Ebola virus outbreak in Africa

[Ian A. York]

In article <3pfpe2$b5i at epx.cis.umn.edu> dool0008 at gold.tc.umn.edu (Miranda T Dooley) writes:
>Ian A. York (york at mbcrr.dfci.harvard.edu) wrote:
>: However, in (for example) Dengue, pre-exposure to one strain may
>: actually make an infection with a second strain worse.  --
>can you explain this? i've heard of some infections making subsequent 
>ones worse, but what are the mechanics?

The mechanics are not completely understood.  At least part of it seems 
to be that non-neutralizing antibody attached to the virus (in the 
absence of neutralizing antibody) enhances uptake of the virus by 
susceptible cells such as macrophages.  (Macrophages, of course, normally 
efficiently phagocytose antibody-coated particles, so the virus is taking 
advantage of a natural phenomenon.)  A reference you might find 
interesting is -
Morens DM.
Antibody-dependent enhancement of infection and the pathogenesis of 
viral disease.
Clinical Infectious Diseases.  19(3):500-12, 1994

One point I'd like to emphasize - since it seems to be widely
misunderstood - is that antiviral antibodies are very often not
neutralizing.  That is, a single antibody specificity has a very good
chance of being useless in control of the virus.  See, for example, some
of the work by Claes Wohlfart and co-workers on adenovirus neutralization. 
With some viruses, such as feline infectious peritonitis, almost all of
the antibody response is non-neutralizing.  In most other cases, the wide
range of specificities produced by a normal immune response includes
enough neutralizing antibodies that the virus is covered. 

However, to further complicate the issue, with many viruses antibodies 
are of little use after the initial infection.  That is, infection can 
generally be prevented by an antibody response, but an ongoing viral 
infection may not be affected at all.  This is particularly true for 
viruses which are capable of cell-to-cell spread, such as the 
herpesviruses.  

Ian
-- 
Ian York   (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-3921     Fax  (617)-632-2627