By Wendy A. Epstein, M.D.,
F.A.A.D, Adjunct Assistant Professor, NYU School of Medicine, Health
Commissioner, Village of Grand View-on-Hudson, NY
Statements and guidelines have
been made so often about Ebola that we come to accept them as fact based. We have been told that all people infected
with Ebola are symptomatic. We have been told that if, after 21 days of
isolation, a person remains asymptomatic they can no longer come down with or
infect others with Ebola. We are told
that the Ebola virus cannot be transmitted through the air, but only by direct
contact with infected bodily fluids. We have been told that temperatures taken
once in airports to screen for potential sick travelers from West Africa are an
effective way to screen. Before we accept any statement about a disease that
most of us have had no experience with, let us look at the evidence and change
our protocols accordingly.
The designation of a 21 day
period of isolation of people exposed to the Ebola virus is based upon a 95%
chance that someone, exposed to Ebola, won’t have Ebola after 21 days. That
means that if 100 people exit quarantine after 21 days, five may still become
sick with Ebola. However, a 25 day period isolation means there is a 99% chance
that someone exposed to Ebola won’t have Ebola, or only one person in a hundred
may still become sick with Ebola after 25 days of isolation. [Sources: Transmission
dynamics and control of Ebola virus disease (EVD): a review Gerardo Chowell12*
and Hiroshi Nishiura3 BMC
Medicine 2014, 12:196 and Osong
Public Health Res Perspect. 2011 Jun;2(1):3-7. doi:
10.1016/j.phrp.2011.04.001. Epub 2011 Apr 12. Incubation period of ebola
hemorrhagic virus subtype zaire. Eichner M1, Dowell SF, Firese N].
While fever
is an early symptom of being infected with Ebola, it is possible to be infected
and have no symptoms whatsoever. In a study [Source: Lancet.
2000 Jun 24;355(9222):2210-5.Human asymptomatic Ebola infection and strong
inflammatory response. Leroy et al.] Clinicians checked the blood for evidence
of Ebola infection in individuals who were family members of symptomatic patients,
and who lived continuously with them taking care of them without any physical
protection such as gloves. The study showed that asymptomatic, replicative Ebola infection can
and does occur in human beings. It seems that people who get infected with
Ebola and either are asymptomatic or symptomatic and recover have a different
immune response than people who get infected and become very ill and die. The
issue then is whether asymptomatic individuals infected with Ebola can infect
others. The risk
of transmission via blood products donated by such individuals or via semen
should be taken into consideration in public-health policy since infectious
filovirus have already been found in semen from symptomatic patients 2–3 months
after symptoms [Source: Lancet. 2000 Jun 24;355(9222):2210-5].
Taking temperatures at an airport is giving the public
a false sense of security. Fever is not specific, as it is an early
manifestation of Ebola and many other infections. Someone infected with Ebola
may never have a fever. Fevers are not constant throughout the course of the
day, but go up and down. Inexpensive temperature dots could be placed on the
wrist of travellers as they check in for flight, and checked prior to boarding
and disembarking. Should they get a temperature in flight, they could be
isolated in one of the plane’s bathrooms, equipped with hazmat suit and
respirator with an intercom. Although
healthcare workers are at greater risk for being infected with Ebola, I see no
reason not to quarantine all travellers from West African countries where Ebola
is present. Furthermore, why not restrict travel to and from West Africa to
those risking their lives trying to stop the epidemic there?
Let’s look at the assumption that Ebola cannot be
transmitted through the air. Evidence exists that Ebola Zaire virus infects
pig’s lungs, and that pigs can infect non-human primates through respiratory
transmission of the virus.. Therefore, pigs could theoretically be a source of
aerosolized transmission of Ebola to humans in West Africa. This study also
showed that the non-human primates did not infect each other through
respiratory tracts, i.e., the air. [Source: Transmission of Ebola virus from
pigs to non-human primates. Sci Rep 2012, 2:811]. Weingartl et
al]. Another study demonstrated there
was evidence of possible aerosol route of transmission between non-human
primates (Transmission of Ebola virus (Zaire strain) to uninfected control
monkeys in a biocontainment laboratory ,[Source: N.Jaax et al, The Lancet, Volume 346, Issue 8991,
Pages 1669 - 1671, 30 December 1995]. What this
underscores is that we don’t know enough about Ebola to make sweeping
generalizations about whether it can or cannot be transmitted through the air.
Humans sitting or standing within close proximity to
each other could transmit Ebola virus by sneezing droplets of infected fluid
onto another person. The viral load, or numbers of viral particles in a sample,
is extremely high in body fluids of infected individuals when they become
symptomatic. It takes as few ten Ebola viruses out of the millions in each
airborne droplet of a sneeze to infect those who breathe it in.
It also is evident that air travel is a major mode of
dissemination of airborne illnesses, such as influenza. A study demonstrated that the post 9/11 restriction
of air travel in the United States delayed the dissemination of that year’s
influenza by 2 weeks. There were no travel restrictions imposed in France in
2001, and consequently, there was no change in the timing of the arrival of influenza,
in France. Given the number of deaths each year from influenza, perhaps it
makes sense not to let sick people with fevers fly in general. [Source: PLoS Med. 2006 Sep;3(10):e401.Empirical evidence for the effect of airline
travel on inter-regional influenza spread in the United States. Brownstein JS1,
Wolfe CJ,
Mandl KD].
One possible explanation for the role of direct physical contact in
transmission is the presence of abundant virus particles and antigens in the
skin in and around sweat glands. Source:
[J Infect Dis. 1999 Feb;179 Suppl 1:S36-47]. The nurses infected with Ebola while caring for Mr. Duncan (the West
African patient who flew into Dallas) were said to have made some mistake in
protecting themselves. It is possible
that Ebola could have been transmitted through the skin of Mr. Duncan,
particularly later in the course of his illness when his viral load was the
greatest. Simply touching a cadaver is
an independent risk factor for contracting Ebola.
As yet, we
know far too little to presume the following: that 21 days is sufficient to
adjudge a person Ebola virus-free; that screening for temperatures at airports
protects the American people; that lack of symptoms indicates no possibility of
infection; and that Ebola cannot be transmitted through the air. We do know
that at least 25 day isolation would add significant protection; that blood
tests are the most reliable way to
confirm an infection with Ebola, and that much more research needs to be done
on how this virus is spread. Until we know enough, we need to set a much higher
bar for containment before we risk further spread of deadly pathogens.
Perhaps, the only way to know if someone is infected with Ebola is to
take serial blood samples spaced over one month, 30 days which is 5 days past
the 25 days of isolation necessary to eliminate 99% of people, exposed to
Ebola, who will become symptomatic. We do not know how many people who are
asymptomatic after the period of isolation are not infected with Ebola unless
their blood is checked for presence of the viral RNA and/or have specific
antibodies to the Ebola virus at the end of their confinement.
Ultimately,
the mass vaccination of vulnerable people in West Africa and those brave
healthcare volunteers who are risking their lives to save the rest of us is key
to ending the spread of Ebola. Until then, public health policy and public
trust, must be dictated by the science about what we know and will learn about
the mode of transmission of Ebola.