sialeck sialeck at globalnet.co.uk
Fri Oct 30 23:16:54 EST 1998

>On 27 Oct 1998 22:02:19 GMT, tdlaing at nospam.dres.dnd.ca (T.D. Laing)
>>In article <363625d1.1312553 at news.virgin.net>, fybog at NOSPAMhotmail.com
>>(fybog) wrote:
>>> On 26 Oct 1998 14:44:27 GMT, tdlaing at nospam.dres.dnd.ca (T.D. Laing)
>>> wrote:
>>> >
>>> >Actually, the Reston variant of Ebola virus, which affected a monkey
>>> >colony in Reston, Virginia about 9 years ago, was an airborne virus.
>>> >keepers were found to have anti-Ebola antibodies in their blood, but
>>> >unaffected by the virus (as at the time it was monkey-specific).  So,
>>> >don't think it can't happen with the human-specific variants.
Also, in 1992, the same strain of Ebola, Ebola Reston, turned up (with the
same consequences) at a monkey house in Siena, Italy.
March 30, 1996 showed the same infection AGAIN in Texas, USA.
For more info see
>OK, it wasn't less virulent by that definition, I should have been
>more specific, but at the same time it is inaccurate to call a virus
>'airborne'. Virus particles are very small and are therefore probably
>airborne a lot of the time outside of their hosts, but not necessarily
>in a viable or infectious state. (But we'll stick to the phrase for

Most viruses can not be airborne outside their natural host (or any host),
as they are broken down by UV light.  Thus, for a virus to become airborne,
it must develop the characteristic protien coat of an airborne virus.
>How do you know that the keepers were infected with the strain anyway,
>they may have just inhaled non-viable virus particles and produced
>antibodies against them as foreign bodies.
Just because clinical signs are not shown, it does not mean that an
infection has not taken place.  The presence of antibodies, unless induced
as a vaccine (artificial immunity), are a form of aquired immunity, hence a
sign of infection.
>You also can't say that it is only a matter of time before airborne
>strains of Ebola occur. You do not know that for a fact. They could
>have been airborne way back down the evolutionary ladder and it wasn't
>a good strategy so the virus evolved other modes of transmission.
The CDC decided that the Ebola Reston strain was later in the evolutionary
chain than the Ziare or Sudan strains.  The strains are mutated by less than
1.6% from eachother.  According to the CDC, this "may indicate that the
genomes of Ebola viruses (and filoviruses in general) are unusually stable
and have evolved to occupy special niches in the wild."
>>Ebola Reston had a 100% mortality rate in the infected monkeys, so I
>>wouldn't exactly call it "less virulent".  That it did not seem to affect
>>the human keepers is irrelevant to the main argument, that it is only a
>>matter of time before airborne strains of human Ebola will occur.  And,
>>lest you've forgotten your epidemic histories, Yersinia pestis can become
>>airborne (i.e. pneumonic plague) with a near 100% mortality rate in
>>itself.  Anthrax also is nearly 100% lethal in its pneumonic form.
>Also, according to "Manual of Clinical Microbiology" (fifth edition,
>which  was 1991, so not too recent) edited by Albert Balows; Y.pestis
>has a mortality of 60% in untreated individuals. I couldn't find a
>figure for the pulmonary form of anthrax, but for untreated cutaneous
>anthrax the mortality is 20%, falling to near zero with treatment.

Both are right.  Except the higher figures are for unhospitalised cases, the
lower ones for patients once they reach suitable medical care.

>>> In whatever way  a bug is modified by genetic engineers or
>>> evolution to become more virulent there is always a cost to the bug.
>>> It may survive for less time outside the body, be less destructive
>>> once it is in there, or be non-viable outside of the nurturing
>>> laboratory setting.

True, but it may also impart 'better' qualities on the virus.
>That wasn't what I was saying. I was saying that the organisms may not
>be able to survive outside of the lab for very long as they have had
>(potentially) costly mutations introduced. And they are not being
>nurtured in the environment, being feed the right things and kept at
>the correct temperature. They are facing dessication and all the rest
>of the challenges that pathogens have to beat in order to be able to
>infect and  propagate.
The microorganisms you refer to next are bacteria.  Bacteria can survive for
long periods of time outside a host.  It is perfectly possible to engineer
them as such, and evolution has already played that role.  Some bacteria can
stand complete dessication.
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