[stem-ebola] WHO seems to acknowledge (rare) possibility of Ebola 'large

[alex@xxxxxxxxxxxxxx]

I understand the possibility of Ebola 'aerosol' transmission is a 
controversial topic.  Ebola aerosol transmission is not well-studied, 
and existing experimental evidence is contradictory (some studies show 
it is possible in animals and primates, wile other studies show it is 
not possible).

I remain unconvinced either way, at the moment.  I think primarily Ebola 
is currently spreading via direct contact right now.  But I don't want 
to make the classic logical fallacy... "Absence of evidence is not 
evidence of absence"   So I'm going to keep an open mind on this one.

In a WHO advisory email sent Monday 10/06 regarding Ebola, the following 
(curious) quotes were included:

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source: http://www.who.int/mediacentre/news/ebola/06-october-2014/en/

“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” -WHO

[ED NOTE:  So here WHO admits that 'large droplets' could spread Ebola, 
but do not give particle sizes.  To me, this suggests that the droplets 
are of size 100 microns to 1000 microns in diameter. If this is the 
droplet size, these would be rapidly deposited on the mouth , face, or 
into the nasopharynx of the second individual.  Particles of this size 
would be unlikely to remain suspended in air for any substantial period 
of time.  If this WHO claim is true, Ebola would not be 'airborne' in a 
traditional understanding, but could transfer without 'direct contact' 
overt short distances, potentially through coughing, sneezing, or 
vomiting.  This area needs immediate further research.]

“[Transmission of Ebola] could happen when virus-laden heavy droplets 
are directly propelled, by coughing or sneezing (which does not mean 
airborne transmission) onto the mucus membranes [ED NOTE: MOUTH & 
NASOPHARYNX] or skin with cuts or abrasions of another person.” -WHO

[ED NOTE: This statement is a bit contradictory.  What is the definition 
for 'airborne' that we will all agree on?  Is it a particle size range 
that WHO refers to?  Does a particle have to land in the alveoli to 
become 'airborne'? Also, what is the source for expelled droplet 
material in this WHO example?  Are we talking about Sputum? Saliva? 
Mucus?  Do we know human levels of PFU/mL in these tissues during the 
phases of disease progression?]

“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.” -WHO

[ED NOTE: So a low sample size... This means we need further research to 
either confirm or disconfirm this information.  What about Sputum and 
Mucus during earlier stages of illness?  When do these fluids start to 
have viral PFUs present within them in regards to the course of the 
disease?  What about tissue tropism in the lung in the 2014 outbreak?  
Do we see viral titers in human lung?  If so, what levels, in Ebola 
PFU/g of wet lung tissue?]

“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” -WHO

[ED Note: Agreed.  We can model this quite well via direct contact.  But 
this particular issue has way more questions than answers, particularly 
in regards to 'long-term' strategies over the next 8 to 36 months, as 
well as what are suitable levels of PPE for healthcare workers.]

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USAMRID reference regarding VHF and Filoviruses:

"All of the VHF agents (except for dengue virus) are laboratory 
infectious hazards by aerosol, even though dengue virus has been 
nosocomially transmitted by blood splash.  There aerosol infectivity for 
many VHF agents has been studied and measured in experimental animal 
models.  VHF agents cause severe disease, and many have extremely high 
fatality rates."

"In several instances, secondary transmission among contacts and medical 
personnel without direct body fluid contact exposure has been 
documented.  These instances prompted concern of a rare phenomenon of 
aerosol transmission of infection. [...] A negative pressure isolation 
room is ideal."

-USAMRIID, Medical Management of Biological Casualties Handbook, Seventh 
Edition (September 2011)
source: 
http://www.usamriid.army.mil/education/bluebookpdf/USAMRIID%20BlueBook%207th%20Edition%20-%20Sep%202011.pdf


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OPERON LABS COMMENTS:

The controversy over 'airborne' transmission is unlikely to end anytime 
soon.  Part of the problem is we do not have a universally agreed upon 
transmission of 'airborne'.  (What aerosol particle sizes are we talking 
about?  What are the levels of virus (PFU/mL) in these droplets?  What 
biological materials are the droplets comprised of? etc).

The size of an expelled particle determines whether it will be deposited 
in the nasopharynx, trachae, alveoli, or other surface.  Many studies on 
aerosol deposition fraction involve drug-delivery rather than infectious 
viral particles.

First, let's look at the epidemiology of aerosol particle sizes... Take 
for example sneezing...

source: 
http://rsif.royalsocietypublishing.org/content/10/88/20130560.long

Characterizations of particle size distribution of the droplets exhaled 
by sneeze
http://rsif.royalsocietypublishing.org/content/10/88/20130560/T1.expansion.html

Measured data and fitting curves of two sample sneezes:
http://rsif.royalsocietypublishing.org/content/10/88/20130560/F4.expansion.html

"For the two peaks of the bimodal distribution, the geometric mean (the 
geometric standard deviation) is 386.2 µm (1.8) for peak 1 and 72.0 µm 
(1.5) for peak 2. "  (sneezing)

From the same study, everyday 'speech' results in the expulsion of 
aerosol particles of sizes ranges from 10 microns to 1000 microns, with 
an average of about 100 microns in diameter.

We can thus expect sneezing to result in particle deposition mainly to 
the upper respiratory tract of another host (mouth, face, eyes, & 
nasopharynx) during coughing, talking, and sneezing.  The question is 
not whether infected hosts expel PFU-laden aerosol particles.  *The 
question is whether these particles contain any viral PFU (Plaque 
Forming Units)*.  We simply don't know that critical fact here in 2014.

At the present time, airborne transmission doesn't seem to be a 
significant mode of transmission.  But we should definitely stay aware 
of this possibility, since it was referenced recently by the WHO.

Droplet Size and Penetration of Respiratory Passages
http://www.globalsecurity.org/wmd/library/policy/army/fm/8-9/fig1-Ip2.gif

source:
http://www.globalsecurity.org/wmd/intro/bio_delivery.htm