From: Date: October 6, 2014 at 8:11:03 AM EDT To: undisclosed-recipients:; Subject: WHO Ebola situation assessment What we know about transmission of the Ebola virus among humans
What we know about transmission of the Ebola virus among humans Ebola situation assessment - 6 October 2014 The
Ebola virus is transmitted among humans through close and direct
physical contact with infected bodily fluids, the most infectious being
blood, faeces and vomit.
The Ebola virus has also been detected
in breast milk, urine and semen. In a convalescent male, the virus can
persist in semen for at least 70 days; one study suggests persistence
for more than 90 days.
Saliva and tears may also carry some risk.
However, the studies implicating these additional bodily fluids were
extremely limited in sample size and the science is inconclusive. In
studies of saliva, the virus was found most frequently in patients at a
severe stage of illness. The whole live virus has never been isolated
from sweat.
The Ebola virus can also be transmitted indirectly,
by contact with previously contaminated surfaces and objects. The risk
of transmission from these surfaces is low and can be reduced even
further by appropriate cleaning and disinfection procedures.
Not an airborne virus Ebola
virus disease is not an airborne infection. Airborne spread among
humans implies inhalation of an infectious dose of virus from a
suspended cloud of small dried droplets.
This mode of transmission has not been observed during extensive studies of the Ebola virus over several decades.
Common
sense and observation tell us that spread of the virus via coughing or
sneezing is rare, if it happens at all. Epidemiological data emerging
from the outbreak are not consistent with the pattern of spread seen
with airborne viruses, like those that cause measles and chickenpox, or
the airborne bacterium that causes tuberculosis.
Theoretically,
wet and bigger droplets from a heavily infected individual, who has
respiratory symptoms caused by other conditions or who vomits violently,
could transmit the virus – over a short distance – to another nearby
person.
This could happen when virus-laden heavy droplets are
directly propelled, by coughing or sneezing (which does not mean
airborne transmission) onto the mucus membranes or skin with cuts or
abrasions of another person.
WHO is not aware of any studies that
actually document this mode of transmission. On the contrary, good
quality studies from previous Ebola outbreaks show that all cases were
infected by direct close contact with symptomatic patients.
No evidence for mutation of this virus Moreover,
scientists are unaware of any virus that has dramatically changed its
mode of transmission. For example, the H5N1 avian influenza virus, which
has caused sporadic human cases since 1997, is now endemic in chickens
and ducks in large parts of Asia.
That virus has probably
circulated through many billions of birds for at least two decades. Its
mode of transmission remains basically unchanged. Speculation that
Ebola virus disease might mutate into a form that could easily spread
among humans through the air is just that: speculation, unsubstantiated
by any evidence.
This kind of speculation is unfounded but
understandable as health officials race to catch up with this
fast-moving and rapidly evolving outbreak. To stop this outbreak,
more needs to be done to implement – on a much larger scale – well-known
protective and preventive measures. Abundant evidence has documented
their effectiveness.
|
No comments:
Post a Comment