Virulence and host range

[ryan at mbcf.stjude.org]

In article <3pmhcd$4db at news3.digex.net>, litekepr at cpcug.org (The LightKeeper) writes:
> PANGELETTI at bmg.bhs.uab.edu whacked the keyboard to produce:
> 
> 
>>The LightKeeper(?) then responded by 
>>asking whether this could explain why "the virus seems transmissible via 
>>air in monkeys but not in humans."  The answer is no, dude.  The 
>>question of whether a virus is airborn is quite a different issue from 
>>pathogenicity and immune response.
> 
> Ok, I phrased it poorly.  I guess my question is:
> 
> Is it possibly that monkeys (or other animals) can contract the
> virus through airborne transmission, while humans can not?  In
> other words, is there something about a monkey lung that differs
> from ours in such a way as to allow easier transission?  
> 
> 
> -Lighty
> 


Sure, that's possible.

To elaborate just a little: differences in host range, like differences in
tissue tropism, reflect the ability of the virus to (1) get to, and (2)
recognize/enter the potential target cell (may or may not require the 
presence of a specific receptor molecule on the cell surface), and (3) once 
in the cell to execute its replication program. Being intracellular parasites 
of a sort, all viruses rely to some extent on host cell components to
replicate, but there are _wide_ differences in the extent to which host 
machinery is needed. Viruses with a wide host range probably rely on host 
factors common to most cells (eg maybe just ribosomes); viruses with a narrow 
host range probably use a specific host factor, for example a surface 
glycoprotein peculiar to one tissue type in just a few host species.  

All this contributes to whether a given virus can replicate in a certain host,
but as Dr. Pangeletti points out, this has little predictive value as to the 
mode of transmission in an as-yet-unknown alternative host. More information 
about the cell components needed for ebola replication would help address the 
possibility you raise, but the way to determine route of transmission is to
test it directly. Determining the exact cell components involved can be a long
and difficult process: for example the cell receptor for measles virus has
only recently been identified, despite long experience with this virus.
 
Cheers, Kevin.
-- 
--
       	==========================================
	Kevin W. Ryan
	Department of Virology & Molecular Biology
	St. Jude Children's Research Hospital
	Memphis, Tennessee 38101-0318, U.S.A.
	
	phone: (901) 522-0411
	fax:   (901) 523-2622
	Internet: ryan at mbcf.stjude.org
	==========================================