidemiological
parameters.
Already Tested for HIV
These epidemiological
values are important in developing strategies to contain the epidemic
and evaluate the effectiveness of these measures. Imposing a curfew
is one measure.
“If the curfew lasts
longer than the incubation period, then only those people who
continue to show symptoms of Ebola are carriers of the disease,”
says Stadler.
In turn, the
reproductive number is one of the most important benchmarks used by
health services. The most pressing aim of these authorities is to
reduce the reproductive number to a value lower than one, as this
would imply that the epidemic has been contained.
The ETH researchers
developed the computer program used to calculate these figures during
the past few years and applied it to data collected from HIV and
hepatitis C patients. They now hope that new sequences of the
currently circulating Ebola virus become available, despite the
adverse conditions in the areas affected by the epidemic.
“Our program is
ready,” says Stadler. “If we are given access to current Ebola
sequences, we will be able to gain a detailed insight into the spread
of the epidemic literally overnight.”
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